Translational approaches to restoring mitochondrial function in Parkinson's disease

Orthogonal analysis of mitochondrial function in Parkinson's disease patients

The etiopathology of Parkinson's disease has been associated with mitochondrial defects at genetic, laboratory, epidemiological, and clinical levels. These converging lines of evidence suggest that mitochondrial defects are systemic and causative factors in the pathophysiology of PD, rather than being mere correlates. Understanding mitochondrial biology in PD at a granular level is therefore crucial from both basic science and translational perspectives. In a recent study, we investigated mitochondrial alterations in fibroblasts obtained from PD patients assessing mitochondrial function in relation to clinical measures. Our findings demonstrated that the magnitude of mitochondrial alterations parallels disease severity. In this study, we extend these investigations to blood cells and dopamine neurons derived from induced pluripotent stem cells reprogrammed from PD patients. To overcome the inherent metabolic heterogeneity of blood cells, we focused our analyses on metabolically homogeneous, accessible, and expandable erythroblasts. Our results confirm the presence of mitochondrial anomalies in erythroblasts and induced dopamine neurons. Consistent with our previous findings in fibroblasts, we observed that mitochondrial alterations are reversible, as evidenced by enhanced mitochondrial respiration when PD erythroblasts were cultured in a galactose medium that restricts glycolysis. This observation indicates that suppression of mitochondrial respiration may constitute a protective, adaptive response in PD pathogenesis. Notably, this effect was not observed in induced dopamine neurons, suggesting their distinct bioenergetic behavior. In summary, we provide additional evidence for the involvement of mitochondria in the disease process by demonstrating mitochondrial abnormalities in additional cell types relevant to PD. These findings contribute to our understanding of PD pathophysiology and may have implications for the development of novel biomarkers and therapeutic strategies.

Quantitative Assessment of Occipital Metabolic and Energetic Changes in Parkinson's Patients, Using In Vivo 31P MRS-Based Metabolic Imaging at 7T

Abnormal energy metabolism associated with mitochondrial dysfunction is thought to be a major contributor to the progression of neurodegenerative diseases such as Parkinson's disease (PD). Recent advancements in the field of magnetic resonance (MR) based metabolic imaging provide state-of-the-art technologies for non-invasively probing cerebral energy metabolism under various brain conditions. In this proof-of-principle clinical study, we employed quantitative ³¹P MR spectroscopy (MRS) imaging techniques to determine a constellation of metabolic and bioenergetic parameters, including cerebral adenosine triphosphate (ATP) and other phosphorous metabolite concentrations, intracellular pH and nicotinamide adenine dinucleotide (NAD) redox ratio, and ATP production rates in the occipital lobe of cognitive-normal PD patients, and then we compared them with age-sex matched healthy controls. Small but statistically significant differences in intracellular pH, NAD and ATP contents and ATPase enzyme activity between the two groups were detected, suggesting that subtle defects in energy metabolism and mitochondrial function are quantifiable before regional neurological deficits or pathogenesis begin to occur in these patients. Pilot data aiming to evaluate the bioenergetic effect of mitochondrial-protective bile acid, ursodeoxycholic acid (UDCA) were also obtained. These results collectively demonstrated that in vivo ³¹P MRS-based neuroimaging can non-invasively and quantitatively assess key metabolic-energetic metrics in the human brain. This provides an exciting opportunity to better understand neurodegenerative diseases, their progression and response to treatment.

Neuroprotective Effects of Cryptotanshinone in a Direct Reprogramming Model of Parkinson's Disease

Parkinson’s disease (PD) is a well-known age-related neurodegenerative disease. Considering the vital importance of disease modeling based on reprogramming technology, we adopted direct reprogramming to human-induced neuronal progenitor cells (hiNPCs) for in vitro assessment of potential therapeutics. In this study, we investigated the neuroprotective effects of cryptotanshinone (CTN), which has been reported to have antioxidant properties, through PD patient-derived hiNPCs (PD-iNPCs) model with induced oxidative stress and cell death by the proteasome inhibitor MG132. A cytotoxicity assay showed that CTN possesses anti-apoptotic properties in PD-hiNPCs. CTN treatment significantly reduced cellular apoptosis through mitochondrial restoration, such as the reduction in mitochondrial reactive oxygen species and increments of mitochondrial membrane potential. These effects of CTN are mediated via the nuclear factor erythroid 2-related factor 2 (NRF2) pathway in PD-hiNPCs. Consequently, CTN could be a potential antioxidant reagent for preventing disease-related pathological phenotypes of PD.

C9orf72 expansion within astrocytes reduces metabolic flexibility in amyotrophic lateral sclerosis

It is important to understand how the disease process affects the metabolic pathways in amyotrophic lateral sclerosis and whether these pathways can be manipulated to ameliorate disease progression. To analyse the basis of the metabolic defect in amyotrophic lateral sclerosis we used a phenotypic metabolic profiling approach. Using fibroblasts and reprogrammed induced astrocytes from C9orf72 and sporadic amyotrophic lateral sclerosis cases we measured the production rate of reduced nicotinamide adenine dinucleotides (NADH) from 91 potential energy substrates simultaneously. Our screening approach identified that C9orf72 and sporadic amyotrophic lateral sclerosis induced astrocytes have distinct metabolic profiles compared to controls and displayed a loss of metabolic flexibility that was not observed in fibroblast models. This loss of metabolic flexibility, involving defects in adenosine, fructose and glycogen metabolism, as well as disruptions in the membrane transport of mitochondrial specific energy substrates, contributed to increased starvation induced toxicity in C9orf72 induced astrocytes. A reduction in glycogen metabolism was attributed to loss of glycogen phosphorylase and phosphoglucomutase at the protein level in both C9orf72 induced astrocytes and induced neurons. In addition, we found alterations in the levels of fructose metabolism enzymes and a reduction in the methylglyoxal removal enzyme GLO1 in both C9orf72 and sporadic models of disease. Our data show that metabolic flexibility is important in the CNS in times of bioenergetic stress.

Serum FGF-21, GDF-15, and blood mtDNA copy number are not biomarkers of Parkinson disease

Background

Strong evidence of mitochondrial dysfunction exists for both familial and sporadic Parkinson disease (PD). A simple test, reliably identifying mitochondrial dysfunction, could be important for future stratified medicine trials in PD. We previously undertook a comparison of serum biomarkers in classic mitochondrial diseases and established that serum growth differentiation factor 15 (GDF-15) outperforms fibroblast growth factor 21 (FGF-21) when distinguishing patients with mitochondrial diseases from healthy controls. This study aimed to systematically assess serum FGF-21 and GDF-15, together with mitochondrial DNA (mtDNA) copy number levels in peripheral blood cells from patients with PD and healthy controls, to determine whether these measures could act as a biomarker of PD.

Methods

One hundred twenty-one patients with PD and 103 age-matched healthy controls were recruited from a single center. Serum FGF-21 and GDF-15, along with blood mtDNA copy number, were quantified using established assays.

Results

There were no meaningful differences identified for any of the measures when comparing patients with PD with healthy controls. This highlights a lack of diagnostic sensitivity that is incompatible with these measures being used as biomarkers for PD.

Conclusion

In this study, serum FGF-21, serum GDF-15, and blood mtDNA levels were similar in patients with PD and healthy controls and therefore unlikely to be satisfactory indicators of mitochondrial dysfunction in patients with PD.

Classification of evidence

This study provides Class III evidence that serum FGF-21, serum GDF-15, and blood mtDNA copy number levels do not distinguish patients with PD from healthy controls. There was no diagnostic uncertainty between patients with PD and healthy controls.

Therapeutic approaches to enhance PINK1/Parkin mediated mitophagy for the treatment of Parkinson's disease

The discovery of rare familial monogenic forms of early-onset Parkinson's disease has led to the identification of a mitochondrial quality control process as a key player in this disease. Loss-of-function mutations in the genes encoding PINK1 or Parkin result in insufficient removal of dysfunctional mitochondria through autophagy, a process termed mitophagy. Understanding the mechanism of this process and the function of its two key players, PINK1 and Parkin, has led to the discovery of new therapeutic approaches. Small molecule activators of mitophagy, either activating PINK1 or Parkin directly or inhibiting Parkin's counterplayer, the ubiquitin-specific protease USP30, are in preclinical development. To enable clinical success of future small molecule mitophagy enhancers, biomarkers for mitochondrial integrity and mitophagy are being developed. Only a few years after the discovery of mitophagy deficits in Parkinson's disease, research of the underlying mechanisms, drug discovery of modulators for this mechanism and identification of biomarkers provide new avenues towards the development of disease-modifying therapies.

Caloric restriction and redox homeostasis in various regions of aging male rat brain: Is caloric restriction still worth trying even after early-adulthood?: Redox homeostasis and caloric restriction in brain

Despite recent studies have shown that caloric restriction (CR) could improve some functional loss associated with brain aging, the biochemical effects of CR on brain aging are still not well understood on a quantifiable biochemical basis, including whether CR could be protective when started around middle adulthood, when age-related neurodegenerative diseases are thought to set in. Therefore, in the light of more than ever aging societies and increasing neurodegenerative diseases, we aimed to test the biochemical effects of CR on redox homeostasis in different parts of male Sprague-Dawley rat brain by using the biomarkers we consistently validated in our previous work (TOS, PCO, AOPP, AGEs, sRAGE, P-SH, LHPs, 4-HNE, TAS, Cu, Zn-SOD). Our results indicate that oxidative stress biomarkers are lower in CR group, implying a more favorable redox status that has been previously shown to be correlated with better neural function. PRACTICAL APPLICATIONS: We report that the beneficial effects of caloric restriction (CR) on various brain tissues result in significant improvements in biochemical markers, even though CR is not started in early adulthood. Hence, our select age group provides a sound redox status-related neurochemical understanding for many recent CR studies, where a functional loss was detected at this age.

MPP+ decreases store-operated calcium entry and TRPC1 expression in Mesenchymal Stem Cell derived dopaminergic neurons

Parkinson's disease is a neurodegenerative disorder involving the progressive loss of dopaminergic neurons (DNs), with currently available therapeutics, such as L-Dopa, only able to relieve some symptoms. Stem cell replacement is an attractive therapeutic option for PD patients, and DNs derived by differentiating patient specific stem cells under defined in-vitro conditions may present a viable opportunity to replace dying neurons. We adopted a previously published approach to differentiate Mesenchymal Stem Cells (MSCs) into DN using a 12-day protocol involving FGF-2, bFGF, SHH ligand and BDNF. While MSC-derived DNs have been characterized for neuronal markers and electrophysiological properties, we investigated store-operated calcium entry (SOCE) mechanisms of these DNs under normal conditions, and upon exposure to environmental neurotoxin, 1-methyl, 4-phenyl pyridinium ion (MPP+). Overall, we show that MSC-derived DNs are functional with regard to SOCE mechanisms, and MPP+ exposure dysregulates calcium signaling, making them vulnerable to neurodegeneration. Since in-vitro differentiation of MSCs into DNs is an important vehicle for PD disease modeling and regenerative medicine, the results of this study may help with understanding of the pathological mechanisms underlying PD.