SMPDL3b modulates insulin receptor signaling in diabetic kidney disease.

Sphingomyelin phosphodiesterase acid-like 3b (SMPDL3b) is a lipid raft enzyme that regulates plasma membrane (PM) fluidity. Here we report that SMPDL3b excess, as observed in podocytes in diabetic kidney disease (DKD), impairs insulin receptor isoform B-dependent pro-survival insulin signaling by interfering with insulin receptor isoforms binding to caveolin-1 in the PM. SMPDL3b excess affects the production of active sphingolipids resulting in decreased ceramide-1-phosphate (C1P) content as observed in human podocytes in vitro and in kidney cortexes of diabetic db/db mice in vivo. Podocyte-specific Smpdl3b deficiency in db/db mice is sufficient to restore kidney cortex C1P content and to protect from DKD. Exogenous administration of C1P restores IR signaling in vitro and prevents established DKD progression in vivo. Taken together, we identify SMPDL3b as a modulator of insulin signaling and demonstrate that supplementation with exogenous C1P may represent a lipid therapeutic strategy to treat diabetic complications such as DKD.

Expression of deoxyribonucleic acid repair enzymes during spermatogenesis in mice.

Meiotic recombination during gametogenesis is critical for proper chromosome segregation. However, the participating proteins and mechanics of recombination are not well understood in mammals. DNA repair enzymes play an essential role in both mitosis and meiosis in yeast. The mammalian mismatch repair system consists of homologues of the bacterial MutH, MutL, and MutS proteins. As part of our goal of understanding the function of enzymes that mediate meiotic recombination, we used a reverse transcription-polymerase chain reaction approach to identify germ cell transcripts for the MutL homologue, Pms2, and two members of the MutS family, Msh2 and Msh3. Both the Pms2 and the Msh2 genes were highly expressed in mitotically proliferating spermatogonia, and early in meiotic prophase in the leptotene and zygotene spermatocytes. Thereafter, expression declined in early and mid pachytene spermatocytes, and was negligible in postmeiotic spermatids. In contrast, expression of Msh3 was at its highest level in pachytene spermatocytes. Protein levels were similar to gene expression patterns, and both PMS2 and MSH2 were localized in spermatogonia and spermatocytes. These patterns of expression for genes encoding mismatch repair enzymes are consistent with the proposed roles of the gene products in mismatch repair during both DNA replication and recombination.