Hypophosphorylated pRb knock‐in mice exhibit hallmarks of aging and vitamin C‐preventable diabetes

Despite extensive analysis of pRB phosphorylation in vitro , how this modification influences development and homeostasis in vivo is unclear. Here, we show that homozygous Rb ∆K4 and Rb ∆K7 knock‐in mice, in which either four or all seven phosphorylation sites in the C‐terminal region of pRb, respectively, have been abolished by Ser/Thr‐to‐Ala substitutions, undergo normal embryogenesis and early development, notwithstanding suppressed phosphorylation of additional upstream sites. Whereas Rb ∆K4 mice exhibit telomere attrition but no other abnormalities, Rb ∆K7 mice are smaller and display additional hallmarks of premature aging including infertility, kyphosis, and diabetes, indicating an accumulative effect of blocking pRb phosphorylation. Diabetes in Rb ∆K7 mice is insulin‐sensitive and associated with failure of quiescent pancreatic β‐cells to re‐enter the cell cycle in response to mitogens, resulting in induction of DNA damage response (DDR), senescence‐associated secretory phenotype (SASP), and reduced pancreatic islet mass and circulating insulin level. Pre‐treatment with the epigenetic regulator vitamin C reduces DDR, increases cell cycle re‐entry, improves islet morphology, and attenuates diabetes. These results have direct implications for cell cycle regulation, CDK‐inhibitor therapeutics, diabetes, and longevity. Synopsis The tumor suppressor pRB is frequently inactivated by mutation or hyper‐phosphorylation in diverse types of cancer, yet the effect of specifically blocking its phosphorylation in vivo is ill‐defined. Here, novel knock‐in mice show that expression of hypo‐phosphorylated pRb does not impede normal development, but promotes hallmarks of aging and diabetes by inhibiting cell‐cycle re‐entry and regeneration. Rb∆K4 and Rb∆K7 knock‐in mice, in which four or all, respectively, phosphorylation sites at the C‐terminal are genetically abolished, exhibit normal embryogenesis and neonatal growth. Inhibition of pRb phosphorylation at the C‐terminal selectively suppresses phosphorylation of additional upstream sites. Rb∆K7 mice develop hallmarks of aging and severe diabetes, caused by inability of pancreatic β‐cells to reduplicate in response to mitogenic signals, leading to a DDR and senescence. Vitamin C diet reduces the DDR and senescence of pancreatic β‐cells and attenuates diabetes in Rb∆K7 mice. Both activation and inactivation of pRb have deleterious long‐term effects on cancer and regeneration/aging. Graphical Abstract Abolishing cell‐