Pueraria lobata and Daidzein Reduce Cytotoxicity by Enhancing Ubiquitin-Proteasome System Function in SCA3-iPSC-Derived Neurons

Abstract

Spinocerebellar ataxia type 3 (SCA3) is an autosomal dominant neurodegenerative disorder caused by a CAG repeat expansion within the ATXN3/MJD1 gene. The expanded CAG repeats encode a polyglutamine (polyQ) tract at the C-terminus of the ATXN3 protein. ATXN3 containing expanded polyQ forms aggregates, leading to subsequent cellular dysfunctions including an impaired ubiquitin-proteasome system (UPS). To investigate the pathogenesis of SCA3 and develop potential therapeutic strategies, we established induced pluripotent stem cell (iPSC) lines from SCA3 patients (SCA3-iPSC). Neurons derived from SCA3-iPSCs formed aggregates that are positive to the polyQ marker 1C2. Treatment with the proteasome inhibitor, MG132, on SCA3-iPSC-derived neurons downregulated proteasome activity, increased production of radical oxygen species (ROS), and upregulated the cleaved caspase 3 level and caspase 3 activity. This increased susceptibility to the proteasome inhibitor can be rescued by a Chinese herbal medicine (CHM) extract NH037 (from Pueraria lobata) and its constituent daidzein via upregulating proteasome activity and reducing protein ubiquitination, oxidative stress, cleaved caspase 3 level, and caspase 3 activity. Our results successfully recapitulate the key phenotypes of the neurons derived from SCA3 patients, as well as indicate the potential of NH037 and daidzein in the treatment for SCA3 patients.

Therapeutic roles of natural remedies in combating hereditary ataxia: A systematic review

“…Caspase-3 activity was also reduced, which prevented polyQ-induced cell death [ 55 ]. These findings were in line with another study by Chen et al [ 56 ] using an in vitro model of SCA3 with MG132-induced pluripotent stem cells (iPSCs). Pre-treatment with 50 μM daidzein for 24 h restored proteasome activity in the cells.…”

“…Chou et al [ 57 ] reported that the activation of A 2A receptor by T1-11 and JMF-1907 could enhance proteasome activity and promote degradation of ubiquitin proteins. Similar findings were later reported by Chen et al [ 55 , 56 ] using puerarin and daidzein compounds extracted from R. glutinosa and P. lobata . Inhibition of A 2A receptor using an A 2A antagonist blocked the effects induced by T1-11 and JMF-1907.…”

“…Pre-treatment with 50 μM daidzein for 24 h restored proteasome activity in the cells. Additionally, daidzein was able to suppress MG132-induced cell death, as indicated by lactate dehydrogenase (LDH) assay [ 56 ].…”

Human Induced Pluripotent Stem Cell-Based Modelling of Spinocerebellar Ataxias

“…Expanded ATXN3 localizes more readily to the nucleus, forming intranuclear aggregates that contribute to neuropathology [72]. The expanded protein is still able to bind ubiquitin in hiPSC-derived neurons [22] and shows normal proteasome activity, with increased sensitivity for proteasome inhibition [73]. This hinted towards toxic gain-of-function rather than a loss-of-function of the protein.…”

“…Recently, these phenotypes have been replicated by Thiruvalluvan et al [75], who additionally showed that aggregates were not formed in NSCs challenged with glutamate. Also, Chen et al showed, by a filter trap assay, that unstimulated SCA3 neurons contained 1C2-positive insoluble protein, while cell viability was not affected [73]. However, others have not been able to reproduce these phenotypes [22,76].…”