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

Mechanical cues that trigger pathological remodeling in smooth muscle tissues remain largely unknown and are thought to be pivotal triggers for strain-induced remodeling. Thus, an understanding of the effects mechanical stimulation is important to elucidate underlying mechanisms of disease states and in the development of methods for smooth muscle tissue regeneration. For example, the urinary bladder wall (UBW) adaptation to spinal cord injury (SCI) includes extensive hypertrophy as well as increased collagen and elastin, all of which profoundly alter its mechanical response. In addition, the pro-fibrotic growth factor TGF-β1 is upregulated in pathologies of other smooth muscle tissues and may contribute to pathological remodeling outcomes. In the present study, we utilized an ex vivo organ culture system to investigate the response of UBW tissue under various strain-based mechanical stimuli and exogenous TGF-β1 to assess extracellular matrix (ECM) synthesis, mechanical responses, and bladder smooth muscle cell (BSMC) phenotype. Results indicated that a 0.5-Hz strain frequency triangular waveform stimulation at 15% strain resulted in fibrillar elastin production, collagen turnover, and a more compliant ECM. Further, this stretch regime induced changes in cell phenotype while the addition of TGF-β1 altered this phenotype. This phenotypic shift was further confirmed by passive strip biomechanical testing, whereby the bladder groups treated with TGF-β1 were more compliant than all other groups. TGF-β1 increased soluble collagen production in the cultured bladders. Overall, the 0.5-Hz strain-induced remodeling caused increased compliance due to elastogenesis, similar to that seen in early SCI bladders. Thus, organ culture of bladder strips can be used as an experimental model to examine ECM remodeling and cellular phenotypic shift and potentially elucidate BMSCs ability to produce fibrillar elastin using mechanical stretch either alone or in combination with growth factors.

触发平滑肌组织病理重塑的力学信号在很大程度上仍然未知，并且被认为是应变诱导重塑的关键触发因素。因此，了解力学刺激的影响对于阐明疾病状态的潜在机制以及平滑肌组织再生方法的开发非常重要。例如，膀胱壁（UBW）对脊髓损伤（SCI）的适应性变化包括广泛的肥大以及胶原蛋白和弹性蛋白的增加，所有这些都极大地改变了其力学响应。此外，促纤维化生长因子TGF -β1在其他平滑肌组织的病理状态下会上调，并可能导致病理重塑结果。在本研究中，我们利用一种离体器官培养系统来研究UBW组织在各种基于应变的力学刺激和外源性TGF -β1作用下的反应，以评估细胞外基质（ECM）的合成、力学响应以及膀胱平滑肌细胞（BSMC）的表型。结果表明，在15%应变下，0.5Hz的应变频率三角波形刺激导致纤维状弹性蛋白的产生、胶原蛋白的周转以及更顺应性的ECM。此外，这种拉伸模式诱导了细胞表型的变化，而TGF -β1的添加改变了这种表型。这种表型转变通过被动条带生物力学测试进一步得到证实，即经TGF -β1处理的膀胱组比所有其他组更具顺应性。TGF -β1增加了培养膀胱中可溶性胶原蛋白的产生。总体而言，0.5Hz应变诱导的重塑由于弹性蛋白生成而导致顺应性增加，这与早期SCI膀胱中所见的情况相似。因此，膀胱条带的器官培养可作为一种实验模型，用于研究ECM重塑和细胞表型转变，并有可能阐明BSMCs单独使用力学拉伸或与生长因子联合使用时产生纤维状弹性蛋白的能力。