Project Summary/Abstract Older people living with HIV (PLWH) are at high risk for multiple adverse geriatric outcomes, including cognitive impairment. Cognitive impairment in older PLWH has been closely linked to CNS immune activation, but the cellular mechanisms driving this abnormal CNS immune activity remain unknown, and the role of epigenetic modifications in promoting CNS immune activation in PLWH has not been examined. Epigenetic changes provide a potential link between HIV, sleep deficiency, and aging-induced CNS immune activation. DNA methylation (DNAm), one of the main and best-characterized epigenetic modifications, is affected by normal aging, by HIV infection, and by sleep deficiency, which is highly prevalent in PLWH. While DNAm changes can occur anywhere in the genome, the epigenetic integrity of circadian clock genes has been specifically tied to maintaining immune homoeostasis in the brain, and the epigenetic disruption of these genes has been associated with neuroinflammation. Our preliminary studies in PLWH demonstrate that DNAm of circardian clock genes within CNS-disease relevant monocytes is differentially altered in PLWH compared to controls, suggesting that these epigenetic changes may contribute to CNS disease in older PLWH. For this proposed administrative supplement to the Yale Pepper Center parent grant, we will measure epigenetic changes in circadian clock genes in both peripheral blood and in cerebrospinal fluid (CSF) immune cells from older PLWH and matched controls, using tissue already biobanked as part of the Yale HARC cohort study of PLWH. In AIm 1, we will assess whether epigenetic changes in circadian-clock genes associate with soluble CSF markers of CNS immune activation. In Aim 2, we will assess whether sleep deficiency associates with epigenetic dysregulation of circadian clock genes, and with CNS immune activation in PLWH. This work will be performed by a multidisciplinary team from the Yale Pepper Center and Weill Cornell, with diverse expertise in aging, HIV neurology, epigenetics, sleep, and biostatistics. The results will inform future interventions to improve sleep deficiency and prevent adverse neurocognitive and functional outcomes in older PLWH.