PINK1 gene mutations or PINK1 silencing result in reduced mtDNA levels, defective ATP production, impaired mitochondrial calcium handling, and increased free radical generation, which in turn result in a fall in mitochondrial membrane potential and an increased susceptibility to apoptosis in neuronal cells, animal models and patient-derived fibroblasts. Recent studies have also demonstrated that PINK1 can initiate the translocation of parkin to mitochondria and the induction of mitophagy. Many of the studies performed to date to define the role of PINK1 have involved artificial cell models with overexpression of wild-type or mutant PINK1, or knock out in cell or animal models, and few have used endogenous expression of mutant protein in host cells. We have previously published on the biochemical effects of mutant PINK1 expression in PD patient fibroblasts. We have now investigated at the level of the single cell,Fuziline the bioenergetic effects of endogenously expressed PINK1 mutations in PD cells and demonstrate that the consequences depend upon the specific underlying mutation. Mutations in the gene for PINK1 are a cause of autosomal recessive Parkinson’s disease. PINK1 is a mitochondrial protein and recent studies have indicated that it plays a significant role in mitochondrial function and calcium homeostasis in particular. These observations were derived from the use of cell culture knockouts including primary neuronal cultures from transgenic mouse models of PINK1 deficiency. Previous studies using PINK1 patient fibroblasts have shown defects of oxidative phosphorylation and the electron transport chain, and oxidative stress. In this study we have for the first time studied PINK1 mitochondrial pathophysiology with single cell analysis of cultured cells derived from patients with PD and PINK1 mutations,Yunaconitine in order to dissect the down-stream consequences on mitochondrial function. These cells represent an important model system as they enable the study of the biochemical effects of PINK1 mutations in intact cells devoid of any manipulation of the PINK1 gene, and in the presence of the host patient genomic background. Furthermore, as in PINK1 knockouts, this phenomenon mutants could be reversed by the provision of additional respiratory chain substrates: the increase in respiration in the presence of additional pyruvate resulted in a concomitant switch in the mechanism of Dym maintenance from hydrolysis of ATP to production of ATP. These studies have demonstrated that fibroblasts from PD patients with PINK1 mutations exhibit very similar bio-energetic mitochondrial abnormalities to knockdown cell models. These patient cells also show that there is substrate dependent limitation on ATP synthesis that can be overcome with substrate replacement or normalization of glucose uptake. This may offer an interesting opportunity to explore in terms of disease modifying therapy in these patients, for which there is some precedent in patients with primary mitochondrial encephalomyopathies. These data also indicate that patients with different PINK1 mutations, but affecting the same domain, can show different biochemical phenotypes. It is notable that the patient with the mildest defect of mitochondrial biochemistry had the latest onset of disease. Whether this observation indicates a valid correlation with disease severity will require further work in additional patients. The defects of mitochondrial function in PINK1 mutant patient cells described here have relevance to the part that PINK1 and parkin play in the removal of mitochondria by mitophagy. It has recently been demonstrated in Drosophila and in mammalian cells that parkin ubiquitinates mitofusins 1 and 2, and this function is PINK1 dependent. This has also recently been cellular mitochondrial function can be restored by parkin overexpression and restoration of mitophagy pathways.