ER and oxidative stresses are common mediators of apoptosis in both neurodegenerative and non-neurodegenerative lysosomal storage disorders and are alleviated by chemical chaperones

It is estimated that more than 40 different lysosomal storage disorders (LSDs) cumulatively affect one in 5000 live births, and in the majority of the LSDs, neurodegeneration is a prominent feature. Neuronal ceroid lipofuscinoses (NCLs), as a group, represent one of the most common (one in 12 500 births) neurodegenerative LSDs. The infantile NCL (INCL) is the most devastating neurodegenerative LSD, which is caused by inactivating mutations in the palmitoyl-protein thioesterase-1 (PPT1) gene. We previously reported that neuronal death by apoptosis in INCL, and in the PPT1-knockout (PPT1-KO) mice that mimic INCL, is at least in part caused by endoplasmic reticulum (ER) and oxidative stresses. In the present study, we sought to determine whether ER and oxidative stresses are unique manifestations of INCL or they are common to both neurodegenerative and non-neurodegenerative LSDs. Unexpectedly, we found that ER and oxidative stresses are common manifestations in cells from both neurodegenerative and non-neurodegenerative LSDs. Moreover, all LSD cells studied show extraordinary sensitivity to brefeldin-A-induced apoptosis, which suggests pre-existing ER stress conditions. Further, we uncovered that chemical disruption of lysosomal homeostasis in normal cells causes ER stress, suggesting a cross-talk between the lysosomes and the ER. Most importantly, we found that chemical chaperones that alleviate ER and oxidative stresses are also cytoprotective in all forms of LSDs studied. We propose that ER and oxidative stresses are common mediators of apoptosis in both neurodegenerative and non-neurodegenerative LSDs and suggest that the beneficial effects of chemical/pharmacological chaperones are exerted, at least in part, by alleviating these stress conditions.