Bone cells, sclerostin, and FGF23: what’s bred in the bone will come out in the flesh

Metabolic Imbalances and Bone Remodeling Agents in Adolescent Idiopathic Scoliosis: A Study in Postmenarcheal Girls

The causes and mechanisms underlying adolescent idiopathic scoliosis (AIS) remain unclear, and the available information regarding metabolic imbalances in AIS is still insufficient. This investigation aimed to evaluate the concentrations of specific bone remodeling-related agents in postmenarcheal girls diagnosed with AIS. The study encompassed thirty-six scoliosis patients and eighteen age-matched healthy individuals assigned to the control group. The patients underwent clinical and radiological examinations to assess the degree of the spinal deformity, type of curvature, and skeletal maturity. Blood and urine samples were collected from all participants and serological markers were measured using an enzyme-linked immunosorbent assay. Our study results demonstrated that the balance of phosphate-calcium and parathormone levels seems normal in individuals with AIS. Furthermore, no statistically significant differences were observed in the content of Klotho protein, osteocalcin, osteoprotegerin, C-terminal telopeptide of type I collagen (CTX), sclerostin, and alkaline phosphatase. Nevertheless, the serum levels of vitamin D (25-OH-D) were lowered, while N-terminal propeptide of type I procollagen (PINP), and fibroblast growth factor-23 (FGF23) were increased in the AIS group, with p-values of 0.044, 0.001, and 0.022, respectively. This finding indicates the potential involvement of these factors in the progression of AIS, which necessitates further studies to uncover the fundamental mechanisms underlying idiopathic scoliosis.

Adynamic bone disease: Revisited

The bone and mineral disorders form an integral part of the management of a chronic kidney disease (CKD) patient. Amongst various types of bone pathologies in chronic kidney disease-mineral bone disorder (CKD-MBD), the prevalence of adynamic bone disease (ABD) is increasing. The present review discusses the updated pathophysiology, risk factors, and management of this disorder.

Impact of FasL Stimulation on Sclerostin Expression and Osteogenic Profile in IDG-SW3 Osteocytes

Simple Summary

FasL used to be considered as a classical ligand triggering cell death (apoptosis) via its receptor, Fas and thefollowing caspase cascade. As such, it is known to be involved in regulation within the bone. Recently, however, the knowledge has expanded about the non-apoptotic and caspase-independent engagement of the Fas/FasL pathway. The present investigation identified that stimulation of osteocytic IDG-SW3 cells by FasL leads to a dramatic decrease in expression of the major osteocytic marker, sclerostin. Additionally, other key components of the osteogenic pathways were impacted, notably in a caspase-independent manner. Such findings are of importance for basic biology as well as biomedical applications since osteocytes are the major population within adult bones and Fas signalling is one of therapeutical targets, e.g., in the anti-osteoporotic treatment.

Abstract

The Fas ligand (FasL) is known from programmed cell death, the immune system, and recently also from bone homeostasis. As such, Fas signalling is a potential target of anti-osteoporotic treatment based on the induction of osteoclastic cell death. Less attention has been paid to osteocytes, although they represent the majority of cells within the mature bone and are the key regulators. To determine the impact of FasL stimulation on osteocytes, differentiated IDG-SW3 cells were challenged by FasL, and their osteogenic expression profiles were evaluated by a pre-designed PCR array. Notably, the most downregulated gene was the one for sclerostin, which is the major marker of osteocytes and a negative regulator of bone formation. FasL stimulation also led to significant changes (over 10-fold) in the expression of other osteogenic markers: Gdf10, Gli1, Ihh, Mmp10, and Phex. To determine whether these alterations involved caspase-dependent or caspase-independent mechanisms, the IDG-SW3 cells were stimulated by FasL with and without a caspase inhibitor: Q-VD-OPh. The alterations were also detected in the samples treated by FasL along with Q-VD-OPh, pointing to the caspase-independent impact of FasL stimulation. These results contribute to an understanding of the recently emerging pleiotropic effects of Fas/FasL signalling and specify its functions in bone cells.

Adynamic bone disease: Revisited

The bone and mineral disorders form an integral part of the management of a chronic kidney disease (CKD) patient. Amongst various types of bone pathologies in chronic kidney disease-mineral bone disorder (CKD-MBD), the prevalence of adynamic bone disease (ABD) is increasing. The present review discusses the updated pathophysiology, risk factors, and management of this disorder.

Dynamic not isometric training blunts osteo-renal disease and improves the sclerostin/FGF23/Klotho axis in maintenance hemodialysis patients: a randomized clinical trial

This study compared the effectiveness of dynamic resistance training (DRT) versus isometric RT (IRT) on osteogenesis and hormonal mechanisms involved in maintenance hemodialysis (MHD) patients. One hundred and ninety-three MHD patients were randomized into three groups: control (CTL) (n = 60), DRT (n = 66), and IRT (n = 67). A first visit was required for an anamnesis to evaluate the number of medications, biochemical, and anthropometric measurements (dialysis adequacy, creatinine, urea, body mass, height, and body mass index). Grip strength, bone mineral density (BMD), and renal-bone markers were assessed pre- and postprotocol. The DRT and IRT training was 6 mo with a frequency of three times per week, on alternate days. Each training session consisted of three sets of 8 to 12 repetitions at lower and moderate intensities. Both training sessions were prescribed approximately 1 h prior to dialysis. Statistical significances were adopted with P < 0.05. There was a greater dropout in the IRT group (24%) as compared with the DRT group (14%), which in turn had less adverse clinical effects (67%, 24%, and 61% for CTL, DRT, and IRT, respectively). DRT promoted gains in BMD in different body locations, in addition to increasing pro-osteogenic factors (Klotho and calcitriol) and reducing those related to bone loss, such as sclerostin, FGF23, and PTH. There was an improvement in Ca × PO₄³ for DRT, whereas these benefits did not occur in the IRT group (P < 0.05). These novel findings suggest that the DRT generates biopositive adaptations in bone tissue in MHD and can be used as a nonpharmacological strategy to improve BMD.NEW & NOTEWORTHY This study shows, for the first time, the effect of dynamic and isometric resistance training on bone mineral density in hemodialysis patients, providing a new understanding of the possible participation of the sclerostin/FGF23/Klotho axis, vitD, PTH, and calcium × phosphate product in this process. However, isometric resistance training may not be sufficient to induce these benefits. Therefore, this study supports the potential therapeutic role of dynamic resistance training counteracting chronic kidney disease-mineral and bone disorder.

Sclerostin levels predict cardiovascular mortality in long-term hemodialysis patients: A prospective observational cohort study

Sclerostin is a protein which is involved in bone metabolism and probably also in vessel wall function. This prospective observational cohort study evaluated the prognostic significance of sclerostin in hemodialysis (HD) patients. In total, 106 HD patients and 25 healthy controls participated in the study. HD patients were prospectively followed up for five years. Sclerostin was measured in serum using standard ELISA kits by Biomedica. Sclerostin concentrations in serum were higher in HD patients compared to the controls (89.2±40.3 pmol/l vs. 32.8±13.0 pmol/l, p<0.001). Sclerostin levels were significant for cardiovascular mortality but not for overall mortality and mortality due to infection. A higher cardiovascular risk was connected to sclerostin concentrations above the median (>84 pmol/l), HR (95 % CI): 2.577 (1.0002-10.207), p=0.04. When sclerostin was evaluated together with residual diuresis in Kaplan-Meier analysis the worst prognosis due to cardiovascular events was observed in the group with high sclerostin and zero residual diuresis compared to all other patients (p=0.007). In summary, serum sclerostin levels in HD patients were increased when compared to healthy subjects. High sclerostin levels were demonstrated as a risk factor for cardiovascular mortality. Further studies are required to clarify the pathophysiological mechanisms of sclerostin action in patients with renal failure before therapeutic measures can be established.

Novel insights into parathyroid hormone: report of The Parathyroid Day in Chronic Kidney Disease

Chronic kidney disease (CKD) is often associated with a mineral and bone disorder globally described as CKD-Mineral and Bone Disease (MBD), including renal osteodystrophy, the latter ranging from high bone turnover, as in case of secondary hyperparathyroidism (SHPT), to low bone turnover. The present article summarizes the important subjects that were covered during ‘The Parathyroid Day in Chronic Kidney Disease’ CME course organized in Paris in September 2017. It includes the latest insights on parathyroid gland growth, parathyroid hormone (PTH) synthesis, secretion and regulation by the calcium-sensing receptor, vitamin D receptor and fibroblast growth factor 23 (FGF23)–Klotho axis, as well as on parathyroid glands imaging. The skeletal action of PTH in early CKD stages to the steadily increasing activation of the often downregulated PTH receptor type 1 has been critically reviewed, emphasizing that therapeutic strategies to decrease PTH levels at these stages might not be recommended. The effects of PTH on the central nervous system, in particular cognitive functions, and on the cardiovascular system are revised, and the reliability and exchangeability of second- and third-generation PTH immunoassays discussed. The article also reviews the different circulating biomarkers used for the diagnosis and monitoring of CKD-MBD, including PTH and alkaline phosphatases isoforms. Moreover, it presents an update on the control of SHPT by vitamin D compounds, old and new calcimimetics, and parathyroidectomy. Finally, it covers the latest insights on the persistence and de novo occurrence of SHPT in renal transplant recipients.

Association of bone-derived biomarkers with vascular calcification in chronic hemodialysis patients

BACKGROUND

Abdominal aortic calcification (AAC) is commonly observed in chronic dialysis patients and is associated with cardiovascular and all-cause mortality. We investigated the factors associated with AAC and analyze the relationship between bone-derived biomarkers and AAC.

METHODS

We enrolled 227 stable hemodialysis patients. Vascular calcifications were assessed using lateral lumbar radiography of the abdominal aorta. Demographic data were collected and serum levels of biochemical and bone-derived biomarkers, including sclerostin, Dickkopf-1 (DKK-1), and fibroblast growth factor 23 (FGF23), were measured.

RESULTS

One hundred sixty-one patients (71.0%) had AAC. Patients with AAC score≧13 were older, with higher body mass index (BMI), serum calcium, calcium phosphate product, high-sensitivity C-reactive protein (hsCRP), and FGF23 levels. Sclerostin and DKK-1 levels were inversely associated with AAC severity, and FGF23 was directly related to vascular calcification. Hypertension, vascular disease, hsCRP, FGF23, and sclerostin were independent AAC determinants.

CONCLUSIONS

Chronic hemodialysis patients have a high prevalence of vascular calcifications. Levels of circulating sclerostin, DKK-1, and FGF23 were related to AAC severity. Sclerostin and FGF23 were independently associated with AAC.