1724-P: DNA Damage Vulnerability of Immature Beta Cells

Introduction & Objective: A healthy reserve of functional β-cells is crucial for maintaining glucose homeostasis and is disrupted in diabetes. Most of this reserve is established in early neonatal life via replication, following which β-cells exit cell-cycle and undergo functional maturation. Although the process of replication is extremely vulnerable to DNA damage and consequent genomic instability, the extent and impact of such vulnerabilities on β-cell maturation and subsequent viability is not clear. Here, we sought to determine the DNA damage vulnerability of replicating β-cells in the neonatal growth phase. Methods: We quantified β-cell replication (Ki67, pHH3) and DNA damage (ɣH2AX) in early (p7) and late (p21) neonatal B6 mice (N=8 animals/ group). We acquired super-resolution 3D images of DNA damage foci and cohesins (modulators of genomic stability) in replicating β-cells using the Zeiss Elyra 7 Lattice SIM^2 and LSM880 with Airyscan, and analyzed using the Imaris software. Results: Our data revealed that while the overall number of β-cells with DNA damage decreased as replication declined from p7 to p21, ~20% of replicating β-cells at each stage harbored DNA damage. Notably, the G2 phase had the highest density of DNA damage foci, which were resolved by the M phase. Single-cell RNA-seq of murine neonatal islets showed the enrichment of DNA damage repair pathways in replicating β-cells. Conclusion: Collectively, our data establish the high DNA damage vulnerability of neonatal β-cells and suggest the existence of robust mechanisms that assist the resolution of DNA damage with cell cycle progression to maintain genomic stability.