The osteogenic regulator THOC5-dependent post-transcriptional control maintains vascular smooth muscle cell homeostasis against chronic kidney disease related vascular calcification.

INTRODUCTION: Osteogenic transdifferentiation of vascular smooth muscle cells (VSMCs) plays a fundamental role in chronic kidney disease (CKD)-associated vascular calcification (VC). Despite its significance, the post-transcriptional control mechanisms driving VSMC osteogenic switching remain poorly understood. Here, we sought to elucidate the THOC5-dependent post-transcriptional regulatory mechanisms that control VSMC transdifferentiation and contribute to CKD-associated VC. METHODS: Von Kossa staining and immunohistochemistry were used to detect calcification and THOC5 expression in arterial tissues from patients with CKD and mice. In vitro and in vivo models of VSMC calcification were used to assess the effects of THOC5. RNA immunoprecipitation sequencing (RIP-Seq), RNA fluorescence in situ hybridization (RNA-FISH), and electrophoretic mobility shift assays (EMSA) were employed to elucidate the underlying regulatory mechanisms. RESULTS: THOC5 expression was upregulated in calcified arteries from patients with CKD and mouse models. Functionally, THOC5 deficiency exacerbated VSMC calcification, while THOC5 overexpression mitigated calcification both in vitro and in vivo. Mechanistically, THOC5 selectively associated with guanine nucleotide exchange factor (GEF) mRNAs and facilitated their nuclear export and maintained their transcript stability, thereby sustaining RhoA GTPase activity. Under pro-calcifying conditions, this engagement was diminished, resulting in reduced RhoA activity and decreased expression of VSMC contractile markers. Pharmacological inhibition of RhoA signaling (Y27632) reversed the protective effects of THOC5. Notably, THOC5 overexpression restored GEF mRNA transport and suppressed osteogenic transition. CONCLUSIONS: Our study identifies a THOC5-GEF-RhoA regulatory axis that post-transcriptionally governs VSMC phenotypic stability during CKD-associated vascular calcification. Endogenous THOC5 upregulation in calcified vasculature likely represents a compensatory but insufficient response, as osteogenic stress impairs the formation of functional THOC5-containing export complexes. THOC5 overexpression restores this process and attenuates vascular calcification.