THE L TYPE CALCIUM CHANNEL CA(v)1.2 MODULATES MITOCHONDRIAL CALCIUM HOMEOSTASIS AND CELL DEATH

Cav1.2 is the predominant voltage‐gated L‐type calcium (Ca2+) channel (LTCC) in the brain and a major regulator of intracellular Ca2+ levels. The CACNA1C gene, which encodes the voltagesensing and ion conducting α1 subunit of Cav1.2, has been linked to an array of chronic, progressive neurological disorders. Previously, we reported that newborn neurons in the adult dentate gyrus of forebrain‐specific Cav1.2 knockout (KO) mice survive at a two‐fold less rate relative to wild‐type (WT) littermates despite exhibiting no differences in initial proliferation, a finding later shown to be independent of released neurotrophic factors. However, the mechanisms by which Cav1.2 influences cell‐intrinsic neuronal death remain unknown. Recently, we have observed elevated accumulation of ubiquitinated protein aggregates in cortical neurons of Cacna1c KO mice relative to WT littermates, indicating that neurons without functional Cav1.2 are more poised towards proteotoxic stress. Furthermore, we found that loss of brain‐Cacna1c increases cortical damage from reactive oxygen species, potentially derived from mitochondrial metabolism. Because aberrant intraneuronal Ca2+ handling is a well‐established trigger for mitochondrially‐mediated cell death in neurological disorders, we assessed the brains of Cacna1c KO mice for signs of mitochondrial dysfunction. To elucidate whether Cav1.2 activity affects mitochondrial function, we measured membrane potential from isolated brain mitochondria. Unexpectedly, we found that the LTCC agonist, FPL 64176, increased WT mitochondrial membrane potential while having no effect on brain‐Cacna1c KO mitochondria. To understand how LTCC activity could directly affect mitochondrial function, we used densitygradient centrifugation and hypotonic lysis to purify and immunoblot brain organelles. Remarkably, we discovered that a subset of Cav1.2 α1 resides in mitochondria in addition to its expected localization at the plasma membrane. Finally, to determine the functional role of Cav1.2 on mitochondrial Ca2+ homeostasis, we used Ca2+ imaging methods in intact neurons and isolated mitochondria. Our data show that, while Cav1.2 inhibition at the plasma membrane produces an expected decrease in cytosolic Ca2+ levels, contrastingly, the same neurons show prolonged elevation in mitochondrial Ca2+ levels. We extended these findings by testing Ca2+ uptake in isolated mitochondria, and found that LTCC activation decreases mitochondrial Ca2+ uptake. Therefore, we hypothesize that Cav1.2 participates in mitochondrial Ca2+ efflux in a novel protective role against mitochondrial Ca2+ overload preceding cell death. This knowledge both advances the fundamental paradigm of mitochondrial Ca2+ handing and broadens Canca1c's contributions to both neuropsychiatric and neurodegenerative disease, thereby illuminating future therapeutic targets for neurological disorders.Support or Funding InformationFunding for this work was provided by the National Institutes of Health (NIH): National Institute of Neurological Disorders and Stroke (R01 NS084190), Neurodegeneration Titan Research Fund, Mary Alice Smith Fund for Neuropsychiatry Research, Department Veterans Affairs Merit Review: 1I01BX002444‐01A ‐ Neuroprotective Small Molecules as Novel Treatments for ALS, NIH: National Institute of Diabetes and Digestive and Kidney Diseases (R01 DK104998), and the National Science Foundation Research Fellowship Grant No. 1048957.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.