Gubernaculum as icebreaker: do matrix metalloproteinases in rodent gubernaculum and inguinal fat pad permit testicular descent?

Purpose: Cryptorchidism is the most common male congenital abnormality. The rodent gubernaculum steers the testis from abdomen to scrotum postnatally by eversion and migration through the developing inguinal fat pad (IFP). We hypothesize that extracellular matrix remodeling in/around the gubernaculum is necessary for eversion and migration and is permitted by timed IFP maturation and aimed to examine regional development and matrix metalloproteinase (MMP) content.

Methods: Embryonic day 19 (E19) and postnatal days 0 and 2 (P0, P2) wild-type Sprague-Dawley rats (n = 10) were prepared for histologic examination (trichrome) and immunohistochemistry (membrane-type MMP-1 [MT1-MMP], MMP2) and analyzed using light/confocal microscopy.

Results: At E19, IFP contained fibroblasts and immature cells in an extensive collagenous extracellular matrix. Cells in the gubernaculum base were cytoplasmic-MT1-MMP-positive (inactive). At P0, the gubernaculum had everted, and adjacent cells were membranous-MT1-MMP-positive (active). At P2, the gubernaculum was migrating through the IFP, and adjacent cells were membranous-MT1-MMP-positive. Adipocyte maturation began cranially in the IFP and proceeded in a craniocaudal gradient until more uniformly mature at P2.

Conclusion: The MT1-MMP-positive cells may remodel the gubernaculum for eversion and provide the collagenolysis necessary for migration, like an icebreaking ship, through the IFP, which matures to permit migration through collagen-rich tissue. Disruption of these processes may cause cryptorchidism.