Conflict of interest: GWB, AF, and SM are inventors on pending or issued patents (US 10,183,038 and US 10,052,345) aimed at diagnosing or treating proteinuric kidney diseases. They stand to gain royalties from the future commercialization of these patents. AF is Chief Scientific Officer of L&F Health LLC and is a consultant for Variant Pharmaceuticals. Variant Pharmaceuticals has licensed worldwide rights from L&F Research to develop and commercialize hydroxypropyl-beta-cyclodextrin for the treatment of kidney disease. AF is Chief Medical Officer of LipoNexT LLC. SM holds equity interest in a company presently commercializing the form of cyclodextrin referenced in this paper. AF and SM are supported by Hoffman-La Roche. AF is supported by Boehringer Ingelheim.

Loss of podocytes by apoptosis characterizes the early stages of diabetic nephropathy. To examine its mechanism we studied glomeruli and podocytes isolated from db/db mice with early diabetic nephropathy and albuminuria. Phosphorylation of AKT (protein kinase B, a key survival protein) was found to be lower in the glomeruli of 12 week old db/db compared to db/+ mice. In vitro, insulin phosphorylated AKT solely in podocytes from db/+ mice. Serum deprivation and exposure to tumor necrosis factor-alpha significantly compromised cell viability in podocytes from db/db but not from db/+ mice, and this was associated with a significant decrease in AKT phosphorylation. Inhibition of AKT was necessary to achieve the same degree of cell death in db/+ podocytes. Our study shows that podocyte inability to respond to insulin and susceptibility to cell death may partially account for the decreased podocyte number seen in early diabetic nephropathy.

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.

Background Binding of the programmed death-1 (PD-1) receptor to its ligands (PD-L1/2) transduces inhibitory signals that promote exhaustion of activated T cells. Blockade of the PD-1 pathway is widely used for cancer treatment, yet the inhibitory signals transduced by PD-1 in T cells remain elusive. Methods Expression profiles of human CD8 + T cells in resting, activated (CD3 + CD28) and PD-1-stimulated cells (CD3 + CD28 + PD-L1-Fc) conditions were evaluated by RNA-seq. Bioinformatic analyses were used to identify signaling pathways differentially regulated in PD-1-stimulated cells. Metabolic analyses were performed with SeaHorse technology, and mitochondrial ultrastructure was determined by transmission electron microscopy. PD-1-regulated mitochondrial genes were silenced using short-hairpin RNA in primary cells. Blue native gel electrophoresis was used to determine respiratory supercomplex assembly. Results PD-1 engagement in human CD8 + T cells triggers a specific, progressive genetic program different from that found in resting cells. Gene ontology identified metabolic processes, including glycolysis and oxidative phosphorylation (OXPHOS), as the main pathways targeted by PD-1. We observed severe functional and structural alterations in the mitochondria of PD-1-stimulated cells, including a reduction in the number and length of mitochondrial cristae. These cristae alterations were associated with reduced expression of CHCHD3 and CHCHD10, two proteins that form part of the mitochondrial contact site and cristae organizing system (MICOS). Although PD-1-stimulated cells showed severe cristae alterations, assembly of respiratory supercomplexes was unexpectedly greater in these cells than in activated T cells. CHCHD3 silencing in primary CD8 + T cells recapitulated some effects induced by PD-1 stimulation, including reduced mitochondrial polarization and interferon-γ production following T cell activation with anti-CD3 and -CD28 activating antibodies. Conclusions Our results suggest that mitochondria are the main targets of PD-1 inhibitory activity. PD-1 reprograms CD8 + T cell metabolism for efficient use of fatty acid oxidation; this mitochondrial phenotype might explain the long-lived phenotype of PD-1-engaged T cells. Electronic supplementary material The online version of this article (10.1186/s40425-019-0628-7) contains supplementary material, which is available to authorized users.

The importance of Discoidin Domain Receptor 1 (DDR1) in renal fibrosis has been shown via gene knockout and use of antisense oligonucleotides; however, these techniques act via a reduction of DDR1 protein, while we prove the therapeutic potential of inhibiting DDR1 phosphorylation with a small molecule. To date, efforts to generate a selective small-molecule to specifically modulate the activity of DDR1 in an in vivo model have been unsuccessful. We performed parallel DNA encoded library screens against DDR1 and DDR2, and discovered a chemical series that is highly selective for DDR1 over DDR2. Structure-guided optimization efforts yielded the potent DDR1 inhibitor 2.45, which possesses excellent kinome selectivity (including 64-fold selectivity over DDR2 in a biochemical assay), a clean in vitro safety profile, and favorable pharmacokinetic and physicochemical properties. As desired, compound 2.45 modulates DDR1 phosphorylation in vitro as well as prevents collagen-induced activation of renal epithelial cells expressing DDR1. Compound 2.45 preserves renal function and reduces tissue damage in Col4a3 –/– mice (the preclinical mouse model of Alport syndrome) when employing a therapeutic dosing regime, indicating the real therapeutic value of selectively inhibiting DDR1 phosphorylation in vivo. Our results may have wider significance as Col4a3 –/– mice also represent a model for chronic kidney disease, a disease which affects 10% of the global population.