L-arginine alleviates intervertebral disc degeneration by suppressing TRIB3/AKAP1-mediated Drp1 phosphorylation dysregulation and mitochondrial fragmentation.

OBJECTIVE

To clarify therapeutic potential and underlying mechanism of L-arginine (L-arg) in intervertebral disc degeneration (IDD).

DESIGN

Human nucleus pulposus (NP) samples (n=36) underwent metabolomics, L-arg quantification, and immunohistochemistry to characterize the relationship between L-arg metabolism and IDD severity. In vitro NP cell experiments integrated RNA-sequencing, Western blot, co-immunoprecipitation, and immunofluorescence colocalization to clarify the therapeutic effects and mechanism of L-arg. In vivo validation using rat models (n=30) was performed with magnetic resonance imaging (MRI) and immunohistochemistry to assess the efficacy of L-arg in alleviating IDD.

RESULTS

Metabolomics revealed a depletion of L-arg in severely degenerated NP tissues. L-arg supplementation mitigated TNFα-induced cellular senescence (β-galactosidase positive rate reduced by 37.4%, 95% CI: 29.5-45.3), extracellular matrix dysfunction (ACAN increased 1.59-fold, 95% CI: 1.19-2.11), and mitochondrial dysfunction (ATP content increased 1.43-fold, 95% CI: 1.29-1.57) in NP cells by inhibiting mitochondrial fragmentation. In rat IDD models, L-arg attenuated disc degeneration (MRI intensity: 3.245-fold vs. degeneration, 95% CI: 2.05-5.13). Mechanistically, L-arg suppressed inflammation-driven Tribbles homolog 3 (TRIB3) expression (0.49-fold vs. TNFα, 95% CI: 0.29-0.84). Elevated TRIB3 disrupted the interaction between A-kinase anchoring protein 1 (AKAP1) and protein kinase A regulatory subunit IIα (PKA RIIα)-an interaction critical for Drp1-S656 phosphorylation that inhibits mitochondrial fission. By preserving the AKAP1-PKA RIIα interaction, L-arg sustained Drp1 phosphorylation at S656 and blocked pathological mitochondrial fission.

CONCLUSION

L-arg may alleviate IDD in vitro and vivo by modulating TRIB3-AKAP1-PKA/Drp1(S656) axis, highlighting its promising therapeutic potential in IDD.