and collect data. BHC helped generate Tug1-transgenic mice and edit the manuscript. PAO helped edit the manuscript, and FRD oversaw experiments, prepared the manuscript, and provided guidance on overall project design.

Mitochondrial fission has been linked to the pathogenesis of diabetic nephropathy (DN). However, how mitochondrial fission affects progression of DN in vivo is unknown. Here, we report the effect of conditional podocyte-specific deletion of dynamin-related protein 1 (Drp1), an essential component of mitochondrial fission, on the pathogenesis and progression of DN. Inducible podocyte-specific deletion of Drp1 in diabetic mice decreased albuminuria and improved mesangial matrix expansion and podocyte morphology. Ultrastructure analysis revealed a significant increase in fragmented mitochondria in the podocytes of wild-type diabetic mice but a marked improvement in mitochondrial structure in Drp1-null podocytes of diabetic mice. When isolated from diabetic mice and cultured in high glucose, Drp1-null podocytes had more elongated mitochondria and better mitochondrial fitness associated with enhanced oxygen consumption and ATP production than wild-type podocytes. Furthermore, administration of a pharmacologic inhibitor of Drp1, Mdivi1, significantly blunted mitochondrial fission and rescued key pathologic features of DN in mice. Taken together, these results provide novel correlations between mitochondrial morphology and the progression of DN and point to Drp1 as a potential therapeutic target in DN.

Diabetic kidney disease remains a major microvascular complication of diabetes and the most common cause of chronic kidney failure requiring dialysis in the United States. Medical advances over the past century have substantially improved the management of diabetes mellitus and thereby have increased patient survival. However, current standards of care reduce but do not eliminate the risk of diabetic kidney disease, and further studies are warranted to define new strategies for reducing the risk of diabetic kidney disease. In this review, we highlight some of the novel and established molecular mechanisms that contribute to the development of the disease and its outcomes. In particular, we discuss recent advances in our understanding of the molecular mechanisms implicated in the pathogenesis and progression of diabetic kidney disease, with special emphasis on the mitochondrial oxidative stress and microRNA targets. Additionally, candidate genes associated with susceptibility to diabetic kidney disease and alterations in various cytokines, chemokines, and growth factors are addressed briefly.

Oxidative stress is an underlying component of acute and chronic kidney disease. Apoptosis signal-regulating kinase 1 (ASK1) is a widely expressed redox-sensitive serine threonine kinase that activates p38 and c-Jun N-terminal kinase (JNK) mitogen-activated protein kinase kinases, and induces apoptotic, inflammatory, and fibrotic signaling in settings of oxidative stress. We describe the discovery and characterization of a potent and selective small-molecule inhibitor of ASK1, GS-444217, and demonstrate the therapeutic potential of ASK1 inhibition to reduce kidney injury and fibrosis. Activation of the ASK1 pathway in glomerular and tubular compartments was confirmed in renal biopsies from patients with diabetic kidney disease (DKD) and was decreased by GS-444217 in several rodent models of kidney injury and fibrosis that collectively represented the hallmarks of DKD pathology. Treatment with GS-444217 reduced progressive inflammation and fibrosis in the kidney and halted glomerular filtration rate decline. Combination of GS-444217 with enalapril, an angiotensin-converting enzyme inhibitor, led to a greater reduction in proteinuria and regression of glomerulosclerosis. These results identify ASK1 as an important target for renal disease and support the clinical development of an ASK1 inhibitor for the treatment of DKD.

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How the kidney responds to the metabolic cues from the environment remains a central question in kidney research. This question is particularly relevant to the pathogenesis of diabetic nephropathy (DN) in which evidence suggests that metabolic events in podocytes regulate chromatin structure. Here, we show that miR-93 is a critical metabolic/epigenetic switch in the diabetic milieu linking the metabolic state to chromatin remodelling. Mice with inducible overexpression of a miR-93 transgene exclusively in podocytes exhibit significant improvements in key features of DN. We identify miR-93 as a regulator of nucleosomal dynamics in podocytes. miR-93 has a critical role in chromatin reorganization and progression of DN by modulating its target Msk2, a histone kinase, and its substrate H3S10. These findings implicate a central role for miR-93 in high glucose-induced chromatin remodelling in the kidney, and provide evidence for a previously unrecognized role for Msk2 as a target for DN therapy.

While increased mitochondrial reactive oxygen species have been commonly implicated in a variety of disease states, their in vivo role in the pathogenesis of diabetic nephropathy remains controversial. Using a two-photon imaging approach with a genetically encoded redox biosensor, we monitored mitochondrial redox state in the kidneys of experimental models of diabetes in real-time in vivo. Diabetic (db/db) mice that express a redox-sensitive Green Fluorescent Protein biosensor (roGFP) specifically in the mitochondrial matrix (db/dbmt-roGFP) were generated, allowing dynamic monitoring of redox changes in the kidneys. These db/dbmt-roGFP mice exhibited a marked increase in mitochondrial reactive oxygen species in the kidneys. Yeast NADH-dehydrogenase, a mammalian Complex I homolog, was ectopically expressed in cultured podocytes and this forced expression in roGFP-expressing podocytes prevented high glucose-induced increases in mitochondrial reactive oxygen species. Thus, in vivo monitoring of mitochondrial roGFP in diabetic mice confirms increased production of mitochondrial reactive oxygen species in the kidneys.

Using a large consortium of undergraduate students in an organized program at the University of California, Los Angeles (UCLA), we have undertaken a functional genomic screen in the Drosophila eye. In addition to the educational value of discovery-based learning, this article presents the first comprehensive genomewide analysis of essential genes involved in eye development. The data reveal the surprising result that the X chromosome has almost twice the frequency of essential genes involved in eye development as that found on the autosomes.