Bone development is characterized by complex regulation mechanisms, including signal transduction and transcription factor-related pathways, glycobiological processes, cellular interactions, transportation mechanisms, and, importantly, chemical formation resulting from hydroxyapatite. Any abnormal regulation in the bone development processes causes skeletal system-related problems. To some extent, the avascularity of cartilage and bone makes drug delivery more challenging than that of soft tissues. Recent studies have implemented many novel bone-targeting approaches to overcome drawbacks. However, none of these strategies fully corrects skeletal dysfunction, particularly in growth plate-related ones. Although direct recombinant enzymes (e.g., Vimizim for Morquio, Cerezyme for Gaucher, Elaprase for Hunter, Mepsevii for Sly diseases) or hormone infusions (estrogen for osteoporosis and osteoarthritis), traditional gene delivery (e.g., direct infusion of viral or non-viral vectors with no modifications on capsid, envelope, or nanoparticles), and cell therapy strategies (healthy bone marrow or hematopoietic stem cell transplantation) partially improve bone lesions, novel delivery methods must be addressed regarding target specificity, less immunogenicity, and duration in circulation. In addition to improvements in bone delivery, potential regulation of bone development mechanisms involving receptor-regulated pathways has also been utilized. Targeted drug delivery using organic and inorganic compounds is a promising approach in mostly preclinical settings and future clinical translation. This review comprehensively summarizes the current bone-targeting strategies based on bone structure and remodeling concepts while emphasizing potential approaches for future bone-targeting systems.

It is not clear as to whether weight bearing and ambulation may affect bone growth. Our goal was to study the role of mechanical loading (one of the components of ambulation) on endochondral ossification and longitudinal bone growth. Thus, we applied cyclical, biologically relevant strains for a prolonged time period (4 weeks) to one tibia of juvenile mice, while using the contralateral one as an internal control. By the end of the 4-week loading period, the mean tibial growth of the loaded tibiae was significantly greater than that of the unloaded tibiae. The mean height and the mean area of the loaded tibial growth plates were greater than those of the unloaded tibiae. In addition, in female mice we found a greater expression of PTHrP in the loaded tibial growth plates than in the unloaded ones. Lastly, microCT analysis revealed no difference between loaded and unloaded tibiae with respect to the fraction of bone volume relative to the total volume of the region of interest or the tibial trabecular bone volume. Thus, our findings suggest that intermittent compressive forces applied on tibiae at mild-moderate strain magnitude induce a significant and persistent longitudinal bone growth. PTHrP expressed in the growth plate appears to be one growth factor responsible for stimulating endochondral ossification and bone growth in female mice.

Energy metabolism, through pathways such as oxidative phosphorylation (OxPhos) and glycolysis, plays a pivotal role in cellular differentiation and function. Our study investigates the impact of OxPhos disruption in cortical bone development by deleting Mitochondrial Transcription Factor A (TFAM). TFAM controls OxPhos by regulating the transcription of mitochondrial genes. The cortical bone, constituting the long bones\' rigid shell, is sheathed by the periosteum, a connective tissue layer populated with skeletal progenitors that spawn osteoblasts, the bone-forming cells. TFAM-deficient mice presented with thinner cortical bone, spontaneous midshaft fractures, and compromised periosteal cell bioenergetics, characterized by reduced ATP levels. Additionally, they exhibited an enlarged periosteal progenitor cell pool with impaired osteoblast differentiation. Increasing Hypoxia-Inducible Factor 1a (HIF1) activity within periosteal cells significantly mitigated the detrimental effects induced by TFAM deletion. HIF1 is known to promote glycolysis in all cell types. Our findings underscore the indispensability of OxPhos for the proper accrual of cortical bone mass and indicate a compensatory mechanism between OxPhos and glycolysis in periosteal cells. The study opens new avenues for understanding the relationship between energy metabolism and skeletal health and suggests that modulating bioenergetic pathways may provide a therapeutic avenue for conditions characterized by bone fragility.

Cadmium (Cd) poses significant risks to aquatic organisms due to its toxicity and ability to disrupt the cellular processes. Given the similar atomic radius of Cd and calcium (Ca), Cd may potentially affect the Ca homeostasis, which can lead to impaired mineralization of skeletal structures and behavioral abnormalities. The formation of the spinal skeleton involves Ca transport and mineralization. In this study, we conducted an in-depth investigation on the effects of Cd at environmental concentrations on zebrafish (Danio rerio) skeletal development and the underlying molecular mechanisms. As the concentration of Cd increased, the accumulation of Cd in zebrafish larvae also rose, while the Ca content decreased significantly by 3.0 %-57.3 %, and vertebral deformities were observed. Transcriptomics analysis revealed that sixteen genes involved in metal absorption were affected. Exposure to 2 µg/L Cd significantly upregulated the expression of these genes, whereas exposure to 10 µg/L resulted in their downregulation. Consequently, exposure of zebrafish larvae to 10 µg/L of Cd inhibited the body segmentation growth and skeletal mineralization development by 29.1 %-56.7 %. This inhibition was evidenced by the downregulation of mineral absorption genes and decreased Ca accumulation. The findings of this study suggested that the inhibition of skeletal mineralization was likely attributed to the disruption of mineral absorption, thus providing novel insights into the mechanisms by which metal pollutants inhibit the skeletal development of fish.

Growth and maturation occur in a predictable pattern throughout the body and within each individual bone. In the appendicular skeleton, endochondral ossification predominates in long bones and growth plates. The ends of these long bones are sites of relative weakness in the immature skeleton and prone to injury from acute insult and overuse. We present the normal histoanatomy and physiology of the growth plate complex, highlighting the unique contribution of each component and shared similarities between primary and secondary complexes. Components of the growth plate complex include the physis proper, subjacent vascularity within the growth cartilage, and the ossification front. The second section describes imaging considerations and features of normal and abnormal growth. Finally, we review the Salter-Harris classification for acute fractures and offer examples of characteristic overuse injury patterns involving the epiphyseal (proximal humerus and distal radius), apophyseal (medial epicondyle and tibial tubercle), and secondary growth plate complexes (medial femoral condyle and capitellar osteochondritis dissecans). This article provides a foundation and basic framework to better understand and anticipate potential complications and growth disturbances and to ensure optimal follow-up and early intervention when treatment can be less invasive.

BACKGROUND: HIV infection and its treatment compromises skeletal development (growth and maturation). Skeletal maturity is assessed as bone age (BA) on hand and wrist radiographs. BA younger than chronological age (CA) indicates delayed development. We conducted a cross-sectional study to determine differences between BA and CA (i.e., skeletal maturity deviation [SMD]), and risk factors associated with SMD in peripubertal children with and without HIV established on antiretroviral therapy (ART) including use of tenofovir disoproxil fumarate (TDF).
METHODS: Children with HIV taking ART for at least two years and a comparison group of HIV-negative children, aged 8-16 years and frequency-matched by age and sex, were recruited from HIV clinics and local schools in the same catchment area, in Harare, Zimbabwe. BA was assessed from non-dominant hand-wrist radiographs using the Tanner Whitehouse 3 method. Negative SMD values correspond to delayed development, i.e., BA younger than CA. Multivariable linear regression models determined factors associated with SMD overall, and in children with HIV.
RESULTS: In total, 534 participants (54% males) were included; by design CA was similar in males and females, whether living with or without HIV. Mean (SD) SMD was more negative in CWH than in HIV-negative children in both males [-1.4(1.4) vs. -0.4(1.1) years] and females [-1.1(1.3) vs. -0.0(1.2) years]. HIV infection and weight-for-age Z-score<-2 were associated with more negative SMD in both males and females after adjusting for socio-economic status, orphanhood, pubertal stage, and calcium intake. Age at ART initiation was associated with SMD in both males and females with those starting ART later more delayed: starting ART aged 4-8 years 1.14 (-1.84, -0.43), or over 8 years 1.47 (-2.30, -0.65) (p-value for trend < 0.001). Similar non-significant trends were seen in males. TDF exposure TDF exposure whether < 4years or ≥ 4 years was not associated with delayed development.
CONCLUSIONS: Perinatally-acquired HIV infection and being underweight were independently associated with delayed skeletal maturation in both males and females. Starting ART later was independently associated with skeletal maturation delay in CWH. Given the known effects of delayed development on later health, it is important to find interventions to ensure healthy weight gain through early years and in CWH to initiate ART as early as possible.

The most widely used synthetic glucocorticoid, dexamethasone (DEX), causes stunted growth in children when used excessively or for long periods of time; however, there are still plenty of pediatric patients require long-term treatment with DEX. As an alternative, growth hormone is used in combination, but it has side effects, a high cost, and psychological factors, and it is not satisfactory in terms of effectiveness. It is necessary to develop a safe and affordable treatment that can replace it. The Korean Food and Drug Administration approved HT042, a standardized functional food ingredient, with the claim that it can help height growth of children. In this study, it was found that HT042 activated the Indian hedgehog/parathyroid hormone-related protein signaling pathway and enhanced the number of growth hormone receptors and insulin-like growth factor-1 receptors on the growth plate surface, which were reduced by DEX treatment, and restored growth retardation. In metatarsal bone and primary chondrocyte models, it was found that HT042 can promote the length of growth plate and recover DEX-induced growth retardation. It was also found that HT042 promotes cell proliferation using bromodeoxyuridine and terminal deoxynucleotidyl transferase dUTP nick end labeling assays; moreover, we verified increased expression of GHR/IGF-1R and Ihh/PTHrP pathway activity using qRT-PCR, western blotting, and siRNA analyses to verify its direct action on the growth plate. The anti-apoptotic effect of HT042 was identified by regulating the expression of apoptotic factors such as caspase-3, Bcl2, Bclx, and Bax. These results were identified using both ex vivo and in vitro models. Our study verified that co-administration of HT042 could recover the DEX induced growth retardation.

RNA-binding proteins (RBPs), which regulate gene expression through post-transcriptional modifications of RNAs, play a role in diverse biological processes that include bone cell development and bone tissue formation. RBP dysregulation may result in aberrant bone homeostasis and contribute to various bone diseases. The function of RBPs in bone physiology and pathophysiology and the underlying molecular mechanisms have been extensively studied in recent years. This article provides a review of such studies, highlighting the potential of RBPs as pivotal targets for therapeutic intervention.

The impact of milk on bone health in rural preschoolers is under-researched. This study, through a clinical trial and a meta-analysis, finds that milk supplementation enhances forearm and calcaneus bone acquisition in children, supporting the benefits of daily milk consumption.
OBJECTIVE: This study evaluated the impact of dairy supplementation on bone acquisition in children\'s limbs through a cluster-randomized controlled trial and a meta-analysis.
METHODS: The trial involved 315 children (4-6 year) from Northwest China, randomized to receive either 390 ml of milk daily (n = 215) or 20-30 g of bread (n = 100) over 12 months. We primarily assessed bone mineral density (BMD) and content (BMC) changes at the limbs, alongside bone-related biomarkers, measured at baseline, the 6th and 12th months. The meta-analysis aggregated BMD or BMC changes in the forearm/legs/calcaneus from published randomized trials involving children aged 3-18 years supplemented with dairy foods (vs. control group).
RESULTS: Of 278 completed the trial, intention-to-treat analysis revealed significant increases in BMD (4.05% and 7.31%) and BMC (4.69% and 7.34%) in the left forearm at the 6th and 12th months in the milk group compared to controls (P < 0.001). The calcaneus showed notable improvements in BMD (2.01%) and BMC (1.87%) at 6 months but not at 12 months. Additionally, milk supplementation was associated with beneficial changes in bone resorption markers, parathyroid hormone (- 12.70%), insulin-like growth factor 1 (6.69%), and the calcium-to-phosphorus ratio (2.22%) (all P < 0.05). The meta-analysis, encompassing 894 children, indicated that dairy supplementation significantly increased BMD (SMD, 0.629; 95%CI: 0.275, 0.983) and BMC (SMD, 0.616; 95%CI: 0.380, 0.851) (P < 0.05) in the arms, but not in the legs (P > 0.05).
CONCLUSIONS: Milk supplementation significantly improves bone health in children\'s forearms, underscoring its potential as a strategic dietary intervention for bone development. Trial registration NCT05074836.

Males and females have long shown disparities in body weight and height; yet, the underlying mechanisms influencing growth and development remain unclear. Male and female Zhedong White Geese (ZDW) geese have long been selected for large body size and egg production, respectively. This led to a large difference in body weight between males and females, making them a unique model for studying the effects of sex on growth and development. This study aimed to elucidate these mechanisms by comparing the transcriptomes of muscle and pituitary tissues in male and female ZDW geese to identify the critical genes responsible for the effects of sex on growth performance. Our analysis revealed 1101 differentially expressed genes (DEGs) in leg musculature (507 upregulated, 594 downregulated), 773 DEGs in breast musculature (311 upregulated, 462 downregulated), and 517 DEGs in the pituitary gland (281 upregulated, 236 downregulated) between male and female geese. These DEGs were significantly enriched in gene ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways associated with endocrine metabolism (e.g., hormonal activities), muscle formation (e.g., sarcomere and myofibril), and bone formation (e.g., bone morphogenesis and cartilage formation). The upregulated genes in males were enriched in KEGG pathways involving nutrient digestion and absorption (vitamin and protein), as well as the secretion of digestive juices (gastric acid and bile). Through protein-protein interaction analyses, we also observed high-density gene networks related to muscle fiber development, calcium ion metabolism, mitochondrial respiratory chain, and bone development. Therefore, our multi-tissue transcriptome analysis provides a deeper understanding of the complex and systematic gender-driven effects on growth and development in geese. IGF1, GHRHR, and NCAPG-LCORL and pathways related to myogenesis might play vital roles in gender differences before hormones exert their effect.