Overbergh, L. | Search bioRxiv

bioRxiv2021

Citrullination of glucokinase linked to autoimmune diabetes

Inflammation, including reactive oxygen species and inflammatory cytokines in tissue microenvironments amplify the appearance of various post-translational modifications (PTMs) of self-proteins. Previously, a number of PTMs have been identified as autoimmune biomarkers in the initiation and progression of Type 1 diabetes (T1D). Herein, we have identified the citrullination of glucokinase (GK) as a result of inflammation, triggering autoimmunity and affecting its biological functions. Glucokinase is predominantly expressed in hepatocytes to regulate glycogen synthesis, and in pancreatic beta cells, where it acts as a glucose sensor to initiate glycolysis and insulin signaling. Herein, we demonstrate that glucokinase is citrullinated in inflamed non-obese diabetic (NOD) islets as well as in human GK. Autoantibodies against both native and citrullinated GK arise in both spontaneous human T1D and murine models. Likewise, autoreactive CD4+ T cells to both native and citrullinated glucokinase epitopes are present in the circulation of T1D patients. Finally, citrullination alters GK biologic activity and suppresses glucose-stimulated insulin secretion. Our studies define glucokinase as a T1D biomarker, providing new insights into altering glucose metabolism, creating neoautoantigens, and better define the broad impact of PTMs on the tissue pathology of T1D.

immunology↗

bioRxiv2020

SARS-CoV-2 receptor Angiotensin I-Converting Enzyme type 2 is expressed in human pancreatic islet β-cells and is upregulated by inflammatory stress

Increasing evidence demonstrated that the expression of Angiotensin I-Converting Enzyme type 2 (ACE2), is a necessary step for SARS-CoV-2 infection permissiveness. In the light of the recent data highlighting an association between COVID-19 and diabetes, a detailed analysis aimed at evaluating ACE2 expression pattern distribution in human pancreas is still lacking. Here, we took advantage of INNODIA network EUnPOD biobank collection to thoroughly analyse ACE2, both at mRNA and protein level, in multiple human pancreatic tissues and using several methodologies. Using multiple reagents and antibodies, we showed that ACE2 is expressed in human pancreatic islets, where it is preferentially expressed in subsets of insulin producing {beta}-cells. ACE2 is also is highly expressed in pancreas microvasculature pericytes and moderately expressed in rare scattered ductal cells. By using different ACE2 antibodies we showed that a recently described short-ACE2 isoform is also prevalently expressed in human {beta}-cells. Finally, using RT-qPCR, RNA-seq and High-Content imaging screening analysis, we demonstrated that pro-inflammatory cytokines, but not palmitate, increases ACE2 expression in the {beta}-cell line EndoC-{beta}H1 and in primary human pancreatic islets. Taken together, our data indicate a potential link between SARS-CoV-2 and diabetes through putative infection of pancreatic microvasculature and/or ductal cells and/or through direct {beta}-cell virus tropism.

cell biology↗