PGC-1α promoter methylation in Parkinson's disease

The etiopathogenesis of sporadic Parkinson's disease (PD) remains elusive although mitochondrial dysfunction has long been implicated. Recent evidence revealed reduced expression of peroxisome proliferator-activated receptor gamma coactivator-1 α (PGC-1α) and downstream regulated nuclear encoded respiratory complex genes in affected brain tissue from PD patients. We sought to determine whether epigenetic modification of the PGC-1 α gene could account for diminished expression. In substantia nigra from PD patients but not control subjects, we show significant promoter-proximal non-canonical cytosine methylation of the PGC-1 α gene but not an adjacent gene. As neuroinflammation is a prominent feature of PD and a mediator of epigenetic change, we evaluated whether the pro-inflammatory fatty acid, palmitate, would stimulate PGC-1 α promoter methylation in different cell types from the CNS. Indeed, in mouse primary cortical neurons, microglia and astrocytes, palmitate causes PGC-1 αgene promoter non-canonical cytosine methylation, reduced expression of the gene and reduced mitochondrial content. Moreover, intracerebroventricular (ICV) injection of palmitate to transgenic human a-synuclein mutant mice resulted in increased PGC-1 α promoter methylation, decreased PGC-1 α expression and reduced mitochondrial content in substantia nigra. Finally we provide evidence that dysregulation of ER stress and inflammatory signaling is associated with PGC-1 α promoter methylation. Together, these data strengthen the connection between saturated fatty acids, neuroflammation, ER stress, epigenetic alteration and bioenergetic compromise in PD.