MICU1 attenuates neuronal apoptosis after subarachnoid hemorrhage by inhibiting mitochondrial calcium overload and damage

Background

Subarachnoid hemorrhage (SAH) is a severe neurological emergency associated with substantial morbidity and mortality. Research into the mechanisms underlying neuronal injury following SAH has identified early brain injury (EBI) as a critical factor influencing clinical outcomes. Among the various pathological processes involved in EBI, calcium overload remains relatively understudied yet plays a pivotal role in neuronal damage. Excessive accumulation of calcium within mitochondria can initiate apoptotic and autophagic pathways, contributing to cell death. Mitochondrial calcium uptake 1 (MICU1), a regulatory protein located on the inner mitochondrial membrane, functions to modulate mitochondrial calcium ions by inhibiting calcium influx under conditions of low intracellular calcium concentration.

Methods

Mitochondria were extracted from the cerebrospinal fluid (CSF) of patients with SAH to evaluate the extent of mitochondrial damage. In vivo and in vitro SAH models were employed to assess mitochondrial damage and dynamic changes in both mitochondrial and cytosolic calcium levels. The interaction between MICU1 and mitochondria was further examined. To investigate the functional role of MICU1, lentivirus vectors were used to upregulate MICU1 expression, while siRNA was applied to knock down its expression in Neuron-2a (N2a) cells. Following hemoglobin (Hb) stimulation, mitochondrial damage and apoptosis were systematically evaluated.

Results

Analysis of CSF from SAH patients revealed decreased MICU1 expression and aggravated mitochondrial damage. Hb stimulation of primary neurons and N2a cells led to reduced MICU1 expression and mitochondrial calcium overload, which mediated mitochondrial damage and promoted the progression of neuronal apoptosis. Following upregulation of MICU1 expression in N2a cells, the cells exhibited enhanced tolerance to Hb-induced calcium overload, resulting in a significant reduction in mitochondrial damage. This protective effect was attenuated by MICU1 siRNA treatment. Moreover, MICU1 overexpression alleviated Hb-induced apoptosis in N2a cells, whereas siRNA-mediated knockdown of MICU1 exacerbated apoptotic responses.

Conclusion

Mitochondrial calcium overload in neurons following SAH contributes to the development of EBI and neuronal damage. MICU1 exerts a neuroprotective role by mitigating mitochondrial calcium overload, thereby reducing mitochondrial damage and neuronal apoptosis.