Cytosolic and mitochondrial Calcium-independent phospholipase A2 (VIA and VIB iPLA2): Non-canonical iPLA2 functions in calcium regulation und mitochondrial functionality as mediator for neuroprotection
Final Report Abstract
The project uses mouse models of INAD (infantile neuroaxonal dystrophy), a neurodegenerative disease, with mutated Pla2g6 gene. PLA2G6 encodes VIA iPLA2. Our aims were analysis of i) non-canonical functions of VIA iPLA2 in brain and ii) molecular mechanisms underlying INAD pathology. Non-canonical functions of group VI iPLA2 are i) regulation of mitochondrial functions and ii) of Ca2+ homeostasis, and iii) apoptotic pathways. We examined in three INAD mouse models covering important scenarios of Pla2g6 mutations isolated mitochondria and brain cells in cultures. Importantly, we study in the project a new INAD model mice strain with KO Pla2g6, which was not available at the time of submission of the application. In all three mutant strains we demonstrate disturbed Ca2+ signaling both in neurons and astrocytes. We attribute changes in Ca2+ signaling to low iPLA2 activity. We can exclude other possible functions of the protein, since the effect was identical in the three mutants (inactive VIA iPLA2, hypomorph VIA iPLA2, and KO Pla2g6) and, importantly, was reproduced by pharmacological VIA iPLA2 inhibition. We give new insights into INAD pathology mechanisms by demonstration of the disturbance of Ca2+ handling by mitochondria from INAD mouse models The Ca2+ signaling, which we found altered in cells with mutated Pla2g6, is a prerequisite for adequate neuronastrocyte signaling. Our data help to understand molecular mechanisms of INAD pathology. We present a new mechanism of regulation Glu-induced Ca2+ signaling in neurons, where mitochondria facilitate the influx via GluR receptors by Ca2+ processing. Mitochondrial Ca2+ processing is defined as joint work of Ca2+ uptake via mitochondrial Ca2+ uniporter (MCU) and a subsequent release via mitochondrial Ca2+ exchanger. Our data link disturbed Ca2+ handling by mitochondria and disturbed Ca2+ homeostasis in cells from INAD mice. We demonstrate that reduced iPLA2 activity leads to increased ROS generation and lipid peroxides and finally to cell death. The main products of iPLA2 activity in brain, docosahexaenoic acid (DHA) and lysophosphatidylcholin ameliorate the negative effects of reduced iPLA2 activity. For DHA we have shown a protective mechanism of “mild uncoupling” supported by adenine nucleotide translocase. Our studies summarized here address all aims presented in our original application. Moreover, the project benefits from extension of our study on the role of mitochondrial Ca2+ processing in regulation of Glu-induced Ca2+ signaling (calcium-processing unit) in neurons and mechanisms of lipotoxicity in brain. This work joins the mechanisms of mitochondrial dysfunctions and disturbances in Ca2+ regulation in INAD and finally with non-canonical functions of VIA iPLA2.
Publications
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(2012). "Severe disturbance in the Ca2+ signaling in astrocytes from mouse models of human infantile neuroaxonal dystrophy with mutated Pla2g6." Hum Mol Genet 21(12): 2807-14
Strokin, M., K. L. Seburn, et al.
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(2014). "Putative roles of Ca2+ -independent phospholipase A2 in respiratory chain-associated ROS production in brain mitochondria: influence of docosahexaenoic acid and bromoenol lactone." J Neurochem 131(2): 163-76
Nordmann, C., M. Strokin, et al.
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(2016) Brain Lipotoxicity of Phytanic Acid and Very Long-chain Fatty Acids. Harmful Cellular/Mitochondrial Activities in Refsum Disease and X-Linked Adrenoleukodystrophy. Aging Dis. Mar 15;7(2):136-49
Schönfeld P, Reiser G
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(2016). "Mitochondria from a mouse model of the human infantile neuroaxonal dystrophy (INAD) with genetic defects in VIA iPLA2 have disturbed Ca2+ regulation with reduction in Ca2+ capacity." Neurochem Int 99: 187-193
Strokin, M. and G. Reiser
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(2016). "Mitochondrial Ca2+ Processing by a Unit of Mitochondrial Ca2+ Uniporter and Na+/Ca2+ Exchanger Supports the Neuronal Ca2+ Influx via Activated Glutamate Receptors." Neurochem Res 41(6): 1250-62
Strokin, M. and G. Reiser
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(2017) Neurons and astrocytes in an infantile neuroaxonal dystrophy (INAD) mouse model show characteristic alterations in glutamate-induced Ca2+ signaling. Neurochem Int.108:121-132
Strokin M, Reiser G
