A Y374X TDP43 truncation leads to an altered metabolic profile in amyotrophic lateral sclerosis fibroblasts driven by pyruvate and TCA cycle intermediate alterations

Mitochondrial and energy metabolism dysfunctions are hallmarks of TDP-43G376D fibroblasts from members of an Amyotrophic Lateral Sclerosis family

Amyotrophic Lateral Sclerosis (ALS) is an incurable neurodegenerative disease, causing degeneration of motor neurons, paralysis, and death. About 5-10% of cases are associated with gene mutations inherited from a family member (fALS). Among them, mutations in the transactive-response (TAR)-DNA-binding protein (TARDBP), which encodes for the TAR DNA binding protein 43 (TDP-43) are responsible for 4-5% of fALS but the molecular mechanisms that initiate and sustain the neurodegenerative process are largely unknown. Metabolic impairments might be involved in the pathogenesis of ALS and are currently under investigation. In order to correlate biochemical and metabolic alterations with disease progression, here, we established the metabolic fingerprint of dermal fibroblasts derived from symptomatic and asymptomatic members of a family with fALS cases carrying to the p.G376D mutation in TDP-43. We found that increased proliferation, unbalanced oxidative homeostasis and higher ATP production rate coupled with enhanced metabolic activity are underlying traits of this family. Fibroblasts from carrier individuals deploy several mechanisms to increase mitochondrial respiration to meet increasing energy demands. This is accompanied by an upregulation of glycolysis corresponding to a metabolic reprograming towards a glycolytic phenotype for ATP production during ALS progression, particularly in late disease stages. In summary, we uncover alterations in energy metabolism in TDP43G376D patient-derived primary fibroblasts that may be used as risk biomarkers and/or to monitor ALS progression.

Multimodal assessment of mitochondrial function in Parkinson's disease

The heterogenous aetiology of Parkinson's disease is increasingly recognized; both mitochondrial and lysosomal dysfunction have been implicated. Powerful, clinically applicable tools are required to enable mechanistic stratification for future precision medicine approaches. The aim of this study was to characterize bioenergetic dysfunction in Parkinson's disease by applying a multimodal approach, combining standardized clinical assessment with midbrain and putaminal 31-phosphorus magnetic resonance spectroscopy (31P-MRS) and deep phenotyping of mitochondrial and lysosomal function in peripheral tissue in patients with recent-onset Parkinson's disease and control subjects. Sixty participants (35 patients with Parkinson's disease and 25 healthy controls) underwent 31P-MRS for quantification of energy-rich metabolites [ATP, inorganic phosphate (Pi) and phosphocreatine] in putamen and midbrain. In parallel, skin biopsies were obtained from all research participants to establish fibroblast cell lines for subsequent quantification of total intracellular ATP and mitochondrial membrane potential (MMP) as well as mitochondrial and lysosomal morphology, using high content live cell imaging. Lower MMP correlated with higher intracellular ATP (r = -0.55, P = 0.0016), higher mitochondrial counts (r = -0.72, P < 0.0001) and higher lysosomal counts (r = -0.62, P = 0.0002) in Parkinson's disease patient-derived fibroblasts only, consistent with impaired mitophagy and mitochondrial uncoupling. 31P-MRS-derived posterior putaminal Pi/ATP ratio variance was considerably greater in Parkinson's disease than in healthy controls (F-tests, P = 0.0036). Furthermore, elevated 31P-MRS-derived putaminal, but not midbrain Pi/ATP ratios (indicative of impaired oxidative phosphorylation) correlated with both greater mitochondrial (r = 0.37, P = 0.0319) and lysosomal counts (r = 0.48, P = 0.0044) as well as lower MMP in both short (r = -0.52, P = 0.0016) and long (r = -0.47, P = 0.0052) mitochondria in Parkinson's disease. Higher 31P-MRS midbrain phosphocreatine correlated with greater risk of rapid disease progression (r = 0.47, P = 0.0384). Our data suggest that impaired oxidative phosphorylation in the striatal dopaminergic nerve terminals exceeds mitochondrial dysfunction in the midbrain of patients with early Parkinson's disease. Our data further support the hypothesis of a prominent link between impaired mitophagy and impaired striatal energy homeostasis as a key event in early Parkinson's disease.