Adaptation to partial urethral obstruction in healthy aging LOU rats and the role of nerve growth factor signaling pathway in the bladder.

AIM: Aging is associated with poor ability to adapt to stress and abnormal nerve growth factor (NGF) profile. Lower urinary tract symptoms frequently disturb the quality of life of the aging population with no optimal treatment for both genders. The aim of the study was to compare the bladder response to bladder outflow obstruction in young and old LOU rats, a model of healthy aging that does not develop insulin resistance, and its relation to proNGF/NGF imbalance.

METHODS: 6- and 36-month-old female LOU rats were subjected to partial bladder urethral obstruction (PUO) for 2 weeks. Morphometric parameters (body and bladder weight) and glycemia were evaluated. Cystometry was carried out to measure functional parameters followed by ex vivo assessment of muscle strip contractile characteristics. Tissue proteins were examined by immunoblotting and morphology was examined by microscopy.

RESULTS: Body weight and glycaemia were not affected by surgery. PUO increases significantly bladder weight with increased thickness and fibrosis of the bladder wall as revealed by histological examination in both age groups. Cystometry showed that old PUO rats had a significant reduction in the intercontraction interval and the bladder capacity, a pattern opposite to young rats with PUO. Contractile properties of bladder strip were not affected by age or PUO. On the molecular level, the old rats had lower abundance of the mature NGF relative to proNGF, with signs of p75NTR activation suggested by the higher expression of TNF-α and JNK phosphorylation in the bladder tissue.

CONCLUSION: Bladder adaptation to PUO occurs only in young LOU rats to maintain efficient bladder contractility. Old LOU rats display proNGF/NGF imbalance and the associated p75NTR activation. This can further induce tissue damage and degeneration through activation of JNK pathway and release of TNF-α which in turn interferes with the necessary bladder adaptation.