Tryptophan and Kynurenine Enhances the Stemness and Osteogenic Differentiation of Bone Marrow-Derived Mesenchymal Stromal Cells In Vitro and In Vivo.

Aging tissues present a progressive decline in homeostasis and regenerative capacities, which has been associated with degenerative changes in tissue-specific stem cells and stem cell niches. We hypothesized that amino acids could regulate the stem cell phenotype and differentiation ability of human bone marrow-derived mesenchymal stromal cells (hBMSCs). Thus, we performed a screening of 22 standard amino acids and found that D-tryptophan (10 µM) increased the number of cells positive for the early stem cell marker SSEA-4, and the gene expression levels of OCT-4, NANOG, and SOX-2 in hBMSCs. Comparison between D- and L-tryptophan isomers showed that the latter presents a stronger effect in inducing the mRNA levels of Oct-4 and Nanog, and in increasing the osteogenic differentiation of hBMSCs. On the other hand, L-tryptophan suppressed adipogenesis. The migration and colony-forming ability of hBMSCs were also enhanced by L-tryptophan treatment. In vivo experiments delivering L-tryptophan (50 mg/kg/day) by intraperitoneal injections for three weeks confirmed that L-tryptophan significantly increased the percentage of cells positive for SSEA-4, mRNA levels of Nanog and Oct-4, and the migration and colony-forming ability of mouse BMSCs. L-kynurenine, a major metabolite of L-tryptophan, also induced similar effects of L-tryptophan in enhancing stemness and osteogenic differentiation of BMSCs in vitro and in vivo, possibly indicating the involvement of the kynurenine pathway as the downstream signaling of L-tryptophan. Finally, since BMSCs migrate to the wound healing site to promote bone healing, surgical defects of 1 mm in diameter were created in mouse femur to evaluate bone formation after two weeks of L-tryptophan or L-kynurenine injection. Both L-tryptophan and L-kynurenine accelerated bone healing compared to the PBS-injected control group. In summary, L-tryptophan enhanced the stemness and osteoblastic differentiation of BMSCs and may be used as an essential factor to maintain the stem cell properties and accelerate bone healing and/or prevent bone loss.

EBV-LMP1 induces APOBEC3s and mitochondrial DNA hypermutation in nasopharyngeal cancer.

An Epstein-Barr virus (EBV)-encoded latent membrane protein 1 (LMP1) is a principal oncogene that plays a pivotal role in EBV-associated malignant tumors including nasopharyngeal cancer (NPC). Recent genomic landscape studies revealed that NPC also contained many genomic mutations, suggesting the role of LMP1 as a driver gene for the induction of these genomic mutations. Nonetheless, its exact mechanism has not been investigated. In this study, we report that LMP1 alters the expression profile of APOBEC3s(A3s), host deaminases that introduce consecutive C-to-U mutations (hypermutation). In vitro, LMP1 induces APOBEC3B (A3B) and 3F(A3F), in a nasopharyngeal cell line, AdAH. Overexpression of LMP1, A3B, or A3F induces mtDNA hypermutation, which is also detectable from NPC specimens. Expression of LMP1 and A3B in NPC was correlated with neck metastasis. These results provide evidence as to which LMP1 induces A3s and mtDNA hypermutation, and how LMP1 facilitates metastasis is also discussed.

Influences of Semaphorin 3A Expression on Clinicopathological Features, Human Papillomavirus Status, and Prognosis in Oropharyngeal Carcinoma.

Human papillomavirus (HPV) infection is now identified as a major etiologic factor for oropharyngeal cancer (OPC), and HPV positivity is well established better prognostic marker in OPC. Now, predictable markers for the prognosis of the patients who are stratified by HPV has been investigated in. Semaphorin 3A (SEMA3A) is a well-known axon guidance molecule in the nervous system. It is also known as a tumor suppressor in various cancers. In the present study, we examined the relationships between SEMA3A and clinicopathologic features, especially HPV status, and neoangiogenesis, and its prognostic significance for OPC patients. Thirty-two OPC patients and 17 normal patients were analyzed for SEMA3A expression by immunohistochemical analysis. We also analyzed 22 OPC specimens for CD34 expression as a marker of neoangiogenesis. SEMA3A was significantly downregulated in OPC compared with chronic tonsillitis tissues (p = 0.005). SEMA3A expression was negatively correlated with CD34 expression (r = -0.466, p = 0.033). Moreover, the higher SEMA3A expression cohort showed better survival than the lower SEMA3A expression cohort regardless of HPV status (p = 0.035). These results suggest that SEMA3A expression is a prognostic marker for survival regardless of HPV status and is associated with anti-angiogenesis in OPC.

Acidic Pre-Conditioning Enhances the Stem Cell Phenotype of Human Bone Marrow Stem/Progenitor Cells.

A deeper understanding of the detailed mechanism of in vivo tissue healing is necessary for the development of novel regenerative therapies. Among several external factors, environmental pH is one of the crucial parameters that greatly affects enzyme activity and cellular biochemical reactions involving tissue repair and homeostasis. In this study, in order to analyze the microenvironmental conditions during bone healing, we first measured the pH in vivo at the bone healing site using a high-resolution fiber optic pH microsensor directly in femur defects and tooth extraction sockets. The pH was shown to decrease from physiological 7.4 to 6.8 during the initial two days of healing (inflammatory phase). In the same initial stages of the inflammatory phase of the bone healing process, mesenchymal stem cells (MSCs) are known to migrate to the healing site to contribute to tissue repair. Therefore, we investigated the effect of a short-term acidic (pH 6.8) pre-treatment on the stemness of bone marrow-derived MSCs (BMSCs). Interestingly, the results showed that pre-treatment of BMSCs with acidic pH enhances the expression of stem cell markers (OCT-4, NANOG, SSEA-4), as well as cell viability and proliferation. On the other hand, acidic pH decreased BMSC migration ability. These results indicate that acidic pH during the initial stages of bone healing is important to enhance the stem cell properties of BMSCs. These findings may enable the development of novel methods for optimization of stem cell function towards tissue engineering or regenerative medicine.

Bone Marrow Cells Inhibit BMP-2-Induced Osteoblast Activity in the Marrow Environment.

Bone morphogenetic protein 2 (BMP-2) is widely known as a potent growth factor that promotes bone formation. However, an increasing number of studies have demonstrated side effects of BMP-2 therapy. A deeper understanding of the effect of BMP-2 on cells other than those involved directly in bone remodeling is of fundamental importance to promote a more effective delivery of BMP-2 to patients. In this study, we aimed to investigate the effect of BMP-2 in the marrow environment. First, BMP-2 adsorbed onto titanium implants was delivered at the tooth extraction socket (marrow-absent site) or in the mandible marrow of beagle dogs. BMP-2 could induce marked bone formation around the implant at the tooth extraction socket. Surprisingly, however, no bone formation was observed in the BMP-2-coated titanium implants inserted in the mandible marrow. In C57BL/6 mice, BMP-2 adsorbed in freeze-dried collagen pellets could induce bone formation in marrow-absent calvarial bone. However, similar to the canine model, BMP-2 could not induce bone formation in the femur marrow. Analysis of osteoblast differentiation using Col1a1(2.3)-GFP transgenic mice revealed a scarce number of osteoblasts in BMP-2-treated femurs, whereas in the control group, osteoblasts were abundant. Ablation of femur marrow recovered the BMP-2 ability to induce bone formation. In vitro experiments analyzing luciferase activity of C2C12 cells with the BMP-responsive element and alkaline phosphatase activity of MC3T3-E1 osteoblasts further revealed that bone marrow cells inhibit the BMP-2 effect on osteoblasts by direct cell-cell contact. Collectively, these results showed that the effect of BMP-2 in inducing bone formation is remarkably repressed by marrow cells via direct cell-cell contact with osteoblasts; this opens new perspectives on the clarification of the side-effects associated with BMP-2 application. © 2018 American Society for Bone and Mineral Research.

Antagonistic Effects of Insulin and TGF-ß3 during Chondrogenic Differentiation of Human BMSCs under a Minimal Amount of Factors.

Growth factors are crucial regulators of cell differentiation towards tissue and organ development. Insulin and transforming growth factor-ß (TGF-ß) have been used as the major factors for chondrogenesis in vitro, by activating the AKT and Smad signaling pathways. Previous reports demonstrated that AKT and Smad3 have a direct interaction that results in the inhibition of TGF-ß-mediated cellular responses. However, the result of this interaction between AKT and Smad3 during the chondrogenesis of human bone marrow-derived stem/progenitor cells (hBMSCs) is unknown. In this study, we performed functional analyses by inducing hBMSCs into chondrogenesis with insulin, TGF-ß3 or in combination, and found that TGF-ß3, when applied concomitantly with insulin, significantly decreases an insulin-induced increase in mRNA levels of the master regulator of chondrogenesis, SOX9, as well as the regulators of the 2 major chondrocyte markers, ACAN and COL2A1. Similarly, the insulin/TGF-ß3-treated group presented a significant decrease in the deposition of cartilage matrix as detected by safranin O staining of histological sections of hBMSC micromass cultures when compared to the group stimulated with insulin alone. Intracellular analysis revealed that insulin-induced activation of AKT suppressed Smad3 activation in a dose-dependent manner. Accordingly, insulin/TGF-ß3 significantly decreased the TGF-ß3-induced increase in mRNA levels of the direct downstream factor of TGF-ß/Smad3, CCN2/CGTF, compared to the group stimulated with TGF-ß3 alone. On the other hand, insulin/TGF-ß3 stimulation did not suppress insulin-induced expression of the downstream targets TSC2 and DDIT4/REDD1. In summary, insulin and TGF-ß3 have antagonistic effects when applied concomitantly, with a minimal number of factors. The application of an insulin/TGF-ß3 combination without further supplementation should be used with caution in the chondrogenic differentiation of hBMSCs.

Fluocinolone Acetonide Is a Potent Synergistic Factor of TGF-ß3-Associated Chondrogenesis of Bone Marrow-Derived Mesenchymal Stem Cells for Articular Surface Regeneration.

Articular cartilage repair remains a challenging problem. Based on a high-throughput screening and functional analysis, we found that fluocinolone acetonide (FA) in combination with transforming growth factor beta 3 (TGF-ß3) strongly potentiated chondrogenic differentiation of human bone marrow-derived mesenchymal stem cells (hBMSCs). In an in vivo cartilage defect model in knee joints of immunocompromised mice, transplantation of FA/TGF-ß3-treated hBMSCs could completely repair the articular surface. Analysis of the intracellular pathways revealed that FA enhanced TGF-ß3-induced phosphorylation of Smad2 and Smad3. Additionally, we performed a pathway array and found that FA activates the mTORC1/AKT pathway. Chemical inhibition of mTORC1 with rapamycin substantially suppressed FA effect, and inhibition of AKT completely repressed chondrogenesis of hBMSCs. Inhibition of glucocorticoid receptor with mifepristone also suppressed FA effect, suggesting that FA involves binding to the glucocorticoid receptor. Comparative analysis with other glucocorticoids (triamcinolone acetonide [TA] and dexamethasone [DEX]) revealed the unique ability of FA to repair articular cartilage surgical defects. Analysis of intracellular pathways showed that the mTORC1/AKT pathway and the glucocorticoid receptor was highly activated with FA and TA, but to a lesser extent with DEX. Collectively, these results show a unique ability of FA to enhance TGF-ß3-associated chondrogenesis, and suggest that the FA/TGF-ß3 combination may be used as major inducer of chondrogenesis in vitro. Additionally, FA/TGF-ß3 could be potentially applied in a clinical setting to increase the efficiency of regenerative approaches based on chondrogenic differentiation of stem cells.

A short-term treatment with tumor necrosis factor-alpha enhances stem cell phenotype of human dental pulp cells.

INTRODUCTION: During normal pulp tissue healing, inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-α) or interleukins, act in the initial 48 hours (inflammatory phase) and play important roles not only as chemo-attractants of inflammatory cells and stem/progenitor cells but also in inducing a cascade of reactions toward tissue regeneration or reparative dentin formation or both. Previous reports have shown that inflammatory cytokines regulate the differentiation capacity of dental pulp stem/progenitor cells (DPCs), but none has interrogated the impact of these cytokines on the stem cell phenotype of stem/progenitor cells. This study investigated the effects of a short-term treatment with TNF-α on the stem cell phenotype and differentiation ability of human DPCs. METHODS: An in vivo mouse model of pulp exposure was performed for analysis of expression of the mesenchymal stem cell marker CD146 in DPCs during the initial stage of inflammatory response. For in vitro studies, human DPCs were isolated and incubated with TNF-α for 2 days and passaged to eliminate TNF-α completely. Analysis of stem cell phenotype was performed by quantification of cells positive for mesenchymal stem cell markers SSEA-4 (stage-specific embryonic antigen 4) and CD146 by flow cytometry as well as by quantitative analysis of telomerase activity and mRNA levels of OCT-4 and NANOG. Cell migration, colony-forming ability, and differentiation toward odontogenesis and adipogenesis were also investigated. RESULTS: The pulp exposure model revealed a strong staining for CD146 during the initial inflammatory response, at 2 days after pulp exposure. In vitro experiments demonstrated that a short-term (2-day) treatment of TNF-α increased by twofold the percentage of SSEA-4+ cells. Accordingly, STRO-1, CD146, and SSEA-4 protein levels as well as OCT-4 and NANOG mRNA levels were also significantly upregulated upon TNF-α treatment. A short-term TNF-α treatment also enhanced DPC function, including the ability to form cell colonies, to migrate, and to differentiate into odontogenic and adipogenic lineages. CONCLUSIONS: A short-term treatment with TNF-α enhanced the stem cell phenotype, migration, and differentiation ability of DPCs.