Cx43 in Cdh5+ cells maintains blood-brain barrier integrity by NAD+-dependent stabilization of mitophagy during aging and inflammation

Vascular dysfunction of the blood-brain barrier (BBB) contributes to brain aging, cognitive impairment and neurodegenerative diseases. It is unclear how the BBB function deteriorates during natural aging. Our single-nucleus transcriptomics analysis identified decreased expression of Cx43 in Cdh5+ cells of cerebral vasculature in natural aging mice. Heterozygous global knockout of Cx43 or Cdh5+ cell-specific depletion of Cx43 in mice exacerbated BBB dysfunction in aging or chronic inflammation. Pharmacological and metabolomic studies revealed that the Cx43-dependent effect was not due to the gap junction canonical function of Cx43 on cell membrane, but associated with the effects of Cx43 influencing intercellular NAD+ levels. Cx43 deficiency reduced NAD+ levels in a cell-autonomous manner, impaired Sirt3-associated mitophagy, caused mitochondrial dysfunction, and compromised Cdh5+ cell proliferation. Long-term dietary supplementation with nicotinamide mononucleotide (NMN) in Cx43-deficient mice to increase NAD+ levels, stabilized mitochondrial function in Cdh5+ cells, and rescued BBB leakage in aging and chronic inflammation. These findings established a central role of the Cx43-dependent metabolic pathway in regulating Cdh5+ cells mitophagy and mitochondrial function during vascular aging, and identified a dietary intervention as a therapeutic strategy to protect against aging-induced disruption of BBB integrity and cognition functions. To investigate BBB-related transcriptomic changes across different cell types during natural aging, we studied the cortex from young (2-3-month-old) and old (18-22-month-old) mice (n = 3 pooled per group) using snRNA-seq with the 10x Genomics Chromium platform (Hu et al., 2017).