The aim of this project is to identify Akt target genes in bladder smooth muscle cells (SMC) exposed to hypertrophic signals. The hypertrophic bladder muscle growth that occurs in response to lower urinary tract obstruction represents a serious health problem in both children and adults. The mechanisms that underlie bladder hypertrophy are almost completely undefined at the molecular level. However, certain phenotypic changes, such as muscle cell hypertrophy and hyperplasia, reactivation of a fetal gene expression program and activation of specific signal transduction cascades are similar, at least superficially, to changes that occur in cardiac hypertrophy. This suggests that similar signaling mechanisms may operate in the heart and bladder exposed to hypertrophic stimuli. Signaling through the phosphoinositide-3-kinase (PI3K)/Akt pathway has been implicated in cardiac and skeletal muscle hypertrophy. We have recently demonstrated activation of the Akt serine-threonine kinase in bladder SMC exposed to mechanical stretch and platelet-derived growth factor-BB (PDGF-BB), stimuli that promote bladder SMC growth. In this proposal we will test the hypothesis that Akt is a mediator of hypertrophic signals in bladder smooth muscle.
The Specific Aims are Aim (1): determine whether Akt activation is necessary and sufficient for growth of human bladder SMC. We will modify Akt activity in bladder SMC using activated and dominant-negative Akt constructs and thereby establish the requirement for Akt in bladder muscle growth.
Aim (2): identify Akt-regulated targets in bladder SMC in response to hypertrophic stimuli. We will identify Akt targets by large-scale mRNA expression analysis of human bladder SMC exposed to stretch, and then validate them in appropriate model systems. At the end of the 2-year project period we will have determined whether Akt is necessary for bladder muscle growth and will also know the identity of the stretch-responsive Akt-regutated genes that potentially mediate the response of bladder muscle to hypertrophic signals. The information obtained from these studies will underpin and inform future studies that will be directed towards elucidation of the mechanism of action of Akt-regulated genes in bladder muscle.
