Bruceine A protects nuclear receptor 4A1 from ubiquitin-degradation to alleviate mesangial proliferative glomerulonephritis

The nuclear receptor 4A1(NR4A1) plays a crucial role in maintaining cellular homeostasis and is involved in various disease processes; however, its functional role and pharmacological potential in mesangial proliferative glomerulonephritis (MsPGN) remain unexplored. In this study, we found that downregulation of NR4A1 promotes the pathogenesis of MsPGN by regulating inflammatory and proliferative responses in mesangial cells (MCs), whereas overexpression of NR4A1 reverses these processes. Bruceine A (BA) binds to NR4A1 at residues D481/Q568 and exhibits NR4A1-dependent anti-inflammatory and anti-proliferative effects both in vitro and in vivo. Notably, adeno-associated virus serotype 9 (AAV9)-mediated overexpression of NR4A1 alleviates glomerular injury and inflammatory cascades, while knockout of NR4A1 impairs the renoprotective effects of BA. BA binds to the ligand-binding domain (LBD) of NR4A1 and further sterically blocks K48-linked polyubiquitination at K558, thereby stabilizing NR4A1 protein levels. This stabilization enables NR4A1 to auto-activate its own promoter, amplifying the transcriptional repression of nuclear factor kappa-B (NF-κB) signaling phosphorylation, which ultimately attenuates inflammatory cascades and mesangial proliferation to confer renal protection. This study provides a promising therapeutic avenue for the development of next-generation therapies against MsPGN.核受体4A1（nuclear receptor 4A1, NR4A1）在维持细胞稳态中发挥关键作用，且参与多种疾病进程；但其在系膜增生性肾小球肾炎（mesangial proliferative glomerulonephritis, MsPGN）中的功能角色与药理学潜力仍未被阐明。本研究发现，NR4A1的下调可通过调控系膜细胞（mesangial cells, MCs）的炎症与增殖反应促进MsPGN的发病进程，而NR4A1过表达则可逆转上述过程。鸦胆子苦素A（Bruceine A, BA）可与NR4A1的D481/Q568残基结合，并在体内外均展现出依赖于NR4A1的抗炎与抗增殖效应。值得注意的是，腺相关病毒血清型9（adeno-associated virus serotype 9, AAV9）介导的NR4A1过表达可减轻肾小球损伤与炎症级联反应，而NR4A1基因敲除则会削弱BA的肾脏保护作用。BA可结合NR4A1的配体结合域（ligand-binding domain, LBD），并通过空间位阻阻断K558位点处的K48连接多泛素化，进而稳定NR4A1的蛋白水平。这种稳定作用使NR4A1能够自主激活其自身的启动子，放大对核因子κB（nuclear factor kappa-B, NF-κB）信号磷酸化的转录抑制，最终减轻炎症级联反应与系膜细胞增殖，从而发挥肾脏保护作用。本研究为开发针对MsPGN的下一代治疗方案提供了极具前景的治疗途径。