Journal of Bone and Mineral Research最新文献

The postnatal growth plate undergoes dynamic morphogenetic changes essential for endochondral bone formation. While morphogen signaling in this context is well studied, microRNA-mediated post-transcriptional control is poorly understood. Here, we identify miR-433-3p (miR-433) as a key regulator of chondrocyte proliferation and hypertrophy, acting in part through direct targeting of vital chondrocyte genes. miR-433 is evolutionarily conserved and prominently expressed in precursor chondrocytes embryonically and in the proliferating zone of the growth plate postnatally. To interrogate miR-433 function in vivo, we generated a conditional miR-433 tough decoy (competitive inhibitor) mouse model to decrease endogenous miR-433 activity in a lineage-restricted manner. Male and female mice expressing miR-433 tough decoy in Prrx1-expressing skeletal progenitors and their progeny exhibited shortened and narrower femurs, while significantly decreased trabecular bone volume was only apparent in males. Male miR-433 decoy mice had disorganized growth plates with fewer resting zone cells, abnormal hypertrophic-like cells in the proliferative zone and delayed secondary ossification center development. These defects were accompanied by elevated expression of Sox9, Ihh, PTHrP, Bmpr1a, as well as increased expression of validated miR-433 targets Runx2, Hdac6, and Hif1a. Tempering miR-433 activity increased proliferation in the resting zone at one and three weeks of age, and intensified SOX9 immunofluorescence throughout growth plate, including the hypertrophic zone. The miR-433 target RUNX2 was ectopically expressed within the proliferating zone and showed increased expression in the hypertrophic zone, consistent with premature hypertrophic transition. Luciferase assays confirmed direct targeting of Bmpr1a and Ihh by miR-433. Given that BMP signaling induces Sox9 and IHH promotes Runx2 expression, miR-433 may act as a molecular brake on both BMP and Hedgehog signaling axes, contributing to the spatial restriction of transcriptional programs driving chondrocyte maturation, thereby safeguarding orderly chondrocyte differentiation and bone elongation.

Hutchinson-Gilford Progeria Syndrome (HGPS) is a devastating ultrarare genetic premature aging disease resulting in early atherosclerosis and death during adolescence due to heart failure. Structures of mesenchymal origin, including bone, fat, and muscle, create a progressive skeletal dysplasia, lifelong failure to thrive, and unique bone phenotype. Characterizing the interaction between muscle and bone has emerged as a powerful tool for defining drivers of bone disease in other conditions but has not been previously explored in HGPS. We examined the "muscle-bone unit" using radial pQCT in youth with HGPS aged 2 to 18 years before and after treatment with lonafarnib, a farnesyltransferase inhibitor that extends HGPS lifespan. Untreated radii displayed highly abnormal shapes in 70% of individuals spanning all ages. Compared to controls, HGPS forearm muscle and radial area were lower (p<0.001) and grew more slowly (muscle β=1.4 cm2/year vs. 0.3 cm2/year in HGPS; radius β=5.8 mm2/year vs. 0.5 mm2/year in HGPS). Fat area decreased with age (β=-0.2 cm2/year, p<0.001) and muscle area, normalized for either BMI or radial length, was reduced in HGPS (p=0.02 and p=<0.001, respectively). These normalized outcomes were similar to controls at younger ages but diverged as patients aged. Radial architectural changes were present even before changes in muscle area and represent a pattern distinct from the normal aging process and other muscle-wasting pediatric conditions. Lonafarnib therapy did not normalize the muscle-bone phenotype after 24 months, although some individuals (25%) had partial normalization of radial shape. These results demonstrate that the muscle-bone unit is uncoupled in children with HGPS. Normal muscle mass for body size at younger ages implies that there is an opportunity for early treatment to avoid impending pathology. New strategies are needed to ameliorate this phenotype in HGPS, and this study provides a benchmark for gauging future therapies.

Fractures and pseudofractures cause considerable morbidity in adults with X-linked hypophosphatemia (XLH). They frequently occur in cortically-enriched bones of the lower extremities. Burosumab, a neutralizing antibody to FGF23, heals fractures in adults with XLH, presumably by healing osteomalacia. Histomorphometry has documented healing of osteomalacia in trabecular bone. The effects of burosumab on cortical bone have not been reported. Therefore, 3D-DXA measurements of the proximal femur were used to examine the impact of 1 yr of burosumab therapy on cortical and trabecular bone in symptomatic adults with XLH. Twenty volunteers from the registration trial for burosumab were separately consented for this study. DXA scans of the hip were obtained before and 6, 12, and 18-24 mo after drug therapy (1 mg/kg every 4 wk). 3D-DXA analyses were performed using 3D-Shaper software (3D-Shaper Medical). Changes in FN areal BMD (aBMD), TH aBMD, TH trabecular volumetric BMD (vBMD), FN trabecular vBMD, TH cortical surface BMD (sBMD), FN cortical sBMD, and FN cross-sectional moment of inertia (CSMI) were analyzed. Both TH and FN trabecular vBMD showed significant increases over the course of therapy (13.6% and 14.1% respectively at the end of treatment compared to baseline; p < .0001 for each). Fractures and pseudofractures often occur in the cortically-enriched FN in XLH. Burosumab induced a significant increase in FN cortical sBMD between 6 and 12 mo (p < .05) and between 6 and 18-24 mo of drug treatment (p < .05). The FN CSMI, an indicator of FN strength, also significantly increased at 12 and 18-24 mo when compared to baseline; p < .05 and p < .01, respectively. These data demonstrate that burosumab increases both cortical and trabecular bone in the hip, a site of frequent fracture in XLH.

Endochondral ossification is a highly coordinated process involving distinct progenitor cell populations within the mesenchymal condensation and subsequent cartilage anlage and perichondrium, all of which drive skeletal formation. Cell-type specific lineage tracing conducted to understand fetal bone development has revealed various fates of early skeletal cells. However, the underlying continuous and precise cellular dynamics of fetal skeletal cells, particularly along the dorsoventral axis, remain unclear. Here, we show that spatiotemporally specific skeletal progenitor cells in the early developmental stage contribute to the dorsal-ventral axis in a manner that is strictly determined during initial developmental stages. Lineage-tracing experiments using Fgfr3-creER and Dlx5-creER lines revealed that Fgfr3+ cells in mesenchymal condensation exclusively contributed to hypertrophic chondrocytes and the dorsal side of the resting and proliferating zones within the cartilage anlage. These cells made dorsal-restricted contributions to skeletal development, including growth plate chondrocytes, trabecular and cortical osteoblasts, and bone marrow stromal cells. Functional ablation of Fgfr3+ cells using the Rosa26iDTA (inducible diphtheria toxin fragment A) allele during the mesenchymal condensation stage caused severe disruption in long-bone development, underscoring its indispensable role in initiating skeletal growth. Collectively, these findings suggest that the condensation stage is pivotal for the formation of skeletal progenitors and dorsoventral patterning during bone development. Understanding these mechanisms will provide insight into skeletal growth disorders and therapeutic strategies for bone regeneration.

Chronic kidney disease (CKD) is associated with disturbances in bone and mineral metabolism, leading to osteoporosis and vascular calcification, which are significant contributors to mortality. Although denosumab, a monoclonal antibody targeting RANKL, has been shown to increase BMD, its effects on vascular calcification remain controversial. This retrospective study investigated the effects of denosumab on vascular calcification and BMD in 25 dialysis patients compared to the control group of 21 dialysis patients without denosumab over 2 yr. All patients underwent BMD assessments at 1-yr intervals, as well as evaluations of abdominal aortic vascular calcification using CT to determine changes in calcification volume and the Agatston score. Denosumab significantly increased BMD in the LS (8.5% vs 1.5%, p = .0079) compared with the control group. In contrast, the rate of increase from baseline in calcification volume and the Agatston score were significantly higher in the denosumab group compared with the controls (32.8% vs 19.3%, p = .0476; 34.6% vs 20.5%, p = .0483, respectively). Although denosumab is beneficial for bone health in patients on dialysis, its vascular effects warrant careful monitoring.

Strategies to reduce weight in people living with obesity (PwO) include calorie restriction, metabolic and bariatric surgery (MBS), and anti-obesity drugs, including glucagon-like peptide-1 receptor agonists (GLP-1Ra). Although weight loss in PwO has many health benefits, it can result in increased bone loss and fracture risk. Indeed, the consequences of weight loss interventions are well known: (1) significant weight loss induced by caloric restriction and MBS results in high turnover bone loss and (2) unlike calorie restriction, PwO experience a substantial deterioration in bone microarchitecture and strength associated with an increased risk of fracture after MBS, especially malabsorptive procedures. GLP-1 may enhance bone metabolism and improve bone quality, and liraglutide appears to have a positive effect on bone health despite significant weight loss in several rodent models. However, most of the positive effects on bone have been observed at concentrations much higher than those approved for obesity care in humans. The effects of GLP-1Ra on bone health in PwO are still limited; however, significant weight loss induced by GLP-1Ra may also result in accelerated bone turnover and bone loss, and semaglutide could lead to an increased risk of fractures in the at-risk population. The mechanisms responsible for the adverse skeletal effects of MBS are not yet fully understood, and there are insufficient human studies supporting pathophysiological hypotheses. However, data suggest that multiple mechanisms are involved, including nutritional factors, mechanical unloading, hormonal factors, adipokines, and alterations in the gut microbiome. Recommendations for the prevention and treatment of osteoporosis secondary to MBS are now available, and the efficacy of anti-osteoporosis medications in preventing bone loss has been evaluated in two randomized controlled trials. Priorities for future research include the development of effective approaches to reduce fracture risk in PwO following MBS and investigation of the effects of anti-obesity drugs on bone health.

X-linked hypophosphatemia (XLH) is a rare disorder of renal phosphate wasting and dysregulated active vitamin D metabolism, ultimately presenting as rickets and osteomalacia, among other manifestations. Lower extremity deformity (genu valgum and/or varum) is frequent in this pediatric population. Despite prompt active vitamin D and phosphate supplementation (active D/Pi), many patients require corrective surgery for lower limb malformation. Burosumab has demonstrated improvements in lower limb malalignment in children with XLH in several studies. We expand on those reports by assessing mechanical femoral tibial angle (mFTA) change in patients enrolled in the XLH Disease Monitoring Program (DMP), (NCT03651505) to determine the impact of initiating burosumab treatment after a history of active D/Pi. Included patients had either switched from active D/Pi to burosumab treatment at the discretion of their treating physician or as part of a burosumab clinical trial, or remained on active D/Pi through Year 3 of the DMP. Year 3 radiographs were compared with baseline to assess mFTA change and gauge improvement. Additional multivariate factor analysis examined 24 attributes to determine which had the greatest association with mFTA change. Change in mFTA was assessed for each limb independently. A greater proportion of limbs of patients switching from active D/Pi to burosumab had improved mFTA compared with those remaining on active D/Pi (p < .023). Odds ratios comparing limbs that improved to those that did not showed that switching to burosumab yields a significantly greater chance of improvement than continuing active D/Pi (OR [95% CI]: 4.38 [1.09-17.50]; p = .0469). Factor analysis identified younger age at burosumab initiation (p = .001) and lower baseline height Z-score (p = .006) as being significantly associated with greater change in mFTA Z-score. This study shows that switching to burosumab significantly improves lower limb malalignment in children with XLH over benefits conferred by active D/Pi, with early burosumab initiation providing the greatest benefit.