Low-Level Laser Irradiation Precondition for Cardiac Regenerative Therapy

Abstract

Objective: The purpose of this article was to review the molecular mechanisms of low-level laser irradiation (LLLI) preconditioning for heart cell therapy. Background data: Stem cell transplantation appears to offer a better alternative to cardiac regenerative therapy. Previous studies have confirmed that the application of LLLI plays a positive role in regulating stem cell proliferation and in remodeling the hostile milieu of infarcted myocardium. Greater understanding of LLLI's underlying mechanisms would be helpful in translating cell transplantation therapy into the clinic. Methods: Studies investigating LLLI preconditioning for cardiac regenerative therapy published up to 2015 were retrieved from library sources and Pubmed databases. Results: LLLI preconditioning stimulates proliferation and differentiation of stem cells through activation of cell proliferation signaling pathways and alteration of microRNA expression. It also could stimulate paracrine secretion of stem cells and alter cardiac cytokine expression in infarcted myocardium. Conclusions: LLLI preconditioning provides a promising approach to maximize the efficacy of cardiac cell-based therapy. Although many studies have reported possible molecular mechanisms involved in LLLI preconditioning, the exact mechanisms are still not clearly understood.

Introduction

Myocardial infarction (MI) has become the leading cause of death worldwide. Great progress has been made in MI management, such as new pharmacological approaches, novel reperfusion strategies, and revascularization procedures. However, adult cardiomyocytes have little regenerative potential, so effective therapies for rescuing critically injured cardiomyocytes are desired.¹ In recent years, there has been a growing enthusiasm for transplanting stem cells into damaged myocardium with hopes of improving cardiac function post-MI.

The first medical application of lasers was reported by Dr. Goldman regarded as the father of lasers in medicine. Ten years later, high-energy CO₂ lasers were utilized for myocardial acupuncture. These lasers are high energy for their high-energy densities, which range from 1 to 100 W/cm². The CO₂ lasers are able to produce microchannels, without debris or fibrosis formation, allowing blood to flow directly from the ventricular cavity into the ischemic myocardium.² This technology is known as transmyocardial laser revascularization (TMR). TMR provides a possible treatment for patients suffering from diffuse coronary artery disease (CAD) that is not amenable to percutaneous coronary interventions or coronary artery bypass grafting.

Low-level lasers, on the other hand, emit nonthermal beams that do not deliver power to damaged tissue, but do deliver sufficient energy for heat-independent biostimulation effects.^3,4 Low-level laser irradiation (LLLI) has been applied in clinical practice for more than 40 years.^5,6 Initial studies have reported that LLLI has an effect on various biological processes, which accelerate wound healing and promote the regeneration of muscle.^7
–9 It could stimulate the photoreceptors that transfer light energy into chemical energy in the form of ATP, which further promotes cell proliferation.¹⁰

In 2000, Dr. Uri from Tel Aviv University began to apply LLLI to treat MI in the rat and dog. He found that infarct size was reduced by 52% in the group that received LLLI treatment after induced MI.¹¹ Later studies indicated that LLLI could stimulate proliferation and differentiation of bone marrow-derived mesenchymal stem cells (BMSCs) and attenuate the hostile pathological microenvironment of damaged myocardium.^4,12 Further, another study reported that LLLI has a positive effect on proliferation of cardiac stem cells (CSCs) in vitro.¹³ Most laser studies use BMSCs as cell sources because it is easy to get through aspiration procedures.

In this review, we summarized published studies on molecular mechanisms of LLLI preconditioning for cardiac cell-based therapy.

Using LLLI to Precondition Stem Cells Before Implantation

Although the beneficial effect of BMSC implantation on infarcted myocardium has been described,^14,15 other studies have failed to find improved cardiac function after implantation.¹⁶ This might be a consequence of the high apoptotic percentage and limited myogenesis ability of BMSCs, so sufficient numbers of BMSCs with improved differentiation ability are necessary before transplantation.¹⁷ On the other hand, when it comes to CSCs, we also encounter the same problem: few autologous CSCs and long preparation time.

In 2005, Abramovitch-Gottlib et al. observed that combining a 3D biomatrix with LLLI biostimulates the proliferation of BMSCs.¹⁸ Another study reported similar results, where LLLI promoted proliferation of BMSCs and CSCs in vitro.¹³ Our studies have also shown that LLLI facilitates proliferation and myogenic differentiation of BMSCs.¹² These findings indicate the positive stimulating effect of LLLI as a potential solution to the abovementioned problem.

LLLI preconditioning promotes stem cell proliferation

Increased proliferation after LLLI has been found in other cell types, such as lymphocytes, fibroblasts, and osteoblasts.¹⁹ However, stem cells are different from these cells due to their multi-lineage differentiation potential. To date, the mechanism of LLLI proliferation effects on stem cells remains poorly understood.

Laser parameters

Laser parameters play a role in the proliferation-stimulating effect of LLLI. Table 1 summarizes laser parameters used in studies from 2006 to 2015, looking at the effect of LLLI on BMSC proliferation. Most studies have observed a positive effect of LLLI on the proliferation of BMSCs.

Table 1.

Summary of Laser Parameters and Main Results in Studies Between 2006 and 2015

Study	Stem cell types	Wavelength (nm)	Energy density (J/cm ² )	Power (mW)	Results
Li et al.⁵⁴	BMSCs	630	1.5 and 2.5	2.8, 4.25 and 8.86	LLLI significantly promotes cell proliferation in the group that received daily doses, but no significant difference is observed in the group receiving a single dose.
Tuby et al.¹³	BMSCs and CSCs	804	1 and 3	400	Cell proliferation rate is significantly increased in the irradiated group.
Hou et al.¹²	BMSCs	635	0.5, 1, 2 and 5	60	LLLI significantly promotes cell proliferation rate, with 0.5 J/cm² being the most effective energy density.
Mvula et al.⁵⁵	ADSCs	635	5	50.2	LLLI could positively affect the proliferation and cellular viability of ADSCs.
Kim et al.⁵⁶	BMSCs	647	0.093, 0.279 and 0.836	9.29	Cell proliferation did not show significant increase in the irradiated group compared with the control group.
Horvat-Karajz et al.⁵⁷	BMSCs	660	1.9, 3.8 and 11.7	60	Low energy of LLLI increases the proliferation rate of BMSCs, but high-energy density inhibits proliferation.
Bouvet-Gerbettaz et al.²⁰	BMSCs	808	4	800	808 nm wavelength LLLI fails to promote proliferation of BMSCs.
Li et al.⁵⁸	BMSCs	630	2 and 4	5 and 15	The irradiated group has a higher cell proliferation than control group.
Wu et al.⁵⁹	BMSCs	660	1, 2 and 4	50	The irradiated group has a significant increase in cell proliferation at 5 days after irradiation.
Peng et al.⁶⁰	BMSCs	620	1, 2 and 4	6.67	The proliferation rate of irradiated group increases significantly.
Wu et al.⁷	BMSCs	635	0.5	60	LLLI stimulates proliferation of BMSCs with significant differences.
Soleimani et al.²¹	BMSCs	810	2, 3, 4 and 6	50	LLLI promotes BMSC proliferation significantly at energy densities of 2, 3 and 4 J/cm², except for 6 J/cm².
Wang et al.³¹	BMSCs	635	0.5	60	The irradiated group shows a higher rate of proliferation compared with the control group.
Leonida et al.⁶¹	BMSCs	1064	2.52 and 3.81	1500 and 2250	Proliferation is significantly increased at 7 days after irradiation, but it does not show any further effect on cell proliferation at 14 days after irradiation.
Giannelli et al.²⁷	BMSCs	635	0.3	89	LLLI stimulates the proliferative potential of BMSCs at a wavelength of 635 nm.
Guo et al.²²	BMSCs	633 and 830	0.5, 1, 1.5 and 2	Not mentioned	Clear differences in cell proliferation are observed between irradiation and control group.

ADSCs, adipose-derived stem cells; BMSC, bone marrow-derived mesenchymal stem cell; CSC, cardiac stem cell; LLLI, low-level laser irradiation.

LLLI stimulates proliferation of BMSCs without cytotoxicity at a wavelength of 635 nm and a power of 60 mW, which is in agreement with later studies.¹² However, Bouvet-Gerbettaz et al. reported that LLLI fails to promote proliferation of BMSCs at a wavelength of 808 nm and a power of 800 mW.²⁰ This indicates that the laser effect on cells depends on optimal wavelength and power. Moreover, Soleimani et al. found that LLLI significantly stimulates BMSC proliferation at 2, 3, or 4 J/cm², but not at 6 J/cm², which indicates that energy density also plays a part in this process.²¹

It has been found that different wavelengths and energy densities lead to different gene expression profiles. Studies have shown that the transforming growth factor (TGF)-β pathway switches from canonical to noncanonical signaling as wavelength increases. Meanwhile, receptor activator of nuclear factor kappa-B ligand and matrix metalloproteinase-10 increase in dose–response curves as energy density increases.²² These results could help to explain paradoxical results in the above studies when wavelengths and energy densities differ. Nevertheless, the optimal wave lengths and energy densities for stimulating cell proliferation are still under debate.

LLLI preconditioning activates cell proliferation signaling pathways

As a downstream effector of PI3K/Akt signaling pathways, Akt is a serine/threonine kinase, which has a positive effect on the proliferation of cells by inhibiting apoptotic processes.^23,24 It has been reported that many growth factors modulate angiogenesis, migration, and cell proliferation through PI3K/Akt signaling pathways.^19,25,26 Microarray technology was applied to investigate the gene expression profiles of BMSCs after LLLI. It was found that 119 genes were differentially expressed between control and irradiated groups.⁷ Among them, five genes (PI3Kca, Akt1, Ptpn6, StK17b, and Ccnd1) were confirmed by real-time polymerase chain reaction (real-time PCR). In the irradiated group, levels of PI3Kca, Akt1, and Ccnd1 were increased, while Ptpn6 and Stk17b were decreased. PI3Kca is the catalytic subunit of PI3K; Akt1 is a family member of Akt; and Ccnd1 is a downstream effector of PI3K/Akt and plays an important role in proliferation. Ptpn6 is able to decrease the level of p-Akt, which increases cell apoptosis, but inhibits proliferation. Stk17b is a kinase, which promotes cell apoptosis as well. Another study also reported that the expression of Akt1 pathway components is increased in BMSCs exposed to infrared radiation wavelengths at a wavelength of 830 nm.²² Interestingly, PI3Kca, Akt1, Ptpn6, and Ccnd1 are all involved in the PI3K/Akt/mTOR/eIF4E signaling pathway. According to the results above, PI3K in BMSCs could be activated after LLLI, which induces phosphatidylinositol 4, 5-bisphosphate (PIP2) phosphorylation and converts it to phosphatidylinositol 3, 4, 5-triphosphate (PIP3). PIP3 facilitates Akt activation by 3-phosphoinositide-dependent protein kinase-1 (PDK1). Activated Akt then activates rapamycin (mTOR), which further phosphorylates eukaryotic initiation factor 4E-binding protein 1 (eIF4EBP1). The phosphorylated eIF4EBP1 dissociates from eukaryotic initiation factor 4E (eIF4E), allowing it to form the initiation complex. This complex triggers Ccnd1 gene translation, which stimulates the proliferation of BMSCs⁷ (Fig. 1).

FIG. 1.

Molecular profiling of LLLI preconditioning in cardiac regenerative therapy. LLLI preconditioning activates the PI3K/Akt signaling pathway and notch-1 signaling pathway, upregulates the expression of miR-193, and the secretion of VEGF and TGF-β1, which stimulates the proliferation and differentiation of stem cells. LLLI, low-level laser irradiation; TGF-β1, transforming growth factor-β1; VEGF, vascular endothelial growth factor.

Notch-1 is a transmembrane receptor whose ligands are located on the surface of neighboring cells.²⁷ It has been reported that Notch signaling plays an important role in the proliferation of mesenchymal stem cells (MSCs).²⁸ Dr. Giannelli and his group found that the expression of Notch-1 and its intracellular domain and ligands were significantly upregulated in BMSCs after LLLI.²⁷ Hes-1, a downstream effector of canonical Notch-1 signaling, was also increased. Moreover, they performed electrophysiological whole cell patch-clamp analysis on BMSCs after LLLI and found that inward rectifier K⁺ current (I_Kir) and L-type Ca²⁺ current (I_{Ca, L}), as well as T-type Ca²⁺ current (I_{Ca, T}), were increased compared with the control group. As a result, suppressed Kir currents significantly reduced MSC proliferation and Notch-1 expression. This suggests the Kir channel plays a central role in regulating Notch-1 activation and controlling LLLI-induced BMSC proliferation (Fig. 1). However, how Kir channels influence the expression of Notch-1 is still unknown, which would be worth investigating in the future.

LLLI preconditioning alters microRNA expression

MicroRNA (miRNA) has an effect on almost every aspect of cellular activity.²⁹ It has been found that a subset of miRNA plays a crucial role in the proliferation of stem cells.³⁰ Global changes in miRNA expression in BMSCs following LLLI treatment were investigated.³¹ As a result, 34 miRNAs were found to be differentially regulated, in which 19 miRNAs were upregulated, while 15 miRNAs were downregulated. Among them, miR-193 was the most significantly upregulated. Further, we found the expression of growth family member 5 (ING5) proteins is 50% lower than the control group in miR-193-overexpressed BMSCs. Anti-miR-193 can increase the expression of ING5. It was also shown that cyclin-dependent kinase 2 (CDK2), a downstream effector of ING5, is upregulated by overexpression of miR-193 and downregulated by inhibiting miR-193. Applying siRNA of ING5 also increases CDK2. Previous studies have demonstrated that CDK2 plays an important role in cell proliferation because of its effect on G1/S transition during mitosis.³² In conclusion, we proposed a possible model of miR-193 regulation of BMSC proliferation promoted by LLLI (Fig. 1).

Moreover, we reported that another miRNA, miR-133b, can be induced by LLLI. It has been reported that miR-133b is able to promote cell proliferation by repressing serum response factor.³² Our results showed that miR-133b can influence the expression of cyclin D1 (CCND1) and CDK2. They both are cell cycle-specific proteins, which indicate that miR-133b may regulate BMSC proliferation through a complicated signaling pathway.

LLLI precondition promotes differentiation of stem cells

When irradiated and nonirradiated BMSCs are treated with myogenic differentiation inductor, 5-azacytidine, we found the expression of myogenic-specific proteins, sarcomeric α-actin, and desmin, is dramatically higher in the irradiated group, which confirms the positive effects of LLLI on BMSC myogenic differentiation.¹²

On the other hand, the therapeutic potential of implanted BMSCs is partly attributed to their potential endothelial cell differentiation, important for angiogenesis in infarcted myocardium.³³ A study has shown that BMSCs are able to enhance vascular density at 5 days after implantation.³⁴

Although a myriad of studies have proposed many molecular mechanisms underlying cardiomyogenesis of BMSCs,^35,36 little is known about the molecular mechanisms behind the myogenic and endothelial conversion of BMSCs by LLLI.

LLLI preconditioning stimulates paracrine secretion

BMSCs can secrete various antiapoptotic as well as angiogenic factors, such as vascular endothelial growth factor (VEGF), insulin-like growth factor 1 (IGF1), and TGF-β1. Different studies have established that these factors mediate an improvement of cardiac function and reduce the infarct scar.^37,38

VEGF is commonly known as a signal protein playing an essential role in angiogenesis and vasculogenesis. Although VEGF can be secreted by BMSCs under standard culture conditions, LLLI preconditioning could significantly increase the production of VEGF.¹² Moreover, studies have reported that VEGF is able to induce BMSC proliferation through binding with platelet-derived growth factor receptors, suggesting that VEGF may contribute to the LLLI proliferation effect on stem cells.³⁹

IGF1 is a multi-functional peptide that regulates cell growth and differentiation.⁴⁰ From the analysis of the mRNA of growth factors in LLLI-treated BMSCs, it was found that the expression level of IGF1 was significantly increased. Further, after cells were treated with IGF1-neutralizing antibodies, proliferation was significantly decreased. The combination of these results provides support for the importance of IGF1 in the biostimulation effect of LLLI.²⁷

TGF-β1 is a multi-functional cytokine involved in the growth and differentiation of various cells.⁴¹ Previous studies have demonstrated that TGF-β1 can promote embryonic stem cell differentiation into cardiomyocytes.⁴² In a recent study, LLLI significantly stimulated the expression of TGF-β1 in BMSCs. They found upregulation of TGF-β1, TGF-β receptor 1 and 2, and Smad1 and 2, components of the canonical TGF-β1 pathway. Further, their TGF array also detected increased phosphoserine 187 of Smad1, phosphothreonine 220 of Smad2, and phosphoserine 179 of Smad3.²² Consistently, another study reported a similar result of increased expression of phosphorylated Smad2 and Smad3 in BMSCs at 24 h after TGF-β1 stimulation.⁴³ Given these facts, it indicates that TGF-β1 may play an important role in the LLLI stimulating effect on myogenic differentiation of BMSCs (Fig. 1).

LLLI Preconditioning Creates a Friendly Milieu in Infarcted Myocardium for Implanted Cells

Although many studies have reported that BMSC transplantation can significantly improve cardiac function, the low survival rate of BMSCs after transplantation limits the efficacy of cell therapy. Numerous strategies have been used in cell preconditioning to improve cell survival.^44,45 However, these direct stem cell interventions are complicated and may lead to undesired effects generating safety problems for clinical application.

Our group applied a preconditioning of 635 nm diode laser with an energy density of 0.96 J/cm² on infarcted myocardium before cell transplantation.⁴ We found that LLLI significantly increased early survival rate of implanted cells by twofold. LLLI also decreased their apoptotic percentage and enhanced vascular density in the myocardium compared with the nonirradiated group, indicating LLLI preconditioning might remodel the hostile milieu of infarcted myocardium.

Our further studies showed that LLLI significantly stimulates the expression of VEGF and glucose-regulated protein (GRP78) in myocardium. Thus, increased VEGF and GRP78 may mediate the remodeling process triggered by LLLI preconditioning. Further, we found that LLLI enhances the activity of superoxide dismutase (SOD) and inhibits the production of malondialdehyde (MDA), which decreases the level of superoxide in infarcted myocardium. It may also contribute to improved survival rate of implanted cells. Taken together, we speculate that LLLI myocardial preconditioning creates a friendly milieu in infarcted myocardium for implanted cells. This is accomplished through increased expression of VEGF and GRP78, as well as enhanced SOD activity and decreased MDA production (Fig. 2).

FIG. 2.

(A) The infarcted myocardial milieu is hostile to implanted cells, which leads to a low cell survival rate. (B) LLLI preconditioning creates a friendly milieu in infarcted myocardium for bone marrow-derived mesenchymal stem cells through increased expression of VEGF and GRP78, enhanced activity of SOD, and decreased production of MDA, as well as enhanced angiogenesis, which improves the survival rate of implanted cells. MDA, malondialdehyde; SOD, superoxide dismutase.

LLLI Preconditioning Alters Cardiac Cytokine Expression in Infarcted Myocardium

Cytokines released from injured myocardium play an important role in the inflammatory response during cardiac repair. Previous studies have shown that LLLI is able to protect tissues through regulating cytokine expression and inhibiting inflammation responses.^46

–49 A cytokine protein array system was applied to screen cardiac cytokines following LLLI preconditioning to explicate the altered cytokine expression profile in damaged myocardium.⁵⁰ The results showed that LLLI preconditioning stimulates the expression of interleukin (IL)-4 and granulocyte/marcrophage colony-stimulating factor (GM-CSF) and decreases the production of chemoattractant-3 (CINC-3) and fractalkine.

It has been reported that GM-CSF can mobilize BMSCs to regenerate the infarcted myocardium.⁵¹ Additionally, a study reported that intracoronary or subcutaneous administration of GM-CSF is able to improve collateral flow in a patient suffering from CAD.⁵² These results indicate that LLLI promotes stem cell homing and stimulates collateral formation by increased expression of GM-CSF. On the other hand, fractalkine plays a role in leukocyte accumulation and modulates local inflammatory activity.⁵³ Decreased fractalkine can inhibit leukocyte accumulation in the infarcted myocardium and alleviate inflammatory responses, which may improve the survival rate of implanted cells. Above all, LLLI preconditioning exerts a protective effect on infarcted myocardium by stimulating the expression of GM-CSF and inhibiting the production of fractalkine, which may benefit implantation.

Conclusions and Summary

In the past, LLLI has been applied for wound healing, inflammation reduction, and pain relief. Recent years have witnessed a growing interest for the application of LLLI in cardiac regenerative therapy. It has been well demonstrated that LLLI preconditioning stimulates proliferation and differentiation of stem cells. Moreover, LLLI could remodel the hostile milieu in infarcted myocardium, but this beneficial effect vanishes rapidly within 1 week. It suggests that repeated irradiation is necessary to amplify its positive effect. Further, a myriad of studies only concentrated on LLLI preconditioning before cell transplantation. In fact, LLLI after transplantation may also increase the survival rate of implanted cells, but evidence is still lacking.

At last, although lots of studies have reported the possible molecular mechanisms involved in LLLI preconditioning, the exact mechanisms of this biological effect are still not clearly understood. In future studies, it will be necessary to use new platforms, such as proteomics and metabolomics, to gain a clear understanding of the molecular profiling of LLLI preconditioning effects in cardiac regenerative therapy.

Footnotes

Acknowledgments

This study was supported by the Program for New Century Excellent Talents in University, Foundation for Young Investigator at Peking Union Medical College (XHQN09 and XR01-YP), the Program for Distinguished professor in PUMC, and National Natural Science Foundation of China (81525002 and 81270225).

Author Disclosure Statement

No competing financial interests exist.

References

van Amerongen

, Engel

. Features of cardiomyocyte proliferation and its potential for cardiac regeneration. J Cell Mol Med, 2008; 12:2233–2244.

Mirhoseini

, Muckerheide

, Cayton

. Transventricular revascularization by laser. Lasers Surg Med, 1982; 2:187–198.

Kushibiki

, Hirasawa

, Okawa

, Ishihara

. Regulation of miRNA expression by low-level laser therapy (LLLT) and photodynamic therapy (PDT). Int J Mol Sci, 2013; 14:13542–13558.

Zhang

, Hou

, Shen

, Wang

, Wei

, Hu

. Low level laser irradiation precondition to create friendly milieu of infarcted myocardium and enhance early survival of transplanted bone marrow cells. J Cell Mol Med, 2010; 14:1975–1987.

Moshkovska

, Mayberry

. It is time to test low level laser therapy in Great Britain. Postgrad Med J, 2005; 81:436–441.

Gavish

, Perez

, Gertz

. Low-level laser irradiation modulates matrix metalloproteinase activity and gene expression in porcine aortic smooth muscle cells. Lasers Surg Med, 2006; 38:779–786.

, Wang

, Gong

, Gu

, Hu

, Zhang

. Effects of low-level laser irradiation on mesenchymal stem cell proliferation: a microarray analysis. Lasers Med Sci, 2012; 27:509–519.

Conlan

, Rapley

, Cobb

. Biostimulation of wound healing by low-energy laser irradiation. A review. J Clin Periodontol, 1996; 23:492–496.

Bibikova

, Oron

. Promotion of muscle regeneration in the toad (Bufo viridis) gastrocnemius muscle by low-energy laser irradiation. Anat Rec, 1993; 235:374–380.

10.

Ginani

, Soares

, Barreto

, Barboza

. Effect of low-level laser therapy on mesenchymal stem cell proliferation: a systematic review. Lasers Med Sci, 2015; 30:2189–2194.

11.

Oron

, Yaakobi

, Oron

, et al. Low-energy laser irradiation reduces formation of scar tissue after myocardial infarction in rats and dogs. Circulation, 2001; 103:296–301.

12.

Hou

, Zhang

, Yuan

, Li

, Wei

, Hu

. In vitro effects of low-level laser irradiation for bone marrow mesenchymal stem cells: proliferation, growth factors secretion and myogenic differentiation. Lasers Surg Med, 2008; 40:726–733.

13.

Tuby

, Maltz

, Oron

. Low-level laser irradiation (LLLI) promotes proliferation of mesenchymal and cardiac stem cells in culture. Lasers Surg Med, 2007; 39:373–378.

14.

Wang

, Shum-Tim

, Galipeau

, Chedrawy

, Eliopoulos

, Chiu

. Marrow stromal cells for cellular cardiomyoplasty: feasibility and potential clinical advantages. J Thorac Cardiovasc Surg, 2000; 120:999–1005.

15.

Peschle

, Condorelli

. Stem cells for cardiomyocyte regeneration: state of the art. Ann N Y Acad Sci, 2005; 1047:376–385.

16.

Grinnemo

, Mansson-Broberg

, Leblanc

, et al. Human mesenchymal stem cells do not differentiate into cardiomyocytes in a cardiac ischemic xenomodel. Ann Med, 2006; 38:144–153.

17.

AlGhamdi

, Kumar

, Moussa

. Low-level laser therapy: a useful technique for enhancing the proliferation of various cultured cells. Lasers Med Sci, 2012; 27:237–249.

18.

Abramovitch-Gottlib

, Gross

, Naveh

, et al. Low level laser irradiation stimulates osteogenic phenotype of mesenchymal stem cells seeded on a three-dimensional biomatrix. Lasers Med Sci, 2005; 20:138–146.

19.

Gao

, Xing

. Molecular mechanisms of cell proliferation induced by low power laser irradiation. J Biomed Sci, 2009; 16:4.

20.

Bouvet-Gerbettaz

, Merigo

, Rocca

, Carle

, Rochet

. Effects of low-level laser therapy on proliferation and differentiation of murine bone marrow cells into osteoblasts and osteoclasts. Lasers Surg Med, 2009; 41:291–297.

21.

Soleimani

, Abbasnia

, Fathi

, Sahraei

, Fathi

, Kaka

. The effects of low-level laser irradiation on differentiation and proliferation of human bone marrow mesenchymal stem cells into neurons and osteoblasts—an in vitro study. Lasers Med Sci, 2012; 27:423–430.

22.

Guo

, Wang

, Wai

, et al. Visible red and infrared light alters gene expression in human marrow stromal fibroblast cells. Orthod Craniofac Res, 2015; 18 Suppl 1:50–61.

23.

Manning

, Cantley

. AKT/PKB signaling: navigating downstream. Cell, 2007; 129:1261–1274.

24.

Chang

, Wang

, Olson

, Mousseau

, Ross

, Wu

. Modification of Akt1 by methylglyoxal promotes the proliferation of vascular smooth muscle cells. FASEB J, 2011; 25:1746–1757.

25.

Uruno

, Sugawara

, Kanatsuka

, et al. Hepatocyte growth factor stimulates nitric oxide production through endothelial nitric oxide synthase activation by the phosphoinositide 3-kinase/Akt pathway and possibly by mitogen-activated protein kinase kinase in vascular endothelial cells. Hypertens Res, 2004; 27:887–895.

26.

Namkoong

, Lee

, Kim

, et al. Prostaglandin E2 stimulates angiogenesis by activating the nitric oxide/cGMP pathway in human umbilical vein endothelial cells. Exp Mol Med, 2005; 37:588–600.

27.

Giannelli

, Chellini

, Sassoli

, et al. Photoactivation of bone marrow mesenchymal stromal cells with diode laser: effects and mechanisms of action. J Cell Physiol, 2013; 228:172–181.

28.

Chen

, Wang

, Chen

, Luo

. Molecular targeting regulation of proliferation and differentiation of the bone marrow-derived mesenchymal stem cells or mesenchymal stromal cells. Curr Drug Targets, 2012; 13:561–571.

29.

Huang

, Shen

, Zou

, Wang

, Tang

, Zhang

. Biological functions of microRNAs: a review. J Physiol Biochem, 2011; 67:129–139.

30.

Gangaraju

, Lin

. MicroRNAs: key regulators of stem cells. Nat Rev Mol Cell Biol, 2009; 10:116–125.

31.

Wang

, Huang

, Wu

, et al. MicroRNA-193 pro-proliferation effects for bone mesenchymal stem cells after low-level laser irradiation treatment through inhibitor of growth family, member 5. Stem Cells Dev, 2012; 21:2508–2519.

32.

Stein

, van Wijnen

, Stein

, et al. An architectural perspective of cell-cycle control at the G1/S phase cell-cycle transition. J Cell Physiol, 2006; 209:706–710.

33.

Pankajakshan

, Kansal

, Agrawal

. In vitro differentiation of bone marrow derived porcine mesenchymal stem cells to endothelial cells. J Tissue Eng Regen Med, 2013; 7:911–920.

34.

Davani

, Marandin

, Mersin

, et al. Mesenchymal progenitor cells differentiate into an endothelial phenotype, enhance vascular density, and improve heart function in a rat cellular cardiomyoplasty model. Circulation, 2003; 108 Suppl 1:II253–II258.

35.

Wang

, Li

, Lu

, Wang

, Gong

. Insulin-like growth factor 1 induces bone mesenchymal stem cells differentiation into cardiomyocyte-like cells. Zhonghua Xin Xue Guan Bing Za Zhi, 2013; 41:150–155.

36.

, Gu

, Zhang

. Hepatocyte growth factor combined with insulin like growth factor-1 improves expression of GATA-4 in mesenchymal stem cells cocultured with cardiomyocytes. Chin Med J (Engl), 2008; 121:336–340.

37.

Gnecchi

, He

, Liang

, et al. Paracrine action accounts for marked protection of ischemic heart by Akt-modified mesenchymal stem cells. Nat Med, 2005; 11:367–368.

38.

Gnecchi

, He

, Noiseux

, et al. Evidence supporting paracrine hypothesis for Akt-modified mesenchymal stem cell-mediated cardiac protection and functional improvement. FASEB J, 2006; 20:661–669.

39.

Ball

, Shuttleworth

, Kielty

. Vascular endothelial growth factor can signal through platelet-derived growth factor receptors. J Cell Biol, 2007; 177:489–500.

40.

Blom

, Holmstrup

, Dabelsteen

. The effect of insulin-like growth factor-I and human growth hormone on periodontal ligament fibroblast morphology, growth pattern, DNA synthesis, and receptor binding. J Periodontol, 1992; 63:960–968.

41.

Ladd

, Yatskievych

, Antin

. Regulation of avian cardiac myogenesis by activin/TGFbeta and bone morphogenetic proteins. Dev Biol, 1998; 204:407–419.

42.

Behfar

, Zingman

, Hodgson

, et al. Stem cell differentiation requires a paracrine pathway in the heart. FASEB J, 2002; 16:1558–1566.

43.

, Komota

, Ohshima

, et al. TGF-beta induces the differentiation of bone marrow stem cells into immature cardiomyocytes. Biochem Biophys Res Commun, 2008; 366:1074–1080.

44.

Pasha

, Wang

, Sheikh

, Zhang

, Zhao

, Ashraf

. Preconditioning enhances cell survival and differentiation of stem cells during transplantation in infarcted myocardium. Cardiovasc Res, 2008; 77:134–142.

45.

Liu

, Hou

, Shi

, et al. Lysophosphatidic acid protects mesenchymal stem cells against ischemia-induced apoptosis in vivo. Stem Cells Dev, 2009; 18:947–954.

46.

Albertini

, Villaverde

, Aimbire

, et al. Anti-inflammatory effects of low-level laser therapy (LLLT) with two different red wavelengths (660 nm and 684 nm) in carrageenan-induced rat paw edema. J Photochem Photobiol B, 2007; 89:50–55.

47.

Boschi

, Leite

, Saciura

, et al. Anti-inflammatory effects of low-level laser therapy (660 nm) in the early phase in carrageenan-induced pleurisy in rat. Lasers Surg Med, 2008; 40:500–508.

48.

Safavi

, Kazemi

, Esmaeili

, Fallah

, Modarresi

, Mir

. Effects of low-level He-Ne laser irradiation on the gene expression of IL-1beta, TNF-alpha, IFN-gamma, TGF-beta, bFGF, and PDGF in rat's gingiva. Lasers Med Sci, 2008; 23:331–335.

49.

Simunovic-Soskic

, Pezelj-Ribaric

, Brumini

, Glazar

, Grzic

, Miletic

. Salivary levels of TNF-alpha and IL-6 in patients with denture stomatitis before and after laser phototherapy. Photomed Laser Surg, 2010; 28:189–193.

50.

Yang

, Wu

, Zhang

, et al. Low-level laser irradiation alters cardiac cytokine expression following acute myocardial infarction: a potential mechanism for laser therapy. Photomed Laser Surg, 2011; 29:391–398.

51.

Deng

, Yang

, Deng

, et al. Effects of GM-CSF on the stem cells mobilization and plasma C-reactive protein levels in patients with acute myocardial infarction. Int J Cardiol, 2006; 113:92–96.

52.

Seiler

, Pohl

, Wustmann

, et al. Promotion of collateral growth by granulocyte-macrophage colony-stimulating factor in patients with coronary artery disease: a randomized, double-blind, placebo-controlled study. Circulation, 2001; 104:2012–2017.

53.

Baggiolini

. Chemokines and leukocyte traffic. Nature, 1998; 392:565–568.

54.

, Chen

, Wang

. Effect of light emitting diode irradiation on proliferation of human bone marrow mesenchymal stem cells. J Med Biol Eng, 2006; 26:35–42.

55.

Mvula

, Mathope

, Moore

, Abrahamse

. The effect of low level laser irradiation on adult human adipose derived stem cells. Lasers Med Sci, 2008; 23:277–282.

56.

Kim

, Kim

, Abbas

, et al. Red light of 647 nm enhances osteogenic differentiation in mesenchymal stem cells. Lasers Med Sci, 2009; 24:214–222.

57.

Horvat-Karajz

, Balogh

, Kovacs

, Drrernat

, Sreter

, Uher

. In vitro effect of carboplatin, cytarabine, paclitaxel, vincristine, and low-power laser irradiation on murine mesenchymal stem cells. Lasers Surg Med, 2009; 41:463–469.

58.

, Leu

, Wu

. Red-light light-emitting diode irradiation increases the proliferation and osteogenic differentiation of rat bone marrow mesenchymal stem cells. Photomed Laser Surg, 2010; 28 Suppl 1:S157–S165.

59.

, Wang

, et al. Low-power GaAlAs laser irradiation promotes the proliferation and osteogenic differentiation of stem cells via IGF1 and BMP2. PLoS One, 2012; 7:e44027.

60.

Peng

, Wu

, Zheng

, Xu

, Yu

. The effect of noncoherent red light irradiation on proliferation and osteogenic differentiation of bone marrow mesenchymal stem cells. Lasers Med Sci, 2012; 27:645–653.

61.

Leonida

, Paiusco

, Rossi

, Carini

, Baldoni

, Caccianiga

. Effects of low-level laser irradiation on proliferation and osteoblastic differentiation of human mesenchymal stem cells seeded on a three-dimensional biomatrix: in vitro pilot study. Lasers Med Sci, 2013; 28:125–132.