Sclerostin: From Molecule to Clinical Biomarker

Relation between serum sclerostin and CTRP3 levels and bone mineral density in diabetic postmenopausal women

BACKGROUND

Osteoporosis (OP) is a common finding in diabetic patients especially high-risk populations such as postmenopausal women. Sclerostin is a glycoprotein chiefly secreted by mature osteocytes and is considered a main regulator of bone formation. The C1q/TNF-Related Protein 3 (CTRP3) was found to be significantly associated with OP in postmenopausal women. The effect of type 2 diabetes mellitus (T2DM) on sclerostin and CTRP3 levels in postmenopausal women is rarely investigated. The present study aimed to assess the impact of T2DM on sclerostin and CTRP3 levels and their relation to OP in postmenopausal women.

METHODS

The study included 60 postmenopausal women with T2DM and 60 age-matched postmenopausal non-diabetic women. Bone mineral density (BMD) was assessed using dual energy X-ray absorptiometry (DEXA). Serum levels of sclerostin and CTRP3 were assessed using enzyme-linked immunosorbent assay (ELISA) technique.

RESULTS

Diabetic group expressed significantly higher serum levels of sclerostin when compared with non-diabetic group (110.0 ± 29.0 versus 51.5 ± 23.2 ng; p < 0.001). Oppositely, CTRP3 were significantly lower in the diabetic group (3.5 ± 3.5 versus 9.9 ± 3.7 ng/ml, p < 0.001). Multivariate logistic regression analysis identified HbA1c levels [OR (95% CI): 0.49 (0.26-0.93), p = 0.028], sclerotin levels [OR (95% CI): 1.06 (1.0-1.012), p = 0.041] and CTRP3 levels [OR (95%) CI: 1.64 (1.0-2.68), p = 0.047] as significant predictors of OP in diabetic patients.

CONCLUSIONS

Sclerostin and CTRP3 levels are involved in OP in postmenopausal diabetic patients.

Comparative Analysis of Myokines and Bone Metabolism Markers in Prepubertal Vegetarian and Omnivorous Children

The role of bone and muscle as endocrine organs may be important contributing factors for children's growth and development. Myokines, secreted by muscle cells, play a role in regulating bone metabolism, either directly or indirectly. Conversely, markers of bone metabolism, reflecting the balance between bone formation and bone resorption, can also influence myokine secretion. This study investigated a panel of serum myokines and their relationships with bone metabolism markers in children following vegetarian and omnivorous diets. A cohort of sixty-eight healthy prepubertal children, comprising 44 vegetarians and 24 omnivores, participated in this study. Anthropometric measurements, dietary assessments, and biochemical analyses were conducted. To evaluate the serum concentrations of bone markers and myokines, an enzyme-linked immunosorbent assay (ELISA) was used. The studied children did not differ regarding their serum myokine levels, except for a higher concentration of decorin in the vegetarian group (p = 0.020). The vegetarians demonstrated distinct pattern of bone metabolism markers compared to the omnivores, with lower levels of N-terminal propeptide of type I procollagen (P1NP) (p = 0.001) and elevated levels of C-terminal telopeptide of type I collagen (CTX-I) (p = 0.018). Consequently, the P1NP/CTX-I ratio was significantly decreased in the vegetarians. The children following a vegetarian diet showed impaired bone metabolism with reduced bone formation and increased bone resorption. Higher levels of decorin, a myokine involved in collagen fibrillogenesis and essential for tissue structure and function, may suggest a potential compensatory mechanism contributing to maintaining bone homeostasis in vegetarians. The observed significant positive correlations between myostatin and bone metabolism markers, including P1NP and soluble receptor activator of nuclear factor kappa-B ligand (sRANKL), suggest an interplay between muscle and bone metabolism, potentially through the RANK/RANKL/OPG signaling pathway.

El diálogo oculto entre el hueso y los tejidos a través del remodelado óseo

El hueso es mucho más que un reservorio de calcio y fósforo. Su disposición lacuno-canalicular ofrece una importante vía de intercambio con la circulación y actualmente, el esqueleto se considera un gran órgano endocrino, con acciones que van más allá del control del balance fosfocálcico mediado por el factor fibroblástico 23 (FGF23). Paralelamente al efecto modulador de las adipoquinas sobre el remodelado óseo, diversas proteínas óseas, como la osteocalcina y la esclerostina, ejercen cierta acción contra-reguladora sobre el metabolismo energético, posiblemente en un intento de asegurar los enormes requerimientos energéticos del remodelado. En esta interacción del hueso con otros tejidos, especialmente el adiposo, participa la señalización canónica Wnt/β-catenina y por ello la esclerostina, una proteína osteocítica que inhibe esta señalización, emerge como un potencial biomarcador. Es más, su participación en diversas patologías le posiciona como diana terapéutica, existiendo un anticuerpo anti-esclerostina, recientemente aprobado en nuestro país para el tratamiento de la osteoporosis. Esta revisión aborda el carácter endocrino del hueso, el papel de la osteocalcina y, especialmente, el papel regulador y modulador de la esclerostina sobre remodelado óseo y la homeóstasis energética a través de su interacción con la señalización canónica Wnt/β-catenina, así como su potencial utilidad como biomarcador.

The hidden cross talk between bone and tissues through bone turnover

Bone is more than a reservoir of calcium and phosphorus. Its lacuno-canalicular arrangement provides an important pathway for exchange with circulation and currently, the skeleton is considered a large endocrine organ with actions that go beyond the control of calcium-phosphorus balance mediated by fibroblastic growth factor 23 (FGF23). Parallel to the modulating effect of adipokines on bone turnover, certain bone proteins, such as osteocalcin and sclerostin, play a counter-regulatory role on energy metabolism, probably in an attempt to ensure its high energy requirement for bone turnover. In this crosstalk between bone and other tissues, especially with adipose tissue, canonical Wnt/β-catenin signaling is involved and therefore, sclerostin, an osteocyte derived protein that inhibits this signalling, emerges as a potential biomarker. Furthermore, its involvement in diverse pathologic conditions supports sclerostin as a therapeutic target, with an anti-sclerostin antibody recently approved in our country for the treatment of osteoporosis. This review addresses the endocrine nature of bone, the role of osteocalcin, and specially, the regulatory and modulatory role of sclerostin on bone turnover and energy homeostasis through its inhibitory effect on canonical Wnt/β-catenin signaling, as well as its potential utility as a biomarker.

ALK1 Signaling in Human Cardiac Progenitor Cells Promotes a Pro-angiogenic Secretome

Pro-angiogenic paracrine/autocrine signaling impacts myocardial repair in cell-based therapies. Activin A receptor-like type 1 (ACVRL1, ALK1) signaling plays a pivotal role in cardiovascular development and maintenance, but its importance in human-derived therapeutic cardiac cells is not well understood. Here, we isolated a subpopulation of human highly proliferative cells (hHiPCs) from adult epicardial tissue and found that they express ALK1, a high affinity receptor for bone morphogenetic protein-9 (BMP9), which signals via SMAD1/5 to regulate paracrine/autocrine signaling and angiogenesis. We show that in humans, circulating BMP9 level is negatively associated with the number of epicardial hHiPC and positively associated with endothelial cell (EC) number in the adult heart, implicating the potential importance of this signaling pathway in cardiac cell fate and vascular maintenance. To investigate BMP9/ALK1 signaling in hHiPCs, we selected a primary cell population of hHiPC from each of 3 individuals and studied their responses to BMP9 and BMP10 treatment in vitro. Proteins were collected in conditioned media (CM) for mass spectrometry and cell-based assays on human ECs and hHiPCs. Proteomic analysis of the hHiPC secretome following BMP9 or BMP10 treatment demonstrates that the secreted proteins, sclerostin (SOST), meflin/immunoglobulin superfamily containing leucine rich repeat (ISLR), and insulin-like growth factor binding protein-3 (IGFBP3), are novel regulated targets of BMP9/ALK1 signaling. Lentiviral shRNA and pharmacological inhibition of ALK1 in hHiPCs suppressed transcription and secretion of SOST, ISLR, and IGFBP3 following BMP9 treatment. Moreover, the BMP9-treated secretome of hHiPC increased capillary-like tube formation of ECs and hHiPCs. Treatment of hHiPCs with recombinant SOST increased VEGF-a expression, increased tube formation and enhanced expression of EC receptor marker annexin A2 (ANXA2). These data provide the first proteomic characterization of hHiPC, identifying BMP9/ALK1-mediated target protein secretion in hHiPCs, and underscore the complex role of BMP9/ALK1 signaling in paracrine/autocrine mediated angiogenesis. Data are available via ProteomeXchange with identifier PXD055302.

Osteocyte Mechanotransduction in Orthodontic Tooth Movement

PURPOSE OF REVIEW

Orthodontic tooth movement is characterized by periodontal tissue responses to mechanical loading, leading to clinically relevant functional adaptation of jaw bone. Since osteocytes are significant in mechanotransduction and orchestrate osteoclast and osteoblast activity, they likely play a central role in orthodontic tooth movement. In this review, we attempt to shed light on the impact and role of osteocyte mechanotransduction during orthodontic tooth movement.

RECENT FINDINGS

Mechanically loaded osteocytes produce signaling molecules, e.g., bone morphogenetic proteins, Wnts, prostaglandins, osteopontin, nitric oxide, sclerostin, and RANKL, which modulate the recruitment, differentiation, and activity of osteoblasts and osteoclasts. The major signaling pathways activated by mechanical loading in osteocytes are the wingless-related integration site (Wnt)/β-catenin and RANKL pathways, which are key regulators of bone metabolism. Moreover, osteocytes are capable of orchestrating bone adaptation during orthodontic tooth movement. A better understanding of the role of osteocyte mechanotransduction is crucial to advance orthodontic treatment. The optimal force level on the periodontal tissues for orthodontic tooth movement producing an adequate biological response, is debated. This review emphasizes that both mechanoresponses and inflammation are essential for achieving tooth movement clinically. To fully comprehend the role of osteocyte mechanotransduction in orthodontic tooth movement, more knowledge is needed of the biological pathways involved. This will contribute to optimization of orthodontic treatment and enhance patient outcomes.

Updates in the chronic kidney disease-mineral bone disorder show the role of osteocytic proteins, a potential mechanism of the bone-Vascular paradox, a therapeutic target, and a biomarker

The chronic kidney disease-mineral bone disorder (CKD-MBD) is a complex multi-component syndrome occurring during kidney disease and its progression. Here, we update progress in the components of the syndrome, and synthesize recent investigations, which suggest a potential mechanism of the bone-vascular paradox. The discovery that calcified arteries in chronic kidney disease inhibit bone remodeling lead to the identification of factors produced by the vasculature that inhibit the skeleton, thus providing a potential explanation for the bone-vascular paradox. Among the factors produced by calcifying arteries, sclerostin secretion is especially enlightening. Sclerostin is a potent inhibitor of bone remodeling and an osteocyte specific protein. Its production by the vasculature in chronic kidney disease identifies the key role of vascular cell osteoblastic/osteocytic transdifferentiation in vascular calcification and renal osteodystrophy. Subsequent studies showing that inhibition of sclerostin activity by a monoclonal antibody improved bone remodeling as expected, but stimulated vascular calcification, demonstrate that vascular sclerostin functions to brake the Wnt stimulation of the calcification milieu. Thus, the target of therapy in the chronic kidney disease-mineral bone disorder is not inhibition of sclerostin function, which would intensify vascular calcification. Rather, decreasing sclerostin production by decreasing the vascular osteoblastic/osteocytic transdifferentiation is the goal. This might decrease vascular calcification, decrease vascular stiffness, decrease cardiac hypertrophy, decrease sclerostin production, reduce serum sclerostin and improve skeletal remodeling. Thus, the therapeutic target of the chronic kidney disease-mineral bone disorder may be vascular osteoblastic transdifferentiation, and sclerostin levels may be a useful biomarker for the diagnosis of the chronic kidney disease-mineral bone disorder and the progress of its therapy.

Impact of radiotherapy on bone health in women with rectal cancer - A prospective cohort study

INTRODUCTION

Pelvic radiotherapy (RT) increases the risk of pelvic insufficiency fractures. The aim was to investigate if RT is associated with changes in serum bone biomarkers in women with rectal cancer, and to examine the incidence of radiation-induced bone injuries and the association with bone biomarkers.

MATERIAL AND METHODS

Women diagnosed with rectal cancer stage I-III, planned for abdominal surgery ± preoperative (chemo) RT, were prospectively included and followed one year. Serum bone biomarkers comprised sclerostin (regulatory of bone formation), CTX (resorption), BALP and PINP (formation). A subgroup was investigated with annual pelvic magnetic resonance imaging (MRI). The association between RT and bone biomarkers was explored in regression models.

RESULTS

Of 134 included women, 104 had surgery with preoperative RT. The formation markers BALP and PINP increased from baseline to one year in the RT-exposed group (p < 0.001, longitudinal comparison). In the adjusted regression analysis, the mean increase in PINP was higher in the RT-exposed than the unexposed group (17.6 (3.6-31.5) μg/L, p = 0.013). Sclerostin and CTX did not change within groups nor differed between groups. Radiation-induced injuries were detected in 16 (42%) of 38 women with available MRI. At one year, BALP was higher among women with than without bone injuries (p = 0.018, cross-sectional comparison).

CONCLUSIONS

Preoperative RT was associated with an increase in the formation marker PINP, which could represent bone recovery following RT-induced injuries, commonly observed in participants evaluated with MRI. These findings should be further explored in larger prospective studies on bone health in rectal cancer patients.

Practical Significance of Biomarkers in Axial Spondyloarthritis: Updates on Diagnosis, Disease Activity, and Prognosis

Axial spondyloarthritis (axSpA) is a chronic inflammatory disease that can lead to ankylosis by secondary ossification of inflammatory lesions, with progressive disability and a significant impact on quality of life. It is also a risk factor for the occurrence of comorbidities, especially cardiovascular diseases (CVDs), mood disorders, osteoporosis, and malignancies. Early diagnosis and treatment are needed to prevent or decrease functional decline and to improve the patient's prognosis. In respect of axSpA, there is an unmet need for biomarkers that can help to diagnose the disease, define disease activity and prognosis, and establish personalized treatment approaches. The aim of this review was to summarize the available information regarding the most promising biomarkers for axSpA. We classified and identified six core categories of biomarkers: (i) systemic markers of inflammation; (ii) molecules involved in bone homeostasis; (iii) HLA-B27 and newer genetic biomarkers; (iv) antibody-based biomarkers; (v) microbiome biomarkers; and (vi) miscellaneous biomarkers. Unfortunately, despite efforts to validate new biomarkers, few of them are used in clinical practice; however, we believe that these studies provide useful data that could aid in better disease management.