Calcium (Ca) homeostasis is essential for neuronal function and survival. Altered Ca homeostasis has been consistently observed in neurological diseases. How Ca homeostasis is achieved in various cellular compartments of disease-relevant cell types is not well understood. Here we show in Parkinson's disease (PD) models that Ca transport from the endoplasmic reticulum (ER) to mitochondria through the ER-mitochondria contact site (ERMCS) critically regulates mitochondrial Ca (mito-Ca) homeostasis in dopaminergic (DA) neurons, and that the PD-associated PINK1 protein modulates this process. In mutant DA neurons, the ERMCS is strengthened and mito-Ca level is elevated, resulting in mitochondrial enlargement and neuronal death. Miro, a well-characterized component of the mitochondrial trafficking machinery, mediates the effects of PINK1 on mito-Ca and mitochondrial morphology, apparently in a transport-independent manner. Miro overexpression mimics loss-of-function effect, whereas inhibition of Miro or components of the ERMCS, or pharmacological modulation of ERMCS function, rescued mutant phenotypes. Mito-Ca homeostasis is also altered in the LRRK2-G2019S model of PD and the PAR-1/MARK model of neurodegeneration, and genetic or pharmacological restoration of mito-Ca level is beneficial in these models. Our results highlight the importance of mito-Ca homeostasis maintained by Miro and the ERMCS to mitochondrial physiology and neuronal integrity. Targeting this mito-Ca homeostasis pathway holds promise for a therapeutic strategy for neurodegenerative diseases.

SUMMARY A common thread among conserved lifespan regulators lies within intertwined roles in metabolism and energy homeostasis. We show that heterozygous mutations of adenosine monophosphate (AMP) biosynthetic enzymes extend Drosophila lifespan. The lifespan benefit of these mutations depends upon increased AMP to adenosine triphosphate (ATP) and adenosine diphosphate (ADP) to ATP ratios and adenosine monophosphate-activated protein kinase (AMPK). Transgenic expression of AMPK in adult fat body or adult muscle, key metabolic tissues, extended lifespan, while AMPK RNAi reduced lifespan. Supplementing adenine, a substrate for AMP biosynthesis, to the diet of long-lived AMP biosynthesis mutants reversed lifespan extension. Remarkably, this simple change in diet also blocked the pro-longevity effects of dietary restriction. These data establish AMP biosynthesis, adenosine nucleotide ratios, and AMPK as determinants of adult lifespan, provide a mechanistic link between cellular anabolism and energy sensing pathways, and indicate that dietary adenine manipulations might alter metabolism to influence animal lifespan.

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SUMMARY Mitochondria play central roles in buffering intracellular Ca2+ transients. While basal mitochondrial Ca2+ (Ca2+mito) is needed to maintain organellar physiology, Ca2+mito overload can lead to cell death. How Ca2+mito homeostasis is regulated is not well understood. Here we show that Miro, a known component of the mitochondrial transport machinery, regulates Drosophila neural stem cell (NSC) development through Ca2+mito homeostasis control independent of its role in mitochondrial transport. Miro interacts with Ca2+ transporters at the ER-mitochondria contact site (ERMCS). Its inactivation causes Ca2+mito depletion and metabolic impairment, whereas its overexpression results in Ca2+mito overload, mitochondrial morphology change, and apoptotic response. Both conditions impaired NSC lineage progression. Ca2+mito homeostasis is influenced by Polo-mediated phosphorylation of a conserved residue in Miro, which positively regulates Miro localization to, and the integrity of, ERMCS. Our results elucidate a regulatory mechanism underlying Ca2+mito homeostasis and how its dysregulation may impact NSC metabolism/development and contribute to disease.