Endothelial Cell Insulin Signaling Regulates CXCR4 (C-X-C Motif Chemokine Receptor 4) and Limits Leukocyte Adhesion to Endothelium.

BACKGROUND: An activated, proinflammatory endothelium is a key feature in the development of complications of obesity and type 2 diabetes and can be caused by insulin resistance in endothelial cells. METHODS: We analyzed primary human endothelial cells by RNA sequencing to discover novel insulin-regulated genes and used endothelial cell culture and animal models to characterize signaling through CXCR4 (C-X-C motif chemokine receptor 4) in endothelial cells. RESULTS: CXCR4 was one of the genes most potently regulated by insulin, and this was mediated by PI3K (phosphatidylinositol 3-kinase), likely through FoxO1, which bound to the CXCR4 promoter. CXCR4 mRNA in CD31+ cells was 77% higher in mice with diet-induced obesity compared with lean controls and 37% higher in db/db mice than db/+ controls, consistent with upregulation of CXCR4 in endothelial cell insulin resistance. SDF-1 (stromal cell-derived factor-1)-the ligand for CXCR4-increased leukocyte adhesion to cultured endothelial cells. This effect was lost after deletion of CXCR4 by gene editing while 80% of the increase was prevented by treatment of endothelial cells with insulin. In vivo microscopy of mesenteric venules showed an increase in leukocyte rolling after intravenous injection of SDF-1, but most of this response was prevented in transgenic mice with endothelial overexpression of IRS-1 (insulin receptor substrate-1). CONCLUSIONS: Endothelial cell insulin signaling limits leukocyte/endothelial cell interaction induced by SDF-1 through downregulation of CXCR4. Improving insulin signaling in endothelial cells or inhibiting endothelial CXCR4 may reduce immune cell recruitment to the vascular wall or tissue parenchyma in insulin resistance and thereby help prevent several vascular complications.

The excess insulin requirement in severe COVID-19 compared to non-COVID-19 viral pneumonitis is related to the severity of respiratory failure and pre-existing diabetes.

Introduction: Severe COVID-19 has been anecdotally associated with high insulin requirements. It has been proposed that this may be driven by a direct diabetogenic effect of the virus that is unique to SARS-CoV-2, but evidence to support this is limited. To explore this, we compared insulin requirements in patients with severe COVID-19 and non-COVID-19 viral pneumonitis. Methods: This is a retrospective cohort study of patients with severe COVID-19 admitted to our intensive care unit between March and June 2020. A historical control cohort of non-COVID-19 viral pneumonitis patients was identified from routinely collected audit data. Results: Insulin requirements were similar in patients with COVID-19 and non-COVID-19 viral pneumonitis after adjustment for pre-existing diabetes and severity of respiratory failure. Conclusions: In this single-centre study, we could not find evidence of a unique diabetogenic effect of COVID-19. We suggest that high insulin requirements in this disease relate to its propensity to cause severe respiratory failure in patients with pre-existing metabolic disease.

The transcriptional coregulator CITED2 suppresses expression of IRS-2 and impairs insulin signaling in endothelial cells.

Endothelial cell insulin resistance contributes to the development of vascular complications in diabetes. Hypoxia-inducible factors (HIFs) modulate insulin sensitivity, and we have previously shown that a negative regulator of HIF activity, CREB-binding protein/p300 (CBP/p300) interacting transactivator-2 (CITED2), is increased in the vasculature of people with type 2 diabetes. Therefore, we examined whether CITED2 regulates endothelial insulin sensitivity. In endothelial cells isolated from mice with a "floxed" mutation in the Cited2 gene, loss of CITED2 markedly enhanced insulin-stimulated Akt phosphorylation without altering extracellular signal-related kinase 1/2 (ERK1/2) phosphorylation. Similarly, insulin-stimulated Akt phosphorylation was increased in aortas of mice with endothelial-specific deletion of CITED2. Consistent with these observations, loss of CITED2 in endothelial cells increased insulin-stimulated endothelial nitric oxide synthase phosphorylation, Vegfa expression, and cell proliferation. Endothelial cells lacking CITED2 exhibited an increase in insulin receptor substrate (IRS)-2 protein, a key mediator of the insulin signaling cascade, whereas IRS-1 was unchanged. Conversely, overexpression of CITED2 in endothelial cells decreased IRS-2 protein by 55% without altering IRS-1, resulting in impaired insulin-stimulated Akt phosphorylation and Vegfa expression. Overexpression of HIF-2α significantly increased activity of the Irs2 promoter, and coexpression of CITED2 abolished this increase. Moreover, chromatin immunoprecipitation (ChIP) showed that loss of CITED2 increased occupancy of p300, a key component of the HIF transcriptional complex, on the Irs2 promoter. Together, these results show that CITED2 selectively inhibits endothelial insulin signaling and action through the phosphoinositide 3-kinase (PI3K)/Akt pathway via repression of HIF-dependent IRS-2 expression. CITED2 is thus a promising target to improve endothelial insulin sensitivity and prevent the vascular complications of diabetes.NEW & NOTEWORTHY Endothelial cell insulin resistance is a major contributor to the development of diabetic complications. In this study, we have shown that CITED2, a transcriptional coregulator, inhibits endothelial insulin signaling through the PI3K/Akt pathway via repression of HIF-dependent IRS-2 expression, and that deletion of CITED2 enhances insulin signaling. Thus, CITED2 represents a novel and promising target to improve insulin sensitivity in endothelial cells and prevent vascular complications in diabetes.

When Two Pandemics Meet: Why Is Obesity Associated with Increased COVID-19 Mortality?

A growing body of evidence indicates that obesity is strongly and independently associated with adverse outcomes of COVID-19, including death. By combining emerging knowledge of the pathological processes involved in COVID-19 with insights into the mechanisms underlying the adverse health consequences of obesity, we present some hypotheses regarding the deleterious impact of obesity on the course of COVID-19. These hypotheses are testable and could guide therapeutic and preventive interventions. As obesity is now almost ubiquitous and no vaccine for COVID-19 is currently available, even a modest reduction in the impact of obesity on mortality and morbidity from this viral infection could have profound consequences for public health.

ACE inhibition and cardiometabolic risk factors, lung ACE2 and TMPRSS2 gene expression, and plasma ACE2 levels: a Mendelian randomization study.

Angiotensin-converting enzyme 2 (ACE2) and serine protease TMPRSS2 have been implicated in cell entry for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus responsible for coronavirus disease 2019 (COVID-19). The expression of ACE2 and TMPRSS2 in the lung epithelium might have implications for the risk of SARS-CoV-2 infection and severity of COVID-19. We use human genetic variants that proxy angiotensin-converting enzyme (ACE) inhibitor drug effects and cardiovascular risk factors to investigate whether these exposures affect lung ACE2 and TMPRSS2 gene expression and circulating ACE2 levels. We observed no consistent evidence of an association of genetically predicted serum ACE levels with any of our outcomes. There was weak evidence for an association of genetically predicted serum ACE levels with ACE2 gene expression in the Lung eQTL Consortium (p = 0.014), but this finding did not replicate. There was evidence of a positive association of genetic liability to type 2 diabetes mellitus with lung ACE2 gene expression in the Gene-Tissue Expression (GTEx) study (p = 4 × 10-4) and with circulating plasma ACE2 levels in the INTERVAL study (p = 0.03), but not with lung ACE2 expression in the Lung eQTL Consortium study (p = 0.68). There were no associations of genetically proxied liability to the other cardiometabolic traits with any outcome. This study does not provide consistent evidence to support an effect of serum ACE levels (as a proxy for ACE inhibitors) or cardiometabolic risk factors on lung ACE2 and TMPRSS2 expression or plasma ACE2 levels.