Osteopontin: A Bone-Derived Protein Involved in Rheumatoid Arthritis and Osteoarthritis Immunopathology

Research progress in Alzheimer's disease and bone-brain axis

Alzheimer's disease (AD) is the most common type of cognitive impairment. AD is closely related to orthopedic diseases, such as osteoporosis and osteoarthritis, in terms of epidemiology and pathogenesis. Brain and bone tissues can regulate each other in different manners through bone-brain axis. This article reviews the research progress of the relationship between AD and orthopedic diseases, bone-brain axis mechanisms of AD, and AD therapy by targeting bone-brain axis, in order to deepen the understanding of bone-brain communication, promote early diagnosis and explore new therapy for AD patients.

Osteopontin, osteoprotegerin and musculoskeletal ultrasound findings in first-degree relatives of rheumatoid arthritis: potential markers of preclinical disease

BACKGROUND

First-degree relatives (FDRs) of rheumatoid arthritis (RA) patients are known to have increased risk of developing the disease. The detection of altered bone metabolism in FDRs could be a predictor of the disease. Musculoskeletal ultrasound (MSUS) is known for its ability to detect subclinical joint inflammation in RA, but changes in FDRs are not yet described. We aimed to study serum Osteopontin (OPN) and Osteoprotegerin (OPG) levels in FDRs of RA patients as markers of altered bone metabolism in relation to clinical, laboratory and musculoskeletal ultrasound (MSUS) findings.

METHODS

Fifty-five individuals were included, 20 had definite RA, 25 were first degree relatives (FDRs) of RA patients, and 10 healthy controls. Clinical evaluation for joint swelling/tenderness was performed for all. ESR, CRP, rheumatoid factor (RF), anti-citrullinated antibodies (ACPA), OPN, OPG, and Musculoskeletal ultrasound (MSUS) by the US7 score were evaluated.

RESULTS

Osteoprotegerin was significantly higher in RA (143.89 pg/ml ± 365.47) than in FDRs (22.23 pg/ml ± 65.73; p = 0.009) and controls (6.20 pg/ml ± 12.43; p = 0.003). OPN was also higher in RA (3.66 ng/ml ± 4.20) than in FDRs (1.97 ng/ml ± 1.04) and controls (2.81 ng/ml ± 1.31), though not significant (p = 0.102). Eight of 25 FDRs (32%) had arthralgia without clinical arthritis and 17/25 (68%) were asymptomatic. FDRs with arthralgia had significantly higher ESR and CRP levels than asymptomatic FDRs (9.82 mm/h ± 4.13; p = 0.003, and 3.93 mg/l ± 3.58; p = 0.003). Osteoprotegerin was higher in FDRs than in controls, and also in those with arthralgia (51.55 pg/ml ± 114.68) than in those without (8.44 pg/ml ± 9.67), though without significant difference. OPN was higher in FDRs with arthralgia (2.09 ng/ml ± 1.19) than in asymptomatic (1.70 ng/ml ± 0.55), also without significant difference. Pathologic findings by US7 were detected in 10/25 (40%) FDRs, of which three (12%) had arthralgia and seven (28%) were asymptomatic.

CONCLUSIONS

The raised OPG and lower OPN in FDRs than in controls reflect an altered bone metabolism which could precede clinical disease phase. OPN and OPG could serve as markers of altered preclinical bone metabolism in FDRs of RA. US7 score might be a useful screening tool to identify 'at-risk' individuals.

Expression pattern of osteopontin isoforms in malignant melanoma cell lines

Osteopontin (OPN) is a secreted integrin-binding protein that plays a role in inflammation, cellular viability, cell adhesion and migration, cancer development, and diabetes through different mechanisms. The splice variants of OPN can play essential roles in cancer development, progression, and metastasis formation; however, limited data are available about the role of OPN isoforms in human malignant melanoma. Our goal was to define the gene expression patterns of five OPN variants (OPN4, OPN5, OPNa, OPNb, and OPNc), integrin, and CD44 receptor genes in primary and metastatic melanoma-originated cell lines (n = 19), and to explore the association of the expression patterns with clinicopathological parameters. We evaluated the invasive property of the cell lines and investigated the potential association between the invasion and gene expression of OPN isoforms. We found a significant rise in the expression of OPNc in the invasive cell lines compared to the noninvasive cells and detected significantly higher expression of the OPN splice variants in melanoma cell lines originating from more advanced stages tumors than cell lines originating from early-stage melanomas. The correlation analysis revealed that all five OPN variants positively correlated with ITGB3 and ITGA9, whereas OPN5 positively correlated with ITGB1, ITGAV, ITGA6, and CD44. OPN can activate extracellular signal-regulated kinase signaling through binding to α9β1 integrin, promoting melanoma tumor cell migration. It is possible that such associations between OPN splice variants and integrin receptors may play a role in melanoma progression. In conclusion, our findings suggest that high expression of OPNc correlates with the invasive behavior of melanoma cells.

The Multifaceted Role of Osteopontin in Prostate Pathologies

The prostate gland, located beneath the bladder and surrounding the proximal urethra in men, plays a vital role in reproductive physiology and sexual health. Despite its importance, the prostate is vulnerable to various pathologies, including prostatitis, benign prostatic hyperplasia (BPH) and prostate cancer (PCa). Osteopontin (OPN), a versatile protein involved in wound healing, inflammatory responses, and fibrotic diseases, has been implicated in all three prostate conditions. The role of OPN in prostatic pathophysiology, affecting both benign and malignant prostate conditions, is significant. Current evidence strongly suggests that OPN is expressed at a higher level in prostate cancer and promotes tumor progression and aggressiveness. Conversely, OPN is primarily secreted by macrophages and foam cells in benign prostate conditions and provokes inflammation and fibrosis. This review discusses the accumulating evidence on the role of OPN in prostatic diseases, cellular sources, and potential roles while also highlighting areas for future investigations.

Exploring the Cellular and Molecular Mechanism of Discoidin Domain Receptors (DDR1 and DDR2) in Bone Formation, Regeneration, and Its Associated Disease Conditions

The tyrosine kinase family receptor of discoidin domain receptors (DDR1 and DDR2) is known to be activated by extracellular matrix collagen catalytic binding protein receptors. They play a remarkable role in cell proliferation, differentiation, migration, and cell survival. DDR1 of the DDR family regulates matrix-metalloproteinase, which causes extracellular matrix (ECM) remodeling and reconstruction during unbalanced homeostasis. Collagenous-rich DDR1 triggers the ECM of cartilage to regenerate the cartilage tissue in osteoarthritis (OA) and temporomandibular disorder (TMD). Moreover, DDR2 is prominently present in the fibroblasts, smooth muscle cells, myofibroblasts, and chondrocytes. It is crucial in generating and breaking collagen vital cellular activities like proliferation, differentiation, and adhesion mechanisms. However, the deficiency of DDR1 rather than DDR2 was detrimental in cases of OA and TMDs. DDR1 stimulated the ECM cartilage and improved bone regeneration. Based on the above information, we made an effort to outline the advancement of the utmost promising DDR1 and DDR2 regulation in bone and cartilage, also summarizing their structural, biological activity, and selectivity.