Lower urinary tract dysfunction (LUTD) is associated with bladder smooth muscle (BSM) hypertrophy secondary to benign prostatic hyperplasia (BPH)-induced partial bladder outlet obstruction (PBOO), neurogenic bladder, and diabetes, and its incidence and prevalence are increasing as the population ages. Existing therapeutic interventions are neither highly effective nor durable and have side effects of their own. Biochemical studies have shown reduced mitochondrial ATP and increased reactive oxygen species (ROS) production in the hypertrophied BSM of obstructed bladders and this is associated with overexpression of the intermediate filament (IF) proteins, desmin and vimentin which are important for muscle and mitochondrial function. Mitochondrial and muscle pathophysiology, including decreased ATP, increased ROS production and diminished contractility of smooth muscle in LUTD suggests a role for desmin and vimentin overexpression in inducing mitochondrial and muscle dysfunction. However, potential mechanisms by which these IF proteins mediate BSM dysfunction remain unexplored. Our preliminary data demonstrate that desmin and vimentin overexpression in human and murine BSM strips and cells significantly reduces mitochondrial ATP synthesis; increases ROS production and inhibits carbachol-and KCl-mediated contraction as also seen in BSM with PBOO. Overexpression of IF proteins in BSM strips and cells enhances mitogen-activated protein kinase (MAPK)/JNK2 phosphorylation which coincides with its increased mitochondrial localization and phosphorylation of desmin and vimentin as also seen in BSM with PBOO. Mitochondrial desmin and vimentin could potentially function to inhibit the mitochondrial voltage-dependent anion channel (VDAC) permeability via mitochondrial JNK2. Based on our preliminary data, we hypothesize that the activation of JNK2 and its increased mitochondrial localization is involved in desmin- and vimentin-induced BSM contractile and mitochondrial dysfunction. we further hypothesize that JNK2 phosphorylated mitochondrial desmin and vimentin interacts with the VDAC and this interaction inhibits ATP synthesis and increases ROS production. We designed three Specific Aims to address these hypotheses.
In Aim 1, we will establish the robustness of increased IF expression in inducing BSM contractile dysfunction, and clarify JNK2 as a critical effector.
In Aim 2, we will determine whether IF protein overexpression-induced BSM contractile and mitochondrial dysfunction is due to JNK2 dependent interaction of desmin and vimentin with VDAC.
In Aim 3, we will ascertain the role of mitochondrial JNK2 in PBOO- induced BSM contractile and mitochondrial dysfunction. We expect our studies to delineate a mechanism of contractile dysfunction mediated by mitochondrial JNK2 signaling promoting the VDAC interaction with desmin and vimentin, and thus identify novel therapeutic targets for the treatment of PBOO/LUTD.
Benign prostatic hyperplasia (BPH) is considered a frequent cause of bladder outlet obstruction (BOO) and lower urinary tract dysfunction (LUTD) in elderly men. Poor mitochondrial function in the bladder is associated with increased intermediate filament proteins which we implicate in the disease process. Our proposed experiments will investigate how the aberrant function of mitochondria and these proteins cause BOO/LUTD, and should identify novel targets enabling new strategies and drugs to treat BOO/LUTD.
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