Post-Translational Modification Networks of Contractile and Cellular Stress Response Proteins in Bladder Ischemia

Differential Post-Translational Modifications of Proteins in Bladder Ischemia

Clinical and basic research suggests that bladder ischemia may be an independent variable in the development of lower urinary tract symptoms (LUTS). We have reported that ischemic changes in the bladder involve differential expression and post-translational modifications (PTMs) of the protein's functional domains. In the present study, we performed in-depth analysis of a previously reported proteomic dataset to further characterize proteins PTMs in bladder ischemia. Our proteomic analysis of proteins in bladder ischemia detected differential formation of non-coded amino acids (ncAAs) that might have resulted from PTMs. In-depth analysis revealed that three groups of proteins in the bladder proteome, including contractile proteins and their associated proteins, stress response proteins, and cell signaling-related proteins, are conspicuously impacted by ischemia. Differential PTMs of proteins by ischemia seemed to affect important signaling pathways in the bladder and provoke critical changes in the post-translational structural integrity of the stress response, contractile, and cell signaling-related proteins. Our data suggest that differential PTMs of proteins may play a role in the development of cellular stress, sensitization of smooth muscle cells to contractile stimuli, and deferential cell signaling in bladder ischemia. These observations may provide the foundation for future research to validate and define clinical translation of the modified biomarkers for precise diagnosis of bladder dysfunction and the development of new therapeutic targets against LUTS.

Pathophysiological Mechanisms Involved in Overactive Bladder/Detrusor Overactivity

Purpose of Review

To examine the latest published findings on the pathophysiological mechanisms involved in the development of overactive bladder (OAB) and detrusor overactivity (DO), and to identify common pathways linked to the risk factors associated with these conditions.

Recent Findings

Evidence is accumulating, both clinical and experimental, that many of the factors linked to the development of OAB/DO, including ageing, bladder outlet obstruction, psychological stress, and obesity are associated with reduced bladder blood flow. This induces local tissue inflammation with cytokine release and enhanced oxidative stress, ultimately resulting in altered detrusor sensitivity, detrusor hypertrophy and fibrosis, together with afferent hypersensitivity. These mechanisms would explain the symptoms of urgency and frequency observed in OAB patients. Although not a characteristic of OAB, undetected low level bacterial infections of the bladder have been proposed to explain the OAB symptoms in patients resistant to standard treatments. In this condition, inflammatory responses without reductions in perfusion activate the inflammatory pathways.

Summary

Evidence is mounting that poor bladder perfusion and local inflammatory responses are central mechanisms involved in the development of OAB/DO. As our understanding of these pathophysiological mechanisms advances, new avenues for drug development will be identified and ultimately treatment may become more individualized depending on the particular pathway involved and the drugs available.

Molecular Regulation of Concomitant Lower Urinary Tract Symptoms and Erectile Dysfunction in Pelvic Ischemia

Aging correlates with greater incidence of lower urinary tract symptoms (LUTS) and erectile dysfunction (ED) in the male population where the pathophysiological link remains elusive. The incidence of LUTS and ED correlates with the prevalence of vascular risk factors, implying potential role of arterial disorders in concomitant development of the two conditions. Human studies have revealed lower bladder and prostate blood flow in patients with LUTS suggesting that the severity of LUTS and ED correlates with the severity of vascular disorders. A close link between increased prostatic vascular resistance and greater incidence of LUTS and ED has been documented. Experimental models of atherosclerosis-induced chronic pelvic ischemia (CPI) showed increased contractile reactivity of prostatic and bladder tissues, impairment of penile erectile tissue relaxation, and simultaneous development of detrusor overactivity and ED. In the bladder, short-term ischemia caused overactive contractions while prolonged ischemia provoked degenerative responses and led to underactivity. CPI compromised structural integrity of the bladder, prostatic, and penile erectile tissues. Downstream molecular mechanisms appear to involve cellular stress and survival signaling, receptor modifications, upregulation of cytokines, and impairment of the nitric oxide pathway in cavernosal tissue. These observations may suggest pelvic ischemia as an important contributing factor in LUTS-associated ED. The aim of this narrative review is to discuss the current evidence on CPI as a possible etiologic mechanism underlying LUTS-associated ED.

Formation of Double Stranded RNA Provokes Smooth Muscle Contractions and Structural Modifications in Bladder Ischemia

PURPOSE

Growing evidence suggests that ischemia provokes detrusor overactivity and degenerative responses in the bladder. Underlying mechanisms appear to involve modification of smooth muscle contractile rudiments by hypoxia, redox, cellular stress and cell survival signaling. Downstream pathways of cellular stress and stress response molecules eliciting bladder dysfunction in ischemia remain largely elusive. Our goal was to define the role of double stranded RNA (dsRNA), a stress response molecule provoked by redox, in ischemia mediated bladder dysfunction.

METHODS

A rat model of pelvic ischemia along with a cell culture hypoxia model were used to investigate the expression levels, functional consequences, structural aspects, and regulatory mechanisms of dsRNA in the bladder. Gene and protein expression were examined by reverse transcription polymerase chain reaction (RT-PCR), dot blot, and Western blotting, respectively. Tissue structure and function were assessed using histological staining and organ bath. Regulatory mechanisms were analyzed in cultured bladder smooth muscle cells.

RESULTS

The data presented here provide the first evidence of the formation of dsRNA in the overactive bladder. dsRNA is a cellular stress response molecule that sensitizes smooth muscle and regulates inflammatory and degenerative rejoinders. Our data suggest that the production of dsRNA in the bladder is provoked by ischemia. Formation of dsRNA appears to augment bladder smooth muscle contractions and provoke fibrotic and apoptotic responses. Downstream actions of dsRNA in the bladder may involve upregulation of dsRNA-activated protein kinase R (PKR) and caspase-3, the executioner of apoptosis.

CONCLUSION

Activation of dsRNA/PKR pathway may play a role in sensitization of bladder smooth muscle cells to contractile stimuli, whereas dsRNA and caspase-3 crosstalk appear to modulate cellular stress and instigate degenerative responses in bladder ischemia. These observations suggest the role of dsRNA in bladder dysfunction and may open new perspectives to overcome overactive smooth muscle contractions and structural damage in the bladder.

Cellular Stress and Molecular Responses in Bladder Ischemia

The concept of bladder ischemia as a contributing factor to detrusor overactivity and lower urinary tract symptoms (LUTS) is evolving. Bladder ischemia as a consequence of pelvic arterial atherosclerosis was first documented in experimental models and later in elderly patients with LUTS. It was shown that early-stage moderate ischemia produces detrusor overactivity, while prolonged severe ischemia provokes changes consistent with detrusor underactivity. Recent studies imply a central role of cellular energy sensors, cellular stress sensors, and stress response molecules in bladder responses to ischemia. The cellular energy sensor adenosine monophosphate-activated protein kinase was shown to play a role in detrusor overactivity and neurodegeneration in bladder ischemia. The cellular stress sensors apoptosis signal-regulating kinase 1 and caspase-3 along with heat shock proteins were characterized as important contributing factors to smooth muscle structural modifications and apoptotic responses in bladder ischemia. Downstream pathways seem to involve hypoxia-inducible factor, transforming growth factor beta, vascular endothelial growth factor, and nerve growth factor. Molecular responses to bladder ischemia were associated with differential protein expression, the accumulation of non-coded amino acids, and post-translational modifications of contractile proteins and stress response molecules. Further insight into cellular stress responses in bladder ischemia may provide novel diagnostic and therapeutic targets against LUTS.