Issue published December 1, 2011

T he pancreas is a complex organ comprised of three critical cell lineages: islet (endocrine), acinar, and ductal. This review will focus upon recent insights and advances in the biology of pancreatic ductal cells. In particular, emphasis will be placed upon the regulation of ductal cells by specific transcriptional factors during development as well as the underpinnings of acinar-ductal metaplasia as an important adaptive response during injury and regeneration. We also address the potential contributions of ductal cells to neoplastic transformation, specifically in pancreatic ductal adenocarcinoma.

S exually transmitted infections (STIs) have plagued humans for millennia and can result in chronic disease, pregnancy complications, infertility, and even death. Recent technological advances have led to a better understanding of the causative agents for these infections as well as aspects of their pathogenesis that might represent novel therapeutic targets. The articles in this Review Series provide excellent updates on the recent advances in understanding of the pathogenesis of some very important and persistent STIs and discuss the importance of considering each pathogen in the broader context of the environment of the individual who it infects.

S yphilis is a fascinating and perplexing infection, with protean clinical manifestations and both diagnostic and management ambiguities. Treponema pallidum subsp. pallidum, the agent of syphilis, is challenging to study in part because it cannot be cultured or genetically manipulated. Here, we review recent progress in the application of modern molecular techniques to understanding the biological basis of this multistage disease and to the development of new tools for diagnosis, for predicting efficacy of treatment with alternative antibiotics, and for studying the transmission of infection through population networks.

T he discovery that certain high-risk strains of human papillomavirus (HR-HPV) cause nearly 100% of invasive cervical cancer has spurred a revolution in cervical cancer prevention by promoting the development of viral vaccines. Although the efficacy of these vaccines has already been demonstrated, a complete understanding of viral latency and natural immunity is lacking, and solving these mysteries could help guide policies of cervical cancer screening and vaccine use. Here, we examine the epidemiological and biological understanding of the natural history of HPV infection, with an eye toward using these studies to guide the implementation of cervical cancer prevention strategies.

H erpes simplex virus type 2 (HSV-2) is one of the most prevalent sexually transmitted infections worldwide. In addition to recurrent genital ulcers, HSV-2 causes neonatal herpes, and it is associated with a 3-fold increased risk for HIV acquisition. Although many HSV-2 vaccines have been studied in animal models, few have reached clinical trials, and those that have been tested in humans were not consistently effective. Here, we review HSV-2 pathogenesis, with a focus on novel understanding of mucosal immunobiology of HSV-2, and vaccine efforts to date, in an attempt to stimulate thinking about future directions for development of effective prophylactic and therapeutic HSV-2 vaccines.

V aginal bacterial communities are thought to help prevent sexually transmitted infections. Bacterial vaginosis (BV) is a common clinical syndrome in which the protective lactic acid–producing bacteria (mainly species of the Lactobacillus genus) are supplanted by a diverse array of anaerobic bacteria. Epidemiologically, BV has been shown to be an independent risk factor for adverse outcomes including preterm birth, development of pelvic inflammatory disease, and acquisition of sexually transmitted infections. Longitudinal studies of the vaginal microbiome using molecular techniques such as 16S ribosomal DNA analysis may lead to interventions that shift the vaginal microbiota toward more protective states.

G enome-wide association studies (GWAS) have identified a large number of SNPs that are linked to human autoimmune diseases. However, the functional consequences of most of these genetic variations remain undefined. T cell protein tyrosine phosphatase (TCPTP, which is encoded by PTPN2) is a JAK/STAT and growth factor receptor phosphatase that has been linked to the pathogenesis of type 1 diabetes, rheumatoid arthritis, and Crohn’s disease by GWAS. In this issue of the JCI, Wiede and colleagues have generated a T cell–specific deletion of TCPTP and identified a novel role for this phosphatase as a negative regulator of TCR signaling. These data provide new insight as to how noncoding PTPN2 SNPs identified in GWAS could drive human autoimmune diseases.

M embers of the ErbB family of cell surface tyrosine kinase receptors are important targets for cancer treatment because they frequently contribute to the pathogenesis of malignancy. In this issue of the JCI, Fukuoka et al. generate data that suggest that using a tyrosine kinase inhibitor (TKI) against epidermal growth factor receptor (EGFR; also known as ErbB1) may be a novel approach for treating patients with hypercortisolemia due to pituitary corticotroph adenomas (Cushing disease). While surgical resection remains the cornerstone of treatment for individuals with such tumors, this study suggests that TKIs could perhaps be used to reduce tumor size prior to surgery or to treat recurrent disease after surgery.

H ereditary neuropathies are common neurological conditions characterized by progressive loss of motor and/or sensory function. There are no effective treatments. Among the many causes of hereditary neuropathies are dominant mutations in serine palmitoyltransferase, long chain base subunit 1 (SPTLC1), which cause hereditary sensory and autonomic neuropathy type 1 (HSAN1). By incorporating l-alanine in place of l-serine, the mutant HSAN1–associated serine palmitoyltransferase generates deoxysphingolipids, which are thought to be neurotoxic. In this issue of the JCI, Garofalo and colleagues report that oral l-serine reverses the accumulation of deoxysphingolipids in humans with HSAN1 and in a transgenic mouse model. As oral l-serine reduces the severity of neuropathy in the mouse model of HSAN1, these data suggest a rational candidate therapy for this devastating condition.

I nclusion body myopathy with Paget disease of the bone and frontotemporal dementia (IBMPFD) is a multisystem degenerative disorder caused by mutations in the valosin-containing protein (VCP) gene. How missense mutations in this abundant, ubiquitously expressed, multifunctional protein lead to the degeneration of disparate tissues is unclear. VCP participates in diverse cellular functions by associating with an expanding collection of substrates and cofactors that dictate its functionality. In this issue of the JCI, Wang and colleagues have further expanded the VCP interactome by identifying neurofibromin-1 (NF1) as a novel VCP interactor in the CNS. IBMPFD-associated mutations disrupt binding of VCP to NF1, resulting in reduced synaptogenesis. Thus, aberrant interactions between VCP and NF1 may explain the dementia phenotype and cognitive delay observed in patients with IBMPFD and neurofibromatosis type 1.

W hile it has been well established that the fetal liver originates from foregut endoderm, the identity of the mechanisms that maintain liver mass under both basal and injury conditions remains controversial. Dramatically different models have been proposed based on the experimental design employed. In this issue of the JCI, Malato and colleagues report their elegant new model for genetic lineage tracing of mature mouse hepatocytes using an adenoassociated virus–driven Cre recombinase. They show convincingly that maintenance of liver mass during normal turnover or in response to mild injury is achieved by mature hepatocytes, rather than cholangiocytes or specialized progenitor cells, as has been suggested by others.

C entral to our ability to hear and sense gravity is a cellular process known as mechanotransduction, which is initiated by the opening of mechanosensitive cation channels located near the tips of the stereocilia of auditory and vestibular inner ear hair cells. The molecular identity of the mechanotransduction channels has eluded researchers despite intensive investigations over the years. In this issue of the JCI, Kawashima et al. report their results obtained using mice with targeted deletion of both transmembrane channel–like 1 (Tmc1) and Tmc2. The use of inner ear hair cells isolated from these mice provided a nearly perfect system for testing the mechanotransduction channels without disrupting functions of other accessory proteins needed in the complicated molecular apparatus, and it allowed the authors to show that the proteins encoded by these genes are integral components of the mechanotransduction complex.

D ecline in immune function with age has been attributed to defects or alterations in both the innate and the adaptive immune system. In this issue of the JCI, Zhao and coworkers provide evidence for a novel mechanism of immune dysfunction in aging mice. They show that migration of respiratory DCs from the site of virus replication to the draining lymph nodes in response to infection with several different respiratory viruses is markedly diminished with increasing age. The impaired DC migration was a result of increased levels of the lipid mediator prostaglandin D₂ (PGD₂) in the respiratory tract with age and could be partially reversed by blockade of PGD₂ synthesis or action.

H uman mutations in or variants of TBX20 are associated with congenital heart disease, cardiomyopathy, and arrhythmias. To investigate whether cardiac disease in patients with these conditions results from an embryonic or ongoing requirement for Tbx20 in myocardium, we ablated Tbx20 specifically in adult cardiomyocytes in mice. This ablation resulted in the onset of severe cardiomyopathy accompanied by arrhythmias, with death ensuing within 1 to 2 weeks of Tbx20 ablation. Accounting for this dramatic phenotype, we identified molecular signatures that posit Tbx20 as a central integrator of a genetic program that maintains cardiomyocyte function in the adult heart. Expression of a number of genes encoding critical transcription factors, ion channels, and cytoskeletal/myofibrillar proteins was downregulated consequent to loss of Tbx20. Genome-wide ChIP analysis of Tbx20-binding regions in the adult heart revealed that many of these genes were direct downstream targets of Tbx20 and uncovered a previously undescribed DNA-binding site for Tbx20. Bioinformatics and in vivo functional analyses revealed a cohort of transcription factors that, working with Tbx20, integrated multiple environmental signals to maintain ion channel gene expression in the adult heart. Our data provide insight into the mechanisms by which mutations in TBX20 cause adult heart disease in humans.

P arathyroid hormone–related protein (PTHrP) is a secreted factor expressed in almost all normal fetal and adult tissues. It is involved in a wide range of developmental and physiological processes, including serum calcium regulation. PTHrP is also associated with the progression of skeletal metastases, and its dysregulated expression in advanced cancers causes malignancy-associated hypercalcemia. Although PTHrP is frequently expressed by breast tumors and other solid cancers, its effects on tumor progression are unclear. Here, we demonstrate in mice pleiotropic involvement of PTHrP in key steps of breast cancer — it influences the initiation and progression of primary tumors and metastases. Pthrp ablation in the mammary epithelium of the PyMT-MMTV breast cancer mouse model caused a delay in primary tumor initiation, inhibited tumor progression, and reduced metastasis to distal sites. Mechanistically, it reduced expression of molecular markers of cell proliferation (Ki67) and angiogenesis (factor VIII), antiapoptotic factor Bcl-2, cell-cycle progression regulator cyclin D1, and survival factor AKT1. PTHrP also influenced expression of the adhesion factor CXCR4, and coexpression of PTHrP and CXCR4 was crucial for metastatic spread. Importantly, PTHrP-specific neutralizing antibodies slowed the progression and metastasis of human breast cancer xenografts. Our data identify what we believe to be new functions for PTHrP in several key steps of breast cancer and suggest that PTHrP may constitute a novel target for therapeutic intervention.

T wo hallmarks of glioblastoma multiforme, the most common malignant brain cancer in humans, are aggressive growth and the ability of single glioma cells to disperse throughout the brain. These characteristics render tumors resistant to current therapies and account for the poor prognosis of patients. Although it is known that oncogenic signaling caused by overexpression of genes such as PDGFRA is responsible for robust glioma growth and cell infiltration, the mechanisms underlying glioblastoma malignancy remain largely elusive. Here, we report that PDGFRα signaling in glioblastomas leads to Src-dependent phosphorylation of the guanine nucleotide exchange factor Dock180 at tyrosine 1811 (Dock180^Y1811) that results in activation of the GTPase Rac1 and subsequent cell growth and invasion. In human glioma cells, knockdown of Dock180 and reversion with an RNAi-resistant Dock180^Y1811F abrogated, whereas an RNAi-resistant Dock180^WT rescued, PDGFRα-promoted glioma growth, survival, and invasion. Phosphorylation of Dock180^Y1811 enhanced its association with CrkII and p130^Cas, causing activation of Rac1 and consequent cell motility. Dock180 also associated with PDGFRα to promote cell migration. Finally, phosphorylated Dock180^Y1811 was detected in clinical samples of gliomas and various types of human cancers, and coexpression of phosphorylated Dock180^Y1811, phosphorylated Src^Y418, and PDGFRα was predictive of extremely poor prognosis of patients with gliomas. Taken together, our findings provide insight into PDGFRα-stimulated gliomagenesis and suggest that phosphorylated Dock180^Y1811 contributes to activation of Rac1 in human cancers with PDGFRA amplification.

T he majority of human pancreatic cancers have activating mutations in the KRAS proto-oncogene. These mutations result in increased activity of the NF-κB pathway and the subsequent constitutive production of proinflammatory cytokines. Here, we show that inhibitor of κB kinase 2 (Ikk2), a component of the canonical NF-κB signaling pathway, synergizes with basal Notch signaling to upregulate transcription of primary Notch target genes, resulting in suppression of antiinflammatory protein expression and promotion of pancreatic carcinogenesis in mice. We found that in the Kras^G12DPdx1-cre mouse model of pancreatic cancer, genetic deletion of Ikk2 in initiated pre-malignant epithelial cells substantially delayed pancreatic oncogenesis and resulted in downregulation of the classical Notch target genes Hes1 and Hey1. Tnf-α stimulated canonical NF-κB signaling and, in collaboration with basal Notch signals, induced optimal expression of Notch targets. Mechanistically, Tnf-α stimulation resulted in phosphorylation of histone H3 at the Hes1 promoter, and this signal was lost with Ikk2 deletion. Hes1 suppresses expression of Pparg, which encodes the antiinflammatory nuclear receptor Pparγ. Thus, crosstalk between Tnf-α/Ikk2 and Notch sustains the intrinsic inflammatory profile of transformed cells. These findings reveal what we believe to be a novel interaction between oncogenic inflammation and a major cell fate pathway and show how these pathways can cooperate to promote cancer progression.

A dvanced human thyroid cancers, particularly those that are refractory to treatment with radioiodine (RAI), have a high prevalence of BRAF (v-raf murine sarcoma viral oncogene homolog B1) mutations. However, the degree to which these cancers are dependent on BRAF expression is still unclear. To address this question, we generated mice expressing one of the most commonly detected BRAF mutations in human papillary thyroid carcinomas (BRAF^V600E) in thyroid follicular cells in a doxycycline-inducible (dox-inducible) manner. Upon dox induction of BRAF^V600E, the mice developed highly penetrant and poorly differentiated thyroid tumors. Discontinuation of dox extinguished BRAF^V600E expression and reestablished thyroid follicular architecture and normal thyroid histology. Switching on BRAF^V600E rapidly induced hypothyroidism and virtually abolished thyroid-specific gene expression and RAI incorporation, all of which were restored to near basal levels upon discontinuation of dox. Treatment of mice with these cancers with small molecule inhibitors of either MEK or mutant BRAF reduced their proliferative index and partially restored thyroid-specific gene expression. Strikingly, treatment with the MAPK pathway inhibitors rendered the tumor cells susceptible to a therapeutic dose of RAI. Our data show that thyroid tumors carrying BRAF^V600E mutations are exquisitely dependent on the oncoprotein for viability and that genetic or pharmacological inhibition of its expression or activity is associated with tumor regression and restoration of RAI uptake in vivo in mice. These findings have potentially significant clinical ramifications.

C ushing disease is a condition in which the pituitary gland releases excessive adrenocorticotropic hormone (ACTH) as a result of an adenoma arising from the ACTH-secreting cells in the anterior pituitary. ACTH-secreting pituitary adenomas lead to hypercortisolemia and cause significant morbidity and mortality. Pituitary-directed medications are mostly ineffective, and new treatment options are needed. As these tumors express EGFR, we tested whether EGFR might provide a therapeutic target for Cushing disease. Here, we show that in surgically resected human and canine corticotroph cultured tumors, blocking EGFR suppressed expression of proopiomelanocortin (POMC), the ACTH precursor. In mouse corticotroph EGFR transfectants, ACTH secretion was enhanced, and EGF increased Pomc promoter activity, an effect that was dependent on MAPK. Blocking EGFR activity with gefitinib, an EGFR tyrosine kinase inhibitor, attenuated Pomc expression, inhibited corticotroph tumor cell proliferation, and induced apoptosis. As predominantly nuclear EGFR expression was observed in canine and human corticotroph tumors, we preferentially targeted EGFR to mouse corticotroph cell nuclei, which resulted in higher Pomc expression and ACTH secretion, both of which were inhibited by gefitinib. In athymic nude mice, EGFR overexpression enhanced the growth of explanted ACTH-secreting tumors and further elevated serum corticosterone levels. Gefitinib treatment decreased both tumor size and corticosterone levels; it also reversed signs of hypercortisolemia, including elevated glucose levels and excess omental fat. These results indicate that inhibiting EGFR signaling may be a novel strategy for treating Cushing disease.

N eural stem cells (NSCs) persist in defined brain niches, including the subventricular zone (SVZ), throughout adulthood and generate new neurons destined to support specific neurological functions. Whether brain diseases such as multiple sclerosis (MS) are associated with changes in adult NSCs and whether this might contribute to the development and/or persistence of neurological deficits remains poorly investigated. We examined SVZ function in mice in which we targeted an MS-like pathology to the forebrain. In these mice, which we refer to herein as targeted EAE (tEAE) mice, there was a reduction in the number of neuroblasts compared with control mice. Altered expression of the transcription factors Olig2 and Dlx2 in the tEAE SVZ niche was associated with amplification of pro-oligodendrogenic transit-amplifying cells and decreased neuroblast generation, which resulted in persistent reduction in olfactory bulb neurogenesis. Altered SVZ neurogenesis led to impaired long-term olfactory memory, mimicking the olfactory dysfunction observed in MS patients. Importantly, we also found that neurogenesis was reduced in the SVZ of MS patients compared with controls. Thus, our findings suggest that neuroinflammation induces functional alteration of adult NSCs that may contribute to olfactory dysfunction in MS patients.

H ereditary sensory and autonomic neuropathy type 1 (HSAN1) causes sensory loss that predominantly affects the lower limbs, often preceded by hyperpathia and spontaneous shooting or lancinating pain. It is caused by several missense mutations in the genes encoding 2 of the 3 subunits of the enzyme serine palmitoyltransferase (SPT). The mutant forms of the enzyme show a shift from their canonical substrate l-serine to the alternative substrate l-alanine. This shift leads to increased formation of neurotoxic deoxysphingolipids (dSLs). Our initial analysis showed that in HEK cells transfected with SPTLC1 mutants, dSL generation was modulated in vitro in the presence of various amino acids. We therefore examined whether in vivo specific amino acid substrate supplementation influenced dSL levels and disease severity in HSAN1. In mice bearing a transgene expressing the C133W SPTLC1 mutant linked to HSAN1, a 10% l-serine–enriched diet reduced dSL levels. l-serine supplementation also improved measures of motor and sensory performance as well as measures of male fertility. In contrast, a 10% l-alanine–enriched diet increased dSL levels and led to severe peripheral neuropathy. In a pilot study with 14 HSAN1 patients, l-serine supplementation similarly reduced dSL levels. These observations support the hypothesis that an altered substrate selectivity of the mutant SPT is key to the pathophysiology of HSAN1 and raise the prospect of l-serine supplementation as a first treatment option for this disorder.

S olid tumors are complex masses with a local microenvironment, or stroma, that supports tumor growth and progression. Among the diverse tumor-supporting stromal cells is a heterogeneous population of myeloid-derived cells. These cells are alternatively activated and contribute to the immunosuppressive environment of the tumor; overcoming their immunosuppressive effects may improve the efficacy of cancer immunotherapies. We recently found that engineering tumor-specific CD8⁺ T cells to secrete the inflammatory cytokine IL-12 improved their therapeutic efficacy in the B16 mouse model of established melanoma. Here, we report the mechanism underlying this finding. Surprisingly, direct binding of IL-12 to receptors on lymphocytes or NK cells was not required. Instead, IL-12 sensitized bone marrow–derived tumor stromal cells, including CD11b⁺F4/80^hi macrophages, CD11b⁺MHCII^hiCD11c^hi dendritic cells, and CD11b⁺Gr-1^hi myeloid–derived suppressor cells, causing them to enhance the effects of adoptively transferred CD8⁺ T cells. This reprogramming of myeloid-derived cells occurred partly through IFN-γ. Surprisingly, direct presentation of antigen to the transferred CD8⁺ T cells by tumor was not necessary; however, MHCI expression on host cells was essential for IL-12–mediated antitumor enhancements. These results are consistent with a model in which IL-12 enhances the ability of CD8⁺ T cells to collapse large vascularized tumors by triggering programmatic changes in otherwise suppressive antigen-presenting cells within tumors and support the use of IL-12 as part of immunotherapy for the treatment of solid tumors.

M any autoimmune diseases exhibit familial aggregation, indicating that they have genetic determinants. Single nucleotide polymorphisms in PTPN2, which encodes T cell protein tyrosine phosphatase (TCPTP), have been linked with the development of several autoimmune diseases, including type 1 diabetes and Crohn’s disease. In this study, we have identified TCPTP as a key negative regulator of TCR signaling, which might explain the association of PTPN2 SNPs with autoimmune disease. We found that TCPTP dephosphorylates and inactivates Src family kinases to regulate T cell responses. Using T cell–specific TCPTP-deficient mice, we established that TCPTP attenuates T cell activation and proliferation in vitro and blunts antigen-induced responses in vivo. TCPTP deficiency lowered the in vivo threshold for TCR-dependent CD8⁺ T cell proliferation. Consistent with this, T cell–specific TCPTP-deficient mice developed widespread inflammation and autoimmunity that was transferable to wild-type recipient mice by CD8⁺ T cells alone. This autoimmunity was associated with increased serum levels of proinflammatory cytokines and anti-nuclear antibodies, T cell infiltrates in non-lymphoid tissues, and liver disease. These data indicate that TCPTP is a critical negative regulator of TCR signaling that sets the threshold for TCR-induced naive T cell responses to prevent autoimmune and inflammatory disorders arising.

N F-κB–inducing kinase (NIK) is an essential upstream kinase in noncanonical NF-κB signaling. NIK-dependent NF-κB activation downstream of several TNF receptor family members mediates lymphoid organ development and B cell homeostasis. Peripheral T cell populations are normal in the absence of NIK, but the role of NIK during in vivo T cell responses to antigen has been obscured by other developmental defects in NIK-deficient mice. Here, we have identified a T cell–intrinsic requirement for NIK in graft-versus-host disease (GVHD), wherein NIK-deficient mouse T cells transferred into MHC class II mismatched recipients failed to cause GVHD. Although NIK was not necessary for antigen receptor signaling, it was absolutely required for costimulation through the TNF receptor family member OX40 (also known as CD134). When we conditionally overexpressed NIK in T cells, mice suffered rapid and fatal autoimmunity characterized by hyperactive effector T cells and poorly suppressive Foxp3⁺ Tregs. Together, these data illuminate a critical T cell–intrinsic role for NIK during immune responses and suggest that its tight regulation is critical for avoiding autoimmunity.

T he two most common forms of inflammatory bowel disease (IBD), Crohn’s disease and ulcerative colitis, affect approximately 1 million people in the United States. Uncontrolled APC reactivity toward commensal bacteria is implicated in the pathogenesis of the disease. A number of functionally distinct APC populations exist in the mucosal lamina propria (LP) below the intestinal epithelium, but their relative contributions to inflammation remain unclear. Here, we demonstrate in mice important roles for the chemokine receptor CX3CR1 in maintaining LP macrophage populations, preventing translocation of commensal bacteria to mesenteric lymph nodes (mLNs), and limiting colitogenic Th17 responses. CX3CR1 was found to be expressed in resident LP macrophages (defined as CD11b⁺F4/80⁺) but not DCs (defined as CD11c⁺CD103⁺). LP macrophage frequency and number were decreased in two strains of CX3CR1-knockout mice and in mice deficient in the CX3CR1 ligand CX3CL1. All these knockout strains displayed markedly increased translocation of commensal bacteria to mLNs. Additionally, the severity of DSS-induced colitis was dramatically enhanced in the knockout mice as compared with controls. Disease severity could be limited by either administration of neutralizing IL-17A antibodies or transfer of CX3CR1-sufficient macrophages. Our data thus suggest key roles for the CX3CR1/CX3CL1 axis in the intestinal mucosa; further clarification of CX3CR1 function will likely direct efforts toward therapeutic intervention for mucosal inflammatory disorders such as IBD.

I nner ear hair cells convert the mechanical stimuli of sound, gravity, and head movement into electrical signals. This mechanotransduction process is initiated by opening of cation channels near the tips of hair cell stereocilia. Since the identity of these ion channels is unknown, and mutations in the gene encoding transmembrane channel–like 1 (TMC1) cause hearing loss without vestibular dysfunction in both mice and humans, we investigated the contribution of Tmc1 and the closely related Tmc2 to mechanotransduction in mice. We found that Tmc1 and Tmc2 were expressed in mouse vestibular and cochlear hair cells and that GFP-tagged TMC proteins localized near stereocilia tips. Tmc2 expression was transient in early postnatal mouse cochlear hair cells but persisted in vestibular hair cells. While mice with a targeted deletion of Tmc1 (Tmc1^Δ mice) were deaf and those with a deletion of Tmc2 (Tmc2^Δ mice) were phenotypically normal, Tmc1^ΔTmc2^Δ mice had profound vestibular dysfunction, deafness, and structurally normal hair cells that lacked all mechanotransduction activity. Expression of either exogenous TMC1 or TMC2 rescued mechanotransduction in Tmc1^ΔTmc2^Δ mutant hair cells. Our results indicate that TMC1 and TMC2 are necessary for hair cell mechanotransduction and may be integral components of the mechanotransduction complex. Our data also suggest that persistent TMC2 expression in vestibular hair cells may preserve vestibular function in humans with hearing loss caused by TMC1 mutations.

E rythropoiesis, the production of red blood cells, must be tightly controlled to ensure adequate oxygen delivery to tissues without causing thrombosis or stroke. Control of physiologic and pathologic erythropoiesis is dependent predominantly on erythropoietin (EPO), the expression of which is regulated by hypoxia-inducible factor (HIF) activity in response to low oxygen tension. Accumulating evidence indicates that oxygen-independent mediators, including inflammatory stimuli, cytokines, and growth factors, also upregulate HIF activity, but it is unclear whether these signals also result in EPO production and erythropoiesis in vivo. Here, we found that signaling through herpesvirus entry mediator (HVEM), a molecule of the TNF receptor superfamily, promoted HIF-1α activity in the kidney and subsequently facilitated renal Epo production and erythropoiesis in vivo under normoxic conditions. This Epo upregulation was mediated by increased production of NO by renal macrophages. Hvem-deficient mice displayed impaired Epo expression and aggravated anemia in response to erythropoietic stress. These data reveal that HVEM signaling functions to promote HIF-1α activity and Epo production, and thus to regulate erythropoiesis. Furthermore, our findings suggest that this molecular mechanism could represent a therapeutic target for Epo-responsive diseases, including anemia.

I nclusion body myopathy with Paget disease of bone and frontotemporal dementia (IBMPFD) is an autosomal dominant disorder characterized by progressive myopathy that is often accompanied by bone weakening and/or frontotemporal dementia. Although it is known to be caused by mutations in the gene encoding valosin-containing protein (VCP), the underlying disease mechanism remains elusive. Like IBMPFD, neurofibromatosis type 1 (NF1) is an autosomal dominant disorder. Neurofibromin, the protein encoded by the NF1 gene, has been shown to regulate synaptogenesis. Here, we show that neurofibromin and VCP interact and work together to control the density of dendritic spines. Certain mutations identified in IBMPFD and NF1 patients reduced the interaction between VCP and neurofibromin and impaired spinogenesis. The functions of neurofibromin and VCP in spinogenesis were shown to correlate with the learning disability and dementia phenotypes seen in patients with IBMPFD. Consistent with the previous finding that treatment with a statin rescues behavioral defects in Nf1^+/– mice and providing further support for our hypothesis that there is crosstalk between neurofibromin and VCP, statin exposure neutralized the effect of VCP knockdown on spinogenesis in cultured hippocampal neurons. The data presented here demonstrate that there is a link between IBMPFD and NF1 and indicate a role for VCP in synapse formation.

C utaneous T cell lymphomas (CTCLs) represent a heterogeneous group of non-Hodgkin lymphomas that affect the skin. The pathogenesis of these conditions is poorly understood. For example, the signaling mechanisms contributing to the dysregulated growth of the neoplastic T cells are not well defined. Here, we demonstrate that loss of nuclear localization of pro–IL-16 facilitates CTCL cell proliferation by causing a decrease in expression of the cyclin dependent–kinase inhibitor p27Kip1. The decrease in p27Kip1 expression was directly attributable to an increase in expression of S-phase kinase-associated protein 2 (Skp2). Regulation of Skp2 is in part attributed to the nuclear presence of the scaffold protein pro–IL-16. T cells isolated from 11 patients with advanced CTCL, but not those from healthy controls or patients with T cell acute lymphocytic leukemia (T-ALL), demonstrated reduction in nuclear pro–IL-16 levels. Sequence analysis identified the presence of mutations in the 5ι end of the PDZ1 region of pro–IL-16, a domain required for association of pro–IL-16 with the nuclear chaperone HSC70 (also known as HSPA8). HSC70 knockdown led to loss of nuclear translocation by pro–IL-16 and subsequent increases in Skp2 levels and decreases in p27Kip1 levels, which ultimately enhanced T cell proliferation. Thus, our data indicate that advanced CTCL cell growth is facilitated, at least in part, by mutations in the scaffold protein pro–IL-16, which directly regulates Skp2 synthesis.

R ecent evidence has contradicted the prevailing view that homeostasis and regeneration of the adult liver are mediated by self duplication of lineage-restricted hepatocytes and biliary epithelial cells. These new data suggest that liver progenitor cells do not function solely as a backup system in chronic liver injury; rather, they also produce hepatocytes after acute injury and are in fact the main source of new hepatocytes during normal hepatocyte turnover. In addition, other evidence suggests that hepatocytes are capable of lineage conversion, acting as precursors of biliary epithelial cells during biliary injury. To test these concepts, we generated a hepatocyte fate-tracing model based on timed and specific Cre recombinase expression and marker gene activation in all hepatocytes of adult Rosa26 reporter mice with an adenoassociated viral vector. We found that newly formed hepatocytes derived from preexisting hepatocytes in the normal liver and that liver progenitor cells contributed minimally to acute hepatocyte regeneration. Further, we found no evidence that biliary injury induced conversion of hepatocytes into biliary epithelial cells. These results therefore restore the previously prevailing paradigms of liver homeostasis and regeneration. In addition, our new vector system will be a valuable tool for timed, efficient, and specific loop out of floxed sequences in hepatocytes.

O xidative modification of LDL is an early pathological event in the development of atherosclerosis. Oxidation events such as malondialdehyde (MDA) formation may produce specific, immunogenic epitopes. Indeed, antibodies to MDA-derived epitopes are widely used in atherosclerosis research and have been demonstrated to enable cardiovascular imaging. In this study, we engineered a transgenic zebrafish with temperature-inducible expression of an EGFP-labeled single-chain human monoclonal antibody, IK17, which binds to MDA-LDL, and used optically transparent zebrafish larvae for imaging studies. Feeding a high-cholesterol diet (HCD) supplemented with a red fluorescent lipid marker to the transgenic zebrafish resulted in vascular lipid accumulation, quantified in live animals using confocal microscopy. After heat shock–induced expression of IK17-EGFP, we measured the time course of vascular accumulation of IK17-specific MDA epitopes. Treatment with either an antioxidant or a regression diet resulted in reduced IK17 binding to vascular lesions. Interestingly, homogenates of IK17-EGFP–expressing larvae bound to MDA-LDL and inhibited MDA-LDL binding to macrophages. Moreover, sustained expression of IK17-EGFP effectively prevented HCD-induced lipid accumulation in the vascular wall, suggesting that the antibody itself may have therapeutic effects. Thus, we conclude that HCD-fed zebrafish larvae with conditional expression of EGFP-labeled oxidation-specific antibodies afford an efficient method of testing dietary and/or other therapeutic antioxidant strategies that may ultimately be applied to humans.

T ype 1 diabetes develops when most insulin-producing β cells of the pancreas are killed by an autoimmune attack. The in vivo conditions modulating the sensitivity and resistance of β cells to this attack remain largely obscure. Here, we show that connexin 36 (Cx36), a trans-membrane protein that forms gap junctions between β cells in the pancreatic islets, protects mouse β cells against both cytotoxic drugs and cytokines that prevail in the islet environment at the onset of type 1 diabetes. We documented that this protection was at least partially dependent on intercellular communication, which Cx36 and other types of connexin channels establish within pancreatic islets. We further found that proinflammatory cytokines decreased expression of Cx36 and that experimental reduction or augmentation of Cx36 levels increased or decreased β cell apoptosis, respectively. Thus, we conclude that Cx36 is central to β cell protection from toxic insults.

I ron overload is the hallmark of hereditary hemochromatosis and a complication of iron-loading anemias such as β-thalassemia. Treatment can be burdensome and have significant side effects, and new therapeutic options are needed. Iron overload in hereditary hemochromatosis and β-thalassemia intermedia is caused by hepcidin deficiency. Although transgenic hepcidin replacement in mouse models of these diseases prevents iron overload or decreases its potential toxicity, natural hepcidin is prohibitively expensive for human application and has unfavorable pharmacologic properties. Here, we report the rational design of hepcidin agonists based on the mutagenesis of hepcidin and the hepcidin-binding region of ferroportin and computer modeling of their docking. We identified specific hydrophobic/aromatic residues required for hepcidin-ferroportin binding and obtained evidence in vitro that a thiol-disulfide interaction between ferroportin C326 and the hepcidin disulfide cage may stabilize binding. Guided by this model, we showed that 7–9 N-terminal amino acids of hepcidin, including a single thiol cysteine, comprised the minimal structure that retained hepcidin activity, as shown by the induction of ferroportin degradation in reporter cells. Further modifications to increase resistance to proteolysis and oral bioavailability yielded minihepcidins that, after parenteral or oral administration to mice, lowered serum iron levels comparably to those after parenteral native hepcidin. Moreover, liver iron concentrations were lower in mice chronically treated with minihepcidins than those in mice treated with solvent alone. Minihepcidins may be useful for the treatment of iron overload disorders.

H erpes simplex encephalitis (HSE) is the most common sporadic viral encephalitis of childhood. Autosomal recessive (AR) UNC-93B and TLR3 deficiencies and autosomal dominant (AD) TLR3 and TRAF3 deficiencies underlie HSE in some children. We report here unrelated HSE children with AR or AD TRIF deficiency. The AR form of the disease was found to be due to a homozygous nonsense mutation that resulted in a complete absence of the TRIF protein. Both the TLR3- and the TRIF-dependent TLR4 signaling pathways were abolished. The AD form of disease was found to be due to a heterozygous missense mutation, resulting in a dysfunctional protein. In this form of the disease, the TLR3 signaling pathway was impaired, whereas the TRIF-dependent TLR4 pathway was unaffected. Both patients, however, showed reduced capacity to respond to stimulation of the DExD/H-box helicases pathway. To date, the TRIF-deficient patients with HSE described herein have suffered from no other infections. Moreover, as observed in patients with other genetic etiologies of HSE, clinical penetrance was found to be incomplete, as some HSV-1–infected TRIF-deficient relatives have not developed HSE. Our results provide what we believe to be the first description of human TRIF deficiency and a new genetic etiology for HSE. They suggest that the TRIF-dependent TLR4 and DExD/H-box helicase pathways are largely redundant in host defense. They further demonstrate the importance of TRIF for the TLR3-dependent production of antiviral IFNs in the CNS during primary infection with HSV-1 in childhood.

I ndividuals who are obese are frequently insulin resistant, putting them at increased risk of developing type 2 diabetes and its associated adverse health conditions. The accumulation in adipose tissue of macrophages in an inflammatory state is a hallmark of obesity-induced insulin resistance. Here, we reveal a role for AMPK β1 in protecting macrophages from inflammation under high lipid exposure. Genetic deletion of the AMPK β1 subunit in mice (referred to herein as β1^–/– mice) reduced macrophage AMPK activity, acetyl-CoA carboxylase phosphorylation, and mitochondrial content, resulting in reduced rates of fatty acid oxidation. β1^–/– macrophages displayed increased levels of diacylglycerol and markers of inflammation, effects that were reproduced in WT macrophages by inhibiting fatty acid oxidation and, conversely, prevented by pharmacological activation of AMPK β1–containing complexes. The effect of AMPK β1 loss in macrophages was tested in vivo by transplantation of bone marrow from WT or β1^–/– mice into WT recipients. When challenged with a high-fat diet, mice that received β1^–/– bone marrow displayed enhanced adipose tissue macrophage inflammation and liver insulin resistance compared with animals that received WT bone marrow. Thus, activation of AMPK β1 and increasing fatty acid oxidation in macrophages may represent a new therapeutic approach for the treatment of insulin resistance.

I ncreased endogenous glucose production (EGP) is a hallmark of type 2 diabetes mellitus. While there is evidence for central regulation of EGP by activation of hypothalamic ATP-sensitive potassium (K_ATP) channels in rodents, whether these central pathways contribute to regulation of EGP in humans remains to be determined. Here we present evidence for central nervous system regulation of EGP in humans that is consistent with complementary rodent studies. Oral administration of the K_ATP channel activator diazoxide under fixed hormonal conditions substantially decreased EGP in nondiabetic humans and Sprague Dawley rats. In rats, comparable doses of oral diazoxide attained appreciable concentrations in the cerebrospinal fluid, and the effects of oral diazoxide were abolished by i.c.v. administration of the K_ATP channel blocker glibenclamide. These results suggest that activation of hypothalamic K_ATP channels may be an important regulator of EGP in humans and that this pathway could be a target for treatment of hyperglycemia in type 2 diabetes mellitus.

T he morbidity and mortality associated with respiratory virus infection is felt most keenly among the elderly. T cells are necessary for viral clearance, and many age-dependent intrinsic T cell defects have been documented. However, the development of robust T cell responses in the lung also requires respiratory DCs (rDCs), which must process antigen and migrate to draining LNs (DLNs), and little is known about age-related defects in these T cell–extrinsic functions. Here, we show that increases in prostaglandin D₂ (PGD₂) expression in mouse lungs upon aging correlate with a progressive impairment in rDC migration to DLNs. Decreased rDC migration resulted in diminished T cell responses and more severe clinical disease in older mice infected with respiratory viruses. Diminished rDC migration associated with virus-specific defects in T cell responses and was not a result of cell-intrinsic defect, rather it reflected the observed age-dependent increases in PGD₂ expression. Blocking PGD₂ function with small-molecule antagonists enhanced rDC migration, T cell responses, and survival. This effect correlated with upregulation on rDCs of CCR7, a chemokine receptor involved in DC chemotaxis. Our results suggest that inhibiting PGD₂ function may be a useful approach to enhance T cell responses against respiratory viruses in older humans.