Defective Mitophagy in XPA via PARP1 activation and NAD+/SIRT1-depletion: Implications for neurodegeneration (human)

Mitochondrial dysfunction is a common feature in neurodegeneration and aging. We identify mitochondrial dysfunction in xeroderma pigmentosum group A (XPA), a nucleotide excision DNA repair disorder with severe neurodegeneration, in silico and in vivo. XPA deficient cells show defective mitophagy with excessive cleavage of PINK1 and increased mitochondrial membrane potential. The mitochondrial abnormalities appear to be caused by decreased activation of the NAD+-SIRT1-PGC-1α axis triggered by hyperactivation of the DNA damage sensor PARP1. This phenotype is rescued by PARP1 inhibition or by supplementation with NAD+ precursors that also rescue the lifespan defect in xpa-1 nematodes. Importantly, this pathogenesis appears common to ataxia-telangiectasia and Cockayne syndrome, two other DNA repair disorders with neurodegeneration, but absent in XPC, a DNA repair disorder without neurodegeneration. Our findings reveal a novel nuclear-mitochondrial cross-talk that is critical for the maintenance of mitochondrial health. Four replicates of XPA-deficient (GM04312C) and the matched complemented (GM15876A) control cells as well as primary fibroblasts, transfected with either the shRNA to XPA or a scrambled version of the shRNA, as a control, were grown and total RNA was extracted. The RNA was labeled using the standard Illumina protocol and hybed overnight to Human-HT12 arrays. The arrays were scanned using the Beadstation 500 X from Illumina.