The fate of chondrocyte in osteoarthritic cartilage of transgenic mice expressing bovine GH

OBJECTIVE

The aim of the present study was to demonstrate whether bGH transgenic mice develop OA. We therefore studied in this animal model the structural features of cartilage and the subchondral bone changes of the knee joints that may be associated with osteoarthritic lesion.

METHOD

Degenerative changes in the knee joints of bGH transgenic female mice (N = 11) and control mice (N = 11) were histologically analyzed at the age of 7 months. Histochemical and stereological studies were conducted. Immunohistochemistry on cell cyclin activity (assessed by anti-PCNA labeling) and cell viability (assessed by bcl-2 expression), as well as ribosomal activity (AgNOR), TNF-alpha expression and apoptosis (TUNEL technique) were performed. In ten 7-month-old female mice (Tg+ N = 5; control N = 5) the knee articular cartilages were studied with electron microscopy techniques.

RESULTS

Disruption of the articular surface (18.2%), cleft (63.7%), cloning (81.8%), hypocellularity of chondrocytes (18.2%), moderate (54.6%) to severe (45.4%) loss of safranin-O staining, and duplication and rupture of the tidemark (54.5%) were some of the main features observed in articular cartilage chondrocytes of bGH transgenic mice. Furthermore, cell cyclin activity and cell viability decreased, while TNF-alpha expression and TUNEL+ cells increased. These chondrocytes also showed an increase in the number of black dots per cell, as revealed by the AgNOR technique.

CONCLUSION

Our results show that bGH transgenic mice develop a lesion of the articular cartilage consistent with that described in osteoarthritis.

Embryonic blastemic changes in retinoic acid-induced hindlimb deformity

In this study we analyzed, on an experimental model, blastemic changes occurring during the embryonic period that may later cause fetal hindlimb deformity. Experimental induction of clubfoot-like deformity in rat fetuses was performed by maternal administration of retinoic acid (RA) (120 mg/kg body weight) as a single intragastric dose on day 10 of pregnancy (previous phase of this assay). The caudal and hindlimb blastemic changes were studied by mitosis count and stereological, immunohistochemistry and AgNOR techniques in the hindlimbs of 15-day embryos and in the caudal somites of 11-day embryos. In 15-day embryos from the assay group, hypoplasia and misorientation of hindlimbs were present in 90% of the cases. The histological study showed a blastemal defect as follows: (a) reduction in mesenchymal cell activity (mitotic and AgNOR activities); (b) increase of volume of vascular lumen; (c) reduction in volume of nerve structures, and (d) reduction in the percentage of pre-rhabdomyoblastic cells. In 11-day embryos from the assay group, caudal somites showed disruption, including loss of usual morphology. Moreover, somitic AgNOR activity decreased compared to the control group. The greatest reduction in the number of black-dots per cell was in the myotome. These findings suggest that a certain pathology of the somites, very little studied to date, might be involved in clubfoot pathogenesis.

Expression of CCAAT/enhancer-binding protein-beta (C/EBPβ) and CHOP in the murine growth plate

Our aim was to evaluate the expression of transcription factors CCAAT/enhancer-binding protein-beta (C/EBPβ) and C/EBP-homologous protein (CHOP) in the growth plate. Proximal tibial epiphyseal growth plates from ten 15-day-old Wistar rats were used. Additionally, anti-proliferating cell nuclear antigen (PCNA), anti-5-bromo-2’-deoxyuridine (BrdU) immunostaining, terminal transferase dUTP nick end-labelling (TUNEL) and nucleolar organiser region-associated proteins (AgNOR) techniques were peformed. The histological morphology of the growth plate from C/EBPβknock-out mice was also analysed.

The normal growth plate showed that C/EBPβ and CHOP factors are expressed both in the germinative/ upper proliferative and in the lower proliferative zones. Furthermore, BdrU+ and PCNA+ cells were present exclusively in the germinative and proliferative zones, while TUNEL+ and AgNOR+ cells were seen in all three zones of the growth plate. Acellular areas, hypocellularity, the increase in cell death and anomalies in the architecture of the cell columns were observed in the growth plates of C/EBPβ (−/ −) knockout mice.

We suggest that C/EBPβ and CHOP transcription factors may be key modulators participating in the chondrocyte differentiation process in the growth plate.

Mechanoreceptors in collateral knee ligaments: an animal experiment

The mechanoreceptors in the collateral ligaments of the knee joint in rat hindlimbs were studied. In group II (n=10) the femoral and obturator nerves were sectioned. In both groups III and V (n=20) the sciatic nerve was sectioned. In group V (n=10) the sectioned sciatic nerve was sutured 4 weeks after sectioning. In group IV (n=10) all three nerves were sectioned. Group I (n=10) served as control. After 4 months all animals were killed. The ligaments of the knee joint were preserved and stained with gold chloride, paraffin-embedded and cut in sagittal serial sections. The results showed that 4 months after partial or total denervation of the limb, there was necrosis and a decrease in the number of mechanoreceptors, which was dependent upon the severity and site of the lesion. After suture of the sciatic nerve the increase in mechanoreceptors suggested a regenerative process.

Retinoic acid-induced clubfoot-like deformity: pathoanatomy in rat fetuses

The purpose of this assay was to study the hindfoot patho-dynamic in clubfoot-like deformity during fetal development. Experimental induction of clubfoot-like deformity in rat fetuses was produced by maternal administration of retinoic acid (120 mg/kg body weight) as a single intragastric dose on day 10 of pregnancy. Hindlimbs from fetuses at 17, 19, and 21 days were removed, and serial sections in three planes were made. Experimental and control hindlimbs were studied. There was clubfoot-like deformity in 86.5% of the experimental fetuses and none in the controls. Other associated malformations found were craniofacial (96.3%), neural tube (75.7%), and club-hand (40.3%) defects. Persistence of the embryonic position of the talus and tibia in fetuses with severe clubfoot-like deformity was observed. No overlapping between talus and calcaneus was seen. An equinus position, medialization of anterior segment, and lateralization and inward torsion of the posterior body of the calcaneous were observed. Results of this study showed that there are rotational anomalies in the hindfoot and full hindlimb from the beginning of the fetal period, and these anomalies increase during development. This simple model may allow us to gain better knowledge in congenital clubfoot deformity.

Cartilage canals in the tarsal navicular of the human foetus and infant

We have analysed the development of the cartilage canals in the tarsal navicular in 26 human foetuses and infants, aged between 12 weeks after gestation and 10 months, using a technique of transparentation and serial histological sections of the bone. The formation of cartilage canals starts in the first 12 to 13 weeks of gestation and can be seen by transparentation at 17 weeks after gestation. They increase in number with the age of the foetus or infant and develop a branching pattern almost to the centre of the tarsal navicular. They begin and are more numerous on the dorsal surface of the cartilage structure.

Cartilage canal growth: experimental approach in the rat tibia

This paper studies the influence of an antimitotic factor (puromycin) and a hormonal factor (thyroid hormone, TH) on canal growth. The tibiae of 15 six-day-old rats were cultured in a serum-free chemically defined medium. The cultures were carried out for as long as 6 days. Our results show: (1) canal growth is not dependent on perichondrium or chondro-epiphysis growth; (2) the canal is greater and has a complex pattern in a triiodothyronine (T3)-treated assay group; (3) round and multinucleated cells are more numerous in the T3-treated assay group than in the other groups. We hypothesize that the canal grows by a physiological phenomenon of programmed cell death and that it is stimulated by TH.

Growth of the perichondrium and the chondroepiphysis: experimental approach in the rat proximal tibial epiphysis

In the present paper we study the participation of the perichondrium in chondroepiphysis development analyzing its in vitro growth pattern without the perichondrium. We also advance the descriptive morphological results. We have observed that the chondroepiphysis without perichondrium grew with an almost normal pattern. Most of the cells that participated in chondroepiphysis growth came from the lateral region of the growth plate.

Morphogenesis of cartilage canals: experimental approach in the rat tibia

This paper studies the participation of vessels in the canal morphogenesis. The proximal chondroepiphysis of the left tibia of 44 five-day-old rats was exposed and the vessels of the intercondylar fossae, near the attachment of cruciate ligaments, were cauterized. In addition to the vascular lesion this assay induced a perichondral lesion. However, the canal appeared and joined to the secondary ossification center. 36 tibiae of 4-day-old rats were removed under sterile conditions and cultured in a serum-free chemically defined medium. The cultures were carried out for as long as 15 days. A canal lumen structure was found on the first days of culture, and grew in depth to the central region of the chondroepiphysis during the culture. The secondary ossification center was not found. The vessels and mesenchymal cells observed in the control canal were not found in the culture. We suggest that the presence of vessels, perivascular cells or perichondrium does not appear to be necessary in canal morphogenesis.