SIRT6 Activation Improves Intervertebral Disc Health in the Aging Spine
Aging is one of the most important risk factors for Intervertebral disc degeneration, a major contributor to chronic low back and neck pain. Recently, we demonstrated a critical role for SIRT6, a nuclear NAD- dependent deacetylase and defatty acylase, in maintaining intervertebral disc health with aging. We therefore investigated whether pharmacological activation of SIRT6 improves disc health by examining the spinal phenotype of 24-month-old mice treated with the well-studied agonist MDL-800 for 6 months. Histological studies revealed healthy disc tissue morphology, enhanced cell viability, and lower degeneration scores in mice treated with MDL-800. Further mechanistic insights revealed that SIRT6 activation decreased H3K9ac levels, improved cell phenotype and matrix quality, and reduced the SASP burden in the disc, characterized by decreased abundance of p21, IL-6, and TGF-{beta}. Tissue RNA-Seq, in vitro measurements of histone 3 modifications, and multi-omics ATAC-seq/RNA-seq analyses revealed that SIRT6 activation altered the epigenetic status (decreased H3K9ac, H3K36me3, and H3K79me2) and transcriptomic landscape of disc cells. Notably, MDL-800 treatment increased LC3II levels in disc cells, indicating enhanced autophagic flux. Furthermore, plasma LC-MS and nuclear magnetic resonance (NMR) analyses revealed minimal systemic metabolomic changes. ScRNA-sequencing of splenocytes and bone marrow cells and systemic cytokine profiling indicated good tolerance and the absence of systemic inflammation following MDL-800 treatment. Our study demonstrates that SIRT6 activation modulates autophagy, cell senescence, and matrix homeostasis in the disc, underscoring the feasibility of targeting SIRT6 activation as a promising pharmacological strategy to maintain disc health in the aging spine.