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Abstract

Patients with cerebral small-vessel disease (CSVD) exhibit perturbed end-artery function and have an increased risk for stroke and age-related cognitive decline. Here, we used targeted genome-wide association (GWA) analysis and defined a CSVD locus adjacent to the forkhead transcription factor FOXC1. Moreover, we determined that the linked SNPs influence FOXC1 transcript levels and demonstrated that patients as young as 1 year of age with altered FOXC1 function exhibit CSVD. MRI analysis of patients with missense and nonsense mutations as well as FOXC1-encompassing segmental duplication and deletion revealed white matter hyperintensities, dilated perivascular spaces, and lacunar infarction. In a zebrafish model, overexpression or morpholino-induced suppression of foxc1 induced cerebral hemorrhage. Inhibition of foxc1 perturbed platelet-derived growth factor (Pdgf) signaling, impairing neural crest migration and the recruitment of mural cells, which are essential for vascular stability. GWA analysis also linked the FOXC1-interacting transcription factor PITX2 to CSVD, and both patients with PITX2 mutations and murine Pitx2–/– mutants displayed brain vascular phenotypes. Together, these results extend the genetic etiology of stroke and demonstrate an increasing developmental basis for human cerebrovascular disease.

Authors

Curtis R. French ... Andrew J. Waskiewicz, Ordan J. Lehmann

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Abstract

Nemaline myopathy (NM) is a genetic muscle disorder characterized by muscle dysfunction and electron-dense protein accumulations (nemaline bodies) in myofibers. Pathogenic mutations have been described in 9 genes to date, but the genetic basis remains unknown in many cases. Here, using an approach that combined whole-exome sequencing (WES) and Sanger sequencing, we identified homozygous or compound heterozygous variants in LMOD3 in 21 patients from 14 families with severe, usually lethal, NM. LMOD3 encodes leiomodin-3 (LMOD3), a 65-kDa protein expressed in skeletal and cardiac muscle. LMOD3 was expressed from early stages of muscle differentiation; localized to actin thin filaments, with enrichment near the pointed ends; and had strong actin filament-nucleating activity. Loss of LMOD3 in patient muscle resulted in shortening and disorganization of thin filaments. Knockdown of lmod3 in zebrafish replicated NM-associated functional and pathological phenotypes. Together, these findings indicate that mutations in the gene encoding LMOD3 underlie congenital myopathy and demonstrate that LMOD3 is essential for the organization of sarcomeric thin filaments in skeletal muscle.

Authors

Michaela Yuen ... Kathryn N. North, Nigel F. Clarke

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Abstract

Activating mutations in the KRAS oncogene are prevalent in pancreatic ductal adenocarcinoma (PDAC). We previously demonstrated that pancreatic intraepithelial neoplasia (PanIN) formation, which precedes malignant transformation, associates with the expression of immediate early response 3 (Ier3) as part of a prooncogenic transcriptional pathway. Here, we evaluated the role of IER3 in PanIN formation and PDAC development. In human pancreatic cancer cells, IER3 expression efficiently sustained ERK1/2 phosphorylation by inhibiting phosphatase PP2A activity. Moreover, IER3 enhanced KrasG12D-dependent oncogenesis in the pancreas, as both PanIN and PDAC development were delayed in IER3-deficient KrasG12D mice. IER3 expression was discrete in healthy acinar cells, becoming highly prominent in peritumoral acini, and particularly high in acinar ductal metaplasia (ADM) and PanIN lesions, where IER3 colocalized with phosphorylated ERK1/2. However, IER3 was absent in undifferentiated PDAC, which suggests that the IER3-dependent pathway is an early event in pancreatic tumorigenesis. IER3 expression was induced by both mild and severe pancreatitis, which promoted PanIN formation and progression to PDAC in KrasG12D mice. In IER3-deficient mice, pancreatitis abolished KrasG12D-induced proliferation, which suggests that pancreatitis enhances the oncogenic effect of KRAS through induction of IER3 expression. Together, our data indicate that IER3 supports KRASG12D-associated oncogenesis in the pancreas by sustaining ERK1/2 phosphorylation via phosphatase PP2A inhibition.

Authors

Maria Noé Garcia ... Raul Urrutia, Juan L. Iovanna

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Abstract

Familial hyperkalemic hypertension (FHHt) is a monogenic disease resulting from mutations in genes encoding WNK kinases, the ubiquitin scaffold protein cullin 3 (CUL3), or the substrate adaptor kelch-like 3 (KLHL3). Disease-associated CUL3 mutations abrogate WNK kinase degradation in cells, but it is not clear how mutant forms of CUL3 promote WNK stability. Here, we demonstrated that an FHHt-causing CUL3 mutant (CUL3 Δ403–459) not only retains the ability to bind and ubiquitylate WNK kinases and KLHL3 in cells, but is also more heavily neddylated and activated than WT CUL3. In cells, activated CUL3 Δ403–459 depleted KLHL3, preventing WNK degradation, despite increased CUL3-mediated WNK ubiquitylation; therefore, CUL3 loss in kidney should phenocopy FHHt in murine models. As predicted, nephron-specific deletion of Cul3 in mice did increase WNK kinase levels and the abundance of phosphorylated Na-Cl cotransporter (NCC). Over time, however, Cul3 deletion caused renal dysfunction, including hypochloremic alkalosis, diabetes insipidus, and salt-sensitive hypotension, with depletion of sodium potassium chloride cotransporter 2 and aquaporin 2. Moreover, these animals exhibited renal inflammation, fibrosis, and increased cyclin E. These results indicate that FHHt-associated CUL3 Δ403–459 targets KLHL3 for degradation, thereby preventing WNK degradation, whereas general loss of CUL3 activity — while also impairing WNK degradation — has widespread toxic effects in the kidney.

Authors

James A. McCormick ... Jeffrey D. Singer, David H. Ellison

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Abstract

Breast cancers that occur in women 2–5 years postpartum are more frequently diagnosed at metastatic stages and correlate with poorer outcomes compared with breast cancers diagnosed in young, premenopausal women. The molecular mechanisms underlying the malignant severity associated with postpartum breast cancers (ppBCs) are unclear but relate to stromal wound-healing events during postpartum involution, a dynamic process characterized by widespread cell death in milk-producing mammary epithelial cells (MECs). Using both spontaneous and allografted mammary tumors in fully immune–competent mice, we discovered that postpartum involution increases mammary tumor metastasis. Cell death was widespread, not only occurring in MECs but also in tumor epithelium. Dying tumor cells were cleared through receptor tyrosine kinase MerTK–dependent efferocytosis, which robustly induced the transcription of genes encoding wound-healing cytokines, including IL-4, IL-10, IL-13, and TGF-β. Animals lacking MerTK and animals treated with a MerTK inhibitor exhibited impaired efferocytosis in postpartum tumors, a reduction of M2-like macrophages but no change in total macrophage levels, decreased TGF-β expression, and a reduction of postpartum tumor metastasis that was similar to the metastasis frequencies observed in nulliparous mice. Moreover, TGF-β blockade reduced postpartum tumor metastasis. These data suggest that widespread cell death during postpartum involution triggers efferocytosis-induced wound-healing cytokines in the tumor microenvironment that promote metastatic tumor progression.

Authors

Jamie C. Stanford ... H. Shelton Earp III, Rebecca S. Cook

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Abstract

Hematopoietic stem cells (HSCs) are highly susceptible to ionizing radiation–mediated death via induction of ROS, DNA double-strand breaks, and apoptotic pathways. The development of therapeutics capable of mitigating ionizing radiation–induced hematopoietic toxicity could benefit both victims of acute radiation sickness and patients undergoing hematopoietic cell transplantation. Unfortunately, therapies capable of accelerating hematopoietic reconstitution following lethal radiation exposure have remained elusive. Here, we found that systemic administration of pleiotrophin (PTN), a protein that is secreted by BM-derived endothelial cells, substantially increased the survival of mice following radiation exposure and after myeloablative BM transplantation. In both models, PTN increased survival by accelerating the recovery of BM hematopoietic stem and progenitor cells in vivo. PTN treatment promoted HSC regeneration via activation of the RAS pathway in mice that expressed protein tyrosine phosphatase receptor-zeta (PTPRZ), whereas PTN treatment did not induce RAS signaling in PTPRZ-deficient mice, suggesting that PTN-mediated activation of RAS was dependent upon signaling through PTPRZ. PTN strongly inhibited HSC cycling following irradiation, whereas RAS inhibition abrogated PTN-mediated induction of HSC quiescence, blocked PTN-mediated recovery of hematopoietic stem and progenitor cells, and abolished PTN-mediated survival of irradiated mice. These studies demonstrate the therapeutic potential of PTN to improve survival after myeloablation and suggest that PTN-mediated hematopoietic regeneration occurs in a RAS-dependent manner.

Authors

Heather A. Himburg ... Dennis J. Slamon, John P. Chute

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Abstract

Transport of oxygen by red blood cells (rbc) is critical for life and embryogenesis. Here, we determined that provision of the lipid mediator sphingosine 1-phosphate (S1P) to the systemic circulation is an essential function of rbc in embryogenesis. Mice with rbc-specific deletion of sphingosine kinases 1 and 2 (Sphk1 and Sphk2) showed embryonic lethality between E11.5 and E12.5 due to defects in vascular development. Administration of an S1P1 receptor agonist to pregnant dams rescued early embryonic lethality. Even though rbc-specific Sphk1 Sphk2–KO embryos were anemic, the erythropoietic capacity of hematopoietic stem cells (HSCs) was not impaired, suggesting that rbc can develop in the absence of sphingosine kinase activity. Indeed, transplantation of HSCs deficient for Sphk1 and Sphk2 into adult mice produced rbc that lacked S1P and attenuated plasma S1P levels in recipients. However, in adult animals, both rbc and endothelium contributed to plasma S1P. Together, these findings demonstrate that rbc are essential for embryogenesis by supplying the lysophospholipid S1P, which regulates embryonic vascular development via its receptors.

Authors

Yuquan Xiong, Peiying Yang, Richard L. Proia, Timothy Hla

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September 2014


124-9-cover

September 2014 Issue

On the cover:
Protecting against interepithelial adhesion

This cover image shows a false-colored murine embryo on day 11.5 of development with GFP labeling of the periderm, an epidermal layer that exists transiently during embryogenesis. On page 3891, Rebecca Richardson, Nigel Hammond, and colleagues uncover a vital role for the periderm in preventing abnormal epithelial adhesion during murine development and in a case of a rare human congenital condition known as cocoon syndrome.

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Jci_impact_2014_09

September 2014 Impact

JCI Impact is a digest of the research, reviews, and other features published in each month's issue of the Journal of Clinical Investigation.

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Review Series - More

Review_series_86
Nephrology
Series edited by John R. Sedor

Nephrology encompasses the study of normal kidney function, kidney disease, and kidney replacement therapy, including kidney transplantation and dialysis. Kidney diseases are a serious public health problem, with nearly 12% of American adults suffering from chronic kidney disease (CKD). Importantly, kidney dysfunction is associated with the increasingly common conditions of obesity, diabetes, and hypertension. Recent technological advances, including genetic and epigenetic screens, metabolic profiling, new model systems, and the use of kidney biopsies for diagnosis and treatment, have created new avenues for the study of kidney pathology. Reviews in this series provide a survey of kidney pathogenesis, including hypertension, diabetic kidney disease, IgA nephropathy, idiopathic membranous nephropathy, acute kidney injury, fibrosis, and mechanisms mediating graft failure after transplantation.

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