Impaired complex-I mitochondrial biogenesis in Parkinson disease frontal cortex

Parkinson's disease (PD) can include a progressive frontal lobe α-synucleinopathy with disability from cognitive decline and cortico-limbic dysregulation that may arise from bioenergetic impairments. We examined in PD frontal cortex regulation of mitochondrial biogenesis (mitobiogenesis) and its effects on Complex-I. We quantified expression of 33 nuclear genome (nDNA)-encoded and 7 mitochondrial genome (mtDNA)-encoded Complex-I genes, 6 Complex-I assembly factors and multiple mitobiogenesis genes. We related these findings to levels of Complex-I proteins and NADH-driven electron flow in mitochondria from these same specimens reported in earlier studies. We found widespread, decreased expression of nDNA Complex-I genes that correlated in some cases with mitochondrial Complex-I protein levels, and of ACAD9, a Complex-I assembly factor. mtDNA-transcribed Complex-I genes showed ~ constant expression within each PD sample but variable expression across PD samples that correlated with NRF1. Relationships among PGC-1α and its downstream targets NRF1 and TFAM were very similar in PD and CTL and were related to mitochondrial NADH-driven electron flow. MicroRNA arrays revealed multiple miRNA's regulated >2-fold predicted to interact with PGC-1α or its upstream regulators. Exposure of cultured human neurons to NO, rotenone and TNF-alpha partially reproduced mitobiogenesis down-regulation. In PD frontal cortex mitobiogenesis signaling relationships are maintained but down-regulated, correlate with impaired mitochondrial NADH-driven electron flow and may arise from combinations of nitrosative/oxidative stresses, inflammatory cytokines, altered levels of mitobiogenesis gene-interacting microRNA's, or other unknown mechanisms. Stimulation of mitobiogenesis in PD may inhibit rostral disease progression and appearance of secondary symptoms referable to frontal cortex.