Sirt1 deficiency promotes dynamic fibroblast-to-myofibroblast transition in ligamentum flavum hypertrophy via the Smad2/3 pathway

Background Ligamentum flavum hypertrophy (LFH), a major pathological feature of lumbar spinal stenosis, is characterized by fibrosis and extracellular matrix (ECM) remodeling. However, the molecular mechanisms remain unclear. This study investigates the role of Sirtuin 1 (Sirt1), a NAD + -dependent deacetylase, in regulating fibroblast-to-myofibroblast transition (FMT) in LFH. Methods Human LF samples and a rat LFH model were examined using histological, immunohistochemical, and molecular analyses. Single-cell RNA sequencing (scRNA-seq) was performed to explore LF cellular heterogeneity and identify fibrosis-related regulators. In vitro, Sirt1 activity was modulated pharmacologically and genetically to assess its role in fibroblast activation. Transcriptomic and bioinformatic analyses were used to identify downstream pathways, and lentiviral overexpression of Sirt1 in vivo was applied to evaluate therapeutic effects. Results scRNA-seq revealed fibroblasts as the dominant cell type in LFH and showed Sirt1 downregulation during fibrosis progression. Sirt1 inhibition enhanced FMT in ligamentum flavum cells, increasing α-SMA, Col-I, and Col-III expression via activation of the Smad2/3 signaling pathway. Conversely, Sirt1 overexpression mitigated LF fibrosis and improved sensory function in rats. Conclusions Loss of Sirt1 promotes fibroblast-to-myofibroblast transition through Smad2/3 activation, while Sirt1 restoration alleviates LFH, suggesting Sirt1 as a promising therapeutic target for LF fibrosis.