Estrogen alone or in combination with parathyroid hormone can decrease vertebral MEF2 and sclerostin expression and increase vertebral bone mass in ovariectomized rats

Network pharmacology and molecular docking approach to elucidate the mechanisms of Liuwei Dihuang pill in diabetic osteoporosis

Background

Diabetic osteoporosis (DOP) is one of the chronic complications of diabetes mellitus, but without a standardized treatment plan till now. Liuwei Dihuang pill (LDP) has gradually exerted a remarkable effect on DOP in recent years; its specific mechanism is not clear yet.

Methods

We adopted network pharmacology approaches, including multi-database search, pharmacokinetic screening, network construction analysis, gene ontology enrichment analysis, Kyoto Encyclopedia of Genes and Genomes pathway analysis and molecular docking to elaborate the active components, signaling pathways and potential mechanisms of LDP in the treatment of DOP.

Results

Twenty-seven active ingredients and 55 related disease targets have been found through integrated network pharmacology. Functional enrichment analysis shows that five key active ingredients, including beta-sitosterol, stigmasterol, diosgenin, tetrahydroalstonine, and kadsurenone, may give full scope to insulin secretion estrogen-level raising and angiogenesis in biological process through the pivotal targets. In addition, the underlying effect of PI3K/AKT/FOXO and VEGF pathways is also suggested in the treatment.

Conclusion

Based on systematic network pharmacology methods, we predicted the basic pharmacological effects and potential mechanisms of LDP in the treatment of DOP, revealing that LDP may treat DOP through multiple targets and multiple signaling pathways, which provide evidence for the further study of pharmacological mechanism and broader clinical thinking.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13018-022-03194-2.

Gestational and lactational exposure to BPA or BPS has minimal effects on skeletal outcomes in adult female mice

Bisphenol-A (BPA) and bisphenol-S (BPS) are estrogen disrupting chemicals (EDCs) found in the environment and common household items. Estrogen is a primary hormonal regulator of bone growth and development; however, the impact of gestational BPA or BPS exposure on skeletal health of offspring remains relatively unknown. In this longitudinal study, adult female mice were randomized into three groups: 200 μg BPA/kg BW (BPA), 200 μg BPS/kg BW (BPS) or control (CON). Animals in each group were further randomized to exercise treatment (EX) or sedentary (SED) control, resulting in six overall groups. BPA/BPS/CON and EX/SED treatment were initiated prior to mating and continued through mating, gestation, and lactation. One female offspring from each dam (n = 6/group) was assessed at 17 weeks of age to evaluate effects of EDC exposure on the adult skeleton. Cortical geometry of the mid-diaphysis and trabecular microarchitecture of the distal femur were assessed via micro-computed tomography. Biomechanical strength and mineral apposition rate of the femoral diaphysis were assessed via three-point bending and dynamic histomorphometry, respectively. Sclerostin expression was measured using immunohistochemistry. Two-factor ANOVA or ANCOVA were used to determine the effects of maternal exercise and BPA or BPS exposure on trabecular and cortical bone outcomes, respectively. Consistent with prior studies, there were no significant differences in body weight, femoral length, cortical geometry, trabecular microarchitecture, or biomechanical strength between groups in female offspring. In conclusion, gestational BPA exposure and maternal exercise have minimal impact on skeletal outcomes in female adult offspring.

Voluntary Wheel Running Partially Compensates for the Effects of Global Estrogen Receptor-α Knockout on Cortical Bone in Young Male Mice

Estrogen receptor-α knockout (ERKO) in female, but not male, mice results in an impaired osteogenic response to exercise, but the mechanisms behind this ability in males are unknown. We explored the main and interactive effects of ERKO and exercise on cortical geometry, trabecular microarchitecture, biomechanical strength, and sclerostin expression in male mice. At 12 weeks of age, male C57BL/6J ERKO and WT animals were randomized into two groups: exercise treatment (EX) and sedentary (SED) controls, until 22 weeks of age. Cortical geometry and trabecular microarchitecture were measured via μCT; biomechanical strength was assessed via three-point bending; sclerostin expression was measured via immunohistochemistry. Two-way ANOVA was used to assess sclerostin expression and trabecular microarchitecture; two-way ANCOVA with body weight was used to assess cortical geometry and biomechanical strength. ERKO positively impacted trabecular microarchitecture, and exercise had little effect on these outcomes. ERKO significantly impaired cortical geometry, but exercise was able to partially reverse these negative alterations. EX increased cortical thickness regardless of genotype. There were no effects of genotype or exercise on sclerostin expression. In conclusion, male ERKO mice retain the ability to build bone in response to exercise, but altering sclerostin expression is not one of the mechanisms involved.

Osteokines and Bone Markers at Rest and following Plyometric Exercise in Pre- and Postmenopausal Women

The effect of plyometric exercise on bone biomarkers has been studied in pediatric and young adult populations in order to better understand how exercise influences bone homeostasis. However, there are no such data in postmenopausal women, a group characterized by an uncoupling of the bone resorption-formation cycle. This study examined the serum concentrations of sclerostin, dickkopf-1 (DKK1), c-terminal crosslinking telopeptides of type I collagen (CTXI), and procollagen type I amino-terminal propeptide (PINP) at rest and following a single bout of plyometric exercise in 20 premenopausal (23.1 ± 2.3 years) and 20 postmenopausal women (57.9 ± 4.3 years). The exercise consisted of 128 jumps, organized into 5 circuit stations. Blood samples were obtained prior to and 5 min, 1 h, and 24 h postexercise. At rest, postmenopausal women had significantly higher sclerostin and CTXI, but lower DKK1 than premenopausal women. Sclerostin increased 5 min postexercise only in the premenopausal group. DKK1 decreased 24 h postexercise in the premenopausal women while it decreased 1 h postexercise in the postmenopausal women. In both groups, CTXI did not change across time and PINP decreased 5 min and 1 h postexercise (p < 0.05). The PINP/CTXI ratio decreased 5 min and 1 h postexercise then significantly increased 24 h postexercise only in premenopausal women. These results indicate that although plyometric exercise is effective in eliciting osteoanabolic effects in younger women; such an effect is not evident in postmenopausal women.

Prevention of bone loss and improvement of pain-related behavior in hind limb-unloaded mice by administration of teriparatide and bisphosphonate

OBJECTIVES

There are few reports on the comparison between teriparatide (PTH) and bisphosphonate (BP) in terms of osteoporosis pain-related behavior and immunohistochemical findings. The aims of this study were to evaluate skeletal pain associated with osteoporosis and to examine the inhibitory effect of PTH and BP on pain and bone loss in hind limb-unloaded (HU) mice. The mechanism of osteoporotic pain in HU mice was evaluated by examining pain-related behavior and immunohistochemical findings. The effects of PTH and alendronate (ALN), a potent osteoclast inhibitor, on these parameters were also assessed.

METHODS

Eight-week-old male ddY mice were tail-suspended for 2 weeks and assigned to four groups: hind limb-loaded (HL) mice with only tail suspension treated with vehicle; HU mice with tail suspension treated with vehicle; HU mice treated with PTH; and HU mice treated with ALN. Starting immediately after reloading, vehicle, PTH, or ALN was injected subcutaneously. After a 2-week treatment, mechanical sensitivity was examined using von Frey filaments. Bilateral hind limbs were removed for micro-computed tomography, immunohistochemical analysis, and messenger RNA (mRNA) expression analysis.

RESULTS

HU mice with tail suspension developed bone loss and mechanical hyperalgesia in the hind limbs. The HU mice showed an increased osteoclasts and sclerostin-positive cells in the hind limb bone. Furthermore, PTH and ALN both prevented HU-induced bone loss and mechanical hyperalgesia in the osteoporotic animal models. Histological examination of the hind limb bone revealed that, similar to ALN, PTH inhibited the osteoclasts and sclerostin-positive cells. The mRNA levels of TNFα and IL-6 tended to decrease with ALN or PTH treatment compared with those without any treatment.

CONCLUSIONS

Treatment with PTH as well as BP prevented bone loss, mechanical hyperalgesia, osteoclast increase, and osteocyte increase. Similar to BP, the inhibitory effect of PTH on osteoclasts might contribute to the improvement of skeletal pain.

Global estrogen receptor-α knockout has differential effects on cortical and cancellous bone in aged male mice

Estrogen receptor-α knockout (ERKO) in female rodents results in bone loss associated with increased osteocyte sclerostin expression; whether this also occurs in males is unknown. Here, we examined the effects of ERKO on femoral cortical geometry, trabecular microarchitecture, and osteocyte sclerostin expression of the femur and lumbar vertebrae. At 14 months of age, male ERKO and wild-type (WT) littermates ( n = 6 per group) were sacrificed, and femora and vertebra were collected. Cortical geometry and trabecular microarchitecture were assessed via micro-computed tomography; osteocyte sclerostin expression was assessed via immunohistochemistry. ANCOVA with body weight was used to compare ERKO and WT for cortical geometry; t-tests were used for all other outcomes. Regardless of skeletal site, ERKO mice had greater trabecular bone volume and trabecular number and decreased trabecular separation compared with WT. In the femoral diaphysis, ERKO had lower total area, cortical area, and cortical thickness compared with WT. The percentage of sclerostin+ osteocytes was increased in ERKO animals in cortical bone but not in cancellous bone of the femur or the lumbar vertebrae. In conclusion, ERKO improved trabecular microarchitecture in aged male mice, but negatively altered femoral cortical geometry associated with a trend towards increased cortical sclerostin expression.

Gender-Affirming Hormone Treatment Decreases Bone Turnover in Transwomen and Older Transmen

Sex steroids play a key role in bone turnover and preserving BMD; hence, gender-affirming hormone treatment (HT) in transgender people affects bone metabolism. Most studies have looked into the effect of HT on changes in BMD; however, they do not provide insights into changes in bone metabolism caused by HT. This study investigated changes in bone turnover markers (BTMs) and sclerostin, as well as their correlations with change in BMD in transwomen and transmen during the first year of HT. Transwomen received estradiol and antiandrogens; transmen received testosterone. Sclerostin; P1NP; alkaline phosphatase (ALP); CTx; and BMD of the total hip, the femoral neck, and the lumbar spine were evaluated at baseline and after 1 year of HT. There were 121 transwomen (median age 30 years, interquartile range [IQR] 24 to 41 years) and 132 transmen (median age 24 years, IQR 21 to 33 years) included in the study. In transwomen, ALP decreased in 19% (95% CI, -21 to-16), CTx in 11% (95% CI, -18 to-4), and sclerostin in 8% (95%CI, -13 to-4) of study participants after 1 year of HT. In contrast, in transmen P1NP, ALP, and sclerostin increased in 33% (95% CI, 24 to 42), 16% (95% CI, 12 to 20), and 15% (95% CI, 10 to 20) of study participants, respectively, after 1 year of HT. No age differences were seen in transwomen, whereas in transmen aged ≥50 years a decrease in all BTMs was found in contrast with the other age groups. These transmen had low estrogen concentration at the start of HT based on their postmenopausal state before the start of HT; their estradiol concentrations increased during testosterone treatment. Changes in BTMs and BMD were weakly correlated (correlation coefficient all <0.30). To conclude, 1 year of HT resulted in decreased bone turnover in transwomen and older transmen, whereas it increased in younger transmen. The decrease in bone resorption in older transmen shows the importance of estrogen as a key regulator of bone turnover. © 2019 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals, Inc.

MEF2 signaling and human diseases

The members of myocyte Enhancer Factor 2 (MEF2) protein family was previously believed to function in the development of heart and muscle. Recent reports indicate that they are also closely associated with development and progression of many human diseases. Although their role in cancer biology is well established, the molecular mechanisms underlying their action is yet largely unknown. MEF2 family is closely associated with various signaling pathways, including Ca²⁺ signaling, MAP kinase signaling, Wnt signaling, PI3K/Akt signaling, etc. microRNAs also contribute to regulate the activities of MEF2. In this review, we summarize the known molecular mechanism by which MEF2 family contribute to human diseases.

N-cadherin restrains PTH repressive effects on sclerostin/SOST by regulating LRP6-PTH1R interaction

Sclerostin/SOST is a robust negative regulator of bone formation. Loss-of-function mutations of the sclerostin gene (SOST) cause sclerosteosis and Van Buchem disease characterized by bone overgrowth. Mediated by myocyte enhancer factor 2 (MEF2) transcription factors, parathyroid hormone (PTH) suppresses SOST expression through formation of complexes of parathyroid hormone-parathyroid hormone-related peptide receptor 1 (PTH1R) and lipoprotein receptor-related protein 6 (LRP6). N-cadherin has been shown to negatively regulate Wnt/β-catenin and PTH induced, protein kinase-dependent β-catenin signaling. Here, we investigated whether N-cadherin mediates the inhibitory effects of PTH on sclerostin/SOST. In vitro, overexpression of N-cadherin resulted in blunted PTH suppressive effects on sclerostin/SOST expression, as detected by immunoblot and qPCR analysis; PTH-induced downregulation of MEF2A, C, and D was impaired by N-cadherin; and N-cadherin reduced LRP6-PTHR1 interaction and endocytosis in response to PTH. In vivo, intermittent PTH (iPTH)-induced suppression of sclerostin/SOST was accentuated in Dmp1-cre; Cdh2^f/f (Cdh2^ΔDmp1 ) mice, compared with Cdh2^f/f mice. Additionally, iPTH had greater bone anabolic effects in Cdh2^ΔDmp1 mice compared to Cdh2^f/f mice. These data indicate that N-cadherin negatively mediates PTH suppressive effects on sclerostin/SOST by regulating LRP6-PTHR1 interaction, ultimately influencing PTH anabolic effects on bone.

Oestrogen and parathyroid hormone alleviate lumbar intervertebral disc degeneration in ovariectomized rats and enhance Wnt/β-catenin pathway activity

To investigate the mitigation effect and mechanism of oestrogen and PTH on disc degeneration in rats after ovariectomy, as well as on Wnt/β-catenin pathway activity, thirty 3-month-old rats were ovariectomized and divided into three groups. Ten additional rats were used as controls. Eight weeks later, the rats were administered oestrogen or PTH for 12 weeks, and then discs were collected for tests. Results showed that nucleus pulposus cells in the Sham group were mostly notochord cells, while in the OVX group, cells gradually developed into chondrocyte-like cells. Oestrogen or PTH could partly recover the notochord cell number. After ovariectomy, the endplate roughened and endplate porosity decreased. After oestrogen or PTH treatment, the smoothness and porosity of endplate recovered. Compared with the Sham group, Aggrecan, Col2a and Wnt/β-catenin pathway expression in OVX group decreased, and either oestrogen or PTH treatment improved their expression. The biomechanical properties of intervertebral disc significantly changed after ovariectomy, and oestrogen or PTH treatment partly recovered them. Disc degeneration occurred with low oestrogen, and the underlying mechanisms involve nutrition supply disorders, cell type changes and decreased Wnt/β-catenin pathway activity. Oestrogen and PTH can retard disc degeneration in OVX rats and enhance Wnt/β-catenin pathway activity in nucleus pulposus.

Naringin ameliorates bone loss induced by sciatic neurectomy and increases Semaphorin 3A expression in denervated bone

Naringin maintains bone mass in various osteoporosis models, while its effect on bone in disuse osteoporosis has not been reported. The present study explores whether naringin can prevent disuse osteoporosis induced by unilateral sciatic neurectomy (USN) and whether the Semaphorin 3A-induced Wnt/β-catenin signalling pathway is involved in the osteoprotection of naringin. Naringin dose-dependently prevented the deterioration of bone mineral density (BMD), trabecular structure and biomechanical strength in femur due to USN. Naringin increased bone formation but inhibited resorption, as indicated by bone-turnover markers in blood and urine and the histological staining of Osteocalcin (OCN) and tartrate-resistant acid phosphatase (TRAP) in femur. Semaphorin 3A (Sema3A) and active β-catenin protein decreased after USN and could be restored by naringin to the levels of the sham-operated rats. In addition, naringin in vitro promoted the differentiation of osteoblasts and inhibited osteoclastic differentiation. Our studies suggest that the down-regulation of Sema3A and the subsequent inactivation of Wnt/β-catenin signalling may be some of the mechanisms involved in USN-induced osteoporosis. Naringin could increase the expression of Sema3A and the activation of Wnt/β-catenin signalling to prevent disuse osteoporosis induced by denervation. Thus, naringin functions in bone maintenance and could be a promising therapeutic alternative in preventing disuse osteoporosis.

The effects of strength training and raloxifene on bone health in aging ovariectomized rats

The aim of this study was to investigate the effects of strength training (ST) and raloxifene (Ral), alone or in combination, on the prevention of bone loss in an aging estrogen-deficient rat model. Aging Wistar female rats were ovariectomized at 14months and allocated to four groups: (1) non-trained and treated with vehicle, NT-Veh; (2) strength training and treated with vehicle, ST-Veh; (3) non-trained and treated with raloxifene, NT-Ral; and (4) strength training and treated with raloxifene, ST-Ral. ST was performed on a ladder three times per week and Ral was administered daily by gavage (1mg/kg/day), both for 120days. Areal bone mineral density (aBMD), strength, microarchitecture, and biomarkers (osteocalcin, OCN; osteoprotegerin, OPG; and tartrate-resistant acid phosphatase, TRAP) were assessed. Immunohistochemistry was performed for runt-related transcription factor 2 (RUNX2), osterix (OSX), OCN, OPG, TRAP, and receptor activator of nuclear factor kappa-B ligand (RANKL). The rats that performed ST (ST-Veh) or were treated with Ral (NT-Ral) showed significant improvements in aBMD (p=0.001 and 0.004), bone strength (p=0.001), and bone microarchitecture, such as BV/TV (%) (p=0.001), BS/TV (mm(2)/mm(3)) (p=0.023 and 0.002), Conn.Dn (1/mm(3)) (p=0.001), Tb.N (1/mm) (p=0.012 and 0.011), Tb.Th (1/mm) (p=0.001), SMI (p=0.001 and 0.002), Tb.Sp (p=0.001), and DA (p=0.002 and 0.007); there was also a significant decrease in plasma levels of OCN (p=0.001 and 0.002) and OPG (p=0.003 and 0.014), compared with animals in the NT-Veh group. Ral, with or without ST, promoted an increased immunolabeling pattern for RUNX2 (p=0.0105 and p=0.0006) and OSX (p=0.0105), but a reduced immunolabeling pattern for TRAP (p=0.0056) and RANKL (p=0.033 and 0.004). ST increased the immunolabeling pattern for RUNX2 (p=0.0105), and association with Ral resulted in an increased immunolabeling pattern for OPG (p=0.0034) and OCN (p=0.0024). In summary, ST and Ral administration in aged, estrogen-deficient Wistar female rats is associated with a decrease in bone turnover marker plasma levels, increased activity of cells that promote osteoblastogenesis, and decreased activity of cells that promote osteoclastogenesis; these are correlated with higher aBMD, bone strength, and bone microarchitecture at the femoral neck. The results indicate that strength training and Ral are potential tools to reduce the risk of fractures at clinically relevant sites.

Lipoprotein receptor-related protein 6 is required for parathyroid hormone-induced Sost suppression

Parathyroid hormone (PTH) suppresses the expression of the bone formation inhibitor sclerostin (Sost) in osteocytes by inducing nuclear accumulation of histone deacetylases (HDACs) to inhibit the myocyte enhancer factor 2 (MEF2)-dependent Sost bone enhancer. Previous studies revealed that lipoprotein receptor-related protein 6 (LRP6) mediates the intracellular signaling activation and the anabolic bone effect of PTH. Here, we investigated whether LRP6 mediates the inhibitory effect of PTH on Sost using an osteoblast-specific Lrp6-knockout (LRP6-KO) mouse model. An increased level of Sost mRNA expression was detected in femur tissue from LRP6-KO mice, compared to wild-type littermates. The number of osteocytes expressing sclerostin protein was also increased in bone tissue of LRP6-KO littermates, indicating a negative regulatory role of LRP6 on Sost/sclerostin. In wild-type littermates, intermittent PTH treatment significantly suppressed Sost mRNA expression in bone and the number of sclerostin(+) osteocytes, while the effect of PTH was much less significant in LRP6-KO mice. Additionally, PTH-induced downregulation of MEF2C and 2D, as well as HDAC changes in osteocytes, were abrogated in LRP6-KO mice. These data indicate that LRP6 is required for PTH suppression of Sost expression.

Transient Effect of 17β-estradiol on Osteoporosis in Ovariectomized Rats Accompanied with Unilateral Disuse in the Early Phase

PURPOSE

It is clinically important to determine the efficacy of estrogen replacement for postmenopausal women combined with mobility difficulties, due to the potential risks of estradiol. The objective of the current study was to investigate the effect of estradiol replacement on osteoporosis induced by the ovariectomy (OVX) combined with unilateral sciatic neurectomy (SN) in a rat model.

METHOD

Female Sprague-Dawley rats were subjected to OVX and unilateral SN on the right hindlimb (OVX+SN) or sham surgery (CTRL). 17β-estradiol (E2) or vehicle was administrated to the rats immediately, and followed by every other day. Bone mass and trabecular microarchitecture were analyzed using micro-Computed Tomography (micro-CT) and histology at days 3, 7, 14, and 28 post-surgery. The local expressions of sclerostin/SOST, secreted exclusively by osteocytes, and tartrate-resistant acid phosphatase 5b (TRAP 5b), produced mostly by osteoclasts, were examined by immunohistochemistry and TRAP staining, respectively. Serum markers of bone resorption, including C-terminal telopeptides of type I collagen (CTx), receptor activator for nuclear factor κB ligand (RANKL), and TRAP 5b, were quantified by enzyme linked immunosorbent assay (ELISA).

RESULT

Based on micro-CT analysis, E2 treatment of OVX+SN rats improved the preservation of the bone volume fraction (BV/TV) and trabecular number (Tb.N) in the tibias at day 14 post-surgery, which were 43% and 46% higher in OVX+SN+E2 rats than those in OVX+SN rats, respectively. However, the impact of E2 was transient and disappeared at day 28. Expression of sclerostin in the tibias of OVX+SN rats was significantly elevated at day 7 post-surgery compared with the CTRL, but was suppressed until day 14 with E2 replacement.

CONCLUSION

Our results showed that estrogen replacement could transiently protect against bone loss in OVX rats combined with mechanical unloading. The up-regulation of sclerostin expression appears to be transiently delayed by E2 treatment in our models.