MIRO-1 Determines Mitochondrial Shape Transition upon GPCR Activation and Ca^(2+) Stress

Mitochondria shape cytosolic calcium ([Ca^(2+)]_c) transients and utilize the mitochondrial Ca_2^+ ([Ca^(2+)]_m) in exchange for bioenergetics output. Conversely, dysregulated [Ca^(2+)]_c causes [Ca^(2+)]_m overload and induces permeability transition pore and cell death. Ablation of MCU-mediated Ca^(2+) uptake exhibited elevated [Ca^(2+)]_c and failed to prevent stress-induced cell death. The mechanisms for these effects remain elusive. Here, we report that mitochondria undergo a cytosolic Ca^(2+)-induced shape change that is distinct from mitochondrial fission and swelling. [Ca^(2+)]_c elevation, but not MCU-mediated Ca^(2+) uptake, appears to be essential for the process we term mitochondrial shape transition (MiST). MiST is mediated by the mitochondrial protein Miro1 through its EF-hand domain 1 in multiple cell types. Moreover, Ca^(2+)-dependent disruption of Miro1/KIF5B/tubulin complex is determined by Miro1 EF1 domain. Functionally, Miro1-dependent MiST is essential for autophagy/mitophagy that is attenuated in Miro1 EF1 mutants. Thus, Miro1 is a cytosolic Ca^(2+) sensor that decodes metazoan Ca^(2+) signals as MiST

MIRO-1 Determines Mitochondrial Shape Transition upon GPCR Activation and Ca^(2+) Stress

Mitochondria shape cytosolic calcium ([Ca^(2+)]_c) transients and utilize the mitochondrial Ca_2^+ ([Ca^(2+)]_m) in exchange for bioenergetics output. Conversely, dysregulated [Ca^(2+)]_c causes [Ca^(2+)]_m overload and induces permeability transition pore and cell death. Ablation of MCU-mediated Ca^(2+) uptake exhibited elevated [Ca^(2+)]_c and failed to prevent stress-induced cell death. The mechanisms for these effects remain elusive. Here, we report that mitochondria undergo a cytosolic Ca^(2+)-induced shape change that is distinct from mitochondrial fission and swelling. [Ca^(2+)]_c elevation, but not MCU-mediated Ca^(2+) uptake, appears to be essential for the process we term mitochondrial shape transition (MiST). MiST is mediated by the mitochondrial protein Miro1 through its EF-hand domain 1 in multiple cell types. Moreover, Ca^(2+)-dependent disruption of Miro1/KIF5B/tubulin complex is determined by Miro1 EF1 domain. Functionally, Miro1-dependent MiST is essential for autophagy/mitophagy that is attenuated in Miro1 EF1 mutants. Thus, Miro1 is a cytosolic Ca^(2+) sensor that decodes metazoan Ca^(2+) signals as MiST

Antiproliferative and uncoupling effects of delocalized, lipophilic, cationic gallic acid derivatives on cancer cell lines. Validation in vivo in singenic mice

Tumor cells principally exhibit increased mitochondrial transmembrane potential (Δψm) and altered metabolic pathways. The therapeutic targeting and delivery of anticancer drugs to the mitochondria might improve treatment efficacy. Gallic acid exhibits a variety of biological activities, and its ester derivatives can induce mitochondrial dysfunction. Four alkyl gallate triphenylphosphonium lipophilic cations were synthesized, each differing in the size of the linker chain at the cationic moiety. These derivatives were selectively cytotoxic toward tumor cells. The better compound (TPP+C10) contained 10 carbon atoms within the linker chain and exhibited an IC50 value of approximately 0.4-1.6 μM for tumor cells and a selectivity index of approximately 17-fold for tumor compared with normal cells. Consequently, its antiproliferative effect was also assessed in vivo. The oxygen consumption rate and NAD(P)H oxidation levels increased in the tumor cell lines (uncoupling effect), resulting in

Non-canonical function of IRE1α determines mitochondria-associated endoplasmic reticulum composition to control calcium transfer and bioenergetics

Mitochondria-associated membranes (MAMs) are central microdomains that fine-tune bioenergetics by the local transfer of calcium from the endoplasmic reticulum to the mitochondrial matrix. Here, we report an unexpected function of the endoplasmic reticulum stress transducer IRE1α as a structural determinant of MAMs that controls mitochondrial calcium uptake. IRE1α deficiency resulted in marked alterations in mitochondrial physiology and energy metabolism under resting conditions. IRE1α determined the distribution of inositol-1,4,5-trisphosphate receptors at MAMs by operating as a scaffold. Using mutagenesis analysis, we separated the housekeeping activity of IRE1α at MAMs from its canonical role in the unfolded protein response. These observations were validated in vivo in the liver of IRE1α conditional knockout mice, revealing broad implications for cellular metabolism. Our results support an alternative function of IRE1α in orchestrating the communication between the endoplasmic reticulum and mitochondria to sustain bioenergetics

Aminochrome induces dopaminergic neuronal dysfunction: a new animal model for Parkinson’s disease

L-Dopa continues to be the gold drug in Parkinson's disease ( PD) treatment from 1967. The failure to translate successful results from preclinical to clinical studies can be explained by the use of preclinical models which do not reflect what happens in the disease since these induce a rapid and extensive degeneration; for example, MPTP induces a severe Parkinsonism in only 3 days in humans contrasting with the slow degeneration and progression of PD. This study presents a new anatomy and develops preclinical model based on aminochrome which induces a slow and progressive dysfunction of dopaminergic neurons. The unilateral injection of aminochrome into rat striatum resulted in ( 1) contralateral rotation when the animals are stimulated with apomorphine; ( 2) absence of significant loss of tyrosine hydroxylase-positive neuronal elements both in substantia nigra and striatum; ( 3) cell shrinkage; ( 4) significant reduction of dopamine release; ( 5) significant increase in GABA release; ( 6) significant decrease in the number of monoaminergic presynaptic vesicles; ( 7) significant increase of dopamine concentration inside of monoaminergic vesicles; ( 8) significant increase of damaged mitochondria; ( 9) significant decrease of ATP level in the striatum ( 10) significant decrease in basal and maximal mitochondrial respiration. These results suggest that aminochrome induces dysfunction of dopaminergic neurons where the contralateral behavior can be explained by aminochrome-induced ATP decrease required both for anterograde transport of synaptic vesicles and dopamine release. Aminochrome could be implemented as a new model neurotoxin to study Parkinson's diseaseFONDECYT 1100165 1120443 3140458 University of Chile ENL014/14 ECOS-CONICYT C10S02 FONDAP 1515001

Publisher Correction: Non-canonical function of IRE1α determines mitochondria-associated endoplasmic reticulum composition to control calcium transfer and bioenergetics (Nature Cell Biology, (2019), 21, 6, (755-767), 10.1038/s41556-019-0329-y)

An amendment to this paper has been published and can be accessed via a link at the top of the paper

Insulin stimulates mitochondrial fusion and function in cardiomyocytes via the AktmTOR-NFkB-Opa-1 signaling pathway

Insulin regulates heart metabolism through the regulation of insulin-stimulated glucose uptake. Studies have indicated that insulin can also regulate mitochondrial function. Relevant to this idea, mitochondrial function is impaired in diabetic individuals. Furthermore, the expression of Opa-1 and mitofusins, proteins of the mitochondrial fusion machinery, is dramatically altered in obese and insulin-resistant patients. Given the role of insulin in the control of cardiac energetics, the goal of this study was to investigate whether insulin affects mitochondrial dynamics in cardiomyocytes. Confocal microscopy and the mitochondrial dye MitoTracker Green were used to obtain three-dimensional images of the mitochondrial network in cardiomyocytes and L6 skeletal muscle cells in culture. Three hours of insulin treatment increased Opa-1 protein levels, promoted mitochondrial fusion, increased mitochondrial membrane potential, and elevated both intracellular ATP levels and oxygen consumption i

Prolonged Activation of the Htr2b Serotonin Receptor Impairs Glucose Stimulated Insulin Secretion and Mitochondrial Function in MIN6 Cells

<div><p>Aims</p><p>Pancreatic β-cells synthesize and release serotonin (5 hydroxytryptamine, 5HT); however, the role of 5HT receptors on glucose stimulated insulin secretion (GSIS) and the mechanisms mediating this function is not fully understood. The aims of this study were to determine the expression profile of 5HT receptors in murine MIN6 β-cells and to examine the effects of pharmacological activation of 5HT receptor Htr2b on GSIS and mitochondrial function.</p><p>Materials and Methods</p><p>mRNA levels of 5HT receptors in MIN6 cells were quantified by RT qPCR. GSIS was assessed in MIN6 cells in response to global serotonergic activation with 5HT and pharmacological Htr2b activation or inhibition with BW723C86 or SB204741, respectively. In response to Htr2b activation also was evaluated the mRNA and protein levels of PGC1α and PPARy by RT-qPCR and western blotting and mitochondrial function by oxygen consumption rate (OCR) and ATP cellular content.</p><p>Results</p><p>We found that mRNA levels of most 5HT receptors were either very low or undetectable in MIN6 cells. By contrast, Htr2b mRNA was present at moderate levels in these cells. Preincubation (6 h) of MIN6 cells with 5HT or BW723C86 reduced GSIS and the effect of 5HT was prevented by SB204741. Preincubation with BW723C86 increased PGC1α and PPARy mRNA and protein levels and decreased mitochondrial respiration and ATP content in MIN6 cells.</p><p>Conclusions</p><p>Our results indicate that prolonged Htr2b activation in murine β-cells decreases glucose-stimulated insulin secretion and mitochondrial activity by mechanisms likely dependent on enhanced PGC1α/PPARy expression.</p></div