Kung, C. | Search bioRxiv

bioRxiv2024

Presynapses are mitophagy pit stops that prevent axon degeneration

Defects in neuronal mitophagy have been linked to neurodegenerative diseases including Parkinsons disease. However, despite the importance of mitophagy in neuronal homeostasis, the mechanistic basis for neurodegeneration when mitophagy is defective is unclear. Here, using human neurons, we discover that presynapses are mitophagy pit stops for damaged axonal mitochondria. We show that while mitochondrial damage and PINK1/Parkin activation events are distributed throughout axons, mitophagy initiation and autophagosome formation are restricted to presynapses, which we show contain the machineries required for mitophagy. Being the primary sites of axonal mitophagy, presynapses were vulnerable when PINK1/Parkin mitophagy was defective. We observed local cytochrome c release within presynapses from an accumulation of damaged mitochondria. This resulted in downstream degradative caspase activation, defining a mechanism for neurodegeneration. Pharmacological rescue of axon degeneration was achieved through synthetic upregulation of receptor mediated mitophagy with the clinically approved compound Roxadustat, revealing a potential therapeutic avenue for disease.

cell biology↗

bioRxiv2020

Pharmacologic activation of the mitochondrial phosphoenolpyruvate cycleenhances islet function in vivo

The mitochondrial GTP (mtGTP)-dependent phosphoenolpyruvate (PEP) cycle is an anaplerotic-cataplerotic mitochondrial shuttle utilizing mitochondrial PEPCK (PCK2) and pyruvate kinase (PK). PEP cycling stimulates insulin secretion via OxPhos-independent lowering of ADP by PK. We assess in vivo whether islet PCK2 is necessary for glucose sensing and if speeding the PEP cycle via pharmacological PK activators amplifies insulin secretion. Pck2-/- mice had severely impaired insulin secretion during islet perifusion, oral glucose tolerance tests and hyperglycemic clamps. Acute and chronic pharmacologic PK activator therapy improved islet insulin secretion from normal, high-fat diet (HFD) fed, or Zucker diabetic fatty (ZDF) rats, and glucolipotoxic or diabetic humans. A similar improvement in insulin secretion was observed in regular chow and HFD rats in vivo. Insulin secretion and cytosolic Ca2+ during PK activation were dependent on PCK2. These data provide a preclinical rationale for strategies, such as PK activation, that target the PEP cycle to improve glucose homeostasis. HighlightsO_LILoss of mitochondrial phosphoenolpyruvate (PEP) impairs insulin release in vivo. C_LIO_LIPyruvate kinase (PK) activators stimulate beta-cells in preclinical diabetes models. C_LIO_LIPEP cycling in vivo depends on PK and mitochondrial PEPCK (PCK2) for insulin release. C_LIO_LIAcute and 3-week oral PK activator amplifies insulin release during hyperglycemia. C_LI eTOC BlurbAbudukadier et al. show that small molecule pyruvate kinase activation in vivo and in vitro increases insulin secretion in rodent and human models of diabetes. The phosphoenolpyruvate (PEP) cycling mechanism and its amplification are dependent on mitochondrial PEPCK (PCK2).

physiology↗