PPP1R3G inhibition impairs OPCs differentiation and myelination in aged mice

Age-related cognitive decline is closely linked to white matter integrity, yet the molecular regulators of myelination during aging remain poorly defined. Protein phosphatase 1 regulatory subunit 3G (PPP1R3G) is implicated in cellular metabolism, but its role in brain aging is unknown. We assessed PPP1R3G expression in the corpus callosum of aging mice (1-18 months) and stratified aged mice into High/Low-PPP1R3G groups. Cognitive function was evaluated using Morris water maze (MWM) and touchscreen tests. Ppp1r3g knockout (KO) mice and primary oligodendrocyte precursor cells (OPCs) were used to investigate mechanisms via immunohistochemistry, TEM, RNA-seq, and mitochondrial functional assays. Brain PPP1R3G levels peaked at 4 months and declined with aging. Low-PPP1R3G aged mice exhibited significant cognitive impairment in spatial learning and memory tasks. Ppp1r3g KO aged mice showed severe myelin loss, reduced MBP/MOG expression, increased g-ratio, and impaired OPC differentiation. KO disrupted mitochondrial dynamics characterized with reduced length/number, fission activation, and impaired membrane potential/ATP production. In vitro, KO inhibited OPC differentiation, reversed by Ppp1r3g overexpression. RNA-seq revealed dysregulated mitochondrial fission/fusion and myelin pathways. PPP1R3G deletion inhibited AMPK. As AMPK negatively regulates Drp-1 phosphorylation, which drives Drp1-mediated fission, AMPK activation rescued the fission defects. Taken together, PPP1R3G is essential for maintaining myelination and cognitive function in aging by promoting OPC differentiation through AMPK-Drp1-dependent mitochondrial homeostasis. Its decline represents a novel mechanism underlying age-related cognitive impairment and a potential therapeutic target.