Aging is associated with an increased incidence and prevalence of renal glomerular diseases. Sirtuin (Sirt) 6, a nicotinamide adenine dinucleotide (NAD)-dependent histone deacetylase, has been shown to protect against multiple age-associated phenotypes; however it is unknown whether Sirt6 has a direct pathophysiologic role in the kidney. In the present study, we demonstrate that Sirt6 is expressed in the kidney and aging Sirt6-deficient mice exhibit renal hypertrophy with glomerular enlargement. Sirt6 deletion induces podocyte injury, including decreases in slit diaphragm proteins, foot process effacement, and cellular loss, resulting in proteinuria. Knockdown of Sirt6 in cultured primary murine podocytes induces shape changes with loss of process formation and cell apoptosis. Moreover, Sirt6 deficiency results in progressive renal inflammation and fibrosis. Collectively, these data provide compelling evidence that Sirt6 is important for podocyte homeostasis and maintenance of glomerular function, and warrant further investigation into the role of Sirt6 in age-associated kidney dysfunction.
Traumatic optic neuropathy (TON) is an acute injury of the optic nerve secondary to trauma. Loss of retinal ganglion cells (RGCs) is a key pathological process in TON, yet mechanisms responsible for RGC death remain unclear. In a mouse model of TON, real-time noninvasive imaging revealed a dramatic increase in leukocyte rolling and adhesion in veins near the optic nerve (ON) head at 9 hours after ON injury. Although RGC dysfunction and loss were not detected at 24 hours after injury, massive leukocyte infiltration was observed in the superficial retina. These cells were identified as T cells, microglia/monocytes, and neutrophils but not B cells. CXCL10 is a chemokine that recruits leukocytes after binding to its receptor C-X-C chemokine receptor (CXCR) 3. The levels of CXCL10 and CXCR3 were markedly elevated in TON, and up-regulation of CXCL10 was mediated by STAT1/3. Deleting CXCR3 in leukocytes significantly reduced leukocyte recruitment, and prevented RGC death at 7 days after ON injury. Treatment with CXCR3 antagonist attenuated TON-induced RGC dysfunction and cell loss. In vitro co-culture of primary RGCs with leukocytes resulted in increased RGC apoptosis, which was exaggerated in the presence of CXCL10. These results indicate that leukocyte recruitment in retinal vessels near the ON head is an early event in TON and the CXCL10/CXCR3 axis has a critical role in recruiting leukocytes and inducing RGC death. (Am J Pathol 2017, 187: 352e365; http://dx
and coverslips were applied with ProLong Gold Antifade Mountant (Thermo Fisher Scientific). Immunofluorescence was captured using a Zeiss LSM 510 laser-scanning confocal microscope. Statistics. Survival curve comparisons were performed using GraphPad Prism software, which uses the log-rank test. Values for viral burden, cytokine production, and antibody and T cell response experiments are presented as the mean ± SEM. P values for these experiments were calculated with an unpaired, 2-tailed Student's t test. Statistical significance was accepted at a P value of less than 0.05. Study approval. All experiments were performed in compliance with and under the approval of the IACUC of UTMB.
PurposeRetinal ganglion cell (RGC) death following axonal injury occurring in traumatic optic neuropathy (TON) causes irreversible vision loss. GRP78 is a molecular chaperone that enhances protein folding and controls activation of endoplasmic reticulum (ER) stress pathways. This study determined whether adeno-associated virus (AAV)-mediated gene transfer of GRP78 protected RGCs from death in a mouse model of TON induced by optic nerve crush (ONC).MethodsONC was induced by a transient crush of optic nerve behind the eye globe. AAV was used to deliver genes into retina. Molecules in the ER stress branches, tau oligomers, and RGC injury were determined by immunohistochemistry or Western blot.ResultsAmong tested AAV serotypes, AAV2 was the most efficient for delivering genes to RGCs. Intravitreal delivery of AAV2-GRP78 markedly attenuated ER stress and RGC death 3 days after ONC, and significantly improved RGC survival and function 7 days after ONC. Protein aggregation is increased during ER stress and aggregated proteins such as tau oligomers are key players in neurodegenerative diseases. AAV2-GRP78 alleviated ONC-induced increases in tau phosphorylation and oligomerization. Furthermore, tau oligomers directly induced RGC death, and blocking tau oligomers with tau oligomer monoclonal antibody (TOMA) attenuated ONC-induced RGC loss.ConclusionThese data indicate that the beneficial effect of AAV2-GRP78 is partially mediated by the reduction of misfolded tau, and provide compelling evidence that gene therapy with AAV2-GRP78 or immunotherapy with TOMA offers novel therapeutic approaches to alleviate RGC loss in TON.
Brain-derived neurotrophic factor (BDNF) is a master regulator of synaptic plasticity in various neural circuits of the mammalian central nervous system. Neuron activity-induced BDNF gene expression is regulated through the Ca/CREB pathway, but other regulatory factors may also be involved in controlling BDNF levels. We report here that Wnt/β-catenin signaling plays a key role in controlling neuron activity-regulated BDNF expression. Using primary cortical cultures, we show that blockade of Wnt/β-catenin signaling inhibits the BDNF up-regulation that is induced by activation of the -methyl-d-aspartic acid (NMDA) receptor and that activation of the Wnt/β-catenin signaling pathway stimulates BDNF expression., Wnt/β-catenin signaling activated BDNF expression and was required for peripheral pain-induced up-regulation of BDNF in the mouse spine. We also found that conditional deletion of one copy of either Wntless (Wls) or β-catenin by Nestin-Cre-mediated recombination is sufficient to inhibit the pain-induced up-regulation of BDNF. We further show that the Wnt/β-catenin/BDNF axis in the spinal neural circuit plays an important role in regulating capsaicin-induced pain. These results indicate that neuron activity-induced Wnt signaling stimulates BDNF expression in the pain neural circuits. We propose that pain-induced Wnt secretion may provide an additional mechanism for intercellular coordination of BDNF expression in the neural circuit.
PurposeRetinal ischemia, a common cause of several vision-threatening diseases, contributes to the death of retinal neurons, particularly retinal ganglion cells (RGCs). Heat shock transcription factor 1 (HSF1), a stress-responsive protein, has been shown to be important in response to cellular stress stimuli, including ischemia. This study is to investigate whether HSF1 has a role in retinal neuronal injury in a mouse model of retinal ischemia-reperfusion (IR).MethodsIR was induced by inserting an infusion needle into the anterior chamber of the right eye and elevating a saline reservoir connected to the needle to raise the intraocular pressure to 110 mm Hg for 45 minutes. HSF1, Hsp70, molecules in the endoplasmic reticulum (ER) stress branches, tau phosphorylation, inflammatory molecules, and RGC injury were determined by immunohistochemistry, Western blot, or quantitative PCR.ResultsHSF1 expression was significantly increased in the retina 6 hours after IR. Using our novel transgenic mice carrying full-length human HSF gene, we demonstrated that IR-induced retinal neuronal apoptosis and necroptosis were abrogated 12 hours after IR. RGCs and their function were preserved in the HSF1 transgenic mice 7 days after IR. Mechanistically, the beneficial effects of HSF1 may be mediated by its induction of chaperone protein Hsp70 and alleviation of ER stress, leading to decreased tau phosphorylation and attenuated inflammatory response 12 to 24 hours after IR.ConclusionsThese data provide compelling evidence that HSF1 is neuroprotective against retinal IR injury, and boosting HSF1 expression may be a beneficial strategy to limit neuronal degeneration in retinal diseases.
Progressive loss of retinal ganglion cells (RGCs) leads to irreversible visual deficits in glaucoma. Here, we found that the level of cyclic AMP and the activity and expression of its mediator Epac1 were increased in retinas of two mouse models of ocular hypertension. Genetic depletion of Epac1 significantly attenuated ocular hypertension–induced detrimental effects in the retina, including vascular inflammation, neuronal apoptosis and necroptosis, thinning of ganglion cell complex layer, RGC loss, and retinal neuronal dysfunction. With bone marrow transplantation and various Epac1 conditional knockout mice, we further demonstrated that Epac1 in retinal neuronal cells (especially RGCs) was responsible for their death. Consistently, pharmacologic inhibition of Epac activity prevented RGC loss. Moreover, in vitro study on primary RGCs showed that Epac1 activation was sufficient to induce RGC death, which was mechanistically mediated by CaMKII activation. Taken together, these findings indicate that neuronal Epac1 plays a critical role in retinal neurodegeneration and suggest that Epac1 could be considered a target for neuroprotection in glaucoma.
Zika virus (ZIKV) infection has been associated with ocular abnormalities such as chorioretinal atrophy, optic nerve abnormalities, posterior uveitis and idiopathic maculopathy. Yet our knowledge about ZIKV infection in retinal cells and its potential contribution to retinal pathology is still very limited. Here we found that primary Müller cells, the principal glial cells in the retina, expressed a high level of ZIKV entry cofactor AXL gene and were highly permissive to ZIKV infection. In addition, ZIKV-infected Müller cells exhibited a pro-inflammatory phenotype and produced many inflammatory and growth factors. While a number of inflammatory signaling pathways such as ERK, p38MAPK, NF-κB, JAK/STAT3 and endoplasmic reticulum stress were activated after ZIKV infection, inhibition of p38MAPK after ZIKV infection most effectively blocked ZIKV-induced inflammatory and growth molecules. In comparison to ZIKV, Dengue virus (DENV), another Flavivirus infected Müller cells more efficiently but induced much lower pro-inflammatory responses. These data suggest that Müller cells play an important role in ZIKV-induced ocular pathology by induction of inflammatory and growth factors in which the p38MAPK pathway has a central role. Blocking p38MAPK may provide a novel approach to control ZIKV-induced ocular inflammation.
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