O-GlcNAcylation controls pro-fibrotic transcriptional regulatory signaling in myofibroblasts.

Tissue injury causes activation of mesenchymal lineage cells into wound-repairing myofibroblasts (MFs), whose uncontrolled activity ultimately leads to fibrosis. Although this process is triggered by deep metabolic and transcriptional reprogramming, functional links between these two key events are not yet understood. Here, we report that the metabolic sensor post-translational modification O-linked ß-D-N-acetylglucosaminylation (O-GlcNAcylation) is increased and required for myofibroblastic activation. Inhibition of protein O-GlcNAcylation impairs archetypal myofibloblast cellular activities including extracellular matrix gene expression and collagen secretion/deposition as defined in vitro and using ex vivo and in vivo murine liver injury models. Mechanistically, a multi-omics approach combining proteomic, epigenomic, and transcriptomic data mining revealed that O-GlcNAcylation controls the MF transcriptional program by targeting the transcription factors Basonuclin 2 (BNC2) and TEA domain transcription factor 4 (TEAD4) together with the Yes-associated protein 1 (YAP1) co-activator. Indeed, inhibition of protein O-GlcNAcylation impedes their stability leading to decreased functionality of the BNC2/TEAD4/YAP1 complex towards promoting activation of the MF transcriptional regulatory landscape. We found that this involves O-GlcNAcylation of BNC2 at Thr455 and Ser490 and of TEAD4 at Ser69 and Ser99. Altogether, this study unravels protein O-GlcNAcylation as a key determinant of myofibroblastic activation and identifies its inhibition as an avenue to intervene with fibrogenic processes.

Genetic Evidence of Causal Relation Between Intestinal Glucose Absorption and Early Postprandial Glucose Response: A Mendelian Randomization Study.

The postprandial glucose response is an independent risk factor for type 2 diabetes. Observationally, early glucose response after an oral glucose challenge has been linked to intestinal glucose absorption, largely influenced by the expression of sodium-glucose cotransporter 1 (SGLT1). This study uses Mendelian randomization (MR) to estimate the causal effect of intestinal SGLT1 expression on early glucose response. Involving 1,547 subjects with class II/III obesity from the Atlas Biologique de l'Obésité Sévère cohort, the study uses SGLT1 genotyping, oral glucose tolerance tests, and jejunal biopsies to measure SGLT1 expression. A loss-of-function SGLT1 haplotype serves as the instrumental variable, with intestinal SGLT1 expression as the exposure and the change in 30-min postload glycemia from fasting glycemia (Δ30 glucose) as the outcome. Results show that 12.8% of the 1,342 genotyped patients carried the SGLT1 loss-of-function haplotype, associated with a mean Δ30 glucose reduction of -0.41 mmol/L and a significant decrease in intestinal SGLT1 expression. The observational study links a 1-SD decrease in SGLT1 expression to a Δ30 glucose reduction of -0.097 mmol/L. MR analysis parallels these findings, associating a statistically significant reduction in genetically instrumented intestinal SGLT1 expression with a Δ30 glucose decrease of -0.353. In conclusion, the MR analysis provides genetic evidence that reducing intestinal SGLT1 expression causally lowers early postload glucose response. This finding has a potential translational impact on managing early glucose response to prevent or treat type 2 diabetes.

Timed use of digoxin prevents heart ischemia-reperfusion injury through a REV-ERBα-UPS signaling pathway.

Myocardial ischemia-reperfusion injury (MIRI) induces life-threatening damages to the cardiac tissue and pharmacological means to achieve cardioprotection are sorely needed. MIRI severity varies along the day-night cycle and is molecularly linked to components of the cellular clock including the nuclear receptor REV-ERBα, a transcriptional repressor. Here we show that digoxin administration in mice is cardioprotective when timed to trigger REV-ERBα protein degradation. In cardiomyocytes, digoxin increases REV-ERBα ubiquitinylation and proteasomal degradation, which depend on REV-ERBα ability to bind its natural ligand, heme. Inhibition of the membrane-bound Src tyrosine-kinase partially alleviated digoxin-induced REV-ERBα degradation. In untreated cardiomyocytes, REV-ERBα proteolysis is controlled by known (HUWE1, FBXW7, SIAH2) or novel (CBL, UBE4B) E3 ubiquitin ligases and the proteasome subunit PSMB5. Only SIAH2 and PSMB5 contributed to digoxin-induced degradation of REV-ERBα. Thus, controlling REV-ERBα proteostasis through the ubiquitin-proteasome system is an appealing cardioprotective strategy. Our data support the timed use of clinically-approved cardiotonic steroids in prophylactic cardioprotection.