It has been previously shown experimentally that fetal urinary matrix metalloproteinase (MMP) activity is abnormal in the setting of obstructive uropathy. We aimed at determining whether the profile of urinary MMP expression correlates with the degree of kidney damage in this setting.

Fetal lambs (n=32) were divided in two groups at 90-100 days gestation (term=145 days): group I (n=15) underwent a sham operation and group II (n=17) underwent creation of a complete urinary tract obstruction. Survivors from both groups were sacrificed at comparable times post-operatively. Urinary MMP profiling was performed by gelatin zymography for 4 MMP species with 10 different molecular weights. Kidney damage was assessed histologically on H&E and Masson’s trichrome stains by semi-quantitative analysis, as well as multiple histomorphometric measurements performed by two blinded pathologists. Statistical analysis was by the Student t-test, the Mann-Whitney U-test, and multiple regression, as appropriate with significance set at p<0.05.

Fetal survival was 84.4% (27/32). At necropsy, all obstructed animals showed bilateral hydronephrosis and bladder dilatation, along with variable degrees of kidney damage on histology. There was a significant correlation between lower medullary thickness and both MMP-9 (p=0.005) and 63kDa MMP-2 (p=0.019) activities. In like manner, the only MMPs associated with kidney fibrosis were MMP-9 and 63kDa MMP-2. Indeed, MMP-9 activity was a highly significant independent predictor of the total combined kidney fibrosis score (p<0.001), as well as of higher fibrosis grades in each of the six areas of the kidney analyzed, namely the pelvis, inner medulla, inner stripe, subcapsular, medullary ray, and labrinyth (all with p<0.01). The activity of 63kDa MMP-2 correlated significantly with higher inner medulla (p=0.032), inner stripe (p=0.013), and subcapsular (p=0.012) fibrosis, however not with medullary ray, labrinyth, or pelvic fibrosis.

In a fetal ovine model, matrix metalloproteinase activity in the urine correlates with the degree of kidney damage. The presence of MMP-9 (in particular) and of 63kDa MMP-2 are independent predictors of increased severity. Prenatal urinary matrix metalloproteinase profiling may enhance patient stratification and counseling in the setting of congenital obstructive uropathy.