Lysosomal TPC2 channel as a new target of chlorpromazine and clomipramine to induce protective autophagy in L-BMAA-induced neurodegeneration

Several neurodegenerative diseases including amyotrophic lateral sclerosis (ALS) are characterized by toxic aggregates accumulation due to autophagy blockade, prompting researchers to identify new autophagy-activating drugs. Here we tested, in an in vitro ALS/PDC model, the neuroprotective effects of the antipsychotic Chlorpromazine (CPZ) and the antidepressant Clomipramine (CMI), chosen by drug repurposing approach for their ability to stimulate TPC2 lysosomal channel. Patch-clamp electrophysiology on enlarged lysosomes in NSC-34 motor neurons showed that CPZ and CMI induced large inwardly-rectifying currents, that were inhibited by TPC2 synthetic blocker trans-Ned-19. The same currents were evoked by TPC2 endogenous agonist NAADP and its mimetic agent TPC2-A1-N, and inhibited by trans-Ned-19 and siRNAs against TPC2 (siTPC2). CPZ and CMI elicited a significant [Ca2+]i increase that rapidly induced nuclear translocation of TFEB (transcription factor EB), the master regulator of autophagy. Accordingly, TPC2 stimulation by both the drugs boosted autophagy, as revealed by the activation of autophagy initiators ULK and AMPK α and modification of LC3-II/p62(SQSTM1) ratio. Furthermore, by normalizing autophagy markers, CPZ and CMI counteracted the detrimental effects induced by L-BMAA, a neurotoxin mimicking ALS/PDC. Notably, siTPC2 partially reverted CMI- and CPZ-induced neuroprotection as well as that produced by NAADP. At mitochondrial level, these drugs prevented ATP reduction and ROS overproduction in motor neurons exposed to L-BMAA for 24 h. For a longer L-BMAA exposure, CPZ and CMI counteracted LDH, cytochrome C and SMAC/DIABLO release, thus preventing cell demise. These findings suggest that TPC2 activation by drug repurposing could provide novel therapeutic options for ALS via autophagy regulation.