Impact of pre-existing elastic matrix on TGFβ1 and HA oligomer-induced regenerative elastin repair by rat aortic smooth muscle cells.

Regenerating elastic matrices lost to disease (e.g. in aneurysms) is vital to re-establishing vascular homeostasis but is challenged by the poor elastogenicity of post-neonatal cells. We previously showed that exogenous hyaluronan oligomers (HA-o) and TGFβ1 synergistically enhance tropo- and matrix elastin deposition by healthy adult rat aortic SMCs (RASMCs). Towards treating aortic aneurysms (AAs), which exhibit cause- and site-specific heterogeneity in matrix content/structure and contain proteolytically-injured SMCs, we investigated the impact of pre-existing elastic matrix degeneration on elastogenic induction of injured RASMCs. Elastin-rich RASMC layers at 21 days of culture were treated with 0.15 U/ml (PPE15) and 0.75 U/ml (PPE75) porcine pancreatic elastase to degrade the elastic matrix variably, or left uninjured (control). One set of cultures was harvested at 21 days, before and after injury, to quantify viable cell count, matrix elastin loss. Other injured cell layers were cultured to 42 days with or without factors (0.2 µg/ml HA oligomers, 1 ng/ml TGFβ1). We showed that: (a) the ability of cultures to self-repair and regenerate elastic matrices following proteolysis is limited when elastolysis is severe; (b) HA oligomers and TGFβ1 elastogenically stimulate RASMCs in mildly-injured (i.e. PPE15) cultures to restore both elastic matrix amounts and elastic fibre deposition to levels in healthy cultures; and (c) in severely injured (i.e. PPE75) cultures, the factors stimulate matrix elastin synthesis and crosslinking, although not to control levels. The outcomes underscore the need to enhance elastogenic factor doses based on the severity of elastin loss. This study will help in customizing therapies for elastin regeneration within AAs, based on cause and location.