CHIP-mediated ubiquitin degradation of BCAT1 regulates glioma cell proliferation and temozolomide sensitivity.

Glioma, a malignant and infiltrative neoplasm of the central nervous system, poses a significant threat due to its high mortality rates. Branched-chain amino acid transaminase 1 (BCAT1), a key enzyme in branched-chain amino acid (BCAA) catabolism, exhibits elevated expression in gliomas and correlates strongly with poor prognosis. Nonetheless, the regulatory mechanisms underlying this increased BCAT1 expression remains incompletely understood. In this study, we reveal that ubiquitination at Lys360 facilitates BCAT1 degradation, with low ubiquitination levels contributing to high BCAT1 expression in glioma cells. The Carboxyl terminus of Hsc70-interacting protein (CHIP), an E3 ubiquitin ligase, interacts with BCAT1 via its coiled-coil (CC) domain, promoting its K48-linkage ubiquitin degradation through proteasomal pathway. Moreover, CHIP-mediated BCAT1 degradation induces metabolic reprogramming, and impedes glioma cell proliferation and tumor growth both in vitro and in vivo. Furthermore, a positive correlation is observed between low CHIP expression, elevated BCAT1 levels, and unfavorable prognosis among glioma patients. Additionally, we show that the CHIP/BCAT1 axis enhances glioma sensitivity to temozolomide by reducing glutathione (GSH) synthesis and increasing oxidative stress. These findings underscore the critical role of CHIP/BCAT1 axis in glioma cell proliferation and temozolomide sensitivity, highlighting its potential as a diagnostic marker and therapeutic target in glioma treatment.

Targeted inhibition of branched-chain amino acid metabolism drives apoptosis of glioblastoma by facilitating ubiquitin degradation of Mfn2 and oxidative stress.

Glioblastoma is one of the most challenging malignancies with high aggressiveness and invasiveness and its development and progression of glioblastoma highly depends on branched-chain amino acid (BCAA) metabolism. The study aimed to investigate effects of inhibition of BCAA metabolism with cytosolic branched-chain amino acid transaminase (BCATc) Inhibitor 2 on glioblastoma, elucidate its underlying mechanisms, and explore therapeutic potential of targeting BCAA metabolism. The expression of BCATc was upregulated in glioblastoma and BCATc Inhibitor 2 precipitated apoptosis both in vivo and in vitro with the activation of Bax/Bcl2/Caspase-3/Caspase-9 axis. In addition, BCATc Inhibitor 2 promoted K63-linkage ubiquitination of mitofusin 2 (Mfn2), which subsequently caused lysosomal degradation of Mfn2, and then oxidative stress, mitochondrial fission and loss of mitochondrial membrane potential. Furthermore, BCATc Inhibitor 2 treatment resulted in metabolic reprogramming, and significant inhibition of expression of ATP5A, UQCRC2, SDHB and COX II, indicative of suppressed oxidative phosphorylation. Moreover, Mfn2 overexpression or scavenging mitochondria-originated reactive oxygen species (ROS) with mito-TEMPO ameliorated BCATc Inhibitor 2-induced oxidative stress, mitochondrial membrane potential disruption and mitochondrial fission, and abrogated the inhibitory effect of BCATc Inhibitor 2 on glioblastoma cells through PI3K/AKT/mTOR signaling. All of these findings indicate suppression of BCAA metabolism promotes glioblastoma cell apoptosis via disruption of Mfn2-mediated mitochondrial dynamics and inhibition of PI3K/AKT/mTOR pathway, and suggest that BCAA metabolism can be targeted for developing therapeutic agents to treat glioblastoma.

Human amniotic mesenchymal stem cells-derived conditioned medium and exosomes alleviate oxidative stress-induced retinal degeneration by activating PI3K/Akt/FoxO3 pathway.

Age-related macular degeneration (AMD) is the leading cause of vision loss among the elderly, which is primarily attributed to oxidative stress-induced damage to the retinal pigment epithelium (RPE). Human amniotic mesenchymal stem cells (hAMSC) were considered to be one of the most promising stem cells for clinical application due to their low immunogenicity, tissue repair ability, pluripotent potential and potent paracrine effects. The conditional medium (hAMSC-CM) and exosomes (hAMSC-exo) derived from hAMSC, as mediators of intercellular communication, play an important role in the treatment of retinal diseases, but their effect and mechanism on oxidative stress-induced retinal degeneration are not explored. Here, we reported that hAMSC-CM alleviated H2O2-induced ARPE-19 cell death through inhibiting mitochondrial-mediated apoptosis pathway in vitro. The overproduction of reactive oxygen species (ROS), alteration in mitochondrial morphology, loss of mitochondrial membrane potential and elevation of Bax/Bcl2 ratio in ARPE-19 cells under oxidative stress were efficiently reversed by hAMSC-CM. Moreover, it was found that hAMSC-CM protected cells against oxidative injury via PI3K/Akt/FoxO3 signaling. Intriguingly, exosome inhibitor GW4869 alleviated the inhibitory effect of hAMSC-CM on H2O2-induced decrease in cell viability of ARPE-19 cells. We further demonstrated that hAMSC-exo exerted the similar protective effect on ARPE-19 cells against oxidative damage as hAMSC-CM. Additionally, both hAMSC-CM and hAMSC-exo ameliorated sodium iodate-induced deterioration of RPE and retinal damage in vivo. These results first indicate that hAMSC-CM and hAMSC-exo protect RPE cells from oxidative damage by regulating PI3K/Akt/FoxO3 pathway, suggesting hAMSC-CM and hAMSC-exo will be a promising cell-free therapy for the treatment of AMD in the future.