Abstract
Recent work has indicated that photobiomodulation (PBM) may beneficially alter the pathological status of several neurological disorders, although the mechanism currently remains unclear. The current study was designed to investigate the beneficial effect of PBM on behavioral deficits and neurogenesis in a photothrombotic (PT) model of ischemic stroke in rats. From day 1 to day 7 after the establishment of PT model, 2-minute daily PBM (CW, 808nm, 350mW/cm2, total 294J at scalp level) was applied on the infarct injury area (1.8mm anterior to the bregma and 2.5mm lateral from the midline). Rats received intraperitoneal injections of 5-bromodeoxyuridine (BrdU) twice daily (50mg/kg) from day 2 to 8 post-stoke, and samples were collected at day 14. We demonstrated that PBM significantly attenuated behavioral deficits and infarct volume induced by PT stroke. Further investigation displayed that PBM remarkably enhanced neurogenesis and synaptogenesis, as evidenced by immunostaining of BrdU, Ki67, DCX, MAP2, spinophilin, and synaptophysin. Mechanistic studies suggested beneficial effects of PBM were accompanied by robust suppression of reactive gliosis and the production of pro-inflammatory cytokines. On the contrary, the release of anti-inflammatory cytokines, cytochrome c oxidase activity and ATP production in peri-infarct regions were elevated following PBM treatment. Intriguingly, PBM could effectively switch an M1 microglial phenotype to an anti-inflammatory M2 phenotype. Our novel findings indicated that PBM is capable of promoting neurogenesis after ischemic stroke. The underlying mechanisms may rely on: 1) promotion of proliferation and differentiation of internal neuroprogenitor cells in the peri-infarct zone; 2) improvement of the neuronal microenvironment by altering inflammatory status and promoting mitochondrial function. These findings provide strong support for the promising therapeutic effect of PBM on neuronal repair following ischemic stroke.
Highlights
Stroke is considered to be the second leading cause of death, constituting a substantial economic burden for families and society (Ozturk, 2014)
The key findings are that PBM markedly improved post-stroke cortical neurogenesis, and this effect was correlated with the improvement of the neuronal microenvironment and the proliferation and differentiation of neural progenitor cells in the peri-infarct zone
The underlying mechanism of PBM responsible for supporting neurogenesis and alleviating behavioral deficits may be related to the findings as illustrated in the current study: 1) restoration of mitochondrial function and providing the nascent neurons with more ATP, 2) suppression of reactive gliosis and neuroinflammation, 3) alteration of the microglial phenotype, as well as 4) enhancement of neural progenitor proliferation and differentiation
Summary
Stroke is considered to be the second leading cause of death, constituting a substantial economic burden for families and society (Ozturk, 2014). The size and the location of this lesion can be modulated by the intensity, the duration and the location of light delivery in concise, reproducible manner with a high rate of survival compared to other stroke models (Watson et al, 1985). In this process, local thrombosis is followed by free radical formation, disturbance of endothelial function, mitochondrial dysfunction, inflammatory response, neuronal injury, and subsequent behavioral deficits (Braeuninger and Kleinschnitz, 2009; Demyanenko et al, 2015; Schroeter et al, 2002; Shanina et al, 2005)
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