The content of myosin heavy chains in hindlimb muscles of female and male rats

The aim of the study was to test whether the considerable differences in the hindlimb muscles mass, the number and diameter of muscles fibers were connected with differences in the myosin heavy chain isoform content (expressed as the percentage of the given isoform in respect to total myosin heavy chains). Therefore, the content of myosin heavy chain (MHC) isoforms was studied in four hindlimb muscles: flexor digitorum brevis, soleus, tibialis anterior and gastrocnemius medialis of female and male rats by means of polyacrylamide gel electrophoresis supplemented with densitometric analyses. Muscles were isolated and homogenized prior to electrophoretic analysis. The most interesting result concerned considerably different composition of myosin isoforms for male and female subjects in the slow soleus muscles, which contained predominantly slow MHC isoform (MHC I). However, in the male muscle about 13% of IIa isoform (MHC IIa) was also detected; this isoform was not found in the majority of the studied female muscles (81% of muscle samples). This dimorphic difference was further confirmed by immunofluorescence stainining for slow and fast skeletal myosin isoforms and by assessment of the fiber ATPase activity. For the three remaining fast muscles (flexor digitorum brevis, tibialis anterior and gastrocnemius medialis) all four MHC isoforms were detected with the fast isoforms being dominant ones. However, there were not statistically significant differences observed between males and females, with the exception of IIx isoform, which was more frequent in male tibialis anterior muscle.

Novel angiotensin-converting enzyme (ACE) inhibitory peptides derived from boneless chicken leg meat

Four peptides that inhibit angiotensin-converting enzyme (ACE) were separated from the hydorlysate of boneless chicken leg meat digested with artificial gastric juice (pepsin). Two peptides were identified as the peptides encrypted in myosin heavy chain. The peptide P1 (MNVKHWPWMK) corresponds to the amino acid sequence from amino acids 825 to 834 of myosin heavy chain, and the peptide P4 (VTVNPYKWLP) corresponds to the amino acid sequence from amino acids 125 to 135 of myosin heavy chain. They are novel ACE inhibitory peptides derived from chicken, and IC(50) values of P1 and P4 were determined as 228 and 5.5 microM, respectively. Although these values were much larger than 0.022 microM for captopril, a typical synthetic ACE inhibitor, they are comparable to IC(50) values reported for various ACE inhibitory peptides derived from foods. Because the peptide P4 has a relatively low IC(50) value, it is a good starting substance for designing food supplements for hypertensive patients.

Thyroid-stimulating hormone restores bone volume, microarchitecture, and strength in aged ovariectomized rats

We show the systemic administration of low levels of TSH increases bone volume and improves bone microarchitecture and strength in aged OVX rats. TSH's actions are mediated by its inhibitory effects on RANKL-induced osteoclast formation and bone resorption coupled with stimulatory effects on osteoblast differentiation and bone formation, suggesting TSH directly affects bone remodeling in vivo.

INTRODUCTION

Thyroid-stimulating hormone (TSH) receptor haploinsufficient mice with normal circulating thyroid hormone levels have reduced bone mass, suggesting that TSH directly affects bone remodeling. We examined whether systemic TSH administration restored bone volume in aged ovariectomized (OVX) rats and influenced osteoclast formation and osteoblast differentiation in vitro.

MATERIALS AND METHODS

Sprague-Dawley rats were OVX at 6 months, and TSH therapy was started immediately after surgery (prevention mode; n = 80) or 7 mo later (restoration mode; n = 152). Hind limbs and lumbar spine BMD was measured at 2- or 4-wk intervals in vivo and ex vivo on termination at 8-16 wk. Long bones were subjected to microCT, histomorphometric, and biomechanical analyses. The direct effect of TSH was examined in osteoclast and osteoblast progenitor cultures and established rat osteosarcoma-derived osteoblastic cells. Data were analyzed by ANOVA Dunnett test.

RESULTS

In the prevention mode, low doses (0.1 and 0.3 microg) of native rat TSH prevented the progressive bone loss, and importantly, did not increase serum triiodothyroxine (T3) and thyroxine (T4) levels in aged OVX rats. In restoration mode, animals receiving 0.1 and 0.3 microg TSH had increased BMD (10-11%), trabecular bone volume (100-130%), trabecular number (25-40%), trabecular thickness (45-60%), cortical thickness (5-16%), mineral apposition and bone formation rate (200-300%), and enhanced mechanical strength of the femur (51-60%) compared with control OVX rats. In vitro studies suggest that TSH's action is mediated by its inhibitory effects on RANKL-induced osteoclast formation, as shown in hematopoietic stem cells cultivated from TSH-treated OVX rats. TSH also stimulates osteoblast differentiation, as shown by effects on alkaline phosphatase activity, osteocalcin expression, and mineralization rate.

CONCLUSIONS

These results show for the first time that systemically administered TSH prevents bone loss and restores bone mass in aged OVX rats through both antiresorptive and anabolic effects on bone remodeling.

Thiazolidinediones enhance skeletal muscle triacylglycerol synthesis while protecting against fatty acid-induced inflammation and insulin resistance

In the present investigation, we studied the effects of thiazolidinedione (TZD) treatment on insulin-stimulated fatty acid (FA) and glucose kinetics in perfused muscle from high-fat (HF)-fed rats. We tested the hypothesis that TZDs prevent FA-induced insulin resistance by attenuating proinflammatory signaling independently of myocellular lipid levels. Male Wistar rats were assigned to one of three 3-wk dietary groups: control chow fed (CON), 65% HF diet (HFD), or TZD- (troglitazone or rosiglitazone) enriched HF diet (TZD + HFD). TZD treatment led to a significant increase in plasma membrane content of CD36 protein in muscle (red: P = 0.01, and white: P = 0.001) that correlated with increased FA uptake (45%, P = 0.002) and triacylglycerol (TG) synthesis (46%, P = 0.03) during the perfusion. Importantly, whereas HF feeding caused increased basal TG (P = 0.047), diacylglycerol (P = 0.002), and ceramide (P = 0.01) levels, TZD treatment only prevented the increase in muscle ceramide. In contrast, all of the muscle inflammatory markers altered by HF feeding ( upward arrowNIK protein content, P = 0.009; upward arrowIKKbeta activity, P = 0.006; downward arrowIkappaB-alpha protein, P = 0.03; and upward arrowJNK phosphorylation, P = 0.003) were completely normalized by TZD treatment. Consistent with this, HFD-induced decrements in insulin action were also prevented by TZD treatment. Thus our findings support the notion that TZD treatment causes increased FA uptake and TG accumulation in skeletal muscle under insulin-stimulated conditions. Despite this, TZDs suppress the inflammatory response to dietary lipid overload, and it is this mechanism that correlates strongly with insulin sensitivity.

Interdigital webbing retention in bat wings illustrates genetic changes underlying amniote limb diversification

Developmentally regulated programmed cell death sculpts the limbs and other embryonic organs in vertebrates. One intriguing example of species-specific differences in apoptotic extent is observed in the tissue between the digits. In chicks and mice, bone morphogenetic proteins (Bmps) trigger apoptosis of the interdigital mesenchyme, leading to freed digits, whereas in ducks, Bmp antagonists inhibit the apoptotic program, resulting in webbed feet. Here, we show that the phyllostomid bat Carollia perspicillata utilizes a distinct mechanism for maintaining interdigit tissue. We find that bat forelimb and hindlimb interdigital tissues express Bmp signaling components but that only bat hindlimbs undergo interdigital apoptosis. Strikingly, the retention of interdigital webbing in the bat forelimb is correlated with a unique pattern of Fgf8 expression in addition to the Bmp inhibitor Gremlin. By using a functional assay, we show that maintenance of interdigit tissue in the bat wing depends on the combined effects of high levels of Fgf signaling and inhibition of Bmp signaling. Our data also indicate that although there is not a conserved mechanism for maintaining interdigit tissue across amniotes, the expression in the bat forelimb interdigits of Gremlin and Fgf8 suggests that these key molecular changes contributed to the evolution of the bat wing.

Inhibition of angiogenesis by interleukin-4 gene therapy in rat adjuvant-induced arthritis

OBJECTIVE

Interleukin-4 (IL-4) can modulate neovascularization. In this study, we used a gene therapy approach to investigate the role of IL-4 in angiogenesis in rat adjuvant-induced arthritis (AIA), a model for rheumatoid arthritis.

METHODS

Rats received an adenovirus producing IL-4 (AxCAIL-4), a control virus without insert, or control vehicle (phosphate buffered saline) intraarticularly before arthritis onset. At peak onset of arthritis, rats were killed. Vascularization was determined in the synovial tissue, and correlations with inflammation were assessed. Ankle homogenates were used in angiogenesis assays in vitro and in vivo, and protein levels of cytokines and growth factors were assessed by enzyme-linked immunosorbent assay. Synovial tissue expression of alphav integrins was determined by immunohistochemistry.

RESULTS

IL-4 induced a reduction in synovial tissue vessel density, which was paralleled by a decrease in inflammation. AxCAIL-4 joint homogenates significantly (P < 0.05) inhibited both endothelial cell (EC) migration and tube formation in vitro. Similarly, AxCAIL-4 inhibited capillary sprouting in the rat aortic ring assay, and vessel growth in the in vivo Matrigel plug assay. The angiostatic effect occurred despite high levels of vascular endothelial growth factor (VEGF), and was associated with down-regulation of the proangiogenic cytokines IL-18, CXCL16, and CXCL5 and up-regulation of the angiogenesis inhibitor endostatin. Of interest, AxCAIL-4 also resulted in decreased EC expression of the alphav and beta3 integrin chains.

CONCLUSION

In rat AIA, IL-4 reduces synovial tissue vascularization via angiostatic effects, mediates inhibition of angiogenesis via an association with altered pro- and antiangiogenic cytokines, and may inhibit VEGF-mediated angiogenesis and exert its angiostatic role in part via alphavbeta3 integrin. This knowledge of the specific angiostatic effects of IL-4 may help optimize target-oriented treatment of inflammatory arthritis.

Maintenance of slow type I myosin protein and mRNA expression in overwintering prairie dogs (Cynomys leucurus and ludovicianus) and black bears (Ursus americanus)

Hibernating mammals have the remarkable ability to withstand long periods of fasting and reduced activity with dramatic maintenance of skeletal muscle function and protein composition. We investigated several hindlimb muscles of white-tailed prairie dogs (Cynomys leucurus) and black bears (Ursus americanus), two very different hibernators who are dormant and fasting during winter. The black-tailed prairie dog (C. ludovicianus) remains active during winter, but suffers minor skeletal muscle atrophy; nevertheless, they also demonstrate apparent skeletal muscle adaptations. Using SDS-PAGE, we measured myosin protein isoform profiles before and after the hibernation season. All species maintained or increased levels of slow myosin, despite the collective physiological challenges of hypophagia and reduced activity. This contrasts markedly with standard mammalian models of skeletal muscle inactivity and atrophy predicting significant loss of slow myosin. A mechanism for changes in myosin isoforms was investigated using reverse-transcription PCR, following partial sequencing of the adult MHC isoforms in C. leucurus and U. americanus. However, mRNA expression was not well correlated with changes in MHC protein isoforms, and other synthesis and degradation pathways may be involved besides transcriptional control. The muscles of hibernating mammals demonstrate surprising and varied physiological responses to inactivity and atrophy with respect to slow MHC expression.

Expression of Xenopus XlSALL4 during limb development and regeneration

The multi-C2H2 zinc-finger domain containing transcriptional regulators of the spalt (SAL) family plays important developmental regulatory roles. In a competitive subtractive hybridization screen of genes expressed in Xenopus laevis hindlimb regeneration blastemas, we identified a SAL family member that, by phylogenetic analysis, falls in the same clade as human SALL4 and have designated it as XlSALL4. Mutations of human SALL4 have been linked to Okihiro syndrome, which includes preaxial (anterior) limb defects. The expression pattern of XlSALL4 transcripts during normal forelimb and hindlimb development and during hindlimb regeneration at the regeneration-competent and regeneration-incompetent stages is temporally and regionally dynamic. We show for the first time that a SAL family member (XlSALL4) is expressed at the right place and time to play a role regulating both digit identity along the anterior/posterior axis and epimorphic limb regeneration.

Conserved and muscle-group-specific gene expression patterns shape postnatal development of the novel extraocular muscle phenotype

Current models in skeletal muscle biology do not fully account for the breadth, causes, and consequences of phenotypic variation among skeletal muscle groups. The muscle allotype concept arose to explain frank differences between limb, masticatory, and extraocular (EOM) muscles, but there is little understanding of the developmental regulation of the skeletal muscle phenotypic range. Here, we used morphological and DNA microarray analyses to generate a comprehensive temporal profile for rat EOM development. Based upon coordinate regulation of morphologic/gene expression traits with key events in visual, vestibular, and oculomotor system development, we propose a model that the EOM phenotype is a consequence of extrinsic factors that are unique to its local environment and sensory-motor control system, acting upon a novel myoblast lineage. We identified a broad spectrum of differences between the postnatal transcriptional patterns of EOM and limb muscle allotypes, including numerous transcripts not traditionally associated with muscle fiber/group differences. Several transcription factors were differentially regulated and may be responsible for signaling muscle allotype specificity. Significant differences in cellular energetic mechanisms defined the EOM and limb allotypes. The allotypes were divergent in many other functional transcript classes that remain to be further explored. Taken together, we suggest that the EOM allotype is the consequence of tissue-specific mechanisms that direct expression of a limited number of EOM-specific transcripts and broader, incremental differences in transcripts that are conserved by the two allotypes. This represents an important first step in dissecting allotype-specific regulatory mechanisms that may, in turn, explain differential muscle group sensitivity to a variety of metabolic and neuromuscular diseases.

Static and dynamic x-ray diffraction recordings from living mammalian and amphibian skeletal muscles

Static and time-resolved two-dimensional x-ray diffraction patterns, recorded from the living mouse diaphragm muscle, were compared with those from living frog sartorius muscle. The resting pattern of mouse muscle was similar to that of frog muscle, and consisted of actin- and myosin-based reflections with spacings basically identical to those of frog. As a notable exception, the sampling pattern of the myosin layer lines (MLL's) indicated that the mouse myofilaments were not organized into a superlattice as in frog. The intensity changes of reflections upon activation were also similar. The MLL's of both muscles were markedly weakened. Stereospecific (rigorlike) actomyosin species were not significantly populated in either muscle, as was evidenced by the 6th actin layer line (ALL), which was substantially enhanced but without a shift in its peak position or a concomitant rise of lower order ALL's. On close examination of the mouse pattern, however, a few lower order ALL's were found to rise, slightly but definitely, at the position expected for stereospecific binding. Their quick rise after the onset of stimulation indicates that this stereospecific complex is generated in the process of normal contraction. However, their rise is still too small to account for the marked enhancement of the 6th ALL, which is better explained by a myosin-induced structural change of actin. Since the forces of the two muscles are comparable regardless of the amount of stereospecific complex, it would be natural to consider that most of the force of skeletal muscle is supported by nonstereospecific actomyosin species.

Age-Related Changes in Bone Mineral Density, Cross-Sectional Area and the Strength of Long Bones in the Hind Limbs and First Lumbar Vertebra in Female Wistar Rats

Age-related changes in bone mineral density (BMD) and cross-sectional area and bone strength index (SSI) of the femur, tibia, humerus, and first lumbar vertebra in female Wistar (WM/MsNrs) rats were examined by a quantitative computed tomography (pQCT) method. One hundred and sixteen virgin female Wistar (WM/MsNrs) rats aged 2-33 months were used. The data indicate that the total BMD values of metaphyses and diaphyses of long bones increased until 12 months, then decreased to a varying degree depending on the bone after 15-24 months, but the values of cortical and trabecular BMD with age were not always similar to the total BMD value. Nevertheless, the values for cross-sectional area and SSI in the long bones increased regardless of the total BMD decrease with age, indicating that this increase might have been due to a characteristic of the modeling pattern in rats. The total and cortical BMD values in the first lumbar vertebra decreased after 18 months, and SSI did after 15 months. The data obtained in this study were compared with those obtained from males in a previous study. In conclusion, it was indicated that in this strain the rats over 12 months with the highest total BMD values in the femur and tibia, and before the onset of various tumors, are useful as a model animal for osteoporosis experiments and observation of senile bone change.

The molecular composition of the sarcomeric M-band correlates with muscle fiber type

The M-band is the transverse structure that cross-links the thick filaments in the center and provides a perfect alignment of the A-band in the activated sarcomere. The molecular composition of the M-bands in adult mouse skeletal muscle is fiber-type dependent. All M-bands in fast fibers contain M-protein while M-bands in slow fibers contain a significant proportion of the EH-myomesin isoform, previously detected only in embryonic heart muscle. This fiber-type specificity develops during the first postnatal weeks. However, the ratio between the amounts of myosin and of myomesin, taken as sum of both isoforms, remains nearly constant in all studied muscles. Ultrastructural analysis demonstrates that some of the soleus fibers show a diffuse appearance of the M-band, resembling the situation in the embryonic heart. A model is proposed to explain the functional consequence of differential M-band composition for the physiological and morphological properties of sarcomeres in different muscle types.

A substance P receptor (NK1) antagonist enhances the widespread osteoporotic effects of sciatic nerve section

The long-term effects of sciatic nerve section on bone mineral density (BMD) were studied using dual-energy X-ray absorptiometry (DEXA) in skeletally mature rats. Unilateral sciatic neurectomy caused the rapid loss of cancellous bone in the proximal and distal femur and tibia in the ipsilateral hindlimb and, to a lesser extent, in the contralateral intact hindlimb. The reduction in BMD rapidly progressed for 4 weeks after sciatic section and then gradually stabilized with no evidence of recovery at 12 weeks. The development of osteoporosis in the contralateral intact hindlimb was a novel finding. There was no evidence of disuse in the normal contralateral hindlimb after unilateral sciatic section; grid-crossing activity over a 24-h interval was unchanged and there was no reduction in weight bearing on the contralateral normal hindpaw during the stance phase of ambulation. Unilateral peripheral nerve lesions have well-documented effects on substance P content and function in the corresponding contralateral intact nerve. We hypothesized that after sciatic section a reduction in substance P signaling might contribute to bone loss in the contralateral hindlimb. Daily administration of the substance P receptor (NK1) antagonist LY303870 for 2 weeks caused significant loss of cancellous bone in the denervated and the contralateral hindlimb, evidence that substance P signaling sustained bone density after nerve section. After sciatic neurectomy there was a 33% reduction in sciatic nerve stimulation-evoked extravasation in the contralateral intact hindlimb, indicating transmedian inhibition of substance P signaling after nerve injury. Furthermore, there was a 50% reduction in the substance P content in both tibias after unilateral sciatic section. Collectively, these data support the hypothesis that a widespread reduction in substance P content in bone contributes to the osteoporotic effects of sciatic neurectomy and that residual substance P signaling maintains bone integrity after nerve section in both the denervated and contralateral intact hindlimb.

An improved external loop resonator for in vivo L-band EPR spectroscopy

An improved external loop resonator (ELR) used for L-band electron paramagnetic resonance (EPR) spectroscopy is reported. This improvement is achieved by shortening the parallel coaxial line. The resonant structure is formed by two single turn coils (10mm in diameter) that are connected to a parallel coaxial line. A resonance frequency of 1197 MHz and a quality factor of 466 were obtained in the absence of biological tissue and were approximately 1130 MHz and approximately 50 with a living animal, respectively. The sensitivity of the new ELR was compared to the previously developed ELR using three types of EPR samples: (1) paramagnetic material with no biological tissue, (2) paramagnetic material in a leg and in the peritoneal cavity of a dead rat, and (3) paramagnetic material in the back of an anesthetized rat. The sensitivity was 1.2-1.6 times greater in the rat and 4.2 times without tissue.

Differences in ratios of GABA, glycine and glutamate immunoreactivities in nerve terminals on rat hindlimb motoneurons: a possible source of post-synaptic variability

Previous pharmacological and physiological data on GABA and glycine receptor-dependent components of miniature inhibitory post-synaptic currents show that the electrophysiological characteristics of synaptic transmission from inhibitory synapses on spinal motoneurons are highly variable. Although post-synaptic factors are thought to be the major underlying cause of this variability, quantitative immunohistochemical data suggest that the transmitter content of afferents also vary from terminal to terminal. To examine whether ratios of amino acid staining densities vary similar to those of components of post-synaptic currents mediated by the corresponding receptors, we quantified immunogold labeling for GABA, glycine and the major excitatory transmitter, glutamate, in nerve terminals contacting the dendrites of motoneurons retrogradely labeled from the rat hindlimb muscle, biceps femoris. Nearly all terminals (94%) were immunoreactive for at least one amino acid and 64% of these contained two or three amino acids. All possible combinations of GABA, glycine and glutamate labeling were found. Over 70% of the terminals contained glycine, of which 60% also labeled for GABA. Of these GABA/glycine boutons, 40% also had glutamate. Half of all terminals contained GABA, but terminals immunoreactive for GABA alone were extremely rare. Immunoreactivity for glutamate occurred in 48% of all terminals and nearly 60% of these also contained glycine. Labeling densities for GABA, glycine and glutamate varied over a wide range from terminal to terminal. We hypothesize that this diversity in amino acid content may be a major underlying cause of variability in GABA- and glycine receptor-mediated components of miniature inhibitory post-synaptic currents in motoneurons.

SAGE profiling of the forelimb and hindlimb

A recent study has used serial analysis of gene expression to compare mouse forelimb and hindlimb gene-expression profiles. The method successfully identified known regulators of limb identity and has generated a candidate set of differentially expressed genes that may regulate limb identity.

GABA and glutamate-like immunoreactivity at synapses on depressor motorneurones of the leg of the crayfish, Procambarus clarkii

To investigate their synaptic relationships, depressor motorneurones of the crayfish leg were impaled with microelectrodes, intracellularly injected with horseradish peroxidase, and prepared for electron microscopy. Post-embedding immunogold labelling with antibodies against gamma-aminobutyric acid (GABA) or glutamate was carried out either alone or together on the same section and allowed the identification of three classes of input synapses: 51% were immunoreactive for glutamate and contained round agranular vesicles, 31% were immunoreactive for GABA and contained pleomorphic agranular vesicles, and the remainder were immunoreactive for neither and also predominantly contained pleomorphic agranular vesicles. Output synapses were abundant in some of the motorneurones but were not seen in others, suggesting that members of the motor pool differ in their connectivity.

Aluminum toxicity perturbs long bone calcification in the embryonic chick

Long bone calcification in chick embryos acutely- or chronically-treated with aluminum (Al) citrate was investigated. Acutely treated embryos received 100 microl of 60 mM Al citrate, 60 mM sodium (Na) citrate, or 0.7% sodium chloride on day 8 of incubation. Chronically treated embryos received a daily 25 microl dose of the above solutions beginning on day 8. Following 2-8 days of additional incubation, blood was collected, embryos killed, hind limbs radiographed, and tibias collected. Radiography indicated that Al administration resulted in a persistent angulation in the mid-diaphysis of tibias and femurs and a transient mineralization defect during the 10- to 12-day period of incubation. Tibias from 10- to 12-day embryos which were administered Al contained significantly less (P < 0.005) bone calcium (Ca) compared with tibias from NaCl-treated embryos. By day 14 there were no significant differences among the Ca content of tibias from embryos acutely treated with Al citrate, Na citrate or NaCl. Similarly, the rate of (45)Ca uptake by tibias of embryos treated with Al was significantly lower on days 10 (acute) and 12 (chronic) with no significant differences in Ca uptake rate among the three treatment groups by day 16. In each treatment group bone alkaline phosphatase (ALPase) activity increased approximately tenfold between days 10 and 16. At all stages, bone ALPase activity was consistently higher and significantly different (chronic) compared with levels in NaCl-treated embryos. In contrast, Al had no significant effect on the rate of tibia collagen and noncollagenous protein synthesis or serum levels of procollagen carboxy-terminal propeptide (PICP), osteocalcin, and parathyroid hormone (PTH).

Mouse model of angiogenesis

Neovascularization of ischemic muscle may be sufficient to preserve tissue integrity and/or function and may thus be considered to be therapeutic. The regulatory role of vascular endothelial growth factor (VEGF) in therapeutic angiogenesis was suggested by experiments in which exogenously administered VEGF was shown to augment collateral blood flow in animals and patients with experimentally induced hindlimb or myocardial ischemia. To address the possible contribution of postnatal endogenous VEGF expression to collateral vessel development in ischemia tissues, we developed a mouse model of hindlimb ischemia. The femoral artery of one hindlimb was ligated and excised. Laser Doppler perfusion imaging (LDPI) was employed to document the consequent reduction in hindlimb blood flow, which typically persisted for up to 7 days. Serial in vivo examinations by LDPI disclosed that hindlimb blood flow was progressively augmented over the course of 14 days, ultimately reaching a plateau between 21 and 28 days. Morphometric analysis of capillary density performed at the same time points selected for in vivo analysis of blood flow by LDPI confirmed that the histological sequence of neovascularization corresponded temporally to blood flow recovery detected in vivo. Endothelial cell proliferation was documented by immunostaining for bromodeoxyuridine injected 24 hours before each of these time points, providing additional evidence that angiogenesis constitutes the basis for improved collateral-dependent flow in this animal model. Neovascularization was shown to develop in association with augmented expression of VEGF mRNA and protein from skeletal myocytes as well as endothelial cells in the ischemic hindlimb; that such reparative angiogenesis is indeed dependent upon VEGF up-regulation was confirmed by impaired neovascularization after administration of a neutralizing VEGF antibody. Sequential characterization of the in vivo, histological, and molecular findings in this novel animal model thus document the role of VEGF as endogenous regulator of angiogenesis in the setting of tissue ischemia. Moreover, this murine model represents a potential means for studying the effects of gene targeting on nutrient angiogenesis in vivo.

Target tissue production and axonal transport of neurotrophin-3 are reduced in streptozotocin-diabetic rats

Neurotrophin-3 (NT-3) acts as a target-derived neurotrophic factor for large calibre sensory neurones and plays a role in the maintenance of the adult phenotype of proprioceptive and mechanoreceptive fibres. Large fibre sensory neuropathy is common in diabetes mellitus and the aim of this study was to determine whether endogenous NT-3-dependent neurotrophic support was sub-optimal in the streptozotocin-diabetic rat. NT-3 gene expression was analysed by Northern blotting and ELISA in hindlimb skeletal muscle and found to be decreased by up to 70% (p < 0.05) in rats with 4-6 weeks of diabetes compared to aged-matched controls. Treatment of other diabetic rats with insulin prevented development of deficits of both NT-3 protein and of its mRNA. The deficits in target tissue production of NT-3 were coincident with significant decreases in its anterograde and retrograde axonal transport in sciatic nerve at 6 weeks of diabetes. The mRNA expression in lumbar dorsal root ganglia of the specific receptor for NT-3, trkC, was also down-regulated at 12 weeks of diabetes by 50% (p < 0.05). The observed decreases in NT-3 target tissue production and related axonal transport suggest that large calibre sensory neurones expressing trkC may be receiving sub-optimal neurotrophic support in experimental diabetes.

Histomorphological and immunohistochemical evaluation of joint changes in a model of osteoarthritis induced by lateral meniscectomy in sheep

OBJECTIVE

To evaluate the histomorphological and immunohistochemical changes induced in cartilages of ovine stifle (knee) joints 6 months after unilateral lateral meniscectomy.

METHODS

Osteochondral sections were obtained from 8 distinct regions of knee joints of 6 adult Merino wethers that 6 months earlier had undergone lateral meniscectomy. Joint regions of 6 age matched sheep housed under identical conditions were used for controls. Serial sections were stained with toluidine blue or immunolocalized with monoclonal antibodies (Mab) 3B3(-), 7D4, and 5B10, which recognize epitopes on proteoglycans.

RESULTS

In control joints the cartilage from the region of the tibial plateau not protected by the meniscus had significantly (p < 0.005) more structural abnormalities than other joint regions. After meniscectomy, only cartilages in the lateral femorotibial compartment showed histomorphological changes consistent with osteoarthritis (OA). The nature and severity of the lesions differed between the topographical regions within the joint. The most severe were found on the lateral femoral condyles and tibial plateaus. Reactivity with Mab 3B3(-), 7D4, and 5B10 was increased only in the lateral compartment cartilages, and was stronger in mild rather than moderate OA.

CONCLUSION

Six month lateral meniscectomy in sheep produces histomorphological and immunohistochemical cartilage changes analogous to those described for early human OA and in other animal models. The severity and type of lesions obtained were dependent on the topographical joint location, but were most evident in cartilages from the lateral compartment.

Immunolocalization of type IX collagen in normal and spontaneously osteoarthritic canine tibial cartilage and isolated chondrons

OBJECTIVE

The pericellular localization of type IX collagen in avian and mammalian hyaline cartilages remains controversial, while its distribution during osteoarthritic degeneration is poorly understood. This study aimed to compare and contrast the immunohistochemical distribution of type IX collagen in normal mature and spontaneously osteoarthritic canine tibial cartilage.

DESIGN

Thick vibratome sectioning techniques were evaluated and compared with isolated chondrons using a range of streptavidin-linked probes in combination with light, confocal and transmission electron microscopy.

RESULTS

In normal intact samples, type IX collagen was concentrated in the pericellular microenvironment, while a weaker extracellular reaction around each chondron separated the territorial matrix from the unstained interterritorial matrix. Further differentiation was evident in isolated chondrons where the fibrous pericellular capsule stained more intensely than the tail and interconnecting segments between columnated chondrons. Two regions of type IX reactivity were identified in osteoarthritic tissue: an intensely stained superficial reactive region below the eroding margins, and normal deep layer cartilage where pericellular staining persists. The superficial reactive region was characterized by chondron swelling and chondrocyte cluster formation, a loss of pericellular type IX staining, and a significant increase in matrix staining between clusters. Disintegration and loss of fibrillar collagens was evident in both the swollen microenvironment and adjacent territorial matrices.

CONCLUSIONS

The results suggest that changes in type IX distribution, expansion of the pericellular microenvironment and chondrocyte proliferation represent key elements in the chondron remodeling and chondrocyte cluster formation associated with osteoarthritic degeneration.

Effects of stress-related signal molecules on cells associated with muscle tissue

OBJECTIVE

To elucidate the physiologic background that makes muscle hypertrophy, especially that due to strenuous exercise, often parallel to stress sensitivity and signs of acute phase immune response.

STUDY DESIGN

We used an animal model: lines of mice with hypertrophied (H) and normally developed (N) hind leg muscles, six in each case. Functional and receptor tests on cells from digested muscle tissue were made and analyzed by microplate cytofluorimetry and flow cytometry.

RESULTS

Higher percentages of cells with a phagocyte marker (> 2-fold) and with opioid (about 1.3-fold) receptors were found, whereas the portion of glucocorticoid receptor-bearing cells tended to differ only among H and N. Naloxone, an opioid receptor antagonist, failed only in H to exert a suppressive effect on dihydrorhodamine 123 oxidation.

CONCLUSION

These results and differences in responses of lipid trafficking and proteolytic activities to cortisol, naloxone and adrenergic receptor agonists suggest that not only the cell population associated with muscle tissue but also receptor-mediated responses that are known to be related to stress coping are different between H and N.

An immunohistochemical study of enthesis development in the medial collateral ligament of the rat knee joint

The changing distributions of collagens and glycosaminoglycans have been studied at the attachments of the medial collateral ligament during postnatal development. The ligament is of particular interest because it has a fibrocartilaginous attachment to the femoral epiphysis, but a fibrous one to the tibial metaphysis. Ligaments were examined in rats killed at birth and at 2, 4, 6, 8, 10, 20, 30, 45, 60, 90 and 120 days after birth. Cryosections were immunolabelled with monoclonal and polyclonal antibodies against types I and II collagen, chondroitin 4 and 6 sulfate, dermatan and keratan sulfate. Although the ligament is attached at both ends to bones that develop from cartilage, there was a striking difference in collagen labelling. Type II collagen was only found in spicules of calcified cartilage in bone beneath the tibial enthesis after ossification had commenced, but there was a continuous band of labelling at all stages of development at the femoral enthesis. Initially, the cartilage at the femoral attachment lacked type I collagen, but by 45 days labelling was continuous from ligament to bone. Continuity of labelling was seen much earlier at the tibial enthesis, as soon as bone had formed. There were also marked changes in glycosaminoglycan distribution. Keratan sulfate was present at both entheses up to 45 days, but only at the femoral enthesis thereafter. Both attachments labelled throughout life for dermatan sulfate, but chondroitin 4 and 6 sulfate were only found at the femoral end. The results suggest that enthesial cartilage at the femoral attachment was initially derived from the cartilaginous bone rudiment but was quickly eroded on its deep surface by endochondral ossification as bone formed at the attachment site. It was replaced by fibrocartilage developing in the ligament. This mechanism allows enthesis cartilage/fibrocartilage to contribute to the growth of a bone at a secondary centre of ossification in addition to dissipating stress at the ligament-bone junction.

Formation of extra digits in the interdigital spaces of the chick leg bud is not preceded by changes in the expression of the Msx and Hoxd genes

By in situ hybridization we studied the expression patterns of Msx and Hoxd genes during the late development of the chick leg autopodium (foot) and compared them to patterns during the experimental development of interdigital extra digits. Extra digits are induced in the third interdigital space after various experimental manipulations, such as transient isolation of the interdigit, or removal of the interdigital marginal ectoderm and mesoderm. Msx1 and Msx2 are normally expressed in the interdigital tissue programmed to die. Our experiment changes the fate of the interdigital tissue from cell death to chondrogenesis and provides a good model for studying Msx involvement in defining areas of programmed cell death. Among the proposed roles of Hoxd genes is their involvement in the specification of digit identity early in development. The induction of extra digits allows us to examine whether this new morphogenetic commitment of the interdigital tissues involves changes in the domains of expression of Hoxd genes. Our results show that extra digits develop without a previous modification of the normal pattern of expression of Msx or Hoxd genes. This observation does not support the correlation between the expression of Msx genes and programmed cell death and suggests a role for these genes in maintaining the interdigital tissue in an undifferentiated state. Our results show that an increased number of digits can be formed without modifications in the pattern of expression of the 5'-located Hoxd genes and suggest the existence of latent or residual digit organization mechanisms past the time when digits are normally determined, independent of Hoxd gene expression.