Deregulation of specific sets of genes detected by microarray analysis of marrow stromal fibroblast cells stimulated by IR and VR light
Jie Guo, Daniel Wai, Qing Wang, YanMing Wang, Cynthia Au Yeung, Stephen L-K Yen, Center for Craniofacial Molecular Biology University of Southern California, Childrens Hospital Los Angeles and Dept. of Orthodontics, Shandong and West China Universities.
Conflicting reports have questioned whether low level laser treatment can have an effect on bone. Purpose:The purpose of this study was to examine how light effects gene expression. Methods: Clones of marrow fibroblast stem cells were isolated from human bone marrow and used for primary cell cultures . The cells were grown without light as a control and with light under eight different conditions: two wavelengths of light(830-IR and 633nm-VR) at four different energy levels(0.5.1.0,1.5 and 2.0 joules /cm2). Results: Light stimulated some cultures to proliferate up to 40% faster depending on the type of light stimulation using BrdU markers. For the light-stimulated cultures, western blot data for osteocalcin, alkaline phosphatase and RUNX 2, markers of osteoblast differentiation and bone formation, did not show a pattern of increased or early gene expression compared to control cultures. Affymetrix Human exon microarrays of 22,000 protein-encoding genes(40 markers per gene) showed distinct sets of genes being deregulated for each of the eight experimental conditions. A two-fold screen for gene expression differences between control and light-stimulated cultures revealed a complex network of gene expression interactions involving dose response and silencing of inhibitor genes for candidate genes such as RANKL, IL-1A and MMP10. Pathway analysis showed the top VR biological gene networks were skeletal and muscular system development and function, tissue development and amino acid metabolism, consistent with bone turnover. The top biological functions associated with IR stimulation are skin condition, genetic disorders, cancer, immune response. Conclusion: This study provides strong evidence for light stimulating different sets of genes according to wavelength and energy level that can alter bone turnover. The data provides a molecular explanation for the conflicting reports in the current literature.
References:
Wu YH et al. Effects of low-level irradiation on mesenchymation stem cell proliferation: a microarray analysis. Lasers Med Sci, 2011(epub, ahead of print)
Zhang Y et al. cDNA microarray analysis of gene expression in human fibroblast cells irradiated with red light J Invest Dermatol 2003, 120(5):849-57