D. D. McCreary1,2, N. Skirtich2, R. M. McEnaney1,2 1VA Pittsburgh Healthcare System,Pittsburgh, PA, USA 2University Of Pittsburg,Department Of Surgery,Pittsburgh, PA, USA
Introduction:
The extracellular matrix is integral to the structure and function of arteries. Elastic fibers provide arteries with their characteristic elasticity and resilience. They are a composite of microfibrils and crosslinked elastin that form the internal elastic lamina (IEL) and several interconnected fenestrated lamellae throughout the vessel wall. It has been documented that elastic fiber architecture can vary widely between different arteries in different locations.We sought to survey the IEL along the arterial tree using multiphoton microscopy.
Methods:
Arteries were harvested from adult male Sprague Dawley rats. Small vessel lengths were imaged whole or cut lengthwise and splayed open for imaging en face using multiphoton microscopy for simultaneous imaging of second harmonic generation of fibrillar collagen and elastin autofluorescence. To analyze fenestrations, random high-powered fields of IEL images were selected in Nikon Elements. Images were corrected for shading and background and denoised, then binary thresholding was then used to select dark spaces. Errors in selection were corrected manually. The resulting objects were measured for surface area, fractional space, and average numerical density (holes per mm2).
Results:
We examined several different arterial samples, including aorta, common iliac, external iliac, common femoral (CFA), saphenous (SA), profunda femoris (PFA), and “second-order” branch arteries – vessels which branched from a major branch (e.g. the PFA) from the axial arterial network. Total fenestrated space, as a fraction of surface area, was similar across most of the arterial samples examined but was far higher in PFA. Fenestration density was also much higher in the PFA than in other arteries, and somewhat higher in SA. Fenestration size was, on average, comparable across all samples, though SA showed a somewhat smaller hole size, and profunda showed greater variability. The fenestrations were also less round and discrete in PFA and second-order branches than in other vessels. In second-order branch arteries, the IEL shows a more cord-like structure, rather than a fenestrated sheet, and did not appear to have clear fenestrations.
Conclusion:
Continuity from the aorta seems to largely correspond with similarity in IEL structure. IEL fenestrations in aorta, common iliac, external iliac, and common femoral artery are rounder and smaller than those of “first-order” branch arteries like the profunda femoris, and even more distinct from the IEL architecture of second-order branches. As degree of separation from the aorta increases, the IEL structure becomes more web-like and variable. Understanding how different parts of the arterial tree differ in ECM structure can help inform on differences in disease states and treatment outcomes.
