Low-level laser irradiation modulates matrix metalloproteinase activity and gene expression in porcine aortic smooth muscle cells

Background and Objectives: The vascular extracellular matrix is maintained by a dynamic balance between matrix synthesis and degradation. This equilibrium is disrupted in arterial pathologies such as abdominal aortic aneurysm. Low-level laser irradiation (LLLI) promotes wound healing. However, its effect on smooth muscle cells (SMCs), a central player in these responses, has not been established. The current study was designed to determine the effects of LLLI on arterial SMC proliferation, inflammatory markers, and matrix proteins. Study Design/Materials and Methods: Porcine primary aortic SMCs were irradiated with a 780 nm laser diode (1 and 2 J/cm²). Trypan blue exclusion assay, immunofluorescent staining for collagen I and III, Sircol assay, gelatin zymography, and RT-PCR were used to monitor proliferation; collagen trihelix formation; collagen synthesis; matrix metalloproteinase-2 (MMP-2) activity, and gene expression of MMP-1, MMP-2, tissue inhibitor of MMP-1 (TIMP-1), TIMP-2, and IL-1-β, respectively. Results: LLLI-increased SMC proliferation by 16 and 22% (1 and 2 J/cm², respectively) compared to non-irradiated cells (P<0.01 and P<0.0005). Immediately after LLLI, trihelices of collagen I and III appeared as perinuclear fluorescent rings. Collagen synthesis was increased twofold (2 days after LLLI: 14.3 ± 3.5 μg, non-irradiated control: 6.6 ± 0.7 μg and TGF-β stimulated control: 7.1 ± 1.2 μg, P<0.05), MMP-2 activity after LLLI was augmented (over non-irradiated control) by 66 ± 18% (2 J/cm²; P<0.05), and MMP-1 gene expression upregulated. However, TIMP-2 was upregulated, and MMP-2 gene expression downregulated. IL-1-β gene expression was reduced. Conclusions: LLLI stimulates SMC proliferation, stimulates collagen synthesis, modulates the equilibrium between regulatory matrix remodeling enzymes, and inhibits proinflammatory IL-1-β gene expression. These findings may be of therapeutic relevance for arterial diseases such as aneurysm where SMC depletion, weakened extracellular matrix, and an increase in pro-inflammatory markers are major pathologic components.