Reducing VEGF-B Signaling Ameliorates Renal Lipotoxicity and Protects against Diabetic Kidney Disease

Diabetic kidney disease (DKD) is the most common cause of severe renal disease, and few treatment options are available today that prevent the progressive loss of renal function. DKD is characterized by altered glomerular filtration and proteinuria. A common observation in DKD is the presence of renal steatosis, but the mechanism(s) underlying this observation and to what extent they contribute to disease progression are unknown. Vascular endothelial growth factor B (VEGF-B) controls muscle lipid accumulation through regulation of endothelial fatty acid transport. Here, we demonstrate in experimental mouse models of DKD that renal VEGF-B expression correlates with the severity of disease. Inhibiting VEGF-B signaling in DKD mouse models reduces renal lipotoxicity, re-sensitizes podocytes to insulin signaling, inhibits the development of DKD-associated pathologies, and prevents renal dysfunction. Further, we show that elevated VEGF-B levels are found in patients with DKD, suggesting that VEGF-B antagonism represents a novel approach to treat DKD.

PGC-1α Coordinates Mitochondrial Respiratory Capacity and Muscular Fatty Acid Uptake via Regulation of VEGF-B

Vascular endothelial growth factor (VEGF) B belongs to the VEGF family, but in contrast to VEGF-A, VEGF-B does not regulate blood vessel growth. Instead, VEGF-B controls endothelial fatty acid (FA) uptake and was identified as a target for the treatment of type 2 diabetes. The regulatory mechanisms controlling Vegfb expression have remained unidentified. We show that peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) together with estrogen-related receptor α (ERR-α) regulates expression of Vegfb Mice overexpressing PGC-1α under the muscle creatine kinase promoter (MPGC-1αTG mice) displayed increased Vegfb expression, and this was accompanied by increased muscular lipid accumulation. Ablation of Vegfb in MPGC-1αTG mice fed a high-fat diet (HFD) normalized glucose intolerance, insulin resistance, and dyslipidemia. We suggest that VEGF-B is the missing link between PGC-1α overexpression and the development of the diabetes-like phenotype in HFD-fed MPGC-1αTG mice. The findings identify Vegfb as a novel gene regulated by the PGC-1α/ERR-α signaling pathway. Furthermore, the study highlights the role of PGC-1α as a master metabolic sensor that by regulating the expression levels of Vegfa and Vegfb coordinates blood vessel growth and FA uptake with mitochondrial FA oxidation.

YfgM is an ancillary subunit of the SecYEG translocon in Escherichia coli

Protein secretion in Gram-negative bacteria is essential for both cell viability and pathogenesis. The vast majority of secreted proteins exit the cytoplasm through a transmembrane conduit called the Sec translocon in a process that is facilitated by ancillary modules, such as SecA, SecDF-YajC, YidC, and PpiD. In this study we have characterized YfgM, a protein with no annotated function. We found it to be a novel ancillary subunit of the Sec translocon as it co-purifies with both PpiD and the SecYEG translocon after immunoprecipitation and blue native/SDS-PAGE. Phenotypic analyses of strains lacking yfgM suggest that its physiological role in the cell overlaps with the periplasmic chaperones SurA and Skp. We, therefore, propose a role for YfgM in mediating the trafficking of proteins from the Sec translocon to the periplasmic chaperone network that contains SurA, Skp, DegP, PpiD, and FkpA.

Application of split-green fluorescent protein for topology mapping membrane proteins in Escherichia coli

A topology map of a membrane protein defines the location of transmembrane helices and the orientation of soluble domains relative to the membrane. In the absence of a high-resolution structure, a topology map is an essential guide for studying structure-function relationships. Although these maps can be predicted directly from amino acid sequence, the predictions are more accurate if combined with experimental data, which are usually obtained by fusing a reporter protein to the C-terminus of the protein. However, as reporter proteins are large, they cannot be used to report on the cytoplasmic/periplasmic location of the N-terminus of a protein. Here, we show that the bimolecular split-green fluorescent protein complementation system can overcome this limitation and can be used to determine the location of both the N- and C-termini of inner membrane proteins in Escherichia coli.

The periplasmic loop provides stability to the open state of the CorA magnesium channel

Crystal structures of the CorA Mg(2+) channel have suggested that metal binding in the cytoplasmic domain stabilizes the pentamer in a closed conformation. The open "metal free" state of the channel is, however, still structurally uncharacterized. Here, we have attempted to map conformational states of CorA from Thermotoga maritima by determining which residues support the pentameric structure in the presence or absence of Mg(2+). We find that when Mg(2+) is present, the pentamer is stabilized by the putative gating sites (M1/M2) in the cytoplasmic domain. Strikingly however, we find that the conserved and functionally important periplasmic loop is vital for the integrity of the pentamer when Mg(2+) is absent from the M1/M2 sites. Thus, although the periplasmic loops were largely disordered in the x-ray structures of the closed channel, our data suggests a prominent role for the loops in stabilizing the open conformation of the CorA channels.