Nonlinear imaging study of extracellular matrix in chemical-induced, developmental dissecting aortic aneurysm: Evidence for defective collagen type III

BACKGROUND: Using a recent model of dissecting aortic aneurysm (DAA) caused by in utero exposure to semicarbazide, we examined the elastin and collagen using standard methods and two nonlinear imaging techniques, multiphoton fluorescence (MPF) and second harmonic generation (SHG) microscopy. METHODS: Sprague-Dawley rat dams were given semicarbazide (6.13 mg/kg/day i.p.) from gestational days 14 to 20 (GD14-20). Fetuses were harvested on GD20 and pups on postnatal day 1 (PND1), PND7, and PND28; matched controls were from dams treated with saline. Aortic immunohistopathology and collagen/elastin signal intensity via MPF and SHG microscopy at an excitation wavelength of 800 nm were studied. RESULTS: Massive DAA of the aortic arch occurred in nearly 100% of pups at birth (i.e., no GD20 fetuses showed lesions). MPF and SHG demonstrated that collagen was significantly degraded at GD20 and in newborns, but normalized by PND28. GD20 fetuses and newborn pups showed a decreased content of medial and adventitial collagen type III in pooled aortas by Western blot and immunohistochemistry. In 7- and 28-day-old pups resolution of DAA blood in vascular media and a recovery of stainable collagen type III was found. Elastin in healed DAA (PND28 pups) was focally disorganized. CONCLUSION: MPF and SHG microscopy provide sensitive and high-resolution information on aortic elastin and collagen. In this model of DAA, collagen displays aberrant imaging quality likely linked to a marked decrease in collagen type III in the developing extracellular matrix.