O-GlcNAc transferase regulates intervertebral disc degeneration by targeting FAM134B-mediated ER-phagy

Abstract

Both O-linked β-N-acetylglucosaminylation (O-GlcNAcylation) and endoplasmic reticulum-phagy (ER-phagy) are well-characterized conserved adaptive regulatory mechanisms that maintain cellular homeostasis and function in response to various stress conditions. Abnormalities in O-GlcNAcylation and ER-phagy have been documented in a wide variety of human pathologies. However, whether O-GlcNAcylation or ER-phagy is involved in the pathogenesis of intervertebral disc degeneration (IDD) is largely unknown. In this study, we investigated the function of O-GlcNAcylation and ER-phagy and the related underlying mechanisms in IDD. We found that the expression profiles of O-GlcNAcylation and O-GlcNAc transferase (OGT) were notably increased in degenerated NP tissues and nutrient-deprived nucleus pulposus (NP) cells. By modulating the O-GlcNAc level through genetic manipulation and specific pharmacological intervention, we revealed that increasing O-GlcNAcylation abundance substantially enhanced cell function and facilitated cell survival under nutrient deprivation (ND) conditions. Moreover, FAM134B-mediated ER-phagy activation was regulated by O-GlcNAcylation, and suppression of ER-phagy by FAM134B knockdown considerably counteracted the protective effects of amplified O-GlcNAcylation. Mechanistically, FAM134B was determined to be a potential target of OGT, and O-GlcNAcylation of FAM134B notably reduced FAM134B ubiquitination-mediated degradation. Correspondingly, the protection conferred by modulating O-GlcNAcylation homeostasis was verified in a rat IDD model. Our data demonstrated that OGT directly associates with and stabilizes FAM134B and subsequently enhances FAM134B-mediated ER-phagy to enhance the adaptive capability of cells in response to nutrient deficiency. These findings may provide a new option for O-GlcNAcylation-based therapeutics in IDD prevention.

Chemical Biology Approaches to Understanding Neuronal O−GlcNAcylation

“…Going forward, we anticipate that new areas of investigation and potential therapeutic applications will continue to emerge. For example, a very recent study reported promising results with Thiamet‐G in ameliorating the phenotypes of intervertebral disc degeneration in a rat model [197] . However, outstanding challenges remain in the field, pointing to the need for further advances in chemical approaches in order to understand the neuronal roles of O−GlcNAc.…”

“…For example, a very recent study reported promising results with Thiamet-G in ameliorating the phenotypes of intervertebral disc degeneration in a rat model. [197] However, outstanding challenges remain in the field, pointing to the need for further advances in chemical approaches in order to understand the neuronal roles of OÀ GlcNAc. We highlight some of these challenges here.…”

ER‐phagy in neurodegeneration

“…Furthermore, there is a reduced delivery of ER proteins to lysosomes for degradation in mouse embryonic fibroblasts (Forrester et al, 2019). Interestingly, overexpression of FAM134B results in enhanced cell death in HeLa cells, with cell death increasing from 15% to 29% (Liao et al, 2019) which is not observed in other HEK293/A549 cell lines (Hill, Mellick and Sykes unpublished data), (Fregno et al, 2018; Jiang et al, 2020), nor in U2OS (Bhaskara et al, 2019; Forrester et al, 2019; Khaminets et al, 2015), HCT116 (Liang et al, 2018), or nucleus pulposus cells (Luo, Li, et al, 2022; Luo, Liang, et al, 2022).…”

“…The importance of the longer isoform of FAM134B to ER‐phagy has been demonstrated in both overexpression and knockout models. Overexpression of FAM134B results in increased fragmentation of the ER and enhanced ER‐phagy, as measured by increased degradation of ER‐resident proteins such as SEC61B or autophagy marker p62 (Bhaskara et al, 2019; Fregno et al, 2018; Jiang et al, 2020; Khaminets et al, 2015; Liang et al, 2018; Liao et al, 2019; Luo, Li, et al, 2022; Luo, Liang, et al, 2022). Conversely, decreasing FAM134B expression leads to expansion of the ER in knockdown experiments (Jiang et al, 2020; Khaminets et al, 2015; Kohno et al, 2019; Kurth et al, 2009; Lennemann & Coyne, 2017; Luo, Liang, et al, 2022; Reggio et al, 2021) and this expansion is also evident in FAM134B knockout mouse embryonic fibroblasts (Chiramel et al, 2016; Reggio et al, 2021).…”

Sal003 alleviated intervertebral disc degeneration by inhibiting apoptosis and extracellular matrix degradation through suppressing endoplasmic reticulum stress pathway in rats

“…Endoplasmic reticulum (ER) stress is generally considered as a series of molecular and biochemical changes inside cells due to ER dyshomeostasis when cells are subjected to various stimuli (Luo et al, 2022). It mainly includes dysfunction of protein folding, impairment of protein transportation, and depletion of Ca 2+ in the ER lumen (Groenendyk and Michalak 2005;Kadowaki et al, 2004;Zhao et al, 2010).…”