OSTEOPOROSIS FROM YESTERDAY TO TODAY – A NARRATIVE REVIEW

Despite different lifestyles, humankind has suffered from osteoporosis for thousands of years. A literature review concerning the history of osteoporosis in the following databases: Index Medicus, Medline, PubMed, and PMC Citations was done. In the final analysis, 18 review articles and 31 original papers were included. The works were published during the period 1705-2020. Although there is evidence of the existence of osteoporosis for many centuries, it was first described as a disease at the beginning of the 18th century. It was first perceived as an unavoidable course of aging with no possibility to cure. This approach changed only in the 20th century thanks to sudden diagnostic and therapeutic progress. This paper presents the milestones and most important researchers in osteoporosis history. Rapid progress in diagnostic and therapeutic possibilities sheds new light on osteoporosis’ nature. A comprehensive outlook on its history may help find answers for the still unsolved problems of this disease.

Nupr1 deficiency downregulates HtrA1, enhances SMAD1 signaling, and suppresses age-related bone loss in male mice

Nuclear protein 1 (NUPR1) is a stress-induced protein activated by various stresses, such as inflammation and oxidative stress. We previously reported that Nupr1 deficiency increased bone volume by enhancing bone formation in 11-week-old mice. Analysis of differentially expressed genes between wild-type (WT) and Nupr1-knockout (Nupr1-KO) osteocytes revealed that high temperature requirement A 1 (HTRA1), a serine protease implicated in osteogenesis and transforming growth factor-β signaling was markedly downregulated in Nupr1-KO osteocytes. Nupr1 deficiency also markedly reduced HtrA1 expression, but enhanced SMAD1 signaling in in vitro-cultured primary osteoblasts. In contrast, Nupr1 overexpression enhanced HtrA1 expression in osteoblasts, suggesting that Nupr1 regulates HtrA1 expression, thereby suppressing osteoblastogenesis. Since HtrA1 is also involved in cellular senescence and age-related diseases, we analyzed aging-related bone loss in Nupr1-KO mice. Significant spine trabecular bone loss was noted in WT male and female mice during 6-19 months of age, whereas aging-related trabecular bone loss was attenuated, especially in Nupr1-KO male mice. Moreover, cellular senescence-related markers were upregulated in the osteocytes of 6-19-month-old WT male mice but markedly downregulated in the osteocytes of 19-month-old Nupr1-KO male mice. Oxidative stress-induced cellular senescence stimulated Nupr1 and HtrA1 expression in in vitro-cultured primary osteoblasts, and Nupr1 overexpression enhanced p16^ink4a expression in osteoblasts. Finally, NUPR1 expression in osteocytes isolated from the bones of patients with osteoarthritis was correlated with age. Collectively, these results indicate that Nupr1 regulates HtrA1-mediated osteoblast differentiation and senescence. Our findings unveil a novel Nupr1/HtrA1 axis, which may play pivotal roles in bone formation and age-related bone loss.

Inflammation produced by senescent osteocytes mediates age-related bone loss

Purpose

The molecular mechanisms of age-related bone loss are unclear and without valid drugs yet. The aims of this study were to explore the molecular changes that occur in bone tissue during age-related bone loss, to further clarify the changes in function, and to predict potential therapeutic drugs.

Methods

We collected bone tissues from children, middle-aged individuals, and elderly people for protein sequencing and compared the three groups of proteins pairwise, and the differentially expressed proteins (DEPs) in each group were analyzed by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG). K-means cluster analysis was then used to screen out proteins that continuously increased/decreased with age. Canonical signaling pathways that were activated or inhibited in bone tissue along with increasing age were identified by Ingenuity Pathway Analysis (IPA). Prediction of potential drugs was performed using the Connectivity Map (CMap). Finally, DEPs from sequencing were verified by Western blot, and the drug treatment effect was verified by quantitative real-time PCR.

Results

The GO and KEGG analyses show that the DEPs were associated with inflammation and bone formation with aging, and the IPA analysis shows that pathways such as IL-8 signaling and acute-phase response signaling were activated, while glycolysis I and EIF2 signaling were inhibited. A total of nine potential drugs were predicted, with rapamycin ranking the highest. In cellular experiments, rapamycin reduced the senescence phenotype produced by the H₂O₂-stimulated osteocyte-like cell MLO-Y4.

Conclusion

With age, inflammatory pathways are activated in bone tissue, and signals that promote bone formation are inhibited. This study contributes to the understanding of the molecular changes that occur in bone tissue during age-related bone loss and provides evidence that rapamycin is a drug of potential clinical value for this disease. The therapeutic effects of the drug are to be further studied in animals.

Analysis of serum bone turnover markers in female cynomolgus monkeys of different ages

OBJECTIVE

The purpose of this study was to examine bone turnover markers, estradiol, parathyroid hormone, and 25 hydroxyvitamin D, in cynomolgus monkeys at different ages to improve our understanding of the changes in bone turnover markers throughout the life cycle of cynomolgus monkeys and to provide a basis for the establishment of a non-human primate model of osteoporosis.

METHODS

Total Body Bone Mineral Density and Total Body Bone Mineral Content were measured using Dual-Energy X-Ray Absorptiometry in cynomolgus monkeys at different ages. Serum bone turnover marker' levels were measured using enzyme immunoassays at each age group, and the relationship between bone turnover markers and age was assessed by Spearman rank correlation analysis to investigate the relationship between bone turnover markers and age in female cynomolgus monkeys.

RESULTS

Total Body Bone Mineral Density in female cynomolgus monkeys peaked at 10 years of age and then formed a plateau that was maintained until old age. Procollagen I Aminoterminal Propeptide, Bone Alkaline Phosphatase, Osteocalcin, and C-Terminal Telopeptide Of Type I Collagen peaked at 1 to 3 years of age and gradually decreased with age, leveling off by 10 years of age. Estradiol, parathyroid hormone, and 25 hydroxyvitamin D, follicle-stimulating hormone, luteinizing hormone, were not significantly different among age groups.

CONCLUSION

This paper provides data on trends in bone turnover markers throughout the life cycle of female cynomolgus monkeys, which are similar to human changes.

Quantifying cortical bone in fragmentary archeological second metacarpals

OBJECTIVES

Skeletal variation in cortical bone thickness is an indicator of bone quality and health in archeological populations. Second metacarpal radiogrammetry, which measures cortical thickness at the shaft midpoint, is traditionally used to evaluate bone loss in bioarcheological and some clinical contexts. However fragmentary elements are regularly omitted because the midpoint cannot be determined. This methodological limitation reduces sample sizes and biases them against individuals prone to fracture, such as older individuals with low bone mass. This study introduces a new technique for measuring cortical bone in second metacarpals, the "Region of Interest" (ROI) method, which quantifies bone in archeological remains with less-than-ideal preservation while accounting for cortical heterogeneity.

MATERIALS AND METHODS

The ROI method was adapted from digital X-ray radiogrammetry (DXR), a clinical method used to estimate bone mineral density, and tested using second metacarpals from Middenbeemster, Netherlands, a 19th century known age and sex skeletal collection. The ROI method quantifies cortical bone area within a 1.9 cm-long, mid-diaphyseal region, standardized for body size differences using total area (CAI_ROI ). CAI_ROI values were compared to traditional radiogrammetric cortical indices (CI) to assess the method's ability to identify age-related bone loss.

RESULTS

CAI_ROI values have high intra- and interobserver replicability and are strongly and significantly correlated with CI values for both males (r[n = 39] = 0.906, p = 0.000) and females (r[n = 58] = 0.925, p = 0.000).

CONCLUSION

The ROI method complements traditional radiogrammetry analyses and provides a reliable way to quantify cortical bone in incomplete second metacarpals, thereby maximizing sample sizes, allowing patterns in bone acquisition and loss to be more comprehensively depicted in archeological assemblages.

Glycinol enhances osteogenic differentiation and attenuates the effects of age on mesenchymal stem cells

AIM

Phytoestrogens, such as glycinol, have recently gained significant attention as an alternative therapy for osteoporosis due to their structural similarity to estradiol and their bone-generating potential.

METHODS

The osteogenic effects of glycinol were investigated in human bone marrow mesenchymal stem cells (BMSCs) derived from older (>50 years old) and younger subjects (<25 years old).

RESULTS

BMSCs isolated from older donors demonstrated reduced osteogenesis. 17β-estradiol and glycinol exposure rescued the age-related reduction in osteogenic differentiation of BMSCs. These results correlated with the induction of osteogenic genes and estrogen receptor-α (ER-α) following glycinol treatment. ER antagonist studies further support that glycinol promotes osteogenesis through ER signaling.

CONCLUSION

The results from these studies support investigating glycinol as a potential preventive or treatment for osteoporosis.

Zinc finger factor 521 enhances adipogenic differentiation of mouse multipotent cells and human bone marrow mesenchymal stem cells

Previously, we found that ZNF521 expression was up-regulated with advancing age in human bone marrow mesenchymal stem cells (bmMSCs). Here, we investigated the regulatory role of ZNF521 in the differentiation of mouse C3H10T1/2 cells and human bmMSCs. Our data show that ZNF521 overexpression repressed osteoblastic differentiation of C3H10T1/2 cells, accompanied by a decrease in Runx2 expression and an increase in PPARγ2 expression. In contrast, ZNF521 overexpression enhanced adipogenic differentiation of C3H10T1/2 cells, concomitant with increased expression of PPARγ2, aP2, adiponectin and C/EBPδ. Chromatin immunoprecipitation followed by quantitative PCR analyses and luciferase reporter assays suggested that ZNF521 overexpression enhances PPARγ2 expression at the transcriptional level. The enhancing effect of ZNF521 overexpression on the adipogenic differentiation of C3H10T1/2 cells was also observed ex vivo. Finally, similar to those noted in C3H10T1/2 cells, ZNF521 overexpression in human bmMSCs was found to promote adipogenic differentiation in vitro and ex vivo, but repressed osteoblastic differentiation in vitro. ZNF521 knockdown significantly repressed adipogenic differentiation in vitro and ex vivo, but promoted osteoblastic differentiation in vitro. We propose that ZNF521 can function as a repressor of osteoblastic differentiation of bmMSCs while promoting adipogenesis, and that elevated ZNF521 expression might play a role in the age-related bone loss.

Correlates of bone quality in older persons

PURPOSE OF THE STUDY

In a population-based sample of older persons, we studied the relationship between tibial bone density and geometry and factors potentially affecting osteoporosis.

METHODS

Of the 1260 participants aged 65 years or older eligible for the InCHIANTI study, 1155 received an interview and 915 (79.2%) had complete data on tibial QCT scans and other variables used in the analysis presented here. The final study population included 807 persons (372 men and 435 women, age range 65-96 years) after exclusion of participants affected by bone diseases or treated with drugs that interfere with bone metabolism.

RESULTS

In both sexes, calf cross-sectional muscle area (CSMA) was significantly and independently associated with total bone cross-sectional area (tCSA) and cortical bone cross-sectional area (cCSA) but not with trabecular or cortical volumetric bone mineral density (vBMD). Bioavailable testosterone (Bio-T) was independently associated with both trabecular and cortical vBMD in both sexes. In women, independently of confounders, 25(OH)-vitamin D was positively associated with tCSA and cortical vBMD, while PTH was negatively associated with cortical vBMD. IL-1 beta was negatively correlated with cortical vBMD in women, while TNF-alpha was associated with enhanced bone geometrical adaptation in men.

CONCLUSIONS

Physiological parameters that are generically considered risk factors for osteoporosis were associated with specific bone parameters assessed by tibial QCT. Factors known to be associated with increased bone reabsorption, such as 25(OH)-vitamin D, PTH and Bio-T, affected mainly volumetric BMD, while factors associated with bone mechanical stimulation, such as CSMA, affected primarily bone geometry. Our results also suggested that pro-inflammatory cytokines might be considered as markers of bone resorption.