The relationship between SARS-CoV-2 infection and type 1 diabetes mellitus

Environmental factors, in particular viral infections, are thought to have an important role in the pathogenesis of type 1 diabetes mellitus (T1DM). The COVID-19 pandemic reinforced this hypothesis as many observational studies and meta-analyses reported a notable increase in the incidence of T1DM following infection with SARS-CoV-2 as well as an association between SARS-CoV-2 infection and the risk of new-onset T1DM. Experimental evidence suggests that human beta-cells express SARS-CoV-2 receptors and that SARS-CoV-2 can infect and replicate in beta-cells, resulting in structural or functional alterations of these cells. These alterations include reduced numbers of insulin-secreting granules, impaired pro-insulin (or insulin) secretion, and beta-cell transdifferentiation or dedifferentiation. The inflammatory environment induced by local or systemic SARS-CoV-2 infection might result in a set of signals (such as pro-inflammatory cytokines) that lead to beta-cell alteration or apoptosis or to a bystander activation of T cells and disruption of peripheral tolerance that triggers autoimmunity. Other mechanisms, such as viral persistence, molecular mimicry and activation of endogenous human retroviruses, are also likely to be involved in the pathogenesis of T1DM following SARS-CoV-2 infection. This Review addresses the issue of the involvement of SARS-CoV-2 infection in the development of T1DM using evidence from epidemiological, clinical and experimental studies. Many studies identified an increase in the incidence of type 1 diabetes mellitus (T1DM) during the COVID-19 pandemic, but other reports do not support this association. This Review addresses the issue of the involvement of SARS-CoV-2 infection in the development of T1DM using evidence from epidemiological, clinical and experimental studies. Epidemiological studies and meta-analyses reported an increase in the incidence of type 1 diabetes mellitus during the COVID-19 pandemic as well as an association between SARS-CoV-2 infection and the risk of new-onset type 1 diabetes mellitus.Angiotensin-converting enzyme 2 (ACE2), transmembrane serine protease 2 (TMPRSS2) and alternative receptors of SARS-CoV-2 have been identified in several human cell types, including pancreatic islet beta-cells.SARS-CoV-2 proteins are detected in both exocrine and endocrine cells (including beta-cells) of post-mortem pancreas samples from patients with COVID-19 and in samples from non-human primates intranasally or intratracheally infected with SARS-CoV-2.SARS-CoV-2 can infect and replicate in pancreatic beta-cells ex vivo, resulting in structural and functional alterations of these cells.Pro-inflammatory cytokines produced during SARS-CoV-2 infection can impair human pancreatic islet function.SARS-CoV-2 infection might promote islet autoimmunity through various mechanisms, including bystander activation of T cells, disruption of peripheral tolerance, viral persistence, molecular mimicry and activation of endogenous human retroviruses.