Organelles storing Ca2+ in the brain cells: New druggable targets in neurodegenerative diseases

Several lines of evidence suggest that targeting dysfunctional calcium (Ca2+)-storing organelles and their defective connections may represent a promising therapeutic strategy counteracting neurodegeneration. Dysfunction in these compartments converges to promote oxidative and endoplasmic reticulum stress, energy failure, autophagy blockade or hyperactivation, and progressive neurodegeneration. Within the intracellular scenario, several dysfunctional organelles have been characterized in terms of their capability to hijack Ca2+ signaling during neurodegeneration to deadly impact on neuronal tasks in amyotrophic lateral sclerosis, Alzheimer's disease, Parkinson's disease, Huntington's disease, brain ischemia, and neonatal hypoxic injury. This review has focused on the endoplasmic reticulum, mitochondria, and lysosomes, as well as their functional interconnection able to maintain the physiological processes such as lysosomal-dependent autophagy and function, lipid trafficking, and protein quality control. Clinically, looking ahead from the already existing therapies, drugs that enhance mitochondrial Ca2+ efflux or modulate mitochondrial Ca2+ uniporter regulation at mitochondria-associated membranes-endoplasmic reticulum sites represent innovative opportunities for next-generation strategies aimed at restoring mitochondrial homeostasis and protecting dopaminergic neurons in Parkinson's disease. Furthermore, functional stabilization of the lysosomal channel transient receptor potential mucolipin 1 by the lipid-based formulation of PI(3,5)P2 may extend the lifespan of amyotrophic lateral sclerosis mice by stimulating the nuclear translocation of the master regulator of autophagy activated by lysosomal Ca2+ release, namely transcription factor EB. Moreover, dysfunction of lysosomal-dependent autophagy can cause mutant huntingtin accumulation in Huntington's disease through the repression of transcription factor EB and lysophagy induction. Collectively, this growing focus may highlight a shift toward recognizing mitochondria, lysosomes, and endoplasmic reticulum, as well as their ionic machinery and interconnections, as a unifying strategy to maintain neuronal viability and mitigate the neurodegeneration progression in amyotrophic lateral sclerosis, Alzheimer's disease, Parkinson's disease, Huntington's disease, lysosomal storage diseases, brain ischemia, and neonatal hypoxic insult.