Beta-Cell Pyroptosis - A Burning Flame in Type 1 Diabetes?
Immune-mediated destruction of the beta-cells in the pancreatic islets of Langerhans is the underlying cause of type 1 diabetes (T1D). Despite decades of research, the exact mechanisms involved at the beta-cell level during the development of disease remain poorly understood. This includes the mode(s) of beta-cell death and signaling events implicated in exacerbating local islet inflammation and immune cell infiltration, commonly known as insulitis. In disease models, beta-cell apoptosis seems to be the predominant cell death form which has led to the general assumption that beta cells mostly die by apoptosis in T1D. However, apoptosis is an anti-inflammatory programmed cell death mechanism, and this dogma is therefore challenged by the pathogenetic nature of T1D, as a progressive increase in islet inflammation is seen. This infers that other modes of beta-cell death that inherently increase insulitis may predominate. One such mechanism could be the newly characterized form of programmed cell death; pyroptosis (from the Greek "fire-falling"). Pyroptosis is characterized by gasdermin-mediated cell lysis with a bursting release of pro-inflammatory factors. Beta-cell death by pyroptosis in T1D may therefore offer a plausible explanation for the exacerbated paracrine islet inflammation that spreads during the progression of insulitis. Here, we briefly debate the evidence supporting beta-cell pyroptosis in T1D as a central mechanism of islet inflammation and beta-cell demise. The paper intends to challenge the current understanding of beta-cell destruction to move the field forward. Importantly, we present experimental data from human islets and EndoC-{beta}H5 cells that directly support beta-cell pyroptosis as a rational death mechanism in T1D. We suggest a model of beta-cell demise in T1D in which pyroptosis plays a prominent role in concert with other cell death mechanisms. As the role of pyroptosis in disease is still in its infancy, we hope also to inspire researchers working in other disease fields.