Biology subjects

Mugabo, Y.

Publications and source records attributed to Mugabo, Y..

4 recordsLinked to original sources

bioRxiv2022

Plakoglobin regulates adipocyte differentiation independently of the Wnt/β-catenin signalling pathway

The scaffold protein 14-3-3{zeta} is an established regulator of adipogenesis and postnatal adiposity. We and others have demonstrated that the 14-3-3{zeta} interactome to be diverse and dynamic, and it can be examined to identify novel regulators of physiological processes, including adipogenesis. In the present study, we sought to determine if factors that influence adipogenesis could be identified in the 14-3-3{zeta} interactome found in white adipose tissue of lean or obese TAP-tagged-14-3-3{zeta} overexpressing mice. Using mass spectrometry, changes in the abundance of novel, as well as established, adipogenic factors within the 14-3-3{zeta} interactome could detected. One novel candidate is plakoglobin, the homolog of the known adipogenic inhibitor {beta}-catenin, and herein, we report that plakoglobin is involved in adipocyte differentiation. Plakoglobin is expressed in murine 3T3-L1 cells and is primarily localized to the nucleus, where its abundance decreases during adipogenesis. Ectopic overexpression and siRNA-mediated depletion of plakoglobin had dual effects on inhibiting adipogenesis and reducing PPAR{gamma}2 expression. Plakoglobin depletion in human adipose-derived stem cells also impaired adipogenesis and reduced lipid accumulation post-differentiation. Transcriptional assays indicated that plakoglobin does not participate in Wnt/{beta}-catenin signaling, as its depletion did not affect Wnt3a-mediated SUPERTOPFlash activity. Taken together, our results establish plakoglobin as a novel regulator of adipogenesis in vitro and highlights the ability of using the 14-3-3{zeta} interactome to discover undiscovered pro-obesogenic factors.

biochemistry↗

bioRxiv2021

A glycerol shunt functions as a glucose excess security valve in pancreatic β-cells

The recently identified glycerol-3-phosphate (Gro3P) phosphatase (G3PP) in mammalian cells, encoded by the PGP gene, was shown to regulate intermediary metabolism by hydrolyzing Gro3P and to control glucose-stimulated insulin secretion (GSIS) in {beta}-cells, in vitro. We now examined in inducible {beta}-cell specific G3PP-KO (BKO) mice, the role of G3PP in the control of insulin secretion in vivo, {beta}-cell function and glucotoxicity. BKO mice, compared to MCre controls, showed increased body weight, adiposity, fed insulinemia, GSIS, reduced plasma triglycerides and mildly altered glucose tolerance. Isolated BKO mouse islets at high (16.7 mM) but not low or intermediate glucose (3-8 mM) showed elevated GSIS, Gro3P, metabolites reflecting {beta}-cell activation, O2 consumption, ATP production and reduced glycerol release. BKO islets chronically exposed to elevated glucose showed increased apoptosis, reduced insulin content and expression of Pdx-1, MafA and Ins-2 genes. As G3PP channels glucose carbons towards glycerol formation and release, the results demonstrate that {beta}-cell are endowed with a "glycerol shunt" acting as a glucose excess security valve. We propose that the glycerol shunt plays a role in glucodetoxification, the prevention of insulin hypersecretion, acts as a defense against excess body weight gain and contributes to {beta}-cell mass preservation in the face of hyperglycemia.

biochemistry↗

bioRxiv2021

14-3-3ζ constrains insulin secretion in pancreatic β-cells by regulating mitochondrial function

While critical for neurotransmitter synthesis in the brain, members of the 14-3-3 protein family are often assumed to have redundant, over-lapping roles due to their high sequence homology and ubiquitous expression. Despite this assumption, various mammalian 14-3-3 isoforms have now been implicated in regulating cellular and organismal metabolism; however, these functions were primarily observed in cell lines or from systemic knockout mouse models. To date, we have begun to define the contributions of 14-3-3{zeta} in adipocytes, but whether 14-3-3{zeta} has additional metabolic roles in other cell types, such as the pancreatic {beta}-cell, is unclear. We previously documented a pro-survival role of 14-3-3{zeta} in MIN6 insulinoma cells, as depletion of 14-3-3{zeta} induced cell death, but paradoxically, whole-body deletion of 14-3-3{zeta} in mice resulted in significantly enlarged {beta}-cell area with no effects on insulin secretion. To better understand the role of 14-3-3{zeta} in {beta}-cells, we generated {beta}-cell-specific 14-3-3{zeta} knockout ({beta}14-3-3{zeta}KO) mice, and while no differences in {beta}-cell mass were observed, {beta}14-3-3{zeta}KO mice displayed potentiated insulin secretion due to enhanced mitochondrial function and ATP synthesis. Deletion of 14-3-3{zeta} led to profound changes to the {beta}-cell transcriptome, where pathways associated with mitochondrial respiration and oxidative phosphorylation were upregulated. Acute treatment of mouse islets and human islets with pan-14-3-3 inhibitors recapitulated the potentiation in glucose-stimulated insulin secretion (GSIS) and mitochondrial function, suggesting that 14-3-3{zeta} is a critical isoform in {beta}-cells that regulates GSIS. In dysfunctional db/db islets and islets from type 2 diabetic donors, expression of Ywhaz/YWHAZ, the gene encoding 14-3-3{zeta}, was inversely associated with insulin secretory capacity, and pan-14-3-3 protein inhibition was capable of enhancing GSIS and mitochondrial function. Taken together, this study demonstrates important regulatory functions of 14-3-3{zeta} and its related isoforms in insulin secretion and mitochondrial function in {beta}-cells. A deeper understanding of how 14-3-3{zeta} influences {beta}-cell function will further advance our knowledge of how insulin secretion from {beta}-cells is regulated.

physiology↗

bioRxiv2017

Elucidation of the 14-3-3ζ interactome reveals critical roles of RNA splicing factors during adipogenesis

Adipogenesis is facilitated by a complex signaling network requiring strict temporal and spatial organization of effector molecules. Molecular scaffolds, such as 14-3-3 proteins, coordinate such events, and we have previously identified 14-3-3{zeta} as an essential scaffold in adipocyte differentiation. The interactome of 14-3-3{zeta} is large and diverse, and it is possible that novel adipogenic factors may be present within it. Mouse embryonic fibroblasts from mice over-expressing a TAP-epitope-tagged 14-3-3{zeta} molecule were generated, and following the induction of adipogenesis, TAP-14-3-3{zeta} complexes were purified, followed by mass spectrometry analysis to determine the 14-3-3{zeta} interactome. Over 100 proteins were identified as being unique to adipocyte differentiation, of which 56 were novel interacting partners. Previously established regulators of adipogenesis (ie, Ptrf/Cavin1 and Phb2) were found within the 14-3-3{zeta} interactome, confirming the ability of this approach to identify regulators of adipocyte differentiation. An enrichment of proteins in the interactome related to RNA metabolism, processing, and splicing was identified, and analysis of transcriptomic data revealed that 14-3-3{zeta} depletion in 3T3-L1 cells affected the alternative splicing of mRNA during adipocyte differentiation. Of the RNA splicing factors within the 14-3-3{zeta} interactome, depletion of Hnrnpf, Hnrnpk, Ddx6, and Sfpq by siRNA revealed essential roles of these proteins in adipogenesis and their roles in the alternative splicing of Lpin1. In summary, novel adipogenic factors can be detected within the 14-3-3{zeta} interactome, and further characterization of additional proteins within the 14-3-3{zeta} interactome has the potential of identifying novel targets to block the expansion of adipose tissue mass that occurs in obesity.

physiology↗