Intermediate Filaments in Bladder Smooth Muscle Dysfunction

Elham Javed, Thomas Jefferson University


Lower urinary tract symptoms (LUTS) is associated with bladder smooth muscle (BSM) hypertrophy secondary to benign prostatic hyperplasia (BPH)-induced partial bladder outlet obstruction (PBOO), and its incidence and prevalence are increasing as the population ages. Symptoms of lower urinary tract disorder (LUTD) are costly to diagnose and treat; existing therapeutic interventions are neither highly effective nor durable and have side effects of their own. Establishing the molecular pathogenesis of PBOO is an important step in identifying new therapeutic targets. Physiological and biochemical studies have shown reduced contraction, decreased mitochondrial ATP levels and increased reactive oxygen species (ROS) production in the hypertrophied BSM of obstructed bladders. Bladder hypertrophy is also associated with overexpression of the intermediate filament (IF) proteins, desmin and vimentin which are important for the cytoskeletal structure, contraction and mitochondrial respiratory 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 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. Ultrastructural and biochemical studies of bladder outlet obstruction (BOO)-induced remodeled BSM reveal accumulation of damaged mitochondria with concomitant decrease in ATP and increase in reactive oxygen species (ROS) in BSM. Based on our preliminary data, we hypothesize that the activation of JNK2 is involved in desmin- and vimentin-induced BSM contractile dysfunction. The research work presented in this PhD thesis demonstrates that the increased expression of desmin and vimentin reduces bladder smooth muscle contractility via JNK2 and induces mitochondrial dysfunction. Studies in Aim 1 were designed to address the hypothesis that increased expression of IF proteins desmin and vimentin induce BSM hypocontractility and this phenomenon is mediated via JNK2, a member of MAP kinase family protein. Overexpression of desmin and vimentin in murine BSM strips resulted in decreased contraction in response to carbachol and KCl with an associated decrease in phosphorylation of myosin light chain kinase (MLC20) and an increased accumulation of phospho-JNK2. Furthermore, desmin and vimentin overexpression-induced loss of BSM contractility was abrogated in strips isolated from JNK2 knockout mice or in BSM strips treated with JNK2 inhibitor. These findings demonstrate that IF regulate BSM contractility via JNK2. Studies in Aim 2 were designed to address the hypothesis that IF-induced BSM hypocontractility involves mitochondrial mechanisms. Using our in vitro overexpression model, our studies demonstrate that increased expression desmin or vimentin in human BSM cells reduces mitochondrial membrane potential (MMP), mitochondrial respiration and ATP production and increases ROS production in BSM. Overall, our findings suggest JNK2 as a major effector of IF protein overexpression induced BSM contractile dysfunction. Further, our data implicate an IFs/JNK2 dependent mechanism that contributes to the pathologic bladder contractility that occurs following bladder outlet obstruction, a condition in which desmin and vimentin protein expressions are known to be up regulated. Together, these findings suggest that desmin-JNK2 and vimentin-JNK2 axes are likely to contribute to diminished BSM contractility associated with obstructive bladder disease and that JNK2 inhibition may have therapeutic application. In addition, desmin- and vimentin- overexpression induces mitochondrial dysfunction which possibly contributes to BSM hypocontractility. Future studies are needed to ascertain the role of JNK2 in inducing mitochondrial dysfunction in obstructed bladder.

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Recommended Citation

Javed, Elham, "Intermediate Filaments in Bladder Smooth Muscle Dysfunction" (2020). ETD Collection for Thomas Jefferson University. AAI27668616.