Hypothesis / aims of study
Benign prostatic obstruction (BPO) in the elderly male causes progressive worsening of bladder contractility, due to remodelling of the bladder ultimately leading to bladder failure. We aimed to study changes of gene expression in the bladder before and after de-obstruction surgery (TURP) to elucidate the molecular mechanisms driving bladder remodelling. We hypothesised that progressive worsening of bladder contractility, evidenced by decreased detrusor pressure (PdetQmax) or inability to void, is reflected in specific gene expression changes. Thus, comparing transcriptomes of bladders with different functional recovery outcomes after TURP might shed light on the biomarkers of the “point of no return” after which contractility is irreversibly lost.
Study design, materials and methods
Bladder dome biopsies were collected from controls (n = 5, urolithiasis patients), and patients with BPO (n = 6) before and 3 months after de-obstruction surgery (TURP). Bladder function was assessed by urodynamics (UDI) at both time points, and all patients had urodynamically established BPO (Abrams Griffiths nomogram). Total RNA was isolated from the biopsies and subjected to next generation sequencing followed by transcriptome analysis. Differentially expressed genes (DEGs) were compared before and after TURP as well as to controls. Principal Component Analysis (PCA) based on 300 most variable genes per sample was performed for the unbiased assessment of DEG profile similarities.
Results
Based on the initial (before TURP) and subsequent (after TURP) UDI, biopsies were allocated into 2 groups: acontractile (AC) (n = 3) who did not void or build bladder pressure either before or after TURP; and hypo-contractile (HC) (n=3) who had low (10-25 cm H2O) Pdet before TURP and low but measurable urine flow. AC showed no functional improvement after de-obstruction, while HC showed increased flow and reduced post-void residual. Only one HC showed improved Pdet after TURP, while in the other two Pdet remained unchanged. PCA grouped AC before and after TURP close together and away from controls and HC, indicating an advanced deterioration of transcriptomes in these bladders. There was no significant change in DEG profiles in AC grfoup after TURP, consistent with the lack of functional improvement. In contrast, HC samples showed a higher expression of contractility markers compared to AC, but lower than controls. PCA analysis of HC clearly separated one patient from the other two based on DEG profile before TURP, and placed him close to controls. After TURP, 2 out of 3 HC showed further down-regulation of contractile gene expression, while the outlier patient showed a significant increase in contractility markers, up-regulation of SRF, HBEGF, NOTCH1, CCN2, THBS1 and other factors, regulating smooth muscle and ECM remodelling, consistent with recovery of contractility.
Interpretation of results
Transcriptomes of AC were characterized by a high prevalence of advanced immune response markers, which remained up-regulated after de-obstruction, and indicated that these patients were well beyond the “point of no return” for surgery. Although hypocontractile bladders preserved contractility and had higher levels of muscle-specific genes compared to the AC, their dysregulated signalling pathways did not revert to control levels. Heterogeneity of HC indicated possible differences in the symptom aetiology. Two HP bladders showed similar transcriptomes, characterized by a significant up-regulation of immune and down-regulation of contractile markers compared to controls. In contrast, the recovered HC patient possibly had an underactive bladder of a different type, as the DEG profile was similar to controls with a down-regulation of a narrow set of genes including those encoding ion channels and proteins involved in calcium homeostasis and muscle contraction.