Photobiomodulation of mineralisation in mesenchymal stem cells.

Mesenchymal stem cells (MSCs) and photobiomodulation (PBM) both offer significant therapeutic potential in regenerative medicine. MSCs have the ability to self-renew and differentiate; giving rise to multiple cellular and tissue lineages that are utilised in repair and regeneration of damaged tissues. PBM utilises light energy delivered at a range of wavelengths to promote wound healing. The positive effects of light on MSC proliferation are well documented; and recently, several studies have determined the outcomes of PBM on mineralised tissue differentiation in MSC populations. As PBM effects are biphasic, it is important to understand the underlying cellular regulatory mechanisms, as well as, provide accurate details of the irradiation conditions, to optimise and standardise outcomes. This review article focuses on the use of red, near-infra-red (R/NIR) and blue wavelengths to promote the mineralisation potential of MSCs; and also reports on the possible molecular mechanisms which underpin transduction of these effects. A variety of potential photon absorbers have been identified which are reported to mediate the signalling mechanisms, including respiratory chain enzymes, flavins, and cryptochromes. Studies report that R/NIR and blue light stimulate MSC differentiation by enhancing respiratory chain activity and increasing reactive oxygen species levels; however, currently, there are considerable variations between irradiation parameters reported. We conclude that due to its non-invasive properties, PBM may, following optimisation, provide an efficient therapeutic approach to clinically support MSC-mediated hard tissue repair. However, to optimise application, further studies are required to identify appropriate light delivery parameters, as well as elucidate the photo-signalling mechanisms involved.