Role of Transforming Growth Factor β in Rat Bladder Smooth Muscle Cell Proliferation

Abstract

Conditions associated with hypertrophy of the urinary bladder have repeatedly been associated with an increased urinary excretion of transforming growth factor (TGF) ␤ in both rats and patients. Because TGF␤ can have both growth-promoting and -inhibiting effects, we have studied its effects on cell growth and death in primary cultures of rat bladder smooth muscle cells. TGF␤1, TGF␤2, or TGF␤3 did not cause apoptosis, but all three isoforms inhibited DNA synthesis with similar potency (EC 50 of approximately 0.1 ng/ml) and efficacy. Such inhibition was antagonized by a specific TGF␤ receptor antagonist and independent of the presence of serum. Mitogen-activated protein kinases (MAPKs) are involved in the control of cell growth, and all three TGF␤ isoforms inhibited activation of the extracellular signal-regulated kinase, c-Jun NH 2 -terminal kinase, and p38 MAPK subfamilies. Nevertheless, the inhibitory effects of the TGF␤ isoforms on DNA synthesis were not affected by presence of inhibitors of the three MAPK pathways. TGF␤ did not alter cell size as measured by flow cytometry or mitochondrial activity, an integrated measure of cell size and number. We conclude that our data do not support the hypothesis that TGF␤ is a mediator of rat bladder hypertrophy.Urinary bladder outlet obstruction (BOO) is a frequent consequence of benign prostatic enlargement or urethral strictures. It leads to an increased bladder size and micturition disorders (Andersson, 2003), the former involving both hypertrophy and hyperplasia at the cellular level. However, the mediators and molecular mechanisms leading to bladder hypertrophy have remained elusive. Studies in rats (Chul Kim et al., 2001) and patients with BOO (MacRae Dell et al., 2000;Monga et al., 2001) have found an increased urinary excretion of transforming growth factor (TGF) ␤. Hence, TGF␤ has been proposed to play a role in the pathophysiology of BOO and bladder hypertrophy.TGF␤ is a pluripotent growth factor that has been implicated in a variety of physiological processes such as proliferation, apoptosis, phenotypic switching, differentiation, and specification of developmental fate (Massagué, 2000). Interestingly, TGF␤ can have differential or even opposite effects depending on the tissue or cell type under investigation (Roberts and Sporn, 1993). For example, TGF␤ can increase the proliferation of airway smooth muscle cells (Chen and Khalil, 2006), but it potently inhibits proliferation in vascular smooth muscle cells due to a G 0 /G 1 arrest via the p38 pathway (Seay et al., 2005). In the heart, TGF␤ can induce cardiomyocyte hypertrophy, whereas cardiac fibroblasts respond with differentiation into myofibroblasts and synthesis of collagen Watkins et al., 2006). Therefore, it remains largely unclear whether increased TGF␤ excretion in experimental and clinical BOO reflects a role as mediator of cell growth, as part of a negative feedback loop limiting cell growth, or as a by-product that at best can be used as a biomarker.The heterogeneity of TGF␤ responses may...

Strain history and TGF-β1 induce urinary bladder wall smooth muscle remodeling and elastogenesis

“…In static culture, the α -SMA appeared to be unchanged with the addition of TGF- β 1. An increase in α -SMA expression has been reported previously in static culture of isolated BSMC as well as aortic smooth muscle cells with the addition of TGF- β 1 to culture (Barendrecht et al 2007). TGF- β 1 has also been shown previously to increase cell hypertrophy in an isolated BSMC study (Howard et al 2005).…”

“…In vitro, we have found that TGF- β 1 alters BSMC phenotype and the organization of the ECM (Parekh et al 2009a,b). In other studies, TGF- β 1 induced hypertrophy, upregulated collagen, and inhibited proliferation of BSMCs (Barendrecht et al 2007), as well as increasing stress fiber expression and reducing gap junctions (Neuhaus et al 2009). TGF- β 1 modulates cellular phenotype in fibrosis (Leask and Abraham 2004) and regulates the RHAMM protein as well as CTGF in the fibrotic bladder (Capolicchio et al 2001; Bagli et al 1999).…”

“…TGF- β 1 has also been implicated in various bladder pathologies in animal and patient studies resulting from diabetes (Gray et al 2008), bladder outlet obstruction (Barendrecht et al 2007), and interstitial cystitis and urologic cancers (Neuhaus et al 2009). We have shown previously that TGF- β 1 gene expression is upregulated only 3 days immediately following SCI in the rat urinary bladder and continues to be upregulated out to 21 days post-SCI (Nagatomi et al 2005; Parekh et al 2009a,b).…”

Simvastatin protects bladder and renal functions following spinal cord injury in rats

“…For example, induction of inositol 1,4,5 triphosphate (IP3) stimulates the initial contractile response of bladder smooth muscle [58], and simvastatin has been shown to increase the cellular level of IP3 [59]. Nevertheless, bladder hypertrophy involves several factors, including M2 receptors [60], neurotransmitters like glutamate [61], transcriptional factors like STAT3 [6], nerve growth factor [62], intracellular calcium [34], transforming growth factor beta [63], basic fibroblast growth factor [7], and protein kinase C [64]. Therefore, the exact signaling cascade involved in simvastatin-mediated bladder and renal functional recovery remains to be elucidated.…”

Spatio-Temporal Distribution of Smads and Role of Smads/TGF-β/BMP-4 in the Regulation of Mouse Bladder Organogenesis

“…Transforming growth factor-β (TGF-β) have been shown to regulate cell growth and differentiation in both urothelium and bladder smooth muscle [5]. Studies have shown that TGF-β induced hyperplasia, upregulated collagen, inhibited proliferation of bladder smooth muscle cells [6] and modulated cellular phenotype in fibrosis. It has been shown to regulate connective tissue growth factor (CTGF) in bladder fibrosis [7].…”