2, University of California, Los Angeles, Los Angeles, California, United States
We have developed a novel polymeric pH-activable, acidifying nanoparticle (acNP) that restores the pH of compromised lysosomes to rescue autophagic flux and cellular function in neurons (PC-12 cells) under exposure to either 1-methyl-4-phenylpyridinium (MPP+) toxin or 6-hydroxydopamine (6-OHDA). Parkinson’s disease (PD) occurs in 13 per 100,000 people in the population, and about 60,000 new cases are identified each year. It is characterized by the accumulation of alpha synuclein (a-syn) within Lewy bodies and neurites of the nervous system in the form of amyloid fibrils. Recent studies have indicated that perturbations in the autophagy-lysosome pathway, especially impaired lysosomal acidification that mediate the degradation of a-syn may play a role in its pathogenesis. Therefore, targeting lysosomal acidity represent a new target for therapeutic development. Although some studies have demonstrated that genetic restoration of autophagy can inhibit the development of PD, to date no effective therapeutic approach has been developed. In this study, we designed an acidic nanoparticle (acNP) that contains caged acid which can be released upon moderate pH changes to enable controlled acidification of the impaired lysosomes under lipotoxicity. The non-cytotoxic acNPs are taken up into the lysosomes of PC-12 cells, rescue cell death caused by MPP+ and 6-OHDA neuro-toxins, restore lysosomal acidity and decrease the accumulation of autophagic proteins LC3II and p62 expression levels, indicating an overall rescue of autophagic flux. The acNPs also decreased a-syn accumulation in the PC-12 cells, effectively improving the function of PC-12 cells. These results established a primary causative role of impaired lysosomal acidification on the de-regulation of autophagic flux and cellular function in neurons, and the acNPs are of potential therapeutic interest for neuro-degenerative pathologies associated with lysosomal acidity impairment, such as PD and Alzheimer’s disease.