Hypothesis / aims of study
MicroRNAs provide valuable clinical and diagnostic information. In recent years, they proved to be particularly useful in the diagnosis of neurodegenerative diseases. We recentlty reported that the urinary ratio of neurotrophins nerve growth factor (NGF) to its precursor (proNGF) was decreased in a cohort of female patients with overactive bladder (OAB), with lower amount of NGF and stable levels of proNGF. These results were linked to increased activity of the matrix metalloproteinase-9 (MMP-9), the protease involved in the proteolysis of NGF. To further understand the relation between OAB and the dysregulation of NGF processing, we compared the levels of miRNAs related to NGF and proNGF synthesis and proteolysis in the urine of OAB subjects and healthy controls. We also investigated the microRNAs regulating the translation of their receptors p75NTR and TrkA.
Study design, materials and methods
Urine and blood samples from 20 control and 20 OAB patients (50-80 years) were gathered together with validated questionnaires. The relative expression of microRNAs was measured by RT-qPCR. Results were further adjusted for age, renal function and insulin resistance. Receiver operating characteristics (ROC) for miRNAs was tested.
Levels of miRNAs involved in the control of the expression of proNGF (miR-98-5p, let-7b-5p and let-7d-5p), of the survival receptor TrkA (MiR-92a-3p and 221-5p), of the indirect regulation of MMP-9 (miR-885-5p) and of the markers of nerve integrity (miR-21-5p, miR-132 and miR-212-5p) were similar between groups. On the other hand, miR-491-5p, which directly controls the translation of MMP-9, was significantly decreased in OAB, which implies a higher translation of MMP-9. Similarly, miR-592, which negatively regulates the p75NTR receptor synthesis was down-regulated in OAB, suggesting that this pro-inflammatory receptor expression is increased in OAB. Age, renal function and insulin resistance did not affect these results. ROC curves confirmed a high sensitivity of miR-491-5p and miR-592 for diagnosis.
Interpretation of results
Levels of miRNAs controlling proNGF synthesis were unchanged which suggest that the regulation of the ratio NGF over proNGF might be post translational particularly at the levels of proteases generating NGF from proNGF and those degrading NGF into peptides. In this context, the decrease in miR-491-5p which binds the UTR sequence of the MMP-9 mRNA could explain the high amount of MMP-9 found in the urine of OAB patients and the imbalance observed between NGF and proNGF. On the other hand, the decrease miR-592 suggest an increase of the proinflammatory receptor p75NTR, which, taken together with the decrease in NGF, might suggest a pro-inflammatory state. Finally, miRNA markers of the nervous system integrity are unaffected, therefore pointing out another site of action for the imbalance of NGF/proNGF.