Mammalian target of rapamycin (mTOR) induces proliferation and de-differentiation responses to three coordinate pathophysiologic stimuli (mechanical strain, hypoxia, and extracellular matrix remodeling) in rat bladder smooth muscle.
Maladaptive bladder muscle overgrowth and de-differentiation in human bladder obstructive conditions is instigated by coordinate responses to three stimuli: mechanical strain, tissue hypoxia, and extracellular matrix remodeling.( 1,2) Pathway analysis of genes induced by obstructive models of injury in bladder smooth muscle cells (BSMCs) identified a mammalian target of rapamycin (mTOR)-specific inhibitor as a potential pharmacological inhibitor. Strain-induced mTOR-specific S6K activation segregated differently from ERK1/2 activation in intact bladder ex vivo. Though rapamycin's antiproliferative effects in vascular smooth muscle cells are well known, its effects on BSMCs were previously unknown. Rapamycin significantly inhibited proliferation of BSMCs in response to mechanical strain, hypoxia, and denatured collagen. Rapamycin inhibited S6K at mTOR-sensitive phosphorylation sites in response to strain and hypoxia. Rapamycin also supported smooth muscle actin expression in response to strain or hypoxia-induced de-differentiation. Importantly, strain plus hypoxia synergistically augmented mTOR-dependent S6K activation, Mmp7 expression and proliferation. Forced expression of wild-type and constitutively active S6K resulted in loss of smooth muscle actin expression. Decreased smooth muscle actin, increased Mmp7 levels and mTOR pathway activation during in vivo partial bladder obstruction paralleled our in vitro studies. These results point to a coordinate role for mTOR in BSMCs responses to the three stimuli and a potential new therapeutic target for myopathic bladder disease.
Aitken
Karen J
KJ
Developmental & Stem Cell Biology, The Hospital For Sick Children Research Institute, Toronto, ON M5G 1X8, Canada.
Tolg
Cornelia
C
Panchal
Trupti
T
Leslie
Bruno
B
Yu
Jeffery
J
Elkelini
Mohamed
M
Sabha
Nesrin
N
Tse
Derrick J
DJ
Lorenzo
Armando J
AJ
Hassouna
Magdy
M
Bägli
Darius J
DJ
D000199:Actins / Q000378:metabolism; D000818:Animals; D002417:Cattle; D054337:Cell Dedifferentiation / Q000187:drug effects; D015687:Cell Hypoxia / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D005109:Extracellular Matrix / Q000187:drug effects / Q000378:metabolism / Q000473:pathology*; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D020783:Matrix Metalloproteinase 7 / Q000378:metabolism; D008934:Mitogens / Q000494:pharmacology; D008954:Models, Biological; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000201:enzymology* / Q000473:pathology*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus / Q000494:pharmacology; D013314:Stress, Mechanical; D058570:TOR Serine-Threonine Kinases; D001743:Urinary Bladder / Q000187:drug effects / Q000473:pathology*
D000199:Actins; D047908:Intracellular Signaling Peptides and Proteins; D020783:Matrix Metalloproteinase 7; D008934:Mitogens; D017346:Protein Serine-Threonine Kinases; D019893:Ribosomal Protein S6 Kinases; D020123:Sirolimus; D058570:TOR Serine-Threonine Kinases; C498862:Acta2 protein, rat; C546842:MTOR protein, human; C546845:mTOR protein, rat; C526901:Rps6kb1 protein, rat