Lack of age-related clinical progression in PGC-1α-deficient mice - implications for mitochondrial encephalopathies

Impaired peroxisome proliferator-activated receptor-gamma coactivator 1-alpha (PGC-1α) function has been demonstrated in several neurodegenerative diseases, and murine whole-body knockouts of PGC-1α have been considered as models for Huntington's disease. Recent neuropathological studies, however, rather propose these animals to be morphological models of mitochondrial encephalopathies, with special reminiscence of Kearns-Sayre syndrome. PGC-1α-deficient animals have already been subjected to behavioral assessments; however, the contradictory findings and the paucity of data assessing long-term progression necessitated further examinations. This study provides a comprehensive neurological phenotypic profiling of full-length-(FL-)PGC-1α-deficient mice in a broad age spectrum, with special focus on previously controversial findings, the issue of long-term phenotypic progression, the histopathological assessment of previously non-characterized tissues of potential clinicopathological relevance, and the gene expression profile of novel brain-specific isoforms of PGC-1α. Our findings demonstrate moderate hypomotility with signs of gait and trunk ataxia in addition to severe impairments in coordination and muscle strength in FL-PGC-1α-deficient mice, phenotypic features consistent of a mitochondrial disease. Intriguingly, however, these early alterations did not progress with age, the understanding of which may unveil mechanisms of potential therapeutic relevance, as discussed. The observed phenotype did not associate with retinal or spinal cord alterations, and was accompanied by mild myopathic changes. Based on these, FL-PGC-1α-deficient mice can be regarded not only as morphological but behavioral models of mitochondrial encephalopathies, with an important temporal limitation that has now been clarified. The mechanisms capable of halting a potentially lethal phenotype are to be unveiled, as they may hold therapeutic value for mitochondrial diseases.

PGC-1α activity in nigral dopamine neurons determines vulnerability to α-synuclein

Introduction

Mitochondrial dysfunction and oxidative stress are critical factors in the pathogenesis of age-dependent neurodegenerative diseases. PGC-1α, a master regulator of mitochondrial biogenesis and cellular antioxidant defense, has emerged as a possible therapeutic target for Parkinson’s disease, with important roles in the function and survival of dopaminergic neurons in the substantia nigra. The objective of this study is to determine if the loss of PGC-1α activity contributes to α-synuclein-induced degeneration.

Results

We explore the vulnerability of PGC-1α null mice to the accumulation of human α-synuclein in nigral neurons, and assess the neuroprotective effect of AAV-mediated PGC-1α expression in this experimental model. Using neuronal cultures derived from these mice, mitochondrial respiration and production of reactive oxygen species are assessed in conditions of human α-synuclein overexpression. We find ultrastructural evidence for abnormal mitochondria and fragmented endoplasmic reticulum in the nigral dopaminergic neurons of PGC-1α null mice. Furthermore, PGC-1α null nigral neurons are more prone to degenerate following overexpression of human α-synuclein, an effect more apparent in male mice. PGC-1α overexpression restores mitochondrial morphology, oxidative stress detoxification and basal respiration, which is consistent with the observed neuroprotection against α-synuclein toxicity in male PGC-1α null mice.

Conclusions

Altogether, our results highlight an important role for PGC-1α in controlling the mitochondrial function of nigral neurons accumulating α-synuclein, which may be critical for gender-dependent vulnerability to Parkinson’s disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s40478-015-0200-8) contains supplementary material, which is available to authorized users.