In the neurodegenerative disease INAD, infantile neuroaxonal dystrophy, glutamate‐ and ATP‐induced Ca2+ signaling is disturbed in neurons and astrocytes, with mitochondrial dysfunction

Abstract

About 85% of cases of INAD (infantile neuroaxonal dystrophy, OMIM #256600), an autosom al recessive inherited degenerative disease with early onset can be associated with mutations of the PLA2G6 gene . Ca2+‐independent phospholipase A2 (VIA iPLA2) is encoded in PLA2G6 . However, connections of these mutations to disease are unclear. For the mainly phospholipid metabolizing VIA iPLA2 also so‐called non‐canonical functions were discussed and reported. These are regulation of store‐regulated Ca2+ entry in cells and change in mitochondrial Ca2+ homeostasis. In this study, we investigate glutamate‐evoked Ca2+ signals in neurons and astrocytes in co‐culture from three INAD mouse models with Pla2g6 gene mutations. The strain‐1 has a hypomorphic Pla2g6 allele with reduced transcript levels (5% of wild type), the strain‐2 has knocked‐out Pla2g6, and strain‐3 has a Pla2g6 point mutation with the VIA iPLA2 inactive. It is shown that homozygous offspring from all strains develop pathology similar to that observed in INAD patients. We demonstrate in our present study a strongly reduced glutamate‐induced Ca2+ response in mutants in astrocytes compared to control cells. When we elucidate the mechanism we find that reduced Ca2+ responses are due to about 2‐fold‐reduced Glu‐induced capacitative Ca2+ entry in astrocytes in all three mouse strains. This effect is based on the lack in VIA iPLA2 activity since we could mimic the decrease by pharmacologically inhibiting iPLA2 with the compound S‐BEL enantiomer. On the contrary, in neurons the Pla2g6 mutation completely disrupted the influence of mitochondrial Ca2+ uptake on the extracellular Glu‐induced Ca2+ influx . We see it in neurons treated with Ru360, a blocker of mitochondrial Ca2+ uniporter or treated with rotenone. The dependency of Glu‐induced Ca2+ influx on mitochondrial Ca2+ uptake was wiped out in neurons with Pla2g6 mutation, whereas a strong reduction was seen in wild‐type cells. Thus, all INAD models have comparable changes, but they are different for astrocytes and neurons, respectively, in Glu‐induced Ca2+ signaling. These modifications in Ca2+ signaling in cells with mutated Pla2g6 are critical for adequate neuron‐astrocyte communication. Thus our data help to understand molecular mechanisms of INAD pathology.Support or Funding InformationDeutsche Forschungsgemeinschaft (Re 563‐22‐1)