The Peroxisome Proliferator-activated Receptor γ (PPARγ) Controls Natural Protective Mechanisms against Lipid Peroxidation in Amyotrophic Lateral Sclerosis

Recent evidence highlights the peroxisome proliferator-activated receptors (PPARs) as critical neuroprotective factors in several neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). To gain new mechanistic insights into the role of these receptors in the context of ALS, here we investigated how PPAR transcriptional activity varies in hSOD1(G93A) ALS transgenic mice. We demonstrate that PPAR gamma-driven transcription selectively increases in the spinal cord of symptomatic hSOD1(G93A) mice. This phenomenon correlates with the up-regulation of target genes, such as lipoprotein lipase and glutathione S-transferase alpha-2, which are implicated in scavenging lipid peroxidation by-products. Such events are associated with enhanced PPAR gamma immunoreactivity within motor neuronal nuclei. This observation, and the fact that PPAR gamma displays increased responsiveness in cultured hSOD1(G93A) motor neurons, points to a role for this receptor in neutralizing deleterious lipoperoxidation derivatives within the motor cells. Consistently, in both motor neuron-like cultures and animal models, we report that PPAR gamma is activated by lipid peroxidation end products, such as 4-hydroxynonenal, whose levels are elevated in the cerebrospinal fluid and spinal cord from ALS patients. We propose that the accumulation of critical concentrations of lipid peroxidation adducts during ALS progression leads to the activation of PPAR gamma in motor neurons. This in turn triggers self-protective mechanisms that involve the up-regulation of lipid detoxification enzymes, such as lipoprotein lipase and glutathione S-transferase alpha-2. Our findings indicate that anticipating natural protective reactions by pharmacologically modulating PPAR gamma transcriptional activity may attenuate neurodegeneration by limiting the damage induced by lipid peroxidation derivatives.