The cellular microenvironment plays a crucial role in tissue growth and homeostasis and is closely linked to disease development [1]. An integral component of the cellular microenvironment is a three-dimensional noncellular network known as the extracellular matrix (ECM), and advancements in research tools have aided its gradual understanding [2]. Biomechanics, a field encompassing a wide range of topics, including solid stress [3], fluid pressure [4,5], and stiffness [6], plays a significant role in this understanding. Specifically, matrix stiffness can convert mechanical signals into biological responses by influencing cellular interactions [7]. Several studies have shown that matrix stiffness can promote fibroblast-myofibroblast transformation (FMT) in a variety of bodily tissues (including the skin, lungs, and vagina), as evidenced by an increased cellular aspect ratio, as well as the expression of α-smooth muscle actin (α-SMA) and connective tissue growth factor (CTGF) [[8], [9], [10]]. Myofibroblasts are abundant in actin and fibronectin, which form cellular matrix junctions and determine the fate of tissue repair [11]. However, sustained FMT can lead to pathological matrix deposition, resulting in reduced tissue compliance and increased stiffness [12]. Previous research has shown that increased ECM stiffness can induce cell autophagy [[13], [14], [15]]. However, the mechanisms underlying the cascade of mechanical cues from the plasma membrane to the cytoplasm—and subsequently to the nucleus—during matrix stiffness-induced myofibroblast transformation remain obscure. Fibroblasts express Kindlin-2, also known as the fermitin family homolog 2 (FERMT2), which plays a crucial role in regulating cell migration and collagen contraction. Additionally, it plays a significant role in the development of the mesoderm, which includes smooth muscles, blood vessels [16], and connective tissue [17]. In the adhesion patch (a mechanical linkage between the ECM and the cytoskeleton), Kindlin-2 binds to the cytoplasmic tails of β1 and β3 integrins and co-activates integrins with Talin to regulate cell-ECM adhesion [18,19]. Furthermore, fibroblasts have been shown to convert physical signals into biological signals through transmembrane integrin transmission and sensory mechanics in focal adhesions [20], thus suggesting the potential role of Kindlin-2 in signal transduction, specifically in the regulation of fibroblast biological properties mediated by ECM stiffness; however, the exact mechanisms remain unexplored. The Yes-associated protein (YAP) and transcriptional coactivator with a PDZ-binding motif (TAZ) of the Hippo pathway are among the most studied transcription factors regulated by matrix stiffness, sensing mechanical stimuli and relaying signals to regulate cell proliferation and transformation [21]. The Hippo pathway is highly conserved in vertebrates and includes mammalian sterile 20-like 1/2 (MST1/2 or ‘STK4/3’), Salvador (SAV1), large tumor suppressor homolog 1/2 (LATS1/2), MOB kinase activator 1A/B (MOB1a/b), and YAP/TAZ proteins [22]. LATS1/2 directly phosphorylates YAP, whereas the full activation of LATS1 depends on MOB1 phosphorylation [23,24]. Several studies have shown that increased ECM stiffness during fibrosis in animal models and human tissues can promote the production of fibrotic mediators and ECM proteins by altering YAP/TAZ activity [25,26]. However, the upstream mechanosensors of YAP/TAZ signaling and downstream transcriptomic responses following YAP/TAZ activation or inhibition have not been fully characterized.

FMT is a crucial component in pelvic organ prolapse (POP) development and leads to increased ECM stiffness in vaginal tissues [8]. POP is a common multifactorial disorder that clinically manifests as prolapsing caused by damage to the supporting structures of the pelvic floor [27]. Transvaginal delivery is the primary risk factor for POP development, which may lead to urinary, defecatory, and sexual dysfunction, seriously impairing physical and mental health [28]. By 2050, symptomatic POP prevalence is expected to increase by 50% [29]. Evidence suggests that the vaginal tissue microenvironment is stiffer in patients with POP than in healthy vaginal tissues and is accompanied by increased levels of FMT [8]; however, the mechanisms involved remain unknown. The main aim of our study was to explore the mechanisms by which increased ECM stiffness leads to FMT and the role of kindlin-2 in fibroblast-myofibroblast transformation.