Homeostatic Regulation of Pro-Angiogenic and Anti-Angiogenic Proteins via Hedgehog, Notch Grid, and Ephrin Signaling in Tibial Dyschondroplasia

Precise coupling of two fundamental mechanisms, chondrogenesis and osteogenesis via angiogenesis, plays a crucial role during rapid proliferation of growth plates, and alteration in their balance might lead to pathogenic conditions. Tibial dyschondroplasia (TD) is characterized by an avascular, non-mineralized, jade-white "cartilaginous wedge" with impaired endochondral ossification and chondrocyte proliferation at the proximal end of a tibial bone in rapidly growing poultry birds. Developing vascular structures are dynamic with cartilage growth and are regulated through homeostatic balance among pro and anti-angiogenic proteins and cytokines. Pro-angiogenic factors involves a wide spectrum of multifactorial mitogens, such as vascular endothelial growth factors (VEGF), platelet-derived growth factors (PDGF), basic fibroblast growth factor (bFGF), placental growth factors, transforming growth factor-β (TGF-β), and TNF-α. Considering their regulatory role via the sonic hedgehog, notch-gridlock, and ephrin-B2/EphB4 pathways and inhibition through anti-angiogenic proteins like angiostatin, endostatin, decoy receptors, vasoinhibin, thrombospondin, PEX, and troponin, their possible role in persisting inflammatory conditions like TD was studied in the current literature review. Balanced apoptosis and angiogenesis are vital for physiological bone growth. Any homeostatic imbalance among apoptotic, angiogenetic, pro-angiogenic, or anti-angiogenic proteins ultimately leads to pathological bone conditions like TD and osteoarthritis. The current review might substantiate solid grounds for developing innovative therapeutics for diseases governed by the disproportion of angiogenesis and anti-angiogenesis proteins.

Mmp2 Deficiency Leads to Defective Parturition and High Dystocia Rates in Mice

Parturition is the final and essential step for mammalian reproduction. While the uterus is quiescent during pregnancy, fundamental changes arise in the myometrial contractility, inducing fetal expulsion. Extracellular matrix (ECM) remodeling is fundamental for these events. The gelatinases subgroup of matrix metalloproteinases (MMPs), MMP2 and MMP9, participate in uterine ECM remodeling throughout pregnancy and parturition. However, their loss-of-function effect is unknown. Here, we determined the result of eliminating Mmp2 and/or Mmp9 on parturition in vivo, using single- and double-knockout (dKO) mice. The dystocia rates were measured in each genotype, and uterine tissue was collected from nulliparous synchronized females at the ages of 2, 4, 9 and 12 months. Very high percentages of dystocia (40-55%) were found in the Mmp2-/- and dKO females, contrary to the Mmp9-/- and wild-type females. The histological analysis of the uterus and cervix revealed that Mmp2-/- tissues undergo marked structural alterations, including highly enlarged myometrial, endometrial and luminal cavity. Increased collagen deposition was also demonstrated, suggesting a mechanism of extensive fibrosis in the Mmp2-/- myometrium, which may result in dystocia. Overall, this study describes a new role for MMP2 in myometrium remodeling during mammalian parturition process, highlighting a novel cause for dystocia due to a loss in MMP2 activity in the uterine tissue.

Ginsenoside Rg1 regulates thiram-induced chondrocytes' apoptosis and angiogenesis in broiler chickens

Tibial dyschondroplasia (TD) is a developmental cartilaginous disease due to thiram toxicity. The abnormity of chondrocytes and insufficient angiogenesis within the growth plate are the major factors leading to the occurrence of TD in most cases. In the current study, we evaluated the beneficial effects of ginsenoside (Rg1) against thiram-induced TD for knowing the possible underlying mechanisms in broiler chickens through in vivo and in vitro assessment. Arbor acres broilers (1-day-old, n = 120) were randomly divided for the in vivo evaluation. The control broilers were fed under normal conditions during the whole experiment cycle (18 days). The TD broilers were fed with 50 mg/kg thiram, while the treatment group was given 40 mg/kg of Rg1. According to our findings, thiram caused a decrease in production performance and tibia parameters (p < 0.05), which were significantly reversed by Rg1 administration. In addition, the results from the histological evaluation showed that the proliferative zone had a smaller number of blood vessels, surrounded by inviable chondrocytes, proving apoptosis during the occurrence of TD, while Rg1 treatment significantly increased blood vessels and decreased apoptotic cells. Furthermore, it was found that Rg1 effectively ameliorated the angiogenesis by regulation of HIF-1α/VEGFA/VEGFR2 signaling pathway and the chondrocytes' apoptosis via the mitochondrial pathway. Hence, these findings suggest that Rg1 might be a perfect choice in the prevention and treatment of TD via regulating chondrocytes apoptosis and angiogenesis. Also, it might be a potential therapeutic drug for humans to overcome different bone disorders, involving chondrocytes.

Enhanced Extracellular Matrix Degradation in Growth Plate Contributes to Manganese Deficiency-Induced Tibial Dyschondroplasia in Broiler Chicks

Manganese (Mn) is a crucial trace element for poultry nutrition, and its deficiency compromises tibial cartilage development, leading to perosis and a higher incidence of slipped tendon. Tibial dyschondroplasia (TD) is a metabolic cartilage disease characterized by disruption of endochondral bone formation, which is closely related to extracellular matrix (ECM) degradation, in which Mn deficiency plays an important role. Previous studies have confirmed the role of matrix metalloproteinases (MMPs) in the pathogenesis of TD, but whether dysregulated ECM degradation and MMP expression profiles in growth plate are involved in Mn deficiency-induced avian TD has not been fully elucidated yet. Thus, this study was conducted to clarify these issues. Firstly, we successfully established TD model induced by Mn deficiency in broiler chicks. Mn deficiency decreased the number of chondrocytes, contents of proteoglycan, and type II collagen in tibial growth plate, demonstrating the tibial growth plate damage with enhanced ECM degradation. Also, Mn deficiency inhibited the Nrf2 signaling pathway and enhanced the protein levels of NLRP3, active caspase-1, and active IL-1β in tibial growth plate, indicating the oxidative stress and inflammatory response in Mn deficiency-induced TD. Additionally, upregulated expression levels of MMPs (MMP1, 9, and 13) were observed in tibial growth plate of Mn deficiency group. In summary, these findings suggest that Mn deficiency-enhanced ECM degradation is involved in avian TD, which may be correlated with oxidative stress, inflammatory response, and upregulation of MMPs.

Taurine is an effective therapy against thiram induced tibial dyschondroplasia via HIF-1α/VEGFA and β-catenin/ GSK-3β pathways in broilers

Thiram causes tibial dyschondroplasia in broilers, leading to a significant economic loss in the poultry industry. Our study explored the effects of taurine in thiram induced tibial dyschondroplasia (TD) through in vivo and in vitro approches. In in vivo study, thiram resulted in lameness disorder, low production parameters ALP, ACP, and a high level of NOS. While, the taurine exhibited promising effect by reducing lameness, increasing ALP, ACP levels, and significantly lowering NOS level with the restoration of the growth plate. In in vitro study, thiram caused distortion and disintegration of chondrocytes. The CCK-8 technique revealed the lower cell activity in TD as compared with the treatment group. Even, the treatment and taurine groups had higher cell activity than control group. Also, the chondrocyte morphology progressively reverted to normal after taurine treatment. It might effectively decreased the symptoms of TD in broilers and their production performance. Further research found that the taurine effectively improved chondrocytes' cell viability and recovered lameness disorder by regulation of HIF-1α, VEGFA, and Wnt/β-catenin signaling pathways. In summary, these results indicate that taurine has a protective effect on thiram-induced broilers and it can enhance the growth activity by directly affecting the development of chondrocytes and blood vessels.

Puerarin enhance vascular proliferation and halt apoptosis in thiram-induced avian tibial dyschondroplasia by regulating HIF-1α, TIMP-3 and BCL-2 expressions

Tetramethyl thiuram disulfide (thiram) is a dithiocarbamate pesticide used for crop protection and storage. But, it's widespread utilization is associated with deleterious growth plate cartilage disorder in broilers termed as avian tibial dyschondroplasia (TD). TD results in non-mineralized and less vascularized proximal tibial growth plate cartilage causing lameness and poor growth performance. This study investigated the therapeutic potential of puerarin against thiram toxicity in TD affected chickens. One-day-old broiler chickens (n = 240) were alienated into three equal groups i.e. control, TD and puerarin (n = 80) and were offered standard feed. Additionally, TD and puerarin groups were offered thiram at 50 mg/kg of feed from 4 to 7 days for TD induction followed by puerarin therapy at 120 mg/kg to puerarin group only from 8 to 18 days for TD treatment. Thiram feeding to TD and puerarin group chickens caused lameness, mortality, and increased the aspartate aminotransferase (AST), alanine aminotransferase (ALT), malondialdehyde (MDA) levels and growth plate (GP) size and upregulated HIF-1α expression. Besides, the production parameters, alkaline phosphatase (ALP), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) levels and the expressions of TIMP-3 and BCL-2 were decreased (p < 0.05). Puerarin alleviated lameness, enhanced angiogenesis and growth performance and serum and antioxidant enzymes, decreased apoptosis and recuperated GP width by significantly downregulating HIF-1α and upregulating the TIMP-3 and BCL-2 mRNA and protein expressions in puerarin group chickens (p < 0.05). In conclusion, the toxic effects associated with thiram can be mitigated using puerarin.

Identification of differentially expressed MiRNAs profile in a thiram-induced tibial dyschondroplasia

Tetramethyl thiuram disulfide (thiram) is a dithiocarbamate, which is widely used on seeds and storing food grains. The incorporation of thiram into the food chain could be a risk for both human beings and animals. Thiram-contaminated feed has been considered a common cause of tibial dyschondrolplasia (TD) in many avian species. The molecular mechanism of action of thiram on TD involving microRNA (miRNA) is not fully understood. For this purpose, the morbidity and pathologic changes were evaluated to understand the TD, and high-throughput RNA sequencing (RNA-Seq) was performed to explore the differentially expressed miRNAs (DEGs). RT-qPCR was used to confirm the validity as compared with sequencing data. The results showed that the marked alterations in the growth plate of the TD chickens were noticeable, with shrinking cells and irregular chondrocyte columns as compared with control group. In this study, we identified total 375 (p < 0.1), 340 (p < 0.05) and 266 (p < 0.01) significant DEGs between the TD and control groups. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis of DEGs showed that the target miRNAs were significantly enriched in different treatment groups, such as apoptosis, mRNA surveillance pathway, mitophagy-animal, etc. This study provides theoretical basis for in-depth understanding the pathogenesis of thiram-induced TD and explore the new insights towards the proposed molecular mechanism of specific miRNA as biomarkers for effective gene diagnosis and treatment of TD in broilers.

Gene expression of matrix metalloproteinase 9 (MMP9), matrix metalloproteinase 13 (MMP13), vascular endothelial growth factor (VEGF) and fibroblast growth factor 23 (FGF23) in femur and vertebra tissues of the hypovitaminosis D kyphotic pig model

The hypovitaminosis D kyphotic pig provides a reliable model to study the initiation of bone lesions caused by maternal vitamin D (D) deficiencies. Matrix metalloproteinases (MMP; specifically, MMP9 and MMP13) and vascular endothelial growth factor (VEGF) are important in endochondral ossification and are potentially regulated by D. Fibroblast growth factor 23 (FGF23) is interrelated with D homoeostasis and bone mineralisation. Relative mRNA expression of MMP9, MMP13, VEGF and FGF23 was measured in pig femur and vertebra. Sows (n 37) were fed diets with 0 (-D), 8·125 (+D) or 43·750 (++D) µg D3/kg throughout gestation and lactation. At weaning (3 weeks), pigs were fed diets with 0 (-D) or 7·0 (+D) µg D3/kg, each with 75 and 95 % (LCaP) or 150 and 120 % (HCaP) of the Ca and P requirements. Pigs at birth (n 27), 3 weeks (n 27) and after the nursery period (7 weeks; n 72) were euthanised for analysis. At 3 weeks, femur MMP9 expression of pigs produced by +D or ++D sows was reduced (P<0·05) to 0·5-fold and VEGF expression to 0·4-fold compared with pigs from -D sows. At 7 weeks, MMP9 expression was reduced (P<0·05) to 0·45-fold in femur and 0·58-fold in vertebra from pigs produced by +D or ++D sows compared with pigs from -D sows. Pig femur VEGF expression was reduced to 0·75-fold in pigs produced by ++D sows. MMP9 and VEGF mRNA expression offer potential markers for the initiation of bone lesions in the hypovitaminosis D kyphotic pig model.

Characterization of Chicken MMP13 Expression and Genetic Effect on Egg Production Traits of Its Promoter Polymorphisms

Extracelluar matrix undergoes constant remodeling, cell–cell, and cell–matrix interactions during chicken ovarian follicle growth, which is coordinated by matrix metalloproteinases (MMPs), and their associated endogenous inhibitors (TIMPs). Transcriptome analysis revealed upregulation of MMP13 in sexually mature chicken ovaries. In this study, we found that the expression of MMP13 in chicken ovary was stably elevated from 60 d to 159 d, and was significantly higher at 159 d than at the other three developmental stages (P < 0.05). The expression of MMP13 mRNA increased from SW (small white follicles) to F5 (fifth largest follicles), then decreased to F1 (first largest follicles), and dramatically increased again in POF1 (newly postovulatory follicles) follicles (P < 0.05). The MMP13 protein was localized in stroma cells and primordial follicles of sexually immature chicken ovaries, in the theca cell layers of all sized follicles of sexually mature chicken ovaries. Furthermore, we identified a positive element (positions –1863 to –1036) controlling chicken MMP13 transcription, and, in this region, six single nucleotide polymorphisms were found and genotyped in chicken populations. In the White Recessive Rock population, hens with A^–1356-C^–1079/A^–1356-C^–1079 genotype had earlier “age at first laying” than those with G^–1356-T^–1079/G^–1356-T^–1079 genotype (P < 0.05), and exhibited significantly lower transcriptional activity (P < 0.01). Collectively, chicken MMP13 plays an important role in ovarian follicle growth and regression, and polymorphisms in its promoter region could be used as molecular markers for improving the trait “age at first laying” in chicken breeding.

The cartilage extracellular matrix as a transient developmental scaffold for growth plate maturation

The cartilage growth plate is a specialized developmental tissue containing characteristic zonal arrangements of chondrocytes. The proliferative and differentiative states of chondrocytes are tightly regulated at all stages including the initial limb bud and rudiment cartilage stages of development, the establishment of the primary and secondary ossification centers, development of the growth plates and laying down of bone. A multitude of spatio-temporal signals, including transcription factors, growth factors, morphogens and hormones, control chondrocyte maturation and terminal chondrocyte differentiation/hypertrophy, cell death/differentiation, calcification and vascular invasion of the growth plate and bone formation during morphogenetic transition of the growth plate. This involves hierarchical, integrated signaling from growth and factors, transcription factors, mechanosensory cues and proteases in the extracellular matrix to regulate these developmental processes to facilitate progressive changes in the growth plate culminating in bone formation and endochondral ossification. This review provides an overview of selected components which have particularly important roles in growth plate biology including collagens, proteoglycans, glycosaminoglycans, growth factors, proteases and enzymes.

The growth plate's response to load is partially mediated by mechano-sensing via the chondrocytic primary cilium

Mechanical load plays a significant role in bone and growth-plate development. Chondrocytes sense and respond to mechanical stimulation; however, the mechanisms by which those signals exert their effects are not fully understood. The primary cilium has been identified as a mechano-sensor in several cell types, including renal epithelial cells and endothelium, and accumulating evidence connects it to mechano-transduction in chondrocytes. In the growth plate, the primary cilium is involved in several regulatory pathways, such as the non-canonical Wnt and Indian Hedgehog. Moreover, it mediates cell shape, orientation, growth, and differentiation in the growth plate. In this work, we show that mechanical load enhances ciliogenesis in the growth plate. This leads to alterations in the expression and localization of key members of the Ihh-PTHrP loop resulting in decreased proliferation and an abnormal switch from proliferation to differentiation, together with abnormal chondrocyte morphology and organization. Moreover, we use the chondrogenic cell line ATDC5, a model for growth-plate chondrocytes, to understand the mechanisms mediating the participation of the primary cilium, and in particular KIF3A, in the cell's response to mechanical stimulation. We show that this key component of the cilium mediates gene expression in response to mechanical stimulation.

Differential expression of extracellular matrix metalloproteinase inducer (EMMPRIN/CD147) in avian tibial dyschondroplasia

Tibial dyschondroplasia (TD) is an avian bone disorder of different aetiologies that may be associated with lameness. The disorder is characterized by focal disruption of endochondral bone formation, with a lack of matrix proteolysis and an accumulation of non-mineralized avascular cartilage. The aim of this study was to determine the expression of extracellular matrix metalloproteinase inducer (EMMPRIN/CD147) in normal, thiram-induced TD lesions and in the process of recovery from TD in broiler chickens. An extracellular matrix (ECM) degrading enzyme, matrix metalloproteinase-9 (MMP-9), was selected to investigate the effects of CD147 in the degradation of ECM. Gene expression was analysed by quantitative real-time polymerase chain reaction and protein levels by immunohistochemistry and western blotting. The birds were divided into three groups: thiram fed; recovery; and controls. Genes encoding CD147 and MMP-9 were down-regulated during the development of the disease, and were up-regulated during recovery. Western blotting also showed lower protein levels of CD147 in TD, which increased during the recovery phase associated with ECM degradation and growth plate repair. The findings of this study suggest that ECM has a crucial role in the occurrence of TD and that CD147 appears to play a pivotal role in matrix proteolysis in the chicken, similar to that in other species.

Screening of differentially expressed genes in the growth plate of broiler chickens with tibial dyschondroplasia by microarray analysis

Background

Tibial dyschondroplasia (TD) is a common skeletal disorder in broiler chickens. It is characterized by the presence of a non-vascularized and unmineralized cartilage in the growth plate. Previous studies have investigated differential expression of genes related to cartilage development during latter stages of TD. The aim of our study was to identify differentially expressed genes (DEGs) in the growth plate of broiler chickens, which were associated with early stage TD. We induced TD using tetramethylthiuram disulfide (thiram) for 1, 2, and 6 days and determined DEGs with chicken Affymetrix GeneChip assays. The identified DEGs were verified by quantitative polymerase chain reaction (qPCR) assays.

Results

We identified 1630 DEGs, with 82, 1385, and 429 exhibiting at least 2.0-fold changes (P < 0.05) at days 1, 2, and 6, respectively. These DEGs participate in a variety of biological processes, including cytokine production, oxidation reduction, and cell surface receptor linked signal transduction on day 1; lipid biosynthesis, regulation of growth, cell cycle, positive and negative gene regulation, transcription and transcription regulation, and anti-apoptosis on day 2; and regulation of cell proliferation, transcription, dephosphorylation, catabolism, proteolysis, and immune responses on day 6. The identified DEGs were associated with the following pathways: neuroactive ligand-receptor interaction on day 1; synthesis and degradation of ketone bodies, terpenoid backbone biosynthesis, ether lipid metabolism, JAK-STAT, GnRH signaling pathway, ubiquitin mediated proteolysis, TGF-β signaling, focal adhesion, and Wnt signaling on day 2; and arachidonic acid metabolism, mitogen-activated protein kinase (MAPK) signaling, JAK-STAT, insulin signaling, and glycolysis on day 6. We validated seven DEGs by qPCR.

Conclusions

Our findings demonstrate previously unrecognized changes in gene transcription associated with early stage TD. The DEGs we identified by microarray analysis will be used in future studies to clarify the molecular pathogenic mechanisms of TD. From these findings, potential pathways involved in early stage TD warrant further investigation.

The role of matrix gla protein in ossification and recovery of the avian growth plate

Extracellular matrix mineralization is an essential physiologic process in bone, teeth, and hypertrophic cartilage. Matrix Gla protein (MGP), an inhibitor of mineralization, is expressed by chondrocytes and vascular smooth muscle cells to inhibit calcification of those soft tissues. Tibial dyschondroplasia (TD), a skeletal abnormality apparent as a plug of non-vascularized, non-mineralized, white opaque cartilage in the tibial growth plate of avian species can serve as a good model for studying process and genes involved in matrix mineralization and calcification. In this work, we studied the involvement of MGP in the development of TD, as well as in the processes of spontaneous and induced recovery from this syndrome. First, we found that during normal bone development, MGP is expressed in specific time and locations, starting from wide-spread expression in the yet un-ossified diaphysis during embryonic development, to specific expression in hypertrophic chondrocytes adjacent to the chondro-osseous junction and the secondary ossification center just prior to calcification. In addition, we show that MGP is not expressed in the impaired TD lesion, however when the lesion begins to heal, it strongly express MGP prior to its calcification. Moreover, we show that when calcification is inhibited, a gap is formed between the expression zones of MGP and BMP2 and that this gap is closed during the healing process. To conclude, we suggest that MGP, directly or through interaction with BMP2, plays a role as ossification regulator that acts prior to ossification, rather then simple inhibitor.

Control of chondrocyte gene expression by actin dynamics: a novel role of cholesterol/Ror-alpha signalling in endochondral bone growth

Elucidating the signalling pathways that regulate chondrocyte differentiation, such as the actin cytoskeleton and Rho GTPases, during development is essential for understanding of pathological conditions of cartilage, such as chondrodysplasias and osteoarthritis. Manipulation of actin dynamics in tibia organ cultures isolated from E15.5 mice results in pronounced enhancement of endochondral bone growth and specific changes in growth plate architecture. Global changes in gene expression were examined of primary chondrocytes isolated from embryonic tibia, treated with the compounds cytochalasin D, jasplakinolide (actin modifiers) and the ROCK inhibitor Y27632. Cytochalasin D elicited the most pronounced response and induced many features of hypertrophic chondrocyte differentiation. Bioinformatics analyses of microarray data and expression validation by real-time PCR and immunohistochemistry resulted in the identification of the nuclear receptor retinoid related orphan receptor-α (Ror-α) as a novel putative regulator of chondrocyte hypertrophy. Expression of Ror-α target genes, (Lpl, fatty acid binding protein 4 [Fabp4], Cd36 and kruppel-like factor 5 [Klf15]) were induced during chondrocyte hypertrophy and by cytochalasin D and are cholesterol dependent. Stimulation of Ror-α by cholesterol results in increased bone growth and enlarged, rounded cells, a phenotype similar to chondrocyte hypertrophy and to the changes induced by cytochalasin D, while inhibition of cholesterol synthesis by lovastatin inhibits cytochalasin D induced bone growth. Additionally, we show that in a mouse model of cartilage specific (Col2-Cre) Rac1, inactivation results in increased Hif-1α (a regulator of Rora gene expression) and Ror-α⁺ cells within hypertrophic growth plates. We provide evidence that cholesterol signalling through increased Ror-α expression stimulates chondrocyte hypertrophy and partially mediates responses of cartilage to actin dynamics.

Matrix metalloproteinase expression in primary lung fibroblasts of layer type chickens

We attempted to determine the growth characteristics of cultured lung fibroblasts of layer type chickens and to investigate presence of matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) in these cells in vitro. Lung fibroblasts were isolated, characterized and subcultured from one-day-old layer type chicken lungs. Two different methods, explant culture and enzymatic techniques, were used for culturing and the results were compared. The presence of MMP-2 and TIMP-1 was shown in cultured fibroblasts by immunocytochemical staining, immune blotting and zymography methods. Immune expressions of neither MMP-9 nor TIMP-2 enzymes could be detected.

Hsp90 and angiogenesis in bone disorders—lessons from the avian growth plate

Thiram-induced tibial dyschondroplasia (TD) and vitamin-D deficiency rickets are avian bone disorders of different etiologies characterized by abnormal chondrocyte differentiation, enlarged and unvascularized growth plates, and lameness. Heat-shock protein 90 (Hsp90) is a proangiogenic factor in mammalian tissues and in tumors; therefore, Hsp90 inhibitors were developed as antiangiogenic factors. In this study, we evaluated the association between Hsp90, hypoxia, and angiogenesis in the chick growth plate. Administration of the Hsp90 inhibitor to TD- and rickets-afflicted chicks at the time of induction resulted in reduction in growth-plate size and, contrary to its antiangiogenic effect in tumors, a major invasion of blood vessels occurred in the growth plates. This was the result of upregulation of the VEGF receptor Flk-1, the major rate-limiting factor of vascularization in TD and rickets. In addition, the abnormal chondrocyte differentiation, as characterized by collagen type II expression and alkaline phosphatase activity, and the changes in hypoxia-inducible factor-1α (HIF-1α) in both disorders were restored. All these changes resulted in prevention of lameness. Inhibition of Hsp90 activity reduced growth-plate size, increased vascularization, and mitigated lameness also in TD chicks with established lesions. In summary, this is the first reported demonstration of involvement of Hsp90 in chondrocyte differentiation and growth-plate vascularization. In contrast to the antiangiogenic effect of Hsp90 inhibitors observed in mammals, inhibition of Hsp90 activity in the unvascularized TD- and rickets-afflicted chicks resulted in activation of the angiogenic switch and reinstated normal growth-plate morphology.