# CDKN2B Inhibits Vascular Smooth Muscle Phenotypic Switching in Corpus Spongiosum Surrounding the Urethral Plate in Hypospadias

## TL;DR

This study finds that CDKN2B helps maintain the contractile state of vascular smooth muscle cells in the corpus spongiosum, and its loss may contribute to abnormal urethral development in hypospadias.

## Contribution

CDKN2B is identified as a novel regulator of vascular smooth muscle cell phenotypic switching in hypospadias through transcriptomic and functional analyses.

## Key findings

- Hypospadias tissue shows a shift in vascular smooth muscle cells from contractile to secretory phenotype.
- CDKN2B is downregulated in hypospadias and its overexpression restores contractile markers and signaling.
- CDKN2B modulates TGF/Smad and SRF/MYOCD pathways to regulate phenotypic switching.

## Abstract

Objective: Phenotypic switching of vascular smooth muscle cells (VSMCs) in the corpus spongiosum may contribute to abnormal urethral development in hypospadias, but the underlying molecular regulators remain unclear. This study aimed to identify hub genes associated with VSMCs phenotypic switching in the corpus spongiosum using RNA sequencing and Weighted Gene Co-expression Network Analysis (WGCNA), and to functionally characterize the top candidate gene CDKN2B. Methods: Corpus spongiosum tissue samples were collected from seven patients with proximal hypospadias and five patients with urethral stricture (control group). The expression of the VSMCs contractile markers Calponin 1 and α-SMA, and the secretory marker OPN, was evaluated by qRT-PCR and Western blotting to assess VSMCs phenotypic state. RNA sequencing and Weighted Gene Co-expression Network Analysis (WGCNA) were performed to identify hub genes, which were then validated by qRT-PCR. Primary VSMCs were isolated from corpus spongiosum tissue and transduced with lentiviral vectors to either suppress or overexpress CDKN2B. Changes in VSMC marker expression and in key signaling pathways associated with phenotypic switching—specifically TGF/Smad and SRF/MYOCD—were analyzed using qRT-PCR and Western blotting. Results: In hypospadias tissue, the decreased expression of α-SMA and Calponin 1, together with increased OPN, indicated a shift in VSMCs from a contractile to a secretory phenotype. RNA-seq and WGCNA identified 11 differentially expressed genes, among which CDKN2B showed a marked downregulation in hypospadias samples. In control VSMCs, CDKN2B inhibition led to reduced α-SMA and Calponin 1, elevated OPN, and suppressed activity of TGF/Smad and SRF/MYOCD signaling. Conversely, CDKN2B overexpression in VSMCs from hypospadias samples restored α-SMA and Calponin 1 expression, decreased OPN, and enhanced TGF/Smad and SRF/MYOCD pathway activation. Conclusions: VSMCs in the corpus spongiosum surrounding the urethral plate in hypospadias undergo a transition from a contractile to a secretory phenotype. CDKN2B emerges from unbiased transcriptomic screening as a key hub gene and functions as a critical regulator of this process, maintaining the contractile phenotype by modulating canonical TGF/Smad and SRF/MYOCD signaling. The CDKN2B–TGF/Smad axis may represent a central pathway linking VSMC phenotypic switching to abnormal vascular remodeling in hypospadias.