A beneficial persistent DNA damage-induced immune response in aging

About This Grant

PRIJECT SUMMARY/ABSTRACT The systemic immune effects of DNA damage in aging and disease remain elusive. It is generally believed that immune responses triggered by transient DNA damage are beneficial while those associated with persistent DNA damage are detrimental. We recently reported that NLRP12 (NOD-like receptor 12), a member of the NLR inflammasome family that plays a central role in innate immunity, is induced by persistent DNA damage, and that persistent DNA damage-induced NLRP12 improves the function of hematopoietic stem and progenitor cells (HSPCs) in both mouse and human models of DNA repair deficiency and aging. These results argue a protective role of NLRP12 in the context of immune response to persistent DNA damage under conditions of DNA repair deficiency and aging. However, the mechanism underpinning the link between persistent DNA damage and NLRP12 expression in disease and aging has not been defined. To exploit this, we performed preliminary mechanistic studies and found that persistent DNA damage induced abundant cytosolic dsDNA and consequently activation of the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway in HSPCs from DNA repair-deficient (Fanca-/-) and aged mice treated with ionizing radiation (IR) or the DNA cross-linker mitomycin C (MMC). Concomitantly, a major transcription factor for Nlrp12, PU.1, was also elevated. We further showed that inhibition of the cGAS-STING pathway PU.1 abolished persistent DNA damage-induced NLRP12 expression in these damaged HSPCs, suggesting a potential link between the cGAS-STING pathway and persistent DNA damage-induced NLRP12 expression. To further investigate this novel mechanistic link and its functional implications, we generated a conditional Nlrp12 mouse model, with which we deleted the Nlrp12 gene specifically in the hematopoietic lineages using the Vav1-Cre deleter strain. We observed exacerbated aging phenotypes in Nlrp12-deficient Fanca-/- and aged mice, accompanied with the senescence associated secretory phenotype (SASP) in the bone marrow (BM) and a significant increase in pyroptosis in BM HSPCs. Furthermore, deletion of Nlrp12 significantly increased cytoplasmic localization of NLRP3, a hallmark of NLRP3 inflammasome activation in the Nlrp12-deficient Fanca-/- and aged HSPCs. These preliminary studies suggest a novel interplay between persistent DNA damage and immune response: cGAS-STING-mediated upregulation of NLRP12 as a systemic pro-homeostatic effector of immune response to otherwise detrimental persistent DNA damage. We hypothesize that persistent DNA damage activates a non-canonical cGAS-STING-PU.1 pathway to induce the upregulation of NLRP12, which suppresses SASP to impede chronic inflammation and inhibits NLRP3 inflammasome to prevent HSPC pyroptosis. The goals of the project are to investigate: (1) the mechanisms linking persistent DNA damage to NLRP12 upregulation and (2) the functional links between persistent DNA damage and upregulated NLRP12 in aging hematopoiesis.