The most common mitochondrial respiratory disorder is MELAS (Mitochondrial Encephalopathy Lactic Acidosis with Stroke-like Episodes), an incurable progressive neurodegenerative disease with early childhood onset. This orphan disease causes heterogeneous clinical symptoms, such as encephalopathy, seizures, stroke-like episodes, cognitive impairment, chronic lactic acidosis, and myopathy. Most MELAS patients harbor a maternally inherited mutation (A3243G) in the mitochondrial-encoded tRNALeu/UUR gene, which affects the oxidative phosphorylation (OXPHOS) system responsible for ATP synthesis. In MELAS cells, the multi-copy mitochondrial genome population is heterogeneous, with variable ratios of mutant mtDNAs and wild type (WT) mtDNAs, a state known as heteroplasmy. Individuals with the MELAS mutation become symptomatic only when the mutant load exceeds a certain threshold of heteroplasmy. Currently, no therapeutic options are available to prevent the progression of the disease, resulting in significant disability, a poo prognosis, and premature death. Our proposed novel pharmacological approach uses butyrates to promote nuclear and mitochondrial metabolic reprogramming by boosting mitochondrial biogenesis and maximizing residual ATP output. Using primary fibroblasts derived from a skin biopsy of two MELAS patients, we performed an Affymetrix-based genome-wide microarray analysis that revealed enrichment of pathways for mitochondrial biogenesis and bioenergetics upon exposure to butyrates. From live cell confocal microscopy, we found that butyrates restored the mitochondrial mass and the pool of bioenergetically competent mitochondria in MELAS fibroblasts. In healthy neuronal cells, we found that butyrates induced mitochondrial biogenesis via expression of essential nuclear-encoded regulators and augmented the pool of bioenergetic mitochondria and ATP levels. Thus, our collective preliminary data validate our pharmaco-epigenomic approach and establish proof-of-principle for the proposed studies. We hypothesize that butyrates can augment the functional mitochondrial mass in skin fibroblasts from 20 MELAS patients. Fibroblasts from this number of patients, each with different nuclear backgrounds and heteroplasmic loads, will ensure the findings extend beyond a case study into a statistically sound and broadly applicable report. We will test whether butyrates:
(Aim 1) induce favorable mitochondrial biogenesis, thereby shifting heteroplasmy toward healthy mitochondria;
and (Aim 2) maximize ATP output via optimization of OXPHOS activity and a metabolic shift toward fatty acid beta oxidation. We anticipate identifying the most promising butyrate candidate for alleviating the symptoms of the MELAS disease. The proposed study will set the stage for future clinical studies with the Children's National Medical Center and the North American Mitochondrial Disease Consortium, in concordance with the PAR-13-023 issued by the NINDS Office of Translational Research for R21 exploratory projects.
The proposed research is relevant to public health and the overall NINDS mission (PAR 13-023) because MELAS is a devastating and incurable childhood-onset neurodegenerative disease for which there is no effective treatment. The emphasis of the proposed study is on a novel pharmacological therapeutic strategy using a pre-clinical cellular MELAS paradigm. We anticipate that the results of this study will set the stage for subsequent clinical study to translate our findings from bench to bedside and accelerate drug development for MELAS patients.
