Age-related Islet Inflammation Marks the Proliferative Decline of Pancreatic Beta-cells in Zebrafish

Individual organisms age at different rates, however, it remains unclear how aging alters the properties of individual cells. Here we show that zebrafish pancreatic beta-cells exhibit heterogeneity in both gene expression and proliferation with age. Individual beta-cells show marked variability in transcripts involved in endoplasmic reticulum stress, inhibition of growth factor signaling and inflammation, including NF-kB signaling. Using a reporter line, we show that NF-kB signaling is indeed activated heterogeneously with age. Notably, beta-cells with higher NF-kB activity proliferate less compared to neighbors with lower activity. Furthermore, NF-kB-signalinghigh beta-cells from younger islets upregulate socs2, a gene naturally expressed in beta-cells from older islets. In turn, socs2 can inhibit proliferation cell-autonomously. NF-kB activation correlates with the recruitment of tnfα-expressing immune cells, pointing towards a role for the islet microenvironment in this activity. We propose that aging is heterogeneous across individual beta-cells and identify NF-kB signaling as a marker of heterogeneity.