Mechanical stretch is a highly selective regulator of gene expression in human bladder smooth muscle cells

Abstract

Application of mechanical stimuli has been shown to alter gene expression in bladder smooth muscle cells (SMC). To date, only a limited number of "stretch-responsive" genes in this cell type have been reported. We employed oligonucleotide arrays to identify stretch-sensitive genes in primary culture human bladder SMC subjected to repetitive mechanical stimulation for 4 h. Differential gene expression between stretched and nonstretched cells was assessed using Significance Analysis of Microarrays (SAM). Expression of 20 out of 11,731 expressed genes ( approximately 0.17%) was altered >2-fold following stretch, with 19 genes induced and one gene (FGF-9) repressed. Using real-time RT-PCR, we tested independently the responsiveness of 15 genes to stretch and to platelet-derived growth factor-BB (PDGF-BB), another hypertrophic stimulus for bladder SMC. In response to both stimuli, expression of 13 genes increased, 1 gene (FGF-9) decreased, and 1 gene was unchanged. Six transcripts (HB-EGF, BMP-2, COX-2, LIF, PAR-2, and FGF-9) were evaluated using an ex vivo rat model of bladder distension. HB-EGF, BMP-2, COX-2, LIF, and PAR-2 increased with bladder stretch ex vivo, whereas FGF-9 decreased, consistent with expression changes observed in vitro. In silico analysis of microarray data using the FIRED algorithm identified c-jun, AP-1, ATF-2, and neurofibromin-1 (NF-1) as potential transcriptional mediators of stretch signals. Furthermore, the promoters of 9 of 13 stretch-responsive genes contained AP-1 binding sites. These observations identify stretch as a highly selective regulator of gene expression in bladder SMC. Moreover, they suggest that mechanical and growth factor signals converge on common transcriptional regulators that include members of the AP-1 family.

An Akt- and Fra-1-Dependent Pathway Mediates Platelet-Derived Growth Factor-Induced Expression of Thrombomodulin, a Novel Regulator of Smooth Muscle Cell Migration

“…RNA was reverse transcribed using the iScript cDNA synthesis reagent (Bio-Rad), and cDNAs were amplified using gene-specific primers as described previously. 13 The relative abundance of a given transcript was estimated using the 2…”

“…10,13,16 Briefly, 45-day-old-female rats were anesthetized with isoflurane inhalation. A low midline incision was made to expose the bladder.…”

“…12 In addition, stretch-sensitive genes in pBSMC were also found to be PDGF responsive. 13 Published reports have suggested that mechanical stimuli can activate the PDGFR in vascular SMC in vitro. However, direct activation of the PDGFR has not been reported in intact tissue.…”

“…We also implicated the phosphatidylinositol 3-kinase (PI3K)/Akt pathway and the activator protein-1 (AP-1) transcriptional complex as mediators of DNA synthesis and gene expression, respectively, in primary human bladder SMC (pBSMC) exposed to cyclic stretch relaxation or PDGF. 12,13 Although Akt and AP-1 have been studied independently in many different contexts, the extent to which they interact to regulate smooth muscle remodeling remains unknown. In this study, we show that the PDGFR is activated in the bladder wall in response to distension and describe a novel Akt-and AP-1-dependent pathway in pBSMC that regulates expression of thrombomodulin (TM).…”

Differentially expressed gene networks in cultured smooth muscle cells from normal and neuropathic bladder

“…A common feature of the neuropathic bladder is the thickening of the smooth muscle layer with hypertrophy and/or hyperplasia of detrusor smooth muscle cells (SMCs). The increase in muscle mass may result from the over distension of the bladder (Adam et al, 2004). Elevated deposition of connective tissue within the muscle bundles is another major feature observed in the neuropathic bladder.…”