Yinghua Zhao

Interplay between Mesenchymal Stem Cells and Lymphocytes Implications for Immunotherapy and Tissue Regeneration

In addition to their potential for replacing damaged and diseased tissues by differentiating into tissue-specific cells, mesenchymal stem cells (MSCs) have been found to interact closely with immune cells, such as lymphocytes. In this review, we will discuss current research regarding the immunomodulatory properties of MSCs and the effects of lymphocytes on MSCs. We will suggest how these findings could be translated to potential clinical treatment. MSCs can regulate immune response by inducing activated T-cell apoptosis through the FAS ligand (FASL)/FAS-mediated death pathway via cell-cell contact, leading to up-regulation of regulatory T-cells (Tregs), which ultimately results in immune tolerance. Conversely, lymphocytes can impair survival and osteogenic differentiation of implanted MSCs by secreting the pro-inflammatory cytokines IFN-γ and TNF-α and/or through the FASL/FAS-mediated death pathway, thereby negatively affecting MSC-mediated tissue regeneration. One novel strategy to improve MSC-based tissue engineering involves the reduction of IFN-γ and TNF-α concentration by systemic infusion of Tregs or local application of aspirin. Further understanding of the mechanisms underlying the interplay between lymphocytes and MSCs may be helpful in the development of promising approaches to improve cell-based regenerative medicine and immune therapies.

IFN‐γ and TNF‐α Synergistically Induce Mesenchymal Stem Cell Impairment and Tumorigenesis via NFκB Signaling

An inflammatory microenvironment may cause organ degenerative diseases and malignant tumors. However, the precise mechanisms of inflammation‐induced diseases are not fully understood. Here, we show that the proinflammatory cytokines interferon‐γ (IFN‐γ) and tumor necrosis factor α (TNF‐α) synergistically impair self‐renewal and differentiation of mesenchymal stem cells (MSCs) via nuclear factor κB (NFκB)‐mediated activation of mothers against decapentaplegic homolog 7 (SMAD7) in ovariectomized (OVX) mice. More interestingly, a long‐term elevated levels of IFN‐γ and TNF‐α result in significantly increased susceptibility to malignant transformation in MSCs through NFκB‐mediated upregulation of the oncogenes c‐Fos and c‐Myc. Depletion of either IFN‐γ or TNF‐α in OVX mice abolishes MSC impairment and the tendency toward malignant transformation with no NFκB‐mediated oncogene activation. Systemic administration of aspirin, which significantly reduces the levels of IFN‐γ and TNF‐α, results in blockage of MSC deficiency and tumorigenesis by inhibition of NFκB/SMAD7 and NFκB/c‐FOS and c‐MYC pathways in OVX mice. In summary, this study reveals that inflammation factors, such as IFN‐γ and TNF‐α, synergistically induce MSC deficiency via NFκB/SMAD7 signaling and tumorigenesis via NFκB‐mediated oncogene activation. STEM Cells2013;31:1383–1395

Fas Ligand Regulates the Immunomodulatory Properties of Dental Pulp Stem Cells

Dental pulp stem cells (DPSCs) possess immunoregulatory properties, but the underlying mechanism is not fully understood. Here we showed that DPSCs were capable of inducing activated T-cell apoptosis in vitro and ameliorating inflammatory-related tissue injuries when systemically infused into a murine colitis model. Mechanistically, DPSC-induced immunoregulation was associated with the expression of Fas ligand (FasL), a transmembrane protein that plays an important role in inducing the Fas apoptotic pathway. Knockdown of FasL expression by siRNA in DPSCs reduced their capacity to induce T-cell apoptosis in vitro and abolished their therapeutic effects in mice with colitis. However, the expression level of FasL did not affect either DPSC proliferation rate or multipotent differentiation potential. In summary, FasL governs the immunoregulatory property of DPSCs in the context of inducing T-cell apoptosis.

Basic fibroblast growth factor inhibits osteogenic differentiation of stem cells from human exfoliated deciduous teeth through ERK signaling

Objective Stem cells from human exfoliated deciduous teeth (SHED) are a unique postnatal stem cell population capable of regenerating mineralized tissue and treating immune disorders. However, the mechanism that controls SHED differentiation is not fully understood. Here, we showed that basic fibroblast growth factor (bFGF) treatment attenuated SHED-mediated mineralized tissue regeneration through activation of the extracellular signal-regulated kinase (ERK) 1/2 pathway.OBJECTIVE Stem cells from human exfoliated deciduous teeth (SHED) are a unique postnatal stem cell population capable of regenerating mineralized tissue and treating immune disorders. However, the mechanism that controls SHED differentiation is not fully understood. Here, we showed that basic fibroblast growth factor (bFGF) treatment attenuated SHED-mediated mineralized tissue regeneration through activation of the extracellular signal-regulated kinase (ERK) 1/2 pathway. MATERIAL AND METHOD The level of mineralized nodule formation was assessed by alizarin red staining. Expression levels of osteogenic genes, osteocalcin and runt-related transcription factor 2, were examined by RT-PCR. Subcutaneous implantation approach was used to assess in vivo bone formation. Downstream signaling pathways of bFGF were examined by Western blotting. RESULT Activation of ERK1/2 signaling by bFGF treatment inhibited WNT/β-catenin pathway, leading to osteogenic deficiency of SHED. ERK1/2 inhibitor treatment rescued bFGF-induced osteogenic differentiation deficiency. CONCLUSION These data suggest that bFGF inhibits osteogenic differentiation of SHED via ERK1/2 pathway. Blockade ERK1/2 signaling by small molecular inhibitor treatment improves bone formation of SHED after bFGF treatment.

Osteoblast-induced osteoclast apoptosis by fas ligand/FAS pathway is required for maintenance of bone mass

The interplay between osteoblasts and osteoclasts has a crucial role in maintaining bone homeostasis. In this study, we reveal that osteoblasts are capable of inducing osteoclast apoptosis by FAS ligand (FASL)/FAS signaling. Conditional knockout of FASL in osteoblasts results in elevated osteoclast numbers and activity, along with reduced bone mass, suggesting that osteoblast-produced FASL is required to maintain physiological bone mass. More interestingly, we show that osteoblasts from ovariectomized (OVX) osteoporotic mice exhibit decreased FASL expression that results from the IFN-γ- and TNF-α-activated NF-κB pathway, leading to reduced osteoclast apoptosis and increased bone resorption. Systemic administration of either IFN-γ or TNF-α ameliorates the osteoporotic phenotype in OVX mice and rescues FASL expression in osteoblasts. In addition, ovariectomy induces more significant bone loss in FASL conditional knockout mice than in control group with increased osteoclast activity in which the levels of RANKL and OPG remain unchanged. Taken together, this study suggests that osteoblast-induced osteoclast apoptosis via FASL/FAS signaling is a previously unrecognized mechanism that has an important role in the maintenance of bone mass in both physiological conditions and OVX osteoporosis.

Effects of locally applied nerve growth factor to the inferior alveolar nerve histology in a rabbit model of mandibular distraction osteogenesis.

Distraction osteogenesis (DO) is widely used in deformities and defects of the craniofacial bone. Accelerating inferior alveolar nerve (IAN) recovery would aid the process. Nerve growth factor (NGF) plays a vital role in peripheral nerve regeneration. In this study, the ability of locally applied human NGF beta (hNGFbeta) to enhance the morphological recovery of the IAN in a rabbit model of mandibular DO was studied. Rabbits underwent bilateral DO with a rate of 0.5mm per 12h. Two doses of 40 microg hNGFbeta in buffer were injected into callus at the beginning the of consolidation time. The contralateral side received injections of placebo. Rabbits were killed at 14 and 28 days. IAN specimens were subjected to histological and histomorphometric analysis. In both 14 and 28 days consolidation experiments, nerve histological analysis showed less degeneration and more regeneration in nerve fibers on the hNGFbeta treated side than the control side. Histomorphometric analysis showed that the myelinated fiber density on the hNGFbeta treated side was significantly higher than on the control side (p<0.01). The data indicate that locally applied hNGFbeta can accelerate the morphological recovery of the IAN and may play a role in reducing nerve injury in mandibular DO clinically.

Technetium-99 conjugated with methylene diphosphonate ameliorates ovariectomy-induced osteoporotic phenotype without causing osteonecrosis in the jaw.

Technetium-99 conjugated with methylene diphosphonate (99Tc-MDP) is a novel bisphosphonate derivative without radioactivity and has been successfully used to treat arthritis in China for years. Since bisphosphonate therapy has the potential to induce bisphosphonate-related osteonecrosis of the jaw (BRONJ), we examined whether 99Tc-MDP represents a new class of bisphosphonate for antiresorptive therapy to ameliorate estrogen deficiency-induced bone resorption with less risk of causing BRONJ. We showed that 99Tc-MDP-treated, ovariectomized (OVX) mice had significantly improved bone mineral density and trabecular bone volume in comparison to the untreated OVX group by inhibiting osteoclasts and enhancing osteogenic differentiation of bone marrow mesenchymal stem cells. To determine the potential of inducing BRONJ, 99Tc-MDP/dexamethasone (Dex) or zoledronate/Dex was administered into C57BL/6J mice via the tail vein, followed by extraction of maxillary first molars. Interestingly, 99Tc-MDP treatment showed less risk to induce osteonecrosis in the maxillary bones compared to zoledronate treatment group, partially because 99Tc-MDP neither suppressed adaptive regulatory T cells nor activated the inflammatory T-helper-producing interleukin-17 cells. Taken together, our findings demonstrate that 99Tc-MDP therapy may be a promising approach in the treatment of osteoporosis with less risk of causing BRONJ.

Effects of nerve growth factor delivery via a gel to inferior alveolar nerve in mandibular distraction osteogenesis.

Inferior alveolar nerve (IAN) injury is a concern in mandible distraction osteogenesis (DO). We have previously demonstrated that repeated local injections of human nerve growth factor &bgr; (NGF-&bgr;) have significantly enhanced the histologic recovery of the IAN in a rabbit model of DO. This study was to further test the effect of a single injection of human NGF-&bgr; delivered via a collagen/nanohydroxyapatite/&kgr;-carrageenan gel to the recovery of the IAN in DO. Rabbits underwent mandibular DO at a rate of 0.75 mm/12 h for 6 days. At the end of the distraction period, injections were performed near the IAN percutaneously as follows: group 1, human NGF-&bgr; in the gel; group 2, human NGF-&bgr; in saline; group 3, the gel alone; and group 4, saline alone. At 14 days after the end of distraction, IAN histologic findings and histomorphometric parameters were evaluated. Histologically, there were less myelin debris and more abundant regenerating nerve fibers in group 1 than the other groups. Both the myelinated fiber density and the myelinated axon area in group 1 were significantly higher than groups 3 and 4 (P < 0.01); the myelinated axon area in the group 1 was significantly higher than group 2 (P < 0.01). In conclusion, the delivery of human NGF-&bgr; in the gel leads to a better acceleration of the IAN injury recovery over the saline delivery. It provides a possible way to enhance the recovery of nerve injuries in craniofacial DO clinically.

Basic fibroblast growth factor inhibits osteogenic differentiation of stem cells from human exfoliated deciduous teeth through ERK signaling: bFGF and SHED differentiation

Objective Stem cells from human exfoliated deciduous teeth (SHED) are a unique postnatal stem cell population capable of regenerating mineralized tissue and treating immune disorders. However, the mechanism that controls SHED differentiation is not fully understood. Here, we showed that basic fibroblast growth factor (bFGF) treatment attenuated SHED-mediated mineralized tissue regeneration through activation of the extracellular signal-regulated kinase (ERK) 1/2 pathway.OBJECTIVE Stem cells from human exfoliated deciduous teeth (SHED) are a unique postnatal stem cell population capable of regenerating mineralized tissue and treating immune disorders. However, the mechanism that controls SHED differentiation is not fully understood. Here, we showed that basic fibroblast growth factor (bFGF) treatment attenuated SHED-mediated mineralized tissue regeneration through activation of the extracellular signal-regulated kinase (ERK) 1/2 pathway. MATERIAL AND METHOD The level of mineralized nodule formation was assessed by alizarin red staining. Expression levels of osteogenic genes, osteocalcin and runt-related transcription factor 2, were examined by RT-PCR. Subcutaneous implantation approach was used to assess in vivo bone formation. Downstream signaling pathways of bFGF were examined by Western blotting. RESULT Activation of ERK1/2 signaling by bFGF treatment inhibited WNT/β-catenin pathway, leading to osteogenic deficiency of SHED. ERK1/2 inhibitor treatment rescued bFGF-induced osteogenic differentiation deficiency. CONCLUSION These data suggest that bFGF inhibits osteogenic differentiation of SHED via ERK1/2 pathway. Blockade ERK1/2 signaling by small molecular inhibitor treatment improves bone formation of SHED after bFGF treatment.