Reducing expression of synapse-restricting protein Ephexin5 ameliorates Alzheimer’s-like impairment in mice

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Abstract

Accumulation of amyloid-β (Aβ) protein may cause synapse degeneration and cognitive impairment in Alzheimer’s disease (AD) by reactivating expression of the developmental synapse repressor protein Ephexin5 (also known as ARHGEF15). Here, we have reported that Aβ is sufficient to acutely promote the production of Ephexin5 in mature hippocampal neurons and in mice expressing human amyloid precursor protein (hAPP mice), a model for familial AD that produces high brain levels of Aβ. Ephexin5 expression was highly elevated in the hippocampi of human AD patients, indicating its potential relevance to AD. We also observed elevated Ephexin5 expression in the hippocampi of hAPP mice. Removal of Ephexin5 expression eliminated hippocampal dendritic spine loss and rescued AD-associated behavioral deficits in the hAPP mice. Furthermore, selective reduction of Ephexin5 expression using shRNA in the dentate gyrus of presymptomatic adolescent hAPP mice was sufficient to protect these mice from developing cognitive impairment. Thus, pathological elevation of Ephexin5 expression critically drives Aβ-induced memory impairment, and strategies aimed at reducing Ephexin5 levels may represent an effective approach to treating AD.

Authors

Gabrielle L. Sell, Thomas B. Schaffer, Seth S. Margolis

Prostaglandin-mediated inhibition of serotonin signaling controls the affective component of inflammatory pain

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Abstract

Pain is fundamentally unpleasant and induces a negative affective state. The affective component of pain is mediated by circuits that are distinct from those mediating the sensory-discriminative component. Here, we have investigated the role of prostaglandins in the affective dimension of pain using a rodent pain assay based on conditioned place aversion to formalin injection, an inflammatory noxious stimulus. We found that place aversion induced by inflammatory pain depends on prostaglandin E₂ that is synthesized by cyclooxygenase 2 in neural cells. Further, mice lacking the prostaglandin E₂ receptor EP₃ selectively on serotonergic cells or selectively in the area of the dorsal raphe nucleus failed to form an aversion to formalin-induced pain, as did mice lacking the serotonin transporter. Chemogenetic manipulations revealed that EP₃ receptor activation elicited conditioned place aversion to pain via inhibition of serotonergic neurons. In contrast to their role in inflammatory pain aversion, EP₃ receptors on serotonergic cells were dispensable for acute nociceptive behaviors and for aversion induced by thermal pain or a κ opioid receptor agonist. Collectively, our findings show that prostaglandin-mediated modulation of serotonergic transmission controls the affective component of inflammatory pain.

Authors

Anand Kumar Singh, Joanna Zajdel, Elahe Mirrasekhian, Nader Almoosawi, Isabell Frisch, Anna M. Klawonn, Maarit Jaarola, Michael Fritz, David Engblom

Mutations in γ-secretase subunit–encoding PSENEN underlie Dowling-Degos disease associated with acne inversa

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Abstract

Dowling-Degos disease (DDD) is an autosomal-dominant disorder of skin pigmentation associated with mutations in keratin 5 (KRT5), protein O-fucosyltransferase 1 (POFUT1), or protein O-glucosyltransferase 1 (POGLUT1). Here, we have identified 6 heterozygous truncating mutations in PSENEN, encoding presenilin enhancer protein 2, in 6 unrelated patients and families with DDD in whom mutations in KRT5, POFUT1, and POGLUT1 have been excluded. Further examination revealed that the histopathologic feature of follicular hyperkeratosis distinguished these 6 patients from previously studied individuals with DDD. Knockdown of psenen in zebrafish larvae resulted in a phenotype with scattered pigmentation that mimicked human DDD. In the developing zebrafish larvae, in vivo monitoring of pigment cells suggested that disturbances in melanocyte migration and differentiation underlie the DDD pathogenesis associated with PSENEN. Six of the PSENEN mutation carriers presented with comorbid acne inversa (AI), an inflammatory hair follicle disorder, and had a history of nicotine abuse and/or obesity, which are known trigger factors for AI. Previously, PSENEN mutations were identified in familial AI, and comanifestation of DDD and AI has been reported for decades. The present work suggests that PSENEN mutations can indeed cause a comanifestation of DDD and AI that is likely triggered by predisposing factors for AI. Thus, the present report describes a DDD subphenotype in PSENEN mutation carriers that is associated with increased susceptibility to AI.

Authors

Damian J. Ralser, F. Buket Ü. Basmanav, Aylar Tafazzoli, Jade Wititsuwannakul, Sarah Delker, Sumita Danda, Holger Thiele, Sabrina Wolf, Michélle Busch, Susanne A. Pulimood, Janine Altmüller, Peter Nürnberg, Didier Lacombe, Uwe Hillen, Jörg Wenzel, Jorge Frank, Benjamin Odermatt, Regina C. Betz

Downregulation of GATA1 drives impaired hematopoiesis in primary myelofibrosis

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Abstract

Primary myelofibrosis (PMF) is a clonal hematologic malignancy characterized by BM fibrosis, extramedullary hematopoiesis, circulating CD34⁺ cells, splenomegaly, and a propensity to evolve to acute myeloid leukemia. Moreover, the spleen and BM of patients harbor atypical, clustered megakaryocytes, which contribute to the disease by secreting profibrotic cytokines. Here, we have revealed that megakaryocytes in PMF show impaired maturation that is associated with reduced GATA1 protein. In investigating the cause of GATA1 downregulation, our gene-expression study revealed the presence of the RPS14-deficient gene signature, which is associated with defective ribosomal protein function and linked to the erythroid lineage in 5q deletion myelodysplastic syndrome. Surprisingly, reduced GATA1 expression and impaired differentiation were limited to megakaryocytes, consistent with a proproliferative effect of a GATA1 deficiency on this lineage. Importantly, expression of GATA1 effectively rescued maturation of PMF megakaryocytes. Together, these results suggest that ribosomal deficiency contributes to impaired megakaryopoiesis in myeloproliferative neoplasms.

Authors

Laure Gilles, Ahmet Dirim Arslan, Christian Marinaccio, Qiang Jeremy Wen, Priyanka Arya, Maureen McNulty, Qiong Yang, Jonathan C. Zhao, Katerina Konstantinoff, Terra Lasho, Animesh Pardanani, Brady Stein, Isabelle Plo, Sriram Sundaravel, Amittha Wickrema, Annarita Migliaccio, Sandeep Gurbuxani, William Vainchenker, Leonidas C. Platanias, Ayalew Tefferi, John D. Crispino

Somatic mutations in telomerase promoter counterbalance germline loss-of-function mutations

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Abstract

Germline coding mutations in different telomere-related genes have been linked to autosomal-dominant familial pulmonary fibrosis. Individuals with these inherited mutations demonstrate incomplete penetrance of clinical phenotypes affecting the lung, blood, liver, skin, and other organs. Here, we describe the somatic acquisition of promoter mutations in telomerase reverse transcriptase (TERT) in blood leukocytes of approximately 5% of individuals with inherited loss-of-function coding mutations in TERT or poly(A)-specific ribonuclease (PARN), another gene linked to telomerase function. While these promoter mutations were initially identified as oncogenic drivers of cancer, individuals expressing the mutations have no history of cancer. Neither promoter mutation was found in population-based cohorts of similar or advanced age. The TERT promoter mutations were found more frequently in cis with the WT allele than was the TERT coding sequence mutation. EBV-transformed lymphoblastoid B cell lines (LCLs) derived from subjects with TERT promoter mutations showed increased telomerase expression and activity compared with cell lines from family members with identical coding mutations. TERT promoter mutations resulted in an increased proliferation of LCLs and demonstrated positive selection over time. The persistence and recurrence of noncoding gain-of-function mutations in these cases suggests that telomerase activation is not only safely tolerated but also advantageous for clonal expansion.

Authors

Lindley Maryoung, Yangbo Yue, Ashley Young, Chad A. Newton, Cindy Barba, Nicolai S. C. van Oers, Richard C. Wang, Christine Kim Garcia

Rapamycin-mediated mTOR inhibition uncouples HIV-1 latency reversal from cytokine-associated toxicity

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Abstract

Current strategies for HIV-1 eradication require the reactivation of latent HIV-1 in resting CD4⁺ T cells (rCD4s). Global T cell activation is a well-characterized means of inducing HIV-1 transcription, but is considered too toxic for clinical applications. Here, we have explored a strategy that involves a combination of immune activation and the immunosuppressive mTOR inhibitor rapamycin. In purified rCD4s from HIV-1–infected individuals on antiretroviral therapy, rapamycin treatment downregulated markers of toxicity, including proinflammatory cytokine release and cellular proliferation that were induced after potent T cell activation using αCD3/αCD28 antibodies. Using an ex vivo assay for HIV-1 mRNA, we demonstrated that despite this immunomodulatory effect, rapamycin did not affect HIV-1 gene expression induced by T cell activation in these rCD4s. In contrast, treating activated rCD4s with the immunosuppressant cyclosporin, a calcineurin inhibitor, robustly inhibited HIV-1 reactivation. Importantly, rapamycin treatment did not impair cytotoxic T lymphocyte (CTL) recognition and killing of infected cells. These findings raise the possibility of using rapamycin in conjunction with T cell–activating agents in HIV-1 cure strategies.

Authors

Alyssa R. Martin, Ross A. Pollack, Adam Capoferri, Richard F. Ambinder, Christine M. Durand, Robert F. Siliciano

Versatile humanized niche model enables study of normal and malignant human hematopoiesis

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Abstract

The BM niche comprises a tightly controlled microenvironment formed by specific tissue and cells that regulates the behavior of hematopoietic stem cells (HSCs). Here, we have provided a 3D model that is tunable in different BM niche components and useful, both in vitro and in vivo, for studying the maintenance of normal and malignant hematopoiesis. Using scaffolds, we tested the capacity of different stromal cell types to support human HSCs. Scaffolds coated with human mesenchymal stromal cells (hMSCs) proved to be superior in terms of HSC engraftment and long-term maintenance when implanted in vivo. Moreover, we found that hMSC-coated scaffolds can be modulated to form humanized bone tissue, which was also able to support human HSC engraftment. Importantly, hMSC-coated humanized scaffolds were able to support the growth of leukemia patient cells in vivo, including the growth of samples that would not engraft the BM of immunodeficient mice. These results demonstrate that an s.c. implantation approach in a 3D carrier scaffold seeded with stromal cells is an effective in vivo niche model for studying human hematopoiesis. The various niche components of this model can be changed depending on the context to improve the engraftment of nonengrafting acute myeloid leukemia (AML) samples.

Authors

Ander Abarrategi, Katie Foster, Ashley Hamilton, Syed A. Mian, Diana Passaro, John Gribben, Ghulam Mufti, Dominique Bonnet

MerTK receptor cleavage promotes plaque necrosis and defective resolution in atherosclerosis

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Abstract

Atherothrombotic vascular disease is often triggered by a distinct type of atherosclerotic lesion that displays features of impaired inflammation resolution, notably a necrotic core and thinning of a protective fibrous cap that overlies the core. A key cause of plaque necrosis is defective clearance of apoptotic cells, or efferocytosis, by lesional macrophages, but the mechanisms underlying defective efferocytosis and its possible links to impaired resolution in atherosclerosis are incompletely understood. Here, we provide evidence that proteolytic cleavage of the macrophage efferocytosis receptor c-Mer tyrosine kinase (MerTK) reduces efferocytosis and promotes plaque necrosis and defective resolution. In human carotid plaques, MerTK cleavage correlated with plaque necrosis and the presence of ischemic symptoms. Moreover, in fat-fed LDL receptor–deficient (Ldlr^–/–) mice whose myeloid cells expressed a cleavage-resistant variant of MerTK, atherosclerotic lesions exhibited higher macrophage MerTK, lower levels of the cleavage product soluble Mer, improved efferocytosis, smaller necrotic cores, thicker fibrous caps, and increased ratio of proresolving versus proinflammatory lipid mediators. These findings provide a plausible molecular-cellular mechanism that contributes to defective efferocytosis, plaque necrosis, and impaired resolution during the progression of atherosclerosis.

Authors

Bishuang Cai, Edward B. Thorp, Amanda C. Doran, Brian E. Sansbury, Mat J.A.P. Daemen, Bernhard Dorweiler, Matthew Spite, Gabrielle Fredman, Ira Tabas

Astrocytic calcium release mediates peri-infarct depolarizations in a rodent stroke model

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Abstract

Stroke is one of the most common diseases and a leading cause of death and disability. Cessation of cerebral blood flow (CBF) leads to cell death in the infarct core, but tissue surrounding the core has the potential to recover if local reductions in CBF are restored. In these areas, detrimental peri-infarct depolarizations (PIDs) contribute to secondary infarct growth and negatively affect stroke outcome. However, the cellular pathways underlying PIDs have remained unclear. Here, we have used in vivo multiphoton microscopy, laser speckle imaging of CBF, and electrophysiological recordings in a mouse model of focal ischemia to demonstrate that PIDs are associated with a strong increase of intracellular calcium in astrocytes and neurons. We found that astroglial calcium elevations during PIDs are mediated by inositol triphosphate receptor type 2–dependent (IP3R2-dependent) release from internal stores. Importantly, Ip3r2-deficient mice displayed a reduction of PID frequency and overall PID burden and showed increased neuronal survival after stroke. These effects were not related to local CBF changes in response to PIDs. However, we showed that the release and extracellular accumulation of glutamate during PIDs is strongly curtailed in Ip3r2-deficient mice, resulting in ameliorated calcium overload in neurons and astrocytes. Together, these data implicate astroglial calcium pathways as potential targets for stroke therapy.

Authors

Cordula Rakers, Gabor C. Petzold

Inhibiting mitochondrial respiration prevents cancer in a mouse model of Li-Fraumeni syndrome

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Abstract

Li-Fraumeni syndrome (LFS) is a cancer predisposition disorder caused by germline mutations in TP53 that can lead to increased mitochondrial metabolism in patients. However, the implications of altered mitochondrial function for tumorigenesis in LFS are unclear. Here, we have reported that genetic or pharmacologic disruption of mitochondrial respiration improves cancer-free survival in a mouse model of LFS that expresses mutant p53. Mechanistically, inhibition of mitochondrial function increased autophagy and decreased the aberrant proliferation signaling caused by mutant p53. In a pilot study, LFS patients treated with metformin exhibited decreases in mitochondrial activity concomitant with activation of antiproliferation signaling, thus reproducing the effects of disrupting mitochondrial function observed in LFS mice. These observations indicate that a commonly prescribed diabetic medicine can restrain mitochondrial metabolism and tumorigenesis in an LFS model, supporting its further consideration for cancer prevention in LFS patients.

Authors

Ping-yuan Wang, Jie Li, Farzana L. Walcott, Ju-Gyeong Kang, Matthew F. Starost, S. Lalith Talagala, Jie Zhuang, Ji-Hoon Park, Rebecca D. Huffstutler, Christina M. Bryla, Phuong L. Mai, Michael Pollak, Christina M. Annunziata, Sharon A. Savage, Antonio Tito Fojo, Paul M. Hwang