Impaired function of tendon-derived stem cells in experimental diabetes mellitus rat tendons: implications for cellular mechanism of diabetic tendon disorder

HMGB1 Modulates High Glucose-Induced Erroneous Differentiation of Tendon Stem/Progenitor Cells through RAGE/β-Catenin Pathway

The association of tendinopathy with diabetes has been well recognized. Tendon stem/progenitor cells (TSPCs) play critical roles in tendon repair, regeneration, and homeostasis maintenance. Diabetic TSPCs exhibit enhanced erroneous differentiation and are involved in the pathogenesis of diabetic tendinopathy, whereas the underlying mechanism of the erroneous differentiation of TSPCs remains unclear. Here, we showed that high glucose treatment promoted the erroneous differentiation of TSPCs with increased osteogenic differentiation capacity and decreased tenogenic differentiation ability, and stimulated the expression and further secretion of HMGB1 in TSPCs and. Functionally, exogenous HMGB1 significantly enhanced the erroneous differentiation of TSPCs, while HMGB1 knockdown mitigated high glucose-promoted erroneous differentiation of TSPCs. Mechanistically, the RAGE/β-catenin signaling was activated in TSPCs under high glucose, and HMGB1 knockdown inhibited the activity of RAGE/β-catenin signaling. Inhibition of RAGE/β-catenin signaling could ameliorate high glucose-induced erroneous differentiation of TSPCs. These results indicated that HMGB1 regulated high glucose-induced erroneous differentiation of TSPCs through the RAGE/β-catenin signaling pathway. Collectively, our findings suggest a novel essential mechanism of the erroneous differentiation of TSPCs, which might contribute to the pathogenesis of diabetic tendinopathy and provide a promising therapeutic target and approach for diabetic tendinopathy.

Effects of adipose-derived mesenchymal stem cell conditioned medium on human tenocytes exposed to high glucose

Introduction

Diabetic tendinopathy is a common invalidating and challenging disease that may be treated using stem cells. However, the effects of adipose-derived mesenchymal stem cell conditioned medium (ASC-CM) in diabetic tendinopathy have never been explored.

Objectives

The present study evaluated the effects of ASC-CM on morphology, cell viability, structure, and scratch wound closure of human tenocytes (HTNC) exposed to high glucose (HG).

Design

Experimental study.

Methods

HTNC were exposed to HG (25 mM) for 7, 14 and 21 days with or without ASC-CM for the last 24 h. CM was collected from 4 × 105 ASCs, centrifuged for 10 min at 200 g and sterilized with 0.22 μm syringe filter.

Results

At 7 days, HG-HTNC had decreased cell viability [72 ± 2%, p < 0.01 versus normal glucose (NG)] compared to NG-HTNC (90 ± 5%). A further decrement was detected after 14 and 21 days (60 ± 4% and 60 ± 5%, both, p < 0.01 versus NG and p < 0.01 versus HG7). While NG-HTNC evidenced a normal fibroblast cell-like elongated morphology, HG-HTNC showed increased cell roundness. In contrast, HG-HTNC exposed to ASC-CM showed a significant increase in cell viability, an improved cell morphology and higher scratch wound closure at all HG time points. Moreover, the exposure to ASC-CM significantly increased thrombospondin 1 and transforming growth factor beta 1 (TGF-β1) content in HG-HTNC. The TGF-β1 elevation was paralleled by higher Collagen I and Vascular Endothelial Growth Factor in HG-HTNC.

Conclusion

ASC-CM may restore the natural morphology, cell viability and structure of HTNC, promoting their scratch wound closure through TGF-β1 increase.

HMGB1: a potential new target for tendinopathy treatment

Tendinopathy describes a complex pathology of the tendon characterized by abnormalities in the microstructure, composition, and cellularity of the tendon, leading to pain, limitation of activity and reduced function. Nevertheless, the mechanism of tendinopathy has not been fully elucidated, and the treatment of tendinopathy remains a challenge. High mobility group box 1 (HMGB1), a highly conserved and multifaceted nuclear protein, exerts multiple roles and high functional variability and is involved in many biological and pathological processes. In recent years, several studies have suggested that HMGB1 is associated with tendinopathy and may play a key role in the pathogenesis of tendinopathy. Therefore, this review summarizes the expression and distribution of HMGB1 in tendinopathy, focuses on the roles of HMGB1 and HMGB1-based potential mechanisms involved in tendinopathy, and finally summarizes the findings on HMGB1-based therapeutic approaches in tendinopathy, probably providing new insight into the mechanism and further potential therapeutic targets of tendinopathy.

LncRNA AC108925 promotes osteoblast differentiation of tendon-derived stem cells by targeting miR-146a-3p

It has been reported that tendon-derived stem cells(TDSCs) conduce to the ostosis in tendon diseases, and the molecular mechanism needs to be discussed. To investigate the function and mechanism of LncRNA in tendinopathy. Tendon of tendinopathy patients and health controls were obtained, and sequencing analysis have been performed to detect the significantly expressed genes and non-coding RNAs. Moreover, to further discuss LncRNA AC108925 in tendinopathy, tendinopathy animal models have been established, and the expression of LncRNA AC108925 expression was examined by RT-qPCR methods. Furthermore, hTDSCs have been treated by osteogenic medium, and the modulating function of LncRNA AC108925 on the osteoblast differentiation of hTDSCs have been examined. Sequencing analysis showed that AC108925 a dramatically elevated LncRNA, and results of animal and cells studies confirmed the finding. Knockdown AC108925 inhibited the osteogenic differentiation of osteogenic medium treated TDSCs by decreasing the expression of osteogenic markers. Furthermore, miR-146a-3p is a target of AC108925 in TDSCs, and miR-146a-3p is a negative modulator of osteogenic differentiation of hTDSCs by inhibiting the effects of AC108925 shRNA on osteogenic differentiation of hTDSCs. AC108925 can regulate the osteogenic differentiation of hTDSCs via regulating the miR-146a-3p. Targeting the AC108925/miR-146a-3p axis might be a latent way to treat tendinopathy.

Advanced glycation end productions and tendon stem/progenitor cells in pathogenesis of diabetic tendinopathy

Tendinopathy is a challenging complication observed in patients with diabetes mellitus. Tendinopathy usually leads to chronic pain, limited joint motion, and even ruptured tendons. Imaging and histological analyses have revealed pathological changes in various tendons of patients with diabetes, including disorganized arrangement of collagen fibers, microtears, calcium nodules, and advanced glycation end product (AGE) deposition. Tendon-derived stem/ progenitor cells (TSPCs) were found to maintain hemostasis and to participate in the reversal of tendinopathy. We also discovered the aberrant osteochondrogenesis of TSPCs in vitro. However, the relationship between AGEs and TSPCs in diabetic tendinopathy and the underlying mechanism remain unclear. In this review, we summarize the current findings in this field and hypothesize that AGEs could alter the properties of tendons in patients with diabetes by regulating the proliferation and differentiation of TSPCs in vivo.

Altered Differentiation of Tendon-Derived Stem Cells in Diabetic Conditions Mediated by Macrophage Migration Inhibitory Factor

The purpose of our study was to evaluate the role of macrophage migration inhibitory factor (MIF) in the differentiation of tendon-derived stem cells (TdSCs) under hyperglycemic conditions. In the in vivo experiment, rats were classified into diabetic (DM) and non-DM groups depending on the intraperitoneal streptozotocin (STZ) or saline injection. Twelve-week after STZ injection, the supraspinatus tendon was harvested and prepared for histological evaluation and real-time reverse transcription polymerase chain reaction for osteochondrogenic (aggrecan, BMP-2, and Sox9) and tenogenic (Egr1, Mkx, scleraxis, type 1 collagen, and Tnmd) markers. For the in vitro experiment, TdSCs were isolated from healthy rat Achilles tendons. Cultured TdSCs were treated with methylglyoxal and recombinant MIF or MIF gene knockdown to determine the effect of hyperglycemic conditions and MIF on the differentiation function of TdSCs. These conditions were classified into four groups: hyperglycemic-control group, hyperglycemic-recombinant-MIF group, hyperglycemic-knockdown-MIF group, and normal-control group. The mRNA expression of osteochondrogenic and tenogenic markers was compared among the groups. In the in vivo experiment, the mRNA expression of all osteochondrogenic and tenogenic differentiation markers in the DM group was significantly higher and lower than that in the non-DM group, respectively. Similarly, in the in vitro experiments, the expression of all osteochondrogenic and tenogenic differentiation markers was significantly upregulated and downregulated, respectively, in the hyperglycemic-control group compared to that in the normal-control group. The hyperglycemic-knockdown-MIF group demonstrated significantly decreased expression of all osteochondrogenic differentiation markers and increased expression of only some tenogenic differentiation markers compared with the hyperglycemic-control group. In contrast, the hyperglycemic-recombinant-MIF group showed significantly increased expression of all osteochondrogenic differentiation markers, but no significant difference in any tenogenic marker level, compared to the hyperglycemic-control group. These results suggest that tendon homeostasis could be affected by hyperglycemic conditions, and MIF appears to alter the differentiation of TdSCs via enhancement of the osteochondrogenic differentiation in hyperglycemic conditions. These are preliminary findings, and must be confirmed in a further study.

Characterization of Tendon-Derived Stem Cells and Rescue Tendon Injury

The natural healing ability of tendon is limited, and it cannot restore the native structure and function of tendon injuries. Tendon-derived stem cells (TDSCs) are a new type of pluripotent stem cells with multi-directional differentiation potential and are expected to become a promising cell-seed for the treatment of tendon injuries in the future. In this review, we outline the latest advances in the culture and identification of TDSCs. In addition, the influencing factors on the differentiation of TDSCs are discussed. Moreover, we aim to discuss recent studies to enhance TDSCs treatment of injured tendons. Finally, we identify the limitations of the current understanding of TDSCs biology, the main challenges of using their use, and potential therapeutic strategies to inform cell-based tendon repair.

Tendon Stem/Progenitor Cell Subpopulations and Their Implications in Tendon Biology

Tendon harbors a cell population that possesses stem cell characteristics such as clonogenicity, multipotency and self-renewal capacity, commonly referred to as tendon stem/progenitor cells (TSPCs). Various techniques have been employed to study how TSPCs are implicated in tendon development, homeostasis and healing. Recent advances in single-cell analysis have enabled much progress in identifying and characterizing distinct subpopulations of TSPCs, which provides a more comprehensive view of TSPCs function in tendon biology. Understanding the mechanisms of physiological and pathological processes regulated by TSPCs, especially a particular subpopulation, would greatly benefit treatment of diseased tendons. Here, we summarize the current scientific literature on the various subpopulations of TSPCs, and discuss how TSPCs can contribute to tissue homeostasis and pathogenesis, as well as examine the key modulatory signaling pathways that determine stem/progenitor cell state. A better understanding of the roles that TSPCs play in tendon biology may facilitate the development of novel treatment strategies for tendon diseases.

Metabolic Regulation of Tendon Inflammation and Healing Following Injury

PURPOSE OF REVIEW

This review seeks to provide an overview of the role of inflammation and metabolism in tendon cell function, tendinopathy, and tendon healing. We have summarized the state of knowledge in both tendon and enthesis.

RECENT FINDINGS

Recent advances in the field include a substantial improvement in our understanding of tendon cell biology, including the heterogeneity of the tenocyte environment during homeostasis, the diversity of the cellular milieu during in vivo tendon healing, and the effects of inflammation and altered metabolism on tendon cell function in vitro. In addition, the mechanisms by which altered systemic metabolism, such as diabetes, disrupts tendon homeostasis continue to be better understood. A central conclusion of this review is the critical need to better define fundamental cellular and signaling mechanisms of inflammation and metabolism during tendon homeostasis, tendinopathy, and tendon healing in order to identify therapies to enhance or maintain tendon function.

Understanding cellular and molecular mechanisms of pathogenesis of diabetic tendinopathy

There is accumulating evidence of an increased incidence of tendon disorders in people with diabetes mellitus. Diabetic tendinopathy is an important cause of chronic pain, restricted activity, and even tendon rupture in individuals. Tenocytes and tendon stem/progenitor cells (TSPCs) are the dominant cellular components associated with tendon homeostasis, maintenance, remodeling, and repair. Some previous studies have shown alterations in tenocytes and TSPCs in high glucose or diabetic conditions that might cause structural and functional variations in diabetic tendons and even accelerate the development and progression of diabetic tendinopathy. In this review, the biomechanical properties and histopathological changes in diabetic tendons are described. Then, the cellular and molecular alterations in both tenocytes and TSPCs are summarized, and the underlying mechanisms involved are also analyzed. A better understanding of the underlying cellular and molecular pathogenesis of diabetic tendinopathy would provide new insight for the exploration and development of effective therapeutics.

Tectorigenin Alleviates Inflammation, Apoptosis, and Ossification in Rat Tendon-Derived Stem Cells via Modulating NF-Kappa B and MAPK Pathways

Tendinopathy is a common musculoskeletal disorder that mainly affects athletes and people of older age. Tumor necrosis factor-α (TNF-α) plays an important role in initiating tendinopathy. Tectorigenin, an extract component of Belam-canda Chinesis, possesses anti-inflammatory and anti-apoptosis activity. The present study was established to investigate the role of tectorigenin against the pathogenetic effects of TNF-α on tendon-derived stem cells (TDSCs) in vivo and in vitro. The findings indicated that TNF-α is able to induce TDSC inflammation, apoptosis, and ossification, as well as activate nuclear factor-kappa B and mitogen-activated protein kinase (MAPK). Furthermore, the results confirmed that tectorigenin is able to inhibit the TNF-α-induced inflammation, apoptosis, and ossification. Tectorigenin treatment decreases activation of NF-kappa B and MAPK signaling in TDSCs. Tectorigenin ameliorates tendinopathy in the in vivo rat model. Thus, these data reveal that tectorigenin can serve as a potential treatment for tendinopathy.

Higher BMP Expression in Tendon Stem/Progenitor Cells Contributes to the Increased Heterotopic Ossification in Achilles Tendon With Aging

Although the mineralization in tendon tissue has been reported in a series of aging and disease models, the underlying mechanisms remain unknown. This study aimed to describe the appearance of heterotopic ossification in rat Achilles tendon and further verify whether this tissue metaplasia is related to the enhanced osteogenic differentiation of tendon stem/progenitor cells (TSPCs) owing to the higher expression of bone morphogenetic proteins (BMP-2/4/7) with aging. The male SD rats, aged 4, 8, and 20 months (M), were used. The analyses of ossification and BMP expression in tendon were tested by radiological view (X-ray and CT), histological staining [hematoxylin and eosin (HE), Alcian blue, and Alizarin red], immunohistochemistry, and Western blot. The osteogenic differentiation potential and BMP expression of TSPCs were examined by Alizarin red S staining and real-time PCR. TSPCs were treated with BMP-2 or noggin, and the osteogenic differentiation potential was also examined. X-ray and CT showed the appearance of heterotopic ossification in tendon, and the volume and density of ossification was increased with aging. Histological staining showed the appearance of calcified region surrounded by chondrocyte-like cells and the increased osteogenesis-related gene and BMP expression in ossified tendon with aging. Moreover, the osteogenic differentiation potential and BMP expression in TSPCs isolated from ossified tendon were increased with aging. Additionally, BMP-2 increased the calcium nodule formation and osteogenesis-related gene expression in TSPCs. The addition of noggin inhibited BMP-induced enhancement of osteogenic differentiation. Thus, these findings suggested that the enhanced osteogenic differentiation of TSPCs contributes to the increased heterotopic ossification in aged tendon, which might be induced by the higher expression of BMPs with aging.

Pioglitazone attenuates advanced glycation end products-induced apoptosis and calcification by modulating autophagy in tendon-derived stem cells

Diabetes mellitus (DM) is one of the prominent risk factors for pathological development and progression of tendinopathy. One feature of DM-related changes in tendinopathy is accumulation of advanced glycation end products (AGEs) in affected tendons. Pioglitazone (Pio), a peroxisome proliferator-activated receptor γ agonist, performs a protective effect against AGEs. The present study aimed to investigate the pathogenetic role of AGEs on tendon-derived stem cells (TDSCs) and to determine the effect of Pio on AGEs-induced TDSC dysfunctions. Results indicated that AGEs induced TDSC apoptosis as well as compensatory activation of autophagy. Pharmacologic activation/inhibition of autophagy leaded to alleviate/exacerbate apoptosis induced by AGEs. We further confirmed the effect of Pio on autophagy, which ameliorated apoptosis and abnormal calcification caused by AGEs both in vitro and in vivo. Thus, we suggest that Pio ameliorates the dysfunctions of TDSCs against AGEs by promoting autophagy, and we also reveal that Pio is a potential pharmacological choice for tendinopathy.

Diabetes and Collagen: Interrelations

This review summarizes information on interrelations between diabetes development and collagen metabolism and structure. The growing global problem of diabetes requires the search for new strategies of its complications correction. Among them collagen structure violations and/or its impaired metabolism most often lead to profound disability. Even after several decades of intense studies, pathophysiological mechanisms underlying collagen changes in diabetes mellitus are still not well clear. The main complication is that not only diabetes cause changes in collagen metabolism and structure. Collagens via some mechanisms also may regulate glucose homeostasis, both directly and indirectly. The author also presented the results of own studies on bone and skin type I collagen amino acid composition changes with diabetes. Deepening our understanding of collagen metabolism and diabetes interrelations allows us to optimize approaches to overcome the collagen-mediated consequences of this disease. Recently, it has been clearly demonstrated that use of only antidiabetic agents cannot fully correct such violations. Preparations on the base of flavonoids, collagens and amino acids could be considered as perspective directions in this area of drug development.

Insulin Enhances the In Vitro Osteogenic Capacity of Flexor Tendon-Derived Progenitor Cells

There is increased incidence of tendon disorders and decreased tendon healing capacity in people with diabetes mellitus (DM). Recent studies have also suggested pathological ossification in repair tendon of people with DM. Therefore, the objective of this study is to investigate the effects of insulin supplementation, an important pathophysiologic stimulus of DM, on tendon progenitor cell (TPC) proliferation and in vitro osteogenic capacity. Passage 3 TPCs were isolated from collagenase-digested, equine superficial digital flexor tendons. TPC proliferation was measured via MTT assay after 3 days of monolayer culture in medium supplemented with 0, 0.007, 0.07, and 0.7 nM insulin. In vitro osteogenic capacity of TPCs (Alizarin Red staining, osteogenic mRNA expression, and alkaline phosphatase bioactivity) was assessed with 0, 0.07, and 0.7 nM insulin-supplemented osteogenic induction medium. Insulin (0.7 nM) significantly increased TPC proliferation after 3 days of monolayer culture. Alizarin Red staining of insulin-treated TPC osteogenic cultures demonstrated robust cell aggregation and mineralized matrix secretion, in a dose-dependent manner. Runx2, alkaline phosphatase, and Osteonectin mRNA and alkaline phosphatase bioactivity of insulin-treated TPC cultures were significantly higher at day 14 of osteogenesis compared to untreated controls. Addition of picropodophyllin (PPP), a selective IGF-I receptor inhibitor, mitigated the increased osteogenic capacity of TPCs, indicating that IGF-I signaling plays an important role. Our findings indicate that hyperinsulinemia may alter TPC phenotype and subsequently impact the quality of repair tendon tissue.

CTGF Attenuates Tendon-Derived Stem/Progenitor Cell Aging

Aged tendon-derived stem/progenitor cells (TSPCs) lead to age-related tendon disorders and impair tendon healing. However, the underlying molecular mechanisms of TSPC aging remain largely unknown. Here, we investigated the role of connective tissue growth factor (CTGF) in TSPC aging. CTGF protein and mRNA levels were markedly decreased in the aged TSPCs. Moreover, recombinant CTGF attenuates TSPC aging and restores the age-associated reduction of self-renewal and differentiation of TSPCs. In addition, cell cycle distribution of aged TSPCs was arrested in the G1/S phase while recombinant CTGF treatment promoted G1/S transition. Recombinant CTGF also rescued decreased levels of cyclin D1 and CDK4 and reduced p27^kip1 expression in aged TSPCs. Our results demonstrated that CTGF plays a vital role in TSPC aging and might be a potential target for molecular therapy of age-related tendon disorders.