(−)-Epigallocatechin gallate reduces transforming growth factor β-stimulated HSP27 induction through the suppression of stress-activated protein kinase/c-Jun N-terminal kinase in osteoblasts

Impact of Non-Invasive Physical Plasma on Heat Shock Protein Functionality in Eukaryotic Cells

Recently, biomedical research has increasingly investigated physical plasma as an innovative therapeutic approach with a number of therapeutic biomedical effects. It is known from radiation and chemotherapy that these applications can lead to the induction and activation of primarily cytoprotective heat shock proteins (HSP). HSP protect cells and tissues from physical, (bio)chemical, and physiological stress and, ultimately, along with other mechanisms, govern resistance and treatment failure. These mechanisms are well known and comparatively well studied in drug therapy. For therapies in the field of physical plasma medicine, however, extremely little data are available to date. In this review article, we provide an overview of the current studies on the interaction of physical plasma with the cellular HSP system.

Upregulation of TGF-β-induced HSP27 by HSP90 inhibitors in osteoblasts

Background

Heat shock protein (HSP) 90 functions as a molecular chaperone and is constitutively expressed and induced in response to stress in many cell types. We have previously demonstrated that transforming growth factor-β (TGF-β), the most abundant cytokine in bone cells, induces the expression of HSP27 through Smad2, p44/p42 mitogen-activated protein kinase (MAPK), p38 MAPK, and stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) in mouse osteoblastic MC3T3-E1 cells. This study investigated the effects of HSP90 on the TGF-β-induced HSP27 expression and the underlying mechanism in mouse osteoblastic MC3T3-E1 cells.

Methods

Clonal osteoblastic MC3T3-E1 cells were treated with the HSP90 inhibitors and then stimulated with TGF-β. HSP27 expression and the phosphorylation of Smad2, p44/p42 MAPK, p38 MAPK, and SAPK/JNK were evaluated by western blot analysis.

Result

HSP90 inhibitors 17-dimethylaminoethylamino-17-demethoxy-geldanamycin (17-DMAG) and onalespib significantly enhanced the TGF-β-induced HSP27 expression. TGF-β inhibitor SB431542 reduced the enhancement by 17-DMAG or onalespib of the TGF-β-induced HSP27 expression levels. HSP90 inhibitors, geldanamycin, onalespib, and 17-DMAG did not affect the TGF-β-stimulated phosphorylation of Smad2. Geldanamycin did not affect the TGF-β-stimulated phosphorylation of p44/p42 MAPK or p38 MAPK but significantly enhanced the TGF-β-stimulated phosphorylation of SAPK/JNK. Onalespib also increased the TGF-β-stimulated phosphorylation of SAPK/JNK. Furthermore, SP600125, a specific inhibitor for SAPK/JNK, significantly suppressed onalespib or geldanamycin’s enhancing effect of the TGF-β-induced HSP27 expression levels.

Conclusion

Our results strongly suggest that HSP90 inhibitors upregulated the TGF-β-induced HSP27 expression and that these effects of HSP90 inhibitors were mediated through SAPK/JNK pathway in osteoblasts.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-022-05419-1.

Osteoprotective Roles of Green Tea Catechins

Osteoporosis is the second most common disease only secondary to cardiovascular disease, with the risk of fracture increasing with age. Osteoporosis is caused by an imbalance between osteoblastogenesis and osteoclastogenesis processes. Osteoclastogenesis may be enhanced, osteoblastogenesis may be reduced, or both may be evident. Inflammation and high reactive oxygen enhance osteoclastogenesis while reducing osteoblastogenesis by inducing osteoblast apoptosis and suppressing osteoblastic proliferation and differentiation. Catechins, the main polyphenols found in green tea with potent anti-oxidant and anti-inflammatory properties, can counteract the deleterious effects of the imbalance of osteoblastogenesis and osteoclastogenesis caused by osteoporosis. Green tea catechins can attenuate osteoclastogenesis by enhancing apoptosis of osteoclasts, hampering osteoclastogenesis, and prohibiting bone resorption in vitro. Catechin effects can be directly exerted on pre-osteoclasts/osteoclasts or indirectly exerted via the modulation of mesenchymal stem cells (MSCs)/stromal cell regulation of pre-osteoclasts through activation of the nuclear factor kB (RANK)/RANK ligand (RANKL)/osteoprotegerin (OPG) system. Catechins also can enhance osteoblastogenesis by enhancing osteogenic differentiation of MSCs and increasing osteoblastic survival, proliferation, differentiation, and mineralization. The in vitro effects of catechins on osteogenesis have been confirmed in several animal models, as well as in epidemiological observational studies on human subjects. Even though randomized control trials have not shown that catechins provide anti-fracture efficacy, safety data in the trials are promising. A large-scale, placebo-controlled, long-term randomized trial with a tea regimen intervention of optimal duration is required to determine anti-fracture efficacy.

Effect of Long-Term Green Tea Polyphenol Supplementation on Bone Architecture, Turnover, and Mechanical Properties in Middle-Aged Ovariectomized Rats

We investigated the effects of 6-month green tea polyphenols (GTP) supplementation on bone architecture, turnover, and mechanical properties in middle-aged ovariectomized (OVX) rats. Female rats were sham-operated (n = 39, 13/group) or OVX (n = 143, 13/group). Sham-control and OVX-control rats (n = 39) receiving no GTP were assigned for sample collection at baseline, 3, or 6 months. The remaining OVX rats (n = 104) were randomized to 0.15%, 0.5%, 1%, and 1.5% (g/dL) GTP for 3 or 6 months. Blood and bone samples were collected. Relative to the OVX-control group, GTP (1% and 1.5%) lowered serum procollagen type 1 N-terminal propeptide at 3 and 6 months, C-terminal telopeptides of type I collagen at 3 months, and insulin-like growth factor-I at 6 months. GTP did not affect bone mineral content and density. At 6 months, no dose of GTP positively affected trabecular bone volume based on microCT, but a higher cortical thickness and improved biomechanical properties of the femur mid-diaphysis was observed in the 1.5% GTP-treated group. At 3 and 6 months, GTP (0.5%, 1%, and 1.5%) had lower rates of trabecular bone formation and resorption than the OVX-control group, but the inhibitory effects of GTP on periosteal and endocortical bone mineralization and formation at the tibial midshaft were only evident at 3 months. GTP at higher doses suppressed bone turnover in the trabecular and cortical bone of OVX rats and resulted in improved cortical bone structural and biomechanical properties, although it was not effective in preventing the ovariectomy-induced dramatic cancellous bone loss.

Catechins enhance skeletal muscle performance

Muscle-related disorders, such as sarcopenia and cachexia, caused by aging and chronic diseases can lead to the loss of muscle mass and strength to different degrees, severely affecting human health. Globally, tea is one of the three most popular beverages, and its major active ingredient catechins have been reported to delay muscular atrophy and enhance movement. However, currently, there is no systematic review to elaborate its roles and the associated mechanisms. This article reviews the (1) functions and mechanisms of catechins in the differentiation of myogenic stem cells, biogenesis of mitochondria, synthesis and degradation of proteins, regulation of glucose level, and metabolism of lipids in muscle cells; and (2) effect of catechins on the blood vessels, bones, and nerves that are closely related to the skeletal muscles. Catechins could prevent, mitigate, delay, and even treat muscle-related disorders caused by aging and diseases.

Heat shock protein 27 (HSPB1) suppresses the PDGF-BB-induced migration of osteoblasts

Heat shock protein 27 (HSP27/HSPB1), one of the small heat shock proteins, is constitutively expressed in various tissues. HSP27 and its phosphorylation state participate in the regulation of multiple physiological and pathophysiological cell functions. However, the exact roles of HSP27 in osteoblasts remain unclear. In the present study, we investigated the role of HSP27 in the platelet-derived growth factor‑BB (PDGF‑BB)‑stimulated migration of osteoblast-like MC3T3-E1 cells. PDGF-BB by itself barely upregulated the expression of HSP27 protein, but stimulated the phosphorylation of HSP27 in these cells. The PDGF-BB‑induced cell migration was significantly downregulated by HSP27 overexpression. The PDGF-BB-induced migrated cell numbers of the wild‑type HSP27-overexpressing cells and the phospho‑mimic HSP27-overexpressing (3D) cells were less than those of the unphosphorylatable HSP27-overexpressing (3A) cells. PD98059, an inhibitor of MEK1/2, SB203580, an inhibitor of p38 mitogen-activated protein kinase, and SP600125, an inhibitor of stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) reduced the PDGF-BB-induced migration of these cells, whereas Akt inhibitor or rapamycin, an inhibitor of upstream kinase of p70 S6 kinase (mTOR), barely affected the migration. However, the PDGF-BB-induced phosphorylation of p44/p42 MAPΚ, p38 MAPK and SAPK/JNK was not affected by HSP27 overexpression. There were no significant differences in the phosphorylation of p44/p42 MAPΚ, p38 MAP kinase or SAPK/JNK between the 3D cells and the 3A cells. These results strongly suggest that HSP27 functions as a negative regulator in the PDGF-BB-stimulated migration of osteoblasts, and the suppressive effect is amplified by the phosphorylation state of HSP27.

Green Tea Extract (GTE) improves differentiation in human osteoblasts during oxidative stress

Background

Oxidative stress is involved in the pathogenesis of bone diseases such as osteoporosis, which has a high coincidence with fractures in elderly. Several studies showed positive effects of herbal bioactive substances on oxidative stress. This study analyses the effect of green tea extract (GTE) Sunphenon 90LB on primary human osteoblasts differentiation and viability during H₂O₂-induced oxidative stress. Moreover, it was analyzed, whether GTE acts during the HO-1 signaling pathway.

Methods

Human osteoblasts were isolated from femoral heads of patients undergoing total hip replacement. Beneficial effects of GTE on osteoblasts were examined in a dose- and time-dependent manner. Furthermore, GTE was given before, simultaneous with and after induction of oxidative stress with 1 mM H₂O₂ to simulate prophylactic, acute and therapeutic use, respectively. Cell damage was measured by LDH leakage and cell viability by MTT assay. Flow cytometry was applied to measure formation of Reactive Oxygen Species by using 2`7`-dichlorofluorescein-diacetate. The formation of Extracellular Matrix after differentiation with GTE supplementation during oxidative stress was visualized with von Kossa and Alizarin Red staining. Last one was additionally photometrically quantified. To assess the effects of H₂O₂ and GTE on the osteogenic genes, RT-PCR was performed. To evaluate the intramolecular influence of GTE after the stimulation the protein levels of HO-1 were analyzed.

Results

Stimulation of primary human osteoblasts with low doses of GTE during oxidative stress over 21 days improved mineralization. Furthermore, GTE supplementation in combination with H₂O₂ leads to a higher gene expression of osteocalcin and collagen1α1 during osteoblasts differentiation. Both are important for bone quality. Pre-incubation, co-incubation and post-incubation of osteoblasts with high doses of GTE protect the osteoblasts against acute oxidative stress as shown by increased cell viability, decreased LDH leakage, and reduced production of intracellular free radicals. Functional analysis revealed an increased HO-1 protein synthesis after stimulation with GTE.

Conclusions

Incubation of human primary osteoblasts with GTE significantly reduces oxidative stress and improves cell viability. GTE also has a beneficial effect on ECM production which might improve the bone quality. Our findings suggest that dietary supplementation of GTE might reduce inflammatory events in bone-associated diseases such as osteoporosis.

(-)-Epicatechin gallate (ECG) stimulates osteoblast differentiation via Runt-related transcription factor 2 (RUNX2) and transcriptional coactivator with PDZ-binding motif (TAZ)-mediated transcriptional activation

Osteoporosis is a degenerative bone disease characterized by low bone mass and is caused by an imbalance between osteoblastic bone formation and osteoclastic bone resorption. It is known that the bioactive compounds present in green tea increase osteogenic activity and decrease the risk of fracture by improving bone mineral density. However, the detailed mechanism underlying these beneficial effects has yet to be elucidated. In this study, we investigated the osteogenic effect of (-)-epicatechin gallate (ECG), a major bioactive compound found in green tea. We found that ECG effectively stimulates osteoblast differentiation, indicated by the increased expression of osteoblastic marker genes. Up-regulation of osteoblast marker genes is mediated by increased expression and interaction of the transcriptional coactivator with PDZ-binding motif (TAZ) and Runt-related transcription factor 2 (RUNX2). ECG facilitates nuclear localization of TAZ through PP1A. PP1A is essential for osteoblast differentiation because inhibition of PP1A activity was shown to suppress ECG-mediated osteogenic differentiation. Taken together, the results showed that ECG stimulates osteoblast differentiation through the activation of TAZ and RUNX2, revealing a novel mechanism for green tea-stimulated osteoblast differentiation.

Tea and bone health: steps forward in translational nutrition

Osteoporosis is a major health problem in the aging population worldwide. Cross-sectional and retrospective evidence indicates that tea consumption may be a promising approach in mitigating bone loss and in reducing risk of osteoporotic fractures among older adults. Tea polyphenols enhance osteoblastogenesis and suppress osteoclastogenesis in vitro. Animal studies reveal that intake of tea polyphenols have pronounced positive effects on bone as shown by higher bone mass and trabecular bone volume, number, and thickness and lower trabecular separation via increasing bone formation and inhibition of bone resorption, resulting in greater bone strength. These osteoprotective effects appear to be mediated through antioxidant or antiinflammatory pathways along with their downstream signaling mechanisms. A short-term clinical trial of green tea polyphenols has translated the findings from ovariectomized animals to postmenopausal osteopenic women through evaluation of bioavailability, safety, bone turnover markers, muscle strength, and quality of life. For future studies, preclinical animal studies to optimize the dose of tea polyphenols for maximum osteoprotective efficacy and a follow-up short-term dose-response trial in postmenopausal osteopenic women are necessary to inform the design of randomized controlled studies in at-risk populations. Advanced imaging technology should also contribute to determining the effective dose of tea polyphenols in achieving better bone mass, microarchitecture integrity, and bone strength, which are critical steps for translating the putative benefit of tea consumption in osteoporosis management into clinical practice and dietary guidelines.

Unphosphorylated heat shock protein 27 suppresses fibroblast growth factor‑2‑stimulated vascular endothelial growth factor release in osteoblasts

Heat shock protein 27 (HSP27) also known as heat shock protein β1 (HSPB1) is a member of the family of small heat shock proteins ubiquitously expressed in all tissues. It has previously been demonstrated that HSP27 regulated the synthesis of osteocalcin and interleukin‑6 in osteoblast‑like MC3T3‑E1 cells. In the present study, the effect of HSP27 on basic fibroblast growth factor (FGF‑2)‑stimulated vascular endothelial growth factor (VEGF) synthesis in MC3T3‑E1 cells, was observed. The levels of VEGF release stimulated by FGF‑2 in the HSP27‑overexpressing MC3T3‑E1 cells were significantly lower compared with those in the control cells. In addition, the levels of VEGF release stimulated by FGF-2 in the phosphomimic HSP27-overexpressing cells were significantly higher compared with those in the non‑phosphorylatable HSP27‑overexpressing cells. Furthermore, no significant differences were observed in the FGF‑2‑induced phosphorylation levels of p44/p42 mitogen‑activated protein (MAP) kinase, p38 MAP kinase, stress‑activated protein kinase/c‑Jun N‑terminal kinase (SAPK/JNK) or p70 S6 kinase among the four types of transfected cells. These results suggested that unphosphorylated HSP27 attenuated the FGF‑2‑stimulated VEGF synthesis in osteoblasts.

Response of preosteoblasts to thermal stress conditioning and osteoinductive growth factors

Conditioning protocols involving mechanical stress independently or with chemical cues such as growth factors (GFs) possess significant potential to enhance bone regeneration. However, utilization of thermal stress conditioning alone or with GFs for bone therapy has been under-investigated. In this study, a preosteoblast cell line (MC3T3-E1) was exposed to treatment with water bath heating (44°C, 4 and 8 min) and osteoinductive GFs (bone morphogenetic protein-2 and transforming growth factor-β1) individually or in combination to investigate whether these stimuli could promote induction of bone-related markers, an angiogenic factor, and heat shock proteins (HSPs). Cells remained viable when heating durations were less than 20 min at 40ºC, 16 min at 42ºC, and 10 min at 44ºC. Increasing heating duration at 44°C, promoted gene expression of HSPs, osteocalcin (OCN), and osteopontin (OPN) at 8 h post-heating (PH). Heating in combination with GFs caused the greatest gene induction of osteoprotegerin (OPG; 6.9- and 1.6-fold induction compared to sham-treated and GF only treated groups, respectively) and vascular endothelial growth factor (VEGF; 16.0- and 1.6-fold compared to sham and GF-only treated groups, respectively) at 8 h PH. Both heating and GFs independently suppressed the matrix metalloproteinase-9 (MMP-9) gene. GF treatment caused a more significant decrease in MMP-9 protein secretion to non-detectable levels compared to heating alone at 72 h PH. Secretion of OCN, OPN, and OPG increased with the addition of GFs but diminished with heating as measured by ELISA at 72 h PH. These results suggest that conditioning protocols utilizing heating and GFs individually or in combination can induce HSPs, bone-related proteins, and VEGF while also causing downregulation of osteoclastic activity, potentially providing a promising bone therapeutic strategy.

Alternative therapies for the prevention and treatment of osteoporosis

Osteoporosis is a medical condition that affects millions of men and women. People with this condition have low bone mass, which places them at increased risk for bone fracture after minor trauma. The surgeries and treatments required to repair and heal bone fractures involve long recovery periods and can be expensive. Because osteoporosis occurs frequently in the elderly, the financial burden it places on society is likely to be large. In the United States, the Food and Drug Administration has approved several drugs for use in the prevention and treatment of osteoporosis. However, all of the currently available agents have severe side effects that limit their efficacy and underscore the urgent need for new treatment options. One promising approach is the development of alternative (nonpharmaceutical) strategies for bone maintenance, as well as for the prevention and treatment of osteoporosis. This review examines the currently available nonpharmaceutical alternatives that have been evaluated in in vitro and in vivo studies. Certain plants from the following families have shown the greatest benefits on bone: Alliceae, Asteraceae, Thecaceae, Fabaceae, Oleaceae, Rosaceae, Ranunculaceae, Vitaceae, Zingiberaceae. The present review discusses the most promising findings from studies of these plant families.

Regulation by heat shock protein 27 of osteocalcin synthesis in osteoblasts

We have previously reported that various stimuli, including sphingosine 1-phosphate, are able to induce heat shock protein (HSP) 27 in osteoblast-like MC3T3-E1 cells. However, the precise role of HSP27 in bone metabolism has not been satisfactory clarified. In this study, we investigated the effect of HSP27 on osteocalcin synthesis induced by bone morphogenetic protein (BMP)-4 or T₃ in these cells. In MC3T3-E1 cells, pretreatment with sphingosine 1-phosphate, sodium arsenite, or heat stress caused the attenuation of osteocalcin synthesis induced by BMP-4 or T₃ with concurrent HSP27 induction. To further investigate the effect of HSP27, we established stable HSP27-transfected cells. The osteocalcin synthesis was significantly reduced in the stable HSP27-transfected MC3T3-E1 cells and normal human osteoblasts compared with empty-vector transfected cells. On the other hand, anisomycin, a p38 MAPK activator, caused the phosphorylation of HSP27 in both sphingosine 1-phosphate-stimulated untransfected MC3T3-E1 cells and HSP27-transfected MC3T3-E1 cells. An immunofluorescence microscopy study showed that the phosphorylated HSP27 induced by anisomycin concentrated perinuclearly in these cells, in which it colocalized with the endoplasmic reticulum. We also established stable mutant-HSP27-transfected cells. Osteocalcin synthesis induced by either BMP-4 or T₃ was markedly suppressed in the nonphosphorylatable HSP27-overexpressing MC3T3-E1 cells compared with the phosphomimic HSP27-overexpressing cells. In contrast, the matrix mineralization was more obvious in nonphosphorylatable HSP27-overexpressing cells than that in phosphomimic HSP27-overexpressing cells. Taken together, these results strongly suggest that unphosphorylated HSP27 has an inhibitory effect on osteocalcin synthesis, but has a stimulatory effect on mineralization, in osteoblasts.

Green tea and bone health: Evidence from laboratory studies

Osteoporosis is a major health problem in the elderly. Epidemiological evidence has shown an association between tea consumption and the prevention of bone loss in the elderly population. Ingestion of green tea and green tea bioactive compounds may be beneficial in mitigating bone loss of this population and decreasing their risk of osteoporotic fractures. This review describes the effect of green tea with its bioactive components on bone health with an emphasis on the following: (i) the etiology of osteoporosis, (ii) evidence of osteo-protective impacts of green tea on bone mass and microarchitecture in various bone loss models in which induced by aging, sex hormone deficiency, and chronic inflammation, (iii) discussion of impacts of green tea on bone mass in two obesity models, (iv) observation of short-term green tea supplementation given to postmenopausal women with low bone mass, (v) possible mechanisms for the osteo-protective effects of green tea bioactive compounds, and (vi) a summary and future research direction of green tea and bone health.

Green tea polyphenol epigallocatechin-3-gallate: inflammation and arthritis. [corrected]

A number of factors including inflammation and oxidative stress are believed to play a role in the development of chronic joint diseases. Green tea has become a popular drink and is consumed throughout the world. Extracts of green tea and polyphenols present therein have been shown to inhibit the inflammatory responses in vitro in different cell types and the development of arthritis in animal model studies. There is considerable evidence that (-)-epigallocatechin-3-gallate (EGCG), the predominant green tea polyphenol which mimic its effects, inhibits enzyme activities and signal transduction pathways that play important roles in inflammation and joint destruction in arthritis. After oral consumption EGCG become bioavailable and proteomic studies suggest that EGCG may directly interact with a large set of protein targets and alter the physiological response of the cells. Taken together these and other studies identify and support the use of EGCG as a possible chemopreventive agent with a potential to inhibit the development of arthritis. Here we review the biological effects of EGCG in an attempt to understand its pivotal molecular targets that directly affect the inflammation and joint destruction process for prevention and/or for the development of new therapeutics for arthritis in humans.

Molecular mechanism of hesperetin-7-O-glucuronide, the main circulating metabolite of hesperidin, involved in osteoblast differentiation

Citrus fruit hesperidin is hydrolyzed by gut microflora into aglycone form (hesperetin) and then conjugated mainly into glucuronides. We previously demonstrated that hesperetin enhanced osteoblast differentiation. In this study, we examined the effect of hesperetin-7-O-glucuronide (Hp7G) on primary rat osteoblast proliferation and differentiation. The impact of Hp7G on specific bone signaling pathways was explored. Osteoblasts were exposed to physiological concentrations of 1 (Hp7G1) and 10 (Hp7G10) microM of conjugate. The glucuronide did not affect proliferation but enhanced differentiation by significantly increasing alkaline phosphatase (ALP) activity from day 14 of exposure. Hp7G significantly induced mRNA expression of ALP, Runx2, and Osterix after 48 h of exposure. Moreover, phosphorylation of Smad1/5/8 was enhanced by Hp7G, while ERK1/2 remained unchanged after 48 h. Hp7G decreased RANKL gene expression. These results suggest that Hp7G may regulate osteoblast differentiation through Runx2 and Osterix stimulation, and might be implicated in the regulation of osteoblast/osteoclast communication.

Green tea and bone metabolism

Osteoporosis is a major health problem in both elderly women and men. Epidemiological evidence has shown an association between tea consumption and the prevention of age-related bone loss in elderly women and men. Ingestion of green tea and green tea bioactive compounds may be beneficial in mitigating bone loss of this population and decreasing their risk of osteoporotic fractures. This review describes the effect of green tea or its bioactive components on bone health, with an emphasis on (i) the prevalence and etiology of osteoporosis; (ii) the role of oxidative stress and antioxidants in osteoporosis; (iii) green tea composition and bioavailability; (iv) the effects of green tea and its active components on osteogenesis, osteoblastogenesis, and osteoclastogenesis from human epidemiological, animal, as well as cell culture studies; (v) possible mechanisms explaining the osteoprotective effects of green tea bioactive compounds; (vi) other bioactive components in tea that benefit bone health; and (vii) a summary and future direction of green tea and bone health research and the translational aspects. In general, tea and its bioactive components might decrease the risk of fracture by improving bone mineral density and supporting osteoblastic activities while suppressing osteoclastic activities.