Immunohistochemical localization of cadherin and catenin adhesion molecules in the murine growth plate

Role of cadherin-11 in synovial joint formation and rheumatoid arthritis pathology

Cadherin-11 is a classic cadherin adhesion molecule that mediates homophilic cell-to-cell adhesion. Cadherin-11 is involved in the function of embryonic development, tissue morphogenesis, tumor invasion and metastasis, and signal transduction. This review summarizes the function of cadherin-11 in synovial joint formation and rheumatoid arthritis (RA), including its relative function with bone and cartilage development and growth plate, synovial, and tendon formation. The role of cadherin-11 in RA is also discussed, both in fibroblasts inflammation and fibroblast-like synoviocyte (FLSs) migration and invasion. The potential of anti-cadherin-11 therapy for RA is introduced in comparison with the other current RA therapies.

Gender- and region-specific variations of estrogen receptor α and β expression in the growth plate of spine and limb during development and adulthood

Although estrogen action is indispensable for normal bone growth in both genders, the roles of estrogen receptors (ERs) in mediating bone growth are not fully understood. The effects of ER inactivation on bone growth are sex and age dependent, and may differ between the axial and appendicular regions. In this study, the spatial and temporal expression of ERα and β in the tibial and spinal growth plates of the female and male rats during postnatal development was examined to explore the possible mechanisms. The level of mRNA was examined and compared with quantitative real-time PCR. The spatial location was determined by immunohistochemical analysis. The 1-, 4-, 7-, 12- and 16-week age stages correspond to early life, puberty and early adulthood after puberty, respectively. Gender- and region-specific differences in ERα and β expression were shown in the growth plates. Mainly nuclear staining of ERα and β immunoreactivity was demonstrated in the spinal and tibial growth plate chondrocytes for both genders. Moreover, our study indicated significant effect of gender on temporal ERα and β expression and of region on temporal ERα/ERβ expression ratio. However, spatial differences of region-related ERα and β expression were not observed. Gender-related spatial changes were detected only at 16 weeks of both spine and limb growth plates. ERα and β immunoreactivity was detected in the resting, proliferative and prehypertrophic chondrocytes in the early life stage and during puberty. After puberty, ERα expression was mainly located in the late proliferative and hypertrophic chondrocytes in female, whereas the expression still extended from the resting to hypertrophic chondrocytes in males. Gender- and region-specific expression patterns of ERα and β gene might be one possible reason for differences in sex- and region-related body growth phenotypes. Gender, age and region differences should be taken into consideration when the roles of ERs in the growth plate are investigated.

Age-related variations of leptin receptor expression in the growth plate of spine and limb: gender- and region-specific changes

Leptin is a potent growth-stimulating factor of bone. The effects of leptin on bone growth differ significantly between axial and appendicular regions. Gender differences of leptin function have also been suggested in normal pubertal development. To explore the mechanisms underlying these effects, we investigated the spatial and temporal expressions of the active form of the leptin receptor (Ob-Rb) in the tibial and spinal growth plates of the female and male rats during postnatal development. The 1-, 4-, 7-, 12- and 16-week age stages are representative for early life, puberty and early adulthood after puberty, respectively. Quantitative real-time PCR was used for Ob-Rb mRNA examination and comparison. The spatial location of Ob-Rb was determined by immunohistochemical analysis. There were gender- and region-specific differences in Ob-Rb mRNA expression in the growth plate. Mainly cytoplasm staining of Ob-Rb immunoreactivity was observed in the spinal and tibial growth plate chondrocytes of both genders. Spatial differences of region- and gender-related Ob-Rb expression were not observed. Ob-Rb immunoreactivity was detected in the resting, proliferative and prehypertrophic chondrocytes in early life stage and during puberty. After puberty, staining was mainly located in the late proliferative and hypertrophic chondrocytes. The results of Ob-Rb HSCORE analysis were similar to those obtained from quantitative real-time PCR. Our study indicated direct effects on the chondrocytes of the growth plate in different development stages. The region-specific expression patterns of Ob-Rb gene might be one possible reason for contrasting phenotypes in limb and spine. Different Ob-Rb expression patterns might partly contribute to age- and gender- related differences in trabecular bone mass.

Innate immune function of the adherens junction protein p120-catenin in endothelial response to endotoxin

Sepsis-induced acute lung injury is a common clinical disorder in critically ill patients that is associated with high mortality. In this study, we investigated the role of p120-catenin (p120), a constituent of endothelial adherens junctions, in regulating the innate immune function of lungs. In mice in which acute lung injury was induced by i.p. administration of LPS, we observed a rapid decrease in the expression of p120 in lungs. The p120 protein expression was correlated inversely with severity of inflammation. Suppression of p120 expression in lung endothelial cells in mice using small interfering RNA resulted in high sensitivity to endotoxin and greatly increased the mortality compared with controls. Knockdown of p120 also increased the expression of ICAM-1, neutrophil recruitment, production of cytokines TNF-α and IL-6, pulmonary transvascular protein permeability, and lung water content in response to LPS. We demonstrated that endothelial p120 modulates lung innate immune function by interfering with the association of TLR4 with its adaptor MyD88 to block TLR4 signaling and NF-κB activation in endothelial cells. In conclusion, these studies have uncovered a novel innate immune function of endothelial p120 in downregulating the lung inflammatory response to endotoxin through the suppression of TLR4 signaling.

Transcriptional profiling and biochemical analysis of mechanically induced cartilaginous tissues in a rat model

OBJECTIVE

To characterize patterns of molecular expression that lead to cartilage formation in vivo in a postnatal setting, by profiling messenger RNA expression across the time course of mechanically induced chondrogenesis.

METHODS

Retired breeder Sprague-Dawley rats underwent a noncritical-sized transverse femoral osteotomy. Experimental animals (n = 45) were subjected to bending stimulation (60 degrees cyclic motion in the sagittal plane for 15 minutes/day) of the osteotomy gap beginning on day 10 after the operation. Control animals (n = 32) experienced continuous rigid fixation. Messenger RNA isolated on days 10, 17, 24, and 38 after surgery was analyzed using a microarray containing 608 genes involved in skeletal development, tissue differentiation, fracture healing, and mechanotransduction. The glycosaminoglycan (GAG) content in the stimulated tissues was compared with that in native articular cartilage as a means of assessing the progression of chondrogenic development of the tissues.

RESULTS

The majority of the 100 genes that were differentially expressed were up-regulated in response to mechanical stimulation. Many of these genes are associated with articular cartilage development and maintenance, diarthrodial joint development, cell adhesion, extracellular matrix synthesis, signal transduction, and skeletal development. Quantitative real-time polymerase chain reaction results were consistent with the microarray findings. The GAG content of the stimulated tissues increased over time and was no different from that of articular cartilage on day 38 after surgery.

CONCLUSION

Our findings indicate that mechanical stimulation causes up-regulation of genes that are principally involved in joint cavity morphogenesis and critical to articular cartilage function. Further study of this type of stimulation may identify key signaling events required for postnatal hyaline cartilage formation.

Microarray analysis of perichondral and reserve growth plate zones identifies differential gene expressions and signal pathways

In the growth plate, the reserve and perichondral zones have been hypothesized to have similar functions, but their exact functions are poorly understood. Our hypothesis was that significant differential gene expression exists between perichondral and reserve chondrocytes that may differentiate the respective functions of these two zones. Normal Sprague-Dawley rat growth plate chondrocytes from the perichondral zone (PC) and reserve zone (RZ) were isolated by laser microdissection and then subjected to microarray analysis. In order to most comprehensively capture the unique features of the two zones, we analyzed both the most highly expressed genes and those that were most significantly different from the proliferative zone (PZ) as a single comparator. Confirmation of the differential expression of selected genes was done by quantitative real-time RT-PCR. A total of 8 transcripts showing high expression unique to the PC included translationally-controlled tumor protein (Tpt1), connective tissue growth factor (Ctgf), mortality factor 4 (Morf4l1), growth arrest specific 6 (Gas6), type V procollagen (Col5a2), frizzled-related protein (Frzb), GDP-dissociation inhibitor 2 (Gdi2) and Jun D proto-oncogene (Jund). In contrast, 8 transcripts showing unique high expression in the RZ included hyaluronan and proteoglycan link protein 1 (Hapln1), hemoglobin beta-2 subunit, type I procollagen (Col1a2), retinoblastoma binding protein 4 (LOC685491), Sparc-related modular calcium binding 2 (Smoc2), and calpastatin (Cast). Other genes were highly expressed in cells from both PC and RZ zones, including collagen II, collagen IX, catenin (cadherin associated protein) beta 1, eukaryotic translation elongation factor, high mobility group, ribosomal protein, microtubule-associated protein, reticulocalbin, thrombospondin, retinoblastoma binding protein, carboxypeptidase E, carnitine palmitoyltransferase 1, cysteine rich glycoprotein, plexin B2 (Plxnb2), and gap junction membrane channel protein. Functional classification of the most highly expressed transcripts were analyzed, and the pathway analysis indicated that ossification, bone remodeling, and cartilage development were uniquely enriched in the PC whereas both the PC and RZ showed pathway enrichment for skeletal development, extracellular matrix structural constituent, proteinaceous extracellular matrix, collagen, extracellular matrix, and extracellular matrix part pathways. We conclude that differential gene expression exists between the RZ and PC chondrocytes and these differentially expressed genes have unique roles to play corresponding to the function of their respective zones.