Fibroproliferative remodeling in the urinary tract is associated with a number of pathologies including hypertrophic bladder growth secondary to outlet obstruction, neurogenic bladder and diabetes. Although the macroscopic changes that occur in the bladder wall exposed to pathologic stimulation, such as wall thickening and loss of muscle contractility, have been appreciated for many years, the signals that underlie tissue remodeling at the molecular level are still poorly understood. The goal of the proposed studies is to uncover the signaling events that regulate growth and differentiation of bladder smooth muscle in response to pathologic stimuli. The identification of key regulators of these processes will reveal novel targets for therapeutic intervention. Because the bladder is unique among hollow organs as a privileged site for drug delivery, these studies may lead directly to opportunities for novel therapies for urinary tract dysfunction particularly in the context of hypertrophy. Data from our group have implicated the phosphoinositide-3-kinase (PI3K)/Akt pathway as a mediator of primary bladder smooth muscle cell (BSMC) growth in response to mechanical stimulation or platelet- derived growth factor (PDGF) treatment. Exposure of SMC to stretch or PDGF in vitro or distension of the intact rodent bladder ex vivo elicited robust phosphorylation of the serine-threonine kinase Akt, a principal effector of PI3K. Expression profiling of primary human BSMC revealed stretch to be a highly selective regulator of gene expression, with <0.2% of the expressed genome identified as mechanically responsive. In silico analysis implicated AP-1 family members as potential regulators of stretch-induced BSMC gene expression. Although Akt and AP-1 are upregulated by mechanical stimuli, the extent to which they interact to regulate hollow organ remodeling is essentially completely unstudied. In this proposal we will test the hypothesis that Akt- and AP-1-regulated signals mediate growth of bladder smooth muscle in response to mechanical stimulation and converge at one or more levels within the cell. We will use an in vitro model of BSMC stretch as well as an animal model of bladder distension to address the following specific aims: (1) Determine how Akt regulates growth in SMC exposed to mechanical stimuli in vitro and in vivo;(2) Determine how AP-1-mediated changes in gene expression regulate SMC growth and the extent of regulation by Akt. We will use several complementary approaches to modulate Akt- and AP-1-dependent signaling in BSMC in vitro and in vivo, including RNA interference, pharmacologic inhibition and protein transduction technology. We anticipate that findings from these experiments will provide novel insights into the mechanisms underlying pathologic bladder smooth muscle growth.Project Narrative Effective treatment of bladder diseases is hampered by a lack of understanding about the molecular signals that regulate tissue growth both in normal and pathologic situations. The proposed experiments will investigate how two protein families, Akt and AP-1, interact to regulate the growth of bladder smooth muscle in response to mechanical stimulation. We anticipate this analysis will shed new light on fundamental mechanisms underlying bladder muscle physiology and may also provide insight into new treatment strategies.
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