The effects of high-fat diet, branched-chainamino acids and exercise on female C57BL/6 mouse Achilles tendon biomechanical properties

Objectives

The goals of this study were: 1) to determine if high-fat diet (HFD) feeding in female mice would negatively impact biomechanical and histologic consequences on the Achilles tendon and quadriceps muscle; and 2) to investigate whether exercise and branched-chain amino acid (BCAA) supplementation would affect these parameters or attenuate any negative consequences resulting from HFD consumption.

Methods

We examined the effects of 16 weeks of 60% HFD feeding, voluntary exercise (free choice wheel running) and BCAA administration in female C57BL/6 mice. The Achilles tendons and quadriceps muscles were removed at the end of the experiment and assessed histologically and biomechanically.

Results

HFD feeding significantly decreased the Achilles tendon modulus without histological alterations. BCAA administration significantly decreased the stiffness of Achilles tendons in the exercised normal diet mice. Exercise partially ameliorated both the weight gain and glucose levels in the HFD-fed mice, led to a significant decrease in the maximum load of the Achilles tendon, and an increase in the average fibril diameter of the quadriceps femoris muscle. There were significant correlations between body weight and several biomechanical properties, demonstrating the importance of controlling obesity for maintaining healthy tendon properties.

Conclusions

In summary, this study showed a significant impact of obesity and body weight on tendon biomechanical properties with limited effects of exercise and BCAAs.

Cite this article: Bone Joint Res 2013;2:186–92.

Molecular and functional characterization of a novel cardiac-specific human tropomyosin isoform

BACKGROUND

Tropomyosin (TM), an essential actin-binding protein, is central to the control of calcium-regulated striated muscle contraction. Although TPM1alpha (also called alpha-TM) is the predominant TM isoform in human hearts, the precise TM isoform composition remains unclear.

METHODS AND RESULTS

In this study, we quantified for the first time the levels of striated muscle TM isoforms in human heart, including a novel isoform called TPM1kappa. By developing a TPM1kappa-specific antibody, we found that the TPM1kappa protein is expressed and incorporated into organized myofibrils in hearts and that its level is increased in human dilated cardiomyopathy and heart failure. To investigate the role of TPM1kappa in sarcomeric function, we generated transgenic mice overexpressing cardiac-specific TPM1kappa. Incorporation of increased levels of TPM1kappa protein in myofilaments leads to dilated cardiomyopathy. Physiological alterations include decreased fractional shortening, systolic and diastolic dysfunction, and decreased myofilament calcium sensitivity with no change in maximum developed tension. Additional biophysical studies demonstrate less structural stability and weaker actin-binding affinity of TPM1kappa compared with TPM1alpha.

CONCLUSIONS

This functional analysis of TPM1kappa provides a possible mechanism for the consequences of the TM isoform switch observed in dilated cardiomyopathy and heart failure patients.

Calcineurin deficiency decreases inflammatory lesions in transforming growth factor beta1-deficient mice

Transforming growth factor (TGF) beta1) is an immunoregulatory cytokine involved in self-tolerance and lymphocyte homeostasis. Tgfb1 knock-out (KO) mice develop severe multi-focal autoimmune inflammatory lesions due to [Ca(2+)]i deregulation in T cells, and die within 3 weeks after birth. Because the calcineurin inhibitor FK506 inhibits the hyperresponsiveness of Tgfb1(-/-) thymocytes, and because calcineurin Abeta (CNAbeta)-deficient mice do not reject allogenic tumours, we have generated Tgfb1(-/-) Cnab(-/-) mice to address whether CNAbeta deficiency prevents T cell activation and inflammation in Tgfb1(-/-) mice. Here we show that in Tgfb1(-/-) Cnab(-/-) mice inflammation is reduced significantly relative to that in Tgfb1(-/-) mice. However, both CD4(+) and CD8(+) T cells in double knock-out (DKO) mice are activated, as revealed by up-regulation of CD11a lymphocyte function-associated antigen-1 (LFA-1), CD44 and CD69 and down-regulation of CD62L. These data suggest that deficiency of CNAbeta decreases inflammatory lesions but does not prevent activation of autoreactive T cells. Also Tgfb1(-/-) T cells can undergo activation in the absence of CNAbeta, probably by using the other isoform of calcineurin (CNAalpha) in a compensatory manner. CNAbeta-deficient T cells undergo spontaneous activation in vivo and are activated upon anti-T cell receptor stimulation in vitro. Understanding the role of calcineurin in T cell regulation should open up new therapeutic opportunities for inflammation and cancer.

An internal domain of beta-tropomyosin increases myofilament Ca(2+) sensitivity

Tropomyosin (TM) is involved in Ca(2+)-mediated muscle contraction and relaxation in the heart. Striated muscle alpha-TM is the major isoform expressed in the heart. The expression of striated muscle beta-TM in the murine myocardium results in a decreased rate of relaxation and increased myofilament Ca(2+) sensitivity. Replacing the carboxyl terminus (amino acids 258-284) of alpha-TM with beta-TM (a troponin T-binding region) results in decreased rates of contraction and relaxation in the heart and decreased myofilament Ca(2+) sensitivity. We hypothesized that the putative internal troponin T-binding domain (amino acids 175-190) of beta-TM may be responsible for the increased myofilament Ca(2+) sensitivity observed when the entire beta-TM is expressed in the heart. To test this hypothesis, we generated transgenic mice that expressed chimeric TM containing beta-TM amino acids 175-190 in the backbone of alpha-TM (amino acids 1-174 and 191-284). These mice expressed 16-57% chimeric TM and did not develop cardiac hypertrophy or any other morphological changes. Physiological analysis showed that these hearts exhibited decreased rates of contraction and relaxation and a positive response to isoproterenol. Skinned fiber bundle analyses showed a significant increase in myofilament Ca(2+) sensitivity. Biophysical experiments demonstrated that the exchanged amino acids did not influence the flexibility of the TM. This is the first study to demonstrate that a specific domain within TM can increase the Ca(2+) sensitivity of the thin filament and affect sarcomeric performance. Furthermore, these results enhance the understanding of why TM mutations associated with familial hypertrophic cardiomyopathy demonstrate increased myofilament sensitivity to Ca(2+).

Dilated cardiomyopathy mutant tropomyosin mice develop cardiac dysfunction with significantly decreased fractional shortening and myofilament calcium sensitivity

Mutations in striated muscle alpha-tropomyosin (alpha-TM), an essential thin filament protein, cause both dilated cardiomyopathy (DCM) and familial hypertrophic cardiomyopathy. Two distinct point mutations within alpha-tropomyosin are associated with the development of DCM in humans: Glu40Lys and Glu54Lys. To investigate the functional consequences of alpha-TM mutations associated with DCM, we generated transgenic mice that express mutant alpha-TM (Glu54Lys) in the adult heart. Results showed that an increase in transgenic protein expression led to a reciprocal decrease in endogenous alpha-TM levels, with total myofilament TM protein levels remaining unaltered. Histological and morphological analyses revealed development of DCM with progression to heart failure and frequently death by 6 months. Echocardiographic analyses confirmed the dilated phenotype of the heart with a significant decrease in the left ventricular fractional shortening. Work-performing heart analyses showed significantly impaired systolic, and diastolic functions and the force measurements of cardiac myofibers revealed that the myofilaments had significantly decreased Ca(2+) sensitivity and tension generation. Real-time RT-PCR quantification demonstrated an increased expression of beta-myosin heavy chain, brain natriuretic peptide, and skeletal actin and a decreased expression of the Ca(2+) handling proteins sarcoplasmic reticulum Ca(2+)-ATPase and ryanodine receptor. Furthermore, our study also indicates that the alpha-TM54 mutation decreases tropomyosin flexibility, which may influence actin binding and myofilament Ca(2+) sensitivity. The pathological and physiological phenotypes exhibited by these mice are consistent with those seen in human DCM and heart failure. As such, this is the first mouse model in which a mutation in a sarcomeric thin filament protein, specifically TM, leads to DCM.

Short-form Ron receptor is required for normal IFN-gamma production in concanavalin A-induced acute liver injury

Abrogation of Ron receptor tyrosine kinase function results in defects in macrophage activation and dysregulated acute inflammatory responses in vivo. Several naturally occurring constitutively active alternative forms of Ron have been identified, including from primary human tumors and tumor cell lines. One of these alternative forms, short-form (SF) Ron, is generated from an alternative start site in intron 10 of the Ron gene that eliminates most of the extracellular portion of the receptor and is overexpressed in several human cancers. To test the physiological significance of SF-Ron in vivo, mice were generated that solely express the full-length form of Ron (FL-Ron). Our results show that elimination of the capacity to express SF-Ron in vivo leads to augmented production of IFN-gamma from splenocytes following stimulation ex vivo with either concanavalin A or anti-CD3/T cell receptor monoclonal antibody. Moreover, in a concanavalin A-induced murine model of acute liver injury, FL-Ron mice have increased production of serum INF-gamma and serum alanine aminotransferase levels and worsened liver histology and overall survival compared with wild-type control mice. Taken together, these results suggest for the first time that SF-Ron impacts the progression of inflammatory immune responses in vivo and further support a role for the Ron receptor and its various forms in liver pathophysiology.

Age-related changes in the biomechanics of healing patellar tendon

By 2030, there will be 70 million people in the United States over the age of 65, and by 2050, 22% of the US population will be considered elderly. It is generally believed that injuries in the elderly heal slower and less completely than in adolescents or young adults. To evaluate aging effects on tissue repair a surgical injury was created in the middle third of one patellar tendon in 1- and 4-5-year-old New Zealand White rabbits. The biomechanical properties of the isolated repair tissues and contralateral normal tendon tissues were compared at 6, 12 and 26 weeks post-injury. We hypothesized that repair tissues would exhibit age-related reductions in biomechanical properties at all time intervals of healing, both based on raw data and when normalized to values from contralateral tendons. Repairs from both age groups were similar, with no significant increase in maximum stress, strain at maximum stress, or modulus between 6 and 12 weeks. At 26 weeks, the repairs in the 4-year-old rabbits had higher maximum stress values than repairs in the 1-year-old rabbits (p=0.03). There were no significant differences in the strain at maximum stress or modulus. When repair tissue properties were normalized to values in the contralateral normal tendon, the maximum stress of the patellar tendon repair tissue from the 4 year old was significantly greater than the corresponding value from the 1 year old at the 26 week time point (p=0.04). In conclusion, these findings do not support the presence of age-related declines in the biomechanics of healing tendon.

Effects of age on the repair ability of mesenchymal stem cells in rabbit tendon

Successful tissue engineered repair in the aging adult requires an abundant source of autologous, multipotent mesenchymal stem cells (MSCs). Although the number of bone marrow-derived MSCs declines dramatically with aging, their effectiveness in repair with increasing age has not been studied. We tested the hypothesis that MSCs harvested from geriatric rabbits would not repair patellar tendon defects as well as MSCs harvested from younger adult rabbits. In a novel within-subjects experiment, autologous MSCs were isolated from 1-year old rabbits, culture expanded, and cryogenically preserved. After housing the rabbits for 3 years, MSCs were re-harvested from the 4-year old rabbits and expanded. Five hundred thousand thawed and fresh MSCs were each separately mixed with type I collagen gel (333.3 x 10(3) cells/mg collagen) 24 h before surgery, and the resulting constructs implanted in bilateral full-length central third tendon defects. Twelve weeks post-surgery, the bone-tendon repair-bone units were failed in tension. Intra-animal (paired) comparisons between repair tissue treated with 1-year old MSCs and repair tissue treated with 4-year old MSCs resulted in no significant differences (alpha=0.05) in material properties including maximum stress (10.8 MPa vs. 9.9 MPa; p=0.762), modulus (139.8 MPa vs. 146.2 MPa; p=0.914), and strain energy density (0.52 N mm/mm(3) vs. 0.53 N mm/mm(3); p=0.966). Despite an age-related trend, there were also no significant differences in structural properties including maximum force (62.9 N vs. 27.0 N; p=0.070), stiffness (24.9 N/mm vs. 12.0 N/mm; p=0.111), and strain energy (87.2 N mm vs. 31.4 N mm; p=0.061). A subset of the rabbits (n=4 1 yrMSC, n=2 4 yrMSC) showed the presence of ectopic bone in the repair region and were not included in the mechanical analyses. We conclude that in the rabbit model MSCs do not lose their benefit as a tendon repair therapy with aging and that MSCs can be cryogenically stored for 3 years and still effectively repair soft tissue injuries.

Mesenchymal stem cells used for rabbit tendon repair can form ectopic bone and express alkaline phosphatase activity in constructs

Mesenchymal stem cells (MSCs) have been used to repair connective tissue defects in several animal models. Compared to "natural healing" controls (no added cells), MSC-collagen gel constructs in rabbit tendon defects significantly improve repair biomechanics. However, ectopic bone forms in 28% of MSC-treated rabbit tendons. To understand the source of bone formation, three studies were performed. In the first study, the hypothesis was tested that MSCs delivered during surgery contribute to bone formation in the in vivo repair site. Adjacent histological sections in the MSC-treated repair tissue were examined for pre-labeled MSCs and for cells showing positive alkaline phosphatase (ALP) activity. Both cells were observed in serial sections in regions of ectopic bone. Contralateral "natural healing" tendons lacked both markers. In the other two studies, the effects of osteogenic supplements and construct geometry (monolayer vs. 3-D) on ALP activity were studied to test three hypotheses: that rabbit MSCs increase ALP activity over time in monolayer culture conditions; that adding osteogenic inducing supplements to the culture medium increases cellular protein in monolayer culture; and that rabbit MSCs increase ALP activity both in monolayer and in 3-D constructs, with and without media supplements. Culture in monolayer under similar conditions to in vivo (as in the first study) did not increase ALP at 2 or 4 weeks. Medium designed to increase osteogenic activity significantly increased cell numbers (cellular protein increased by 260%) but did not affect ALP activity either in monolayer or 3-D constructs (p>0.12). However, MSCs in 3-D constructs exhibited higher ALP activity than cells in monolayer, both in the presence (p<0.045) and absence of supplement (p<0.005). These results suggest that in vitro conditions may critically influence cell differentiation and protein expression. Mechanisms responsible for these effects are currently under investigation.

A mouse model of familial hypertrophic cardiomyopathy caused by a alpha-tropomyosin mutation

Familial hypertrophic cardiomyopathy, a disease caused by mutations in cardiac contractile proteins, is characterized by left and/or right ventricular hypertrophy, myocyte disarray, fibrosis, and cardiac arrhythmias that may lead to premature sudden death. Five distinct point mutations within alpha-tropomyosin are associated with the development of familial hypertrophic cardiomyopathy. Two of these mutations are found within a troponin T binding site, located at amino acids 175 and 180. In this study, we analyze a transgenic mouse model for one of the mutations that occur at codon 180: a substitution of a glutamic acid for a glycine. These mice develop severe cardiac hypertrophy, substantial interstitial fibrosis, and have an increased heart weight/ body weight ratio. Results show that calcium-handling proteins associated with the sarcoplasmic reticulum exhibit decreased expression. These alterations in gene expression, coupled with the structurally-altered tropomyosin, may contribute to the demonstrated decreased physiological performance exhibited by these transgenic mice. A DNA hybridization microarray analysis of the transgenic vs. control ventricular RNAs shows that 50 transcripts are differentially expressed by more than 100% during the onset of the hypertrophic process, many of which are associated with the extracellular matrix. This study demonstrates that mutations within tropomyosin can be severely disruptive of sarcomeric function, triggering a hypertrophic response coupled with a cascade of alterations in gene expression.

A potential mechanism for age-related declines in patellar tendon biomechanics

Injuries to soft tissues such as tendons are becoming ever more frequent among the elderly. While increasing levels of activity likely contribute to these injuries, age-related declines in tendon strength may also be important. Whether these declines in biomechanical properties are associated with changes in fibril diameter or collagen type remains in question. In this study, age-related changes were investigated in patellar tendons from young adult rabbits (1-year old, n = 17) and from rabbits at the onset of senescence (4-year old, n = 33). Patellar tendon biomechanics was correlated with both collagen fibril diameter and with the presence of type V collagen, a known regulator of collagen fibril diameter. We hypothesize that (a) aging from I to 4 years results in significant reductions in patellar tendon biomechanical properties, and (b) these age-related declines are associated with smaller fibril diameters and with the presence of type V collagen. Maximum stress declined 25% between I and 4 years of age (100.7 +/- 5.6 MPa and 74.3 +/- 3.4 MPa, respectively, p < 0.0003) (mean +/- SEM) and strain energy density declined 40% (p < 0.001). The distribution of collagen fibrils from 4-year old rabbits was skewed significantly towards smaller diameters compared to fibrils from 1-year old rabbits (p < 0.001). Type V collagen was observed only in the 4-year old rabbit tendons. These correlations suggest that with increasing age after skeletal maturity, type V collagen may help to regulate the assembly and thus diameter of collagen fibrils and thereby adversely affect patellar tendon strength.

Tropomyosin 3 expression leads to hypercontractility and attenuates myofilament length-dependent Ca(2+) activation

Tropomyosin (TM), an integral component of the thin filament, is encoded by three striated muscle isoforms: alpha-TM, beta-TM, and TPM 3. Although the alpha-TM and beta-TM isoforms are well characterized, less is known about the function of the TPM 3 isoform, which is predominantly found in the slow-twitch musculature of mammals. To determine its functional significance, we ectopically expressed this isoform in the hearts of transgenic mice. We generated six transgenic mouse lines that produce varying levels of TPM 3 message with ectopic TPM 3 protein accounting for 40-60% of the total striated muscle tropomyosin. The transgenic mice have normal life spans and exhibit no morphological abnormalities in their sarcomeres or hearts. However, there are significant functional alterations in cardiac performance. Physiological assessment of these mice by using closed-chest analyses and a work-performing model reveals a hyperdynamic effect on systolic and diastolic function. Analysis of detergent-extracted fiber bundles demonstrates a decreased sensitivity to Ca(2+) in force generation and a decrease in length-dependent Ca(2+) activation with no detectable change in interfilament spacing as determined by using X-ray diffraction. Our data are the first to demonstrate that TM isoforms can affect sarcomeric performance by decreasing sensitivity to Ca(2+) and influencing the length-dependent Ca(2+) activation.

MR imaging of murine arthritis using ultrasmall superparamagnetic iron oxide particles

The objective of this work was to determine the ability of magnetic resonance (MR) imaging with ultrasmall superparamagnetic iron oxide (USPIO) particles to provide quantitative measures of inflammation in autoimmune arthritis. Mice were injected intravenously or intra-articularly with USPIO followed by magnetic resonance and histological assessment of the knee joint. Comparisons were made between MR microimages and histology in naïve mice and mice with collagen-induced arthritis.Following intravenous administration, accumulation of USPIO was observed in the popliteal lymph nodes, but not the joint. Administration of USPIO intra-articularly resulted in signal loss in the joint. The MR signal intensity could be quantified and correlated with iron staining in the synovial lining. A marked increase in USPIO uptake and a corresponding decrease in signal intensity were observed in arthritic, compared to naïve mice. Areas of focal signal loss corresponded to foci of iron staining by histology. These studies may provide a basis for the clinical application of USPIO in arthritis for assessing disease severity and monitoring response to therapy.

A familial hypertrophic cardiomyopathy alpha-tropomyosin mutation causes severe cardiac hypertrophy and death in mice

Tropomyosin, an essential component of the sarcomere, regulates muscle contraction through Ca(2+)-mediated activation. Familial hypertrophic cardiomyopathy (FHC) is caused by mutations in numerous cardiac sarcomeric proteins, including myosin heavy and light chains, actin, troponin T and I, myosin binding protein C, and alpha-tropomyosin. This study developed transgenic mouse lines that encode an FHC mutation in alpha-tropomyosin; this mutation is an amino acid substitution at codon 180 (Glu180Gly) which occurs in a troponin T binding region. Non-transgenic and control mice expressing wild-type alpha-tropomyosin demonstrate no morphological or physiological changes. Expression of exogenous mutant tropomyosin leads to a concomitant decrease in endogenous alpha-tropomyosin without altering the expression of other contractile proteins. Histological analysis shows that initial pathological changes, which include ventricular concentric hypertrophy, fibrosis and atrial enlargement, are detected within 1 month. The disease-associated changes progressively increase and result in death between 4 and 5 months. Physiological analyses of the FHC mice using echocardiography, work-performing heart analyses, and force measurements of cardiac myofibers, demonstrate dramatic functional differences in diastolic performance and increased sensitivity to calcium. This report demonstrates that mutations in alpha-tropomyosin can be severely disruptive of sarcomeric function, which consequently triggers a dramatic hypertrophic response that culminates in lethality.

Squamous cell tumors in mice heterozygous for a null allele of Atp2a2, encoding the sarco(endo)plasmic reticulum Ca2+-ATPase isoform 2 Ca2+ pump

Mutations in the human ATP2A2 gene, encoding sarco(endo)plasmic reticulum Ca(2+)-ATPase isoform 2 (SERCA2), cause Darier disease, an autosomal dominant skin disease characterized by multiple keratotic papules in the seborrheic regions of the body. Mice with a single functional Atp2a2 allele (the mouse homolog of ATP2A2) were shown previously to have reduced levels of SERCA2 in heart and mildly impaired cardiac contractility and relaxation. Here we show that aged heterozygous mutant (Atp2a2(+/-)) mice develop squamous cell tumors of the forestomach, esophagus, oral mucosa, tongue, and skin. Squamous cell tumors occurred in 13/14 Atp2a2(+/-) mice but were not observed in age- and sex-matched wild-type controls. Hyperkeratinized squamous cell papillomas and carcinomas of the upper digestive tract were the most frequent finding among Atp2a2(+/-) mice, and many animals had multiple tumors. Western blot analyses showed that SERCA2 protein levels were reduced in skin and other affected tissues of heterozygous mice. The development of squamous cell tumors in aged Atp2a2(+/-) mice indicates that SERCA2 haploinsufficiency predisposes murine keratinocytes to neoplasia. These findings provide the first direct demonstration that a perturbation of Ca(2+) homeostasis or signaling can serve as a primary initiating event in cancer.

Expression of angiogenic factors in juvenile rheumatoid arthritis: correlation with revascularization of human synovium engrafted into SCID mice

OBJECTIVE

Although increased vascularity was noted in early histopathologic studies of juvenile rheumatoid arthritis (JRA) synovium, the available data on angiogenesis in JRA are very limited. The main purposes of this study were to assess expression of the key angiogenic factors in JRA synovium, and to evaluate a SCID mouse model of JRA as an approach to study in vivo regulation of the expression of these factors in JRA.

METHODS

RNase protection assay was used to assess the expression of the key angiogenic factors in fresh JRA synovium and in JRA synovial tissue fragments that had been minced and then implanted into SCID mice. Vascularity of the samples was assessed by immunohistochemical staining for von Willebrand factor. Synovial specimens obtained from patients with osteoarthritis (OA) or other noninflammatory arthropathies were used as controls.

RESULTS

Detectable levels of messenger RNA for vascular endothelial growth factor and angiopoietin 1 and their respective receptors, as well as endoglin and thrombin receptors, were present in all JRA tissue specimens studied. The levels of expression of these factors in JRA tissues were significantly higher than those in tissues obtained from patients with OA or other noninflammatory arthropathies. Furthermore, increased expression of the key angiogenic factors in the fresh JRA tissues correlated with the exuberant revascularization of JRA minced tissue fragments implanted into SCID mice. This was in sharp contrast to the poor revascularization of implanted OA tissues.

CONCLUSION

JRA synovium is characterized by high angiogenic activity. SCID mouse-human JRA synovium chimeras may provide a good approach to study the in vivo regulation of angiogenesis in JRA.

Variant form of diffuse corporal gastritis in NHE2 knockout mice

Mice lacking the NHE2 Na+/H+ gene develop gastritis of the glandular mucosa as early as the tenth day of life, achieving maximal intensity of inflammation from 17 to 19 days after birth and maximal atrophy at one year. We assessed the effects of this process in such mice to 16 months of age. The stomach of NHE2 null mutants was examined at 10, 17 to 20, 24 to 35 and 49 to 70 days, and at 12 to 16 months. The NHE2 wild-type (+/+) and NHE2 heterozygous (+/-) mice were compared with the NHE2 homozygous mutant mice (-/-). The stomach of the mutant mice at all ages was characterized by a substantially reduced number of parietal cells. The 10-day-old mouse stomach had a transmural infiltrate of primarily neutrophils. With increasing age, neutrophils were replaced by lymphocytes and plasma cells in the glandular mucosa of the mutant mice. Young adult 49- to 70-day-old mice had surface cell hyperplasia and expansion of the replicating cell population. Hyperplasia of enterochromaffin-like cells and antral gastrin cells accompanied profound fundic gland and surface cell hyperplasia, and became progressively more severe with increasing age of the NHE2-/- mice. Neoplasms were not found in the mutant or control mice. This gastritis differs from that of autoimmune gastritis in that it is transmural, begins in infancy, and is associated with a predominantly neutrophilic infiltrate in its early stages. Some of the histologic changes in the adult mice can be explained on the basis of prolonged achlorhydria. This mouse may be a suitable model for prolonged effects of achlorhydria.

Adeno-associated virus mediates long-term gene transfer and delivery of chondroprotective IL-4 to murine synovium

Treatments for rheumatoid arthritis and other inflammatory arthropathies are often ineffective at preventing joint destruction. Long-term genetic modification of the cells lining the joint space (synoviocytes) in vivo represents a potential method for the treatment of these chronic conditions. However, a vector capable of efficiently transducing synoviocytes in vivo for a persistent period has not been available. The present report describes the genetic modification of synoviocytes in vivo using recombinant adeno-associated virus. High-titer adeno-associated virus encoding the gene for Escherichia coli beta-galactosidase was injected into the knee joints of mice. Synovial tissues were then examined for beta-galactosidase transgene expression by in situ staining and by fluorometry. High-efficiency, persistent transgene expression was observed in the synovium with no evidence of vector-induced inflammation. Expression was observed for at least 7 months and was higher in arthritic than nonarthritic mice. Gene transfer of murine IL-4 to the joints of mice with collagen-induced arthritis led to detectable levels of IL-4 in the joint and protection from articular cartilage destruction. These data suggest that adeno-associated virus may be a useful vector for gene delivery to the synovium for the treatment of inflammatory arthropathies.

In vitro characterization of mesenchymal stem cell-seeded collagen scaffolds for tendon repair: effects of initial seeding density on contraction kinetics

Mesenchymal stem cells (MSCs) were isolated from bone marrow, culture-expanded, and then seeded at 1, 4, and 8 million cells/mL onto collagen gel constructs designed to augment tendon repair in vivo. To investigate the effects of seeding density on the contraction kinetics and cellular morphology, the contraction of the cell/collagen constructs was monitored over time up to 72 h in culture conditions. Constructs seeded at 4 and 8 million cells/mL showed no significant differences in their gross appearance and dimensions throughout the contraction process. By contrast, constructs seeded at 1 million cells/mL initially contracted more slowly and their diameters at 72 h were 62 to 73% larger than those seeded at higher densities. During contraction, MSCs reoriented and elongated significantly with time. Implants prepared at higher seeding densities showed more well aligned and elongated cell nuclei after 72 h of contraction. Changes in nuclear morphology of the MSCs in response to physical constraints provided by the contracted collagen fibrils may trigger differentiation pathways toward the fibroblastic lineage and influence the cell synthetic activity. Controlling the contraction and organization of the cells and matrix will be critical for successfully creating tissue engineered grafts.

Heterogeneous effects of IL-2 on collagen-induced arthritis

IL-2 is generally considered a pro-inflammatory cytokine that exacerbates Th1-mediated disease states, such as autoimmune arthritis. Consistent with this role for IL-2, recent studies from our laboratory demonstrate that IL-2 mRNA is markedly increased during the acute stage of collagen-induced arthritis (CIA), an animal model of rheumatoid arthritis. To further define the role of IL-2 in CIA, the levels of IL-2 protein and its receptor and the effects of IL-2 administration were analyzed during CIA. IL-2 protein and IL-2R were preferentially expressed at disease onset, compared with later stages of disease. Administration of recombinant human IL-2 (rhIL-2) at, or just before, disease onset exacerbated disease; surprisingly, rhIL-2 given before disease onset inhibited CIA, associated with reduced cellular and humoral responses to type II collagen. Determination of in vivo serum levels of Th1 and Th2 cytokines in response to rhIL-2 treatment demonstrated that IFN-gamma, but not IL-4, was markedly up-regulated in response to IL-2. In mice treated with anti-IFN-gamma Ab, both early and late IL-2 administration exacerbated CIA. Thus, IL-2 can have two opposite effects on autoimmune arthritis, a direct stimulatory effect and an indirect suppressive effect that is mediated by IFN-gamma.

An in vivo model for load-modulated remodeling in the rabbit flexor tendon

This study tested the hypothesis that eliminating in vivo compression to the wrap-around, fibrocartilage-rich zone of the flexor digitorum profundus tendon results in rapid depletion of fibrocartilage and changes in its mechanical properties, microstructure, extracellular matrix composition, and cellularity. The right flexor digitorum profundus tendons of 2.5-3-year-old rabbits were translocated anteriorly to eliminate in vivo compression and shear to the fibrocartilage zone and, at 4 weeks after surgery, were compared with tendons that had sham surgery and with untreated tendons. The translocated tissue showed a significant increase in equilibrium strain under a compressive creep load (p < 0.05). The thickness and area of the fibrocartilage zone also decreased significantly (p < 0.05). The nuclear density decreased by 40% in the fibrocartilage zone (p < 0.005); however, nuclear shape and orientation were not significantly altered. Glycosaminoglycan content in the fibrocartilage zone was also depleted by 40% (p < 0.02). The tightly woven basket weave-like mesh of collagen fibers in the zone appeared more loosely organized, suggesting matrix reorganization due to translocation. Moreover, immunoreactive type-II collagen and link protein in the fibrocartilage zone also decreased. With use of this unique in vivo model, this research clearly elucidates how changing tissue function (by removing compressive forces) rapidly alters tissue form.

Rescue of high expression beta-tropomyosin transgenic mice by 5-propyl-2-thiouracil. Regulating the alpha-myosin heavy chain promoter

Tropomyosin is an essential component of the sarcomeric thin filament in striated muscle that participates in the regulation of muscle contraction through Ca(2+)-mediated activation. The two predominant tropomyosin isoforms expressed in striated muscle are alpha- and beta-tropomyosin, which exhibit an 86% amino acid identity between themselves. Previous studies by our laboratory utilized a transgenic mouse system to overexpress beta-tropomyosin in the heart to address the functional differences between these two tropomyosin isoforms. Interestingly, when a high percentage of beta-tropomyosin replaces alpha-tropomyosin in the hearts of transgenic mice, the mice die due to severe cardiac abnormalities. In this study, we have rescued these high expression beta-tropomyosin mice by turning off the alpha-myosin heavy chain promoter, which is driving the beta-tropomyosin transgene. This down-regulation of the alpha-myosin heavy chain promoter was accomplished by the administration of 5-propyl-2-thiouracil, which disrupts thyroid hormone synthesis and inhibits promoter activity through thyroid regulatory elements located in the 5'-flanking region of the promoter. Results show that as beta-tropomyosin expression is down-regulated, alpha-tropomyosin expression is increased. Also, alpha- and beta-myosin heavy chain expression is modified in response to the changes in thyroid hormone expression. Morphological analysis of these rescued mice show a moderate pathological phenotype, characterized by atrial myocytolysis; echocardiographic analyses demonstrate altered ventricular functions, such as peak filling rates and left ventricular fractional shortening. This is the first report demonstrating that transcriptional regulatory elements located within the alpha-myosin heavy chain promoter can be manipulated to rescue potentially lethal phenotypes, such as high expression beta-tropomyosin transgenic mice.

Transforming growth factor beta1 suppresses nonmetastatic colon cancer at an early stage of tumorigenesis

The transforming growth factor beta (TGF-beta) pathway is known to play an important role in both human and urine colon cancer. However, the staging, ligand specificity, and mechanism underlying the tumor suppressive activity of this pathway are unknown. We developed a mouse model for colon cancer that identifies an early role for TGF-beta1 in tumor suppression and implicates TGF-beta2 or TGF-beta3 in the prevention of metastasis. Analysis of the development of colon cancer in TGF-beta1 knockout mice pinpoints the defect to the hyperplasty/adenoma transition and reveals that the mechanism involves an inability to maintain epithelial tissue organization and not a loss of growth control, increased inflammatory activity, or increased genetic instability. These mice provide a unique opportunity to investigate the specific role of TGF-beta1 at this critical transition in the development of colon cancer.

Mouse model of a familial hypertrophic cardiomyopathy mutation in alpha-tropomyosin manifests cardiac dysfunction

To investigate the functional consequences of a tropomyosin (TM) mutation associated with familial hypertrophic cardiomyopathy (FHC), we generated transgenic mice that express mutant alpha-TM in the adult heart. The missense mutation, which results in the substitution of asparagine for aspartic acid at amino acid position 175, occurs in a troponin T binding region of TM. S1 nuclease mapping and Western blot analyses demonstrate that increased expression of the alpha-TM 175 transgene in different lines causes a concomitant decrease in levels of endogenous alpha-TM mRNA and protein expression. In vivo physiological analyses show a severe impairment of both contractility and relaxation in hearts of the FHC mice, with a significant change in left ventricular fractional shortening. Myofilaments that contain alpha-TM 175 demonstrate an increased activation of the thin filament through enhanced Ca2+ sensitivity of steady-state force. Histological analyses show patchy areas of mild ventricular myocyte disorganization and hypertrophy, with occasional thrombi formation in the left atria. Thus, the FHC alpha-TM transgenic mouse can serve as a model system for the examination of pathological and physiological alterations imparted through aberrant TM isoforms.

Autologous mesenchymal stem cell-mediated repair of tendon

Mesenchymal stem cells (MSCs) were isolated from bone marrow of 18 adult New Zealand White rabbits. These cells were culture expanded, suspended in type I collagen gel, and implanted into a surgically induced defect in the donor s right patellar tendon. A cell-free collagen gel was implanted into an identical control defect in the left patellar tendon. Repair tissues were evaluated biomechanically (n = 13) and histomorphometrically (n = 5) at 4 weeks after surgery. Compared to their matched controls, the MSC-mediated repair tissue demonstrated significant increases of 26% (p < 0.001), 18% (p < 0. 01), and 33% (p < 0.02) in maximum stress, modulus, and strain energy density, respectively. Qualitatively, there appeared to be minor improvements in the histological appearance of some of the MSC- mediated repairs, including increased number of tenocytes and larger and more mature-looking collagen fiber bundles. Morphometrically, however, there were no significant left-right differences in nuclear aspect ratio (shape) or nuclear alignment (orientation). Therefore, delivering a large number of mesenchymal stem cells to a wound site can significantly improve its biomechanical properties by only 4 weeks but produce no visible improvement in its microstructure.

Association of the course of collagen-induced arthritis with distinct patterns of cytokine and chemokine messenger RNA expression

OBJECTIVE

To quantitate changes in cytokine and chemokine messenger RNA (mRNA) levels during the development and progression of collagen-induced arthritis (CIA) in mice.

METHODS

Mice with CIA were scored for arthritis and killed at weekly intervals. Cytokine and chemokine mRNA levels were determined by RNase protection assays of total paw RNA.

RESULTS

Arthritic paws exhibited mRNA levels of interleukin-1beta (IL-1beta), IL-2, macrophage inflammatory protein 2 (MIP-2), IL-6, IL-1 receptor antagonist, RANTES, tumor necrosis factor alpha (TNFalpha), TNFbeta, MIP-1alpha, IL-11, transforming growth factor beta1 (TGFbeta1), TGFbeta2, and TGFbeta3 that were increased above mRNA levels in paws of normal, unimmunized mice and that exhibited distinct temporal patterns of mRNA expression. Clinically uninvolved paws also exhibited an increase in mRNA levels of IL-11, RANTES, TNFalpha, TNFbeta, and MIP-1alpha.

CONCLUSION

The observed differential temporal cytokine and chemokine mRNA expression patterns suggest that specific cytokines and chemokines have defined roles at various times during the course of autoimmune arthritis. Since most of these cytokines and chemokines are found in human rheumatoid arthritis (RA) synovium and synovial fluids, these findings may have relevance to RA.

Overexpression of alpha1B-adrenergic receptor induces left ventricular dysfunction in the absence of hypertrophy

The stimulation of cardiac alpha1-adrenergic receptors (AR) modulates the heart's inotropic response and plays a role in the induction of cardiomyocyte hypertrophy. We have analyzed transgenic mouse lines overexpressing a wild-type alpha1B-AR specifically in the heart. Basal level systolic and diastolic left ventricular (LV) contractile function was depressed both in the anesthetized closed-chest mouse and the perfused working-heart preparation. Intrinsic LV function was further characterized under controlled preload and afterload conditions using the perfusion model. Contractile parameters were restored by chronic treatment with the alpha-AR antagonist prazosin. In ventricular function curves, the load-dependent force increases (length-tension effects) remained intact, although the transgenic curve was shifted to lower levels. The basal level contractile deficits were paralleled by a decrease in calcium transients in isolated LV cardiomyocytes. LV function comparable to controls was restored by isoproterenol stimulation. The physiological changes occurred in the absence of cardiomyocyte hypertrophy. This transgenic model will be useful for studying the potential role of alpha1-AR in cardiac contractility and hypertrophy.

Altered susceptibility to collagen-induced arthritis in transgenic mice with aberrant expression of interleukin-1 receptor antagonist

OBJECTIVE

To determine the effect of overexpression or deletion of interleukin-1 receptor antagonist (IL-1Ra) in collagen-induced arthritis (CIA).

METHODS

Mice overexpressing the IL-1Ra gene under the control of its endogenous promoter, mice lacking IL-1Ra, and normal littermate controls were immunized with bovine type II collagen (CII) and compared in terms of features of CIA.

RESULTS

Mice overexpressing IL-1Ra had a significant reduction in the incidence and severity of CIA. After CII immunization, IL-1Ra messenger RNA was overexpressed in the spleens, but not in the paws, of transgenic mice. Minimal differences were observed in the humoral or cellular immune responses to CII. Mice lacking IL-1Ra had a significantly earlier onset of CIA, with increased severity.

CONCLUSION

Endogenous expression of IL-1Ra is a critical determinant of susceptibility to CIA. These findings suggest potential therapeutic interventions for autoimmune arthritis.

Inhibition of collagen-induced arthritis in mice by viral IL-10 gene transfer

Autoimmune arthritides are characterized by an imbalance between pro- and anti-inflammatory cytokines. Viral IL-10 (vIL-10) shares many of the anti-inflammatory properties of mouse and human IL-10, but lacks their immunostimulatory properties and may therefore offer superior immunosuppression. Viral IL-10 has a short half-life; however, genetic modification of cells in vivo offers a potential means of achieving prolonged therapeutic titers. To determine the effects on collagen-induced arthritis of vIL-10 gene transfer, DBA/1 mice were administered i.v. or intra-articular injections of Av(vIL-10), a replication-deficient adenovirus encoding vIL-10. The i.v. injection of Av(vIL-10) before disease onset delayed the onset and reduced the severity of collagen-induced arthritis, but treatment of established disease was ineffective. The preventative effects were not due to decreased anti-type II collagen Ab production. Rather, T cells from mice treated with Av(vIL-10) demonstrated a decreased in vitro proliferative response to type II collagen, and a delay was observed in up-regulation of synovial mRNA for the proinflammatory cytokines IL-2 and IL-1beta. Intra-articular injection of Av(vIL-10) into knee joints did not reduce arthritis in the knees, but inhibited the development of arthritis in the paws. Humoral and cellular immune responses against Av(vIL-10) were observed. These results demonstrate that vIL-10 can significantly alter the course of autoimmune arthritis and emphasize the complexities of using gene transfer as a method of drug delivery for arthritis.

Beta-tropomyosin overexpression induces severe cardiac abnormalities

Tropomyosin, a coiled-coil dimer, stabilizes actin filaments and is central to the control of calcium-regulated striated muscle contraction. Striated muscle-specific alpha-tropomyosin is the predominant isoform in cardiac muscle, with low levels of beta-tropomyosin restricted to fetal development in the mouse. To understand the functional role of various tropomyosin isoforms during myofilament activation and regulation in the intact sarcomere, we generated transgenic mice that overexpress striated muscle-specific beta-tropomyosin in the adult heart. Our earlier results succinctly demonstrate that overexpression of beta-tropomyosin in the hearts of transgenic mice decreases endogeneous alpha-tropomyosin levels while altering diastolic function of the myocardium. To explore further the significance of altering the alpha- to beta-tropomyosin isoform ratio in developing murine myocardium, we generated transgenic mice which express beta-tropomyosin at high levels in the heart. The data show that higher levels of beta-tropomyosin expression are lethal with death ensuing between 10-14 days postnatally. A detailed histological analysis demonstrates that the hearts of these mice exhibit several pathological abnormalities, including thrombus formation in the lumen of both atria and in the subendocardium of the left ventricle. Other changes include atrial enlargement and fibrosis, and diffuse myocytolysis, Physiological analyses using ventricular muscle strip preparations from these mice reveal that both myocardial contraction and relaxation parameters are severely impaired. Thus, these results firmly demonstrate an essential difference in tropomyosin isoform function in physiologically regulating cardiac performance.

Chronic renal failure in a mouse model of human adenine phosphoribosyltransferase deficiency

In humans, adenine phosphoribosyltransferase (APRT, EC 2.4.2.7) deficiency can manifest as nephrolithiasis, interstitial nephritis, and chronic renal failure. APRT catalyzes synthesis of AMP from adenine and 5-phosphoribosyl-1-pyrophosphate. In the absence of APRT, 2,8-dihydroxyadenine (DHA) is produced from adenine by xanthine dehydrogenase (XDH) and can precipitate in the renal interstitium, resulting in kidney disease. Treatment with allopurinol controls formation of DHA stones by inhibiting XDH activity. Kidney disease in APRT-deficient mice resembles that seen in humans. By age 12 wk, APRT-deficient male mice are, on average, mildly anemic and smaller than normal males. They have extensive renal interstitial damage (assessed by image analysis) and elevated blood urea nitrogen (BUN), and their creatinine clearance rates, which measure excretion of infused creatinine as an estimate of glomerular filtration rate (GFR), are about half that of wild-type males. APRT-deficient males treated with allopurinol in the drinking water had normal BUN and less extensive visible renal damage, but creatinine clearance remained low. Throughout their lifespans, homozygous null female mice manifested significantly less renal damage than homozygous null males of the same age. APRT-deficient females showed no significant impairment of GFR at age 12 wk. Consequences of APRT deficiency in male mice are more pronounced than in females, possibly due to differences in rates of adenine or DHA synthesis or to sex-determined responses of the kidneys.

Thrombospondin-1 is a major activator of TGF-beta1 in vivo

The activity of TGF-beta1 is regulated primarily extracellularly where the secreted latent form must be modified to expose the active molecule. Here we show that thrombospondin-1 is responsible for a significant proportion of the activation of TGF-beta1 in vivo. Histological abnormalities in young TGF-beta1 null and thrombospondin-1 null mice were strikingly similar in nine organ systems. Lung and pancreas pathologies similar to those observed in TGF-beta1 null animals could be induced in wild-type pups by systemic treatment with a peptide that blocked the activation of TGF-beta1 by thrombospondin-1. Although these organs produced little active TGF-beta1 in thrombospondin null mice, when pups were treated with a peptide derived from thrombospondin-1 that could activate TGF-beta1, active cytokine was detected in situ, and the lung and pancreatic abnormalities reverted toward wild type.

Targeted disruption of the murine Na+/H+ exchanger isoform 2 gene causes reduced viability of gastric parietal cells and loss of net acid secretion

Multiple isoforms of the Na+/H+ exchanger (NHE) are expressed at high levels in gastric epithelium, but the physiological role of individual isoforms is unclear. To study the function of NHE2, which is expressed in mucous, zymogenic, and parietal cells, we prepared mice with a null mutation in the NHE2 gene. Homozygous null mutants exhibit no overt disease phenotype, but the cellular composition of the oxyntic mucosa of the gastric corpus is altered, with parietal and zymogenic cells reduced markedly in number. Net acid secretion in null mutants is reduced slightly relative to wild-type levels just before weaning and is abolished in adult animals. Although mature parietal cells are observed, and appear morphologically to be engaged in active acid secretion, many of the parietal cells are in various stages of degeneration. These results indicate that NHE2 is not required for acid secretion by the parietal cell, but is essential for its long-term viability. This suggests that the unique sensitivity of NHE2 to inhibition by extracellular H+, which would allow upregulation of its activity by the increased interstitial alkalinity that accompanies acid secretion, might enable this isoform to play a specialized role in maintaining the long-term viability of the parietal cell.

Effect of superoxide dismutase on a rabbit model of chronic allergic asthma

BACKGROUND

In bronchial asthma, inflammatory cells infiltrating the airway mucosa release oxygen radicals that cause tissue damage and amplify the airway inflammation. Antioxidant enzymes may have a protective effect on the airways.

OBJECTIVE

The purpose of this study was to determine whether treatment of a rabbit model of chronic allergic asthma with the antioxidant enzyme superoxide dismutase conjugated to polyethylene glycol will protect the airways from oxygen radical injury, decrease airway inflammation, and attenuate the asthmatic response.

METHODS

New Zealand white rabbits were sensitized to ragweed. Baseline histamine PC30, ragweed PD30, and early and late phase asthmatic response to ragweed bronchial challenge were measured. The rabbits were then randomized into two groups that received every 48 hours an intravenous dose of either superoxide dismutase-polyethylene glycol 10,000 U/kg or inactivated superoxide dismutase-polyethylene glycol as control, followed by a 1-hour exposure to aerosolized ragweed extract. After 4 weeks the rabbits had a second bronchial challenge, were sacrificed, and lung histology was studied.

RESULTS

On the posttreatment challenge, the superoxide dismutase-polyethylene glycol group had a rise in ragweed PD30, while the control group had no change in ragweed PD30, and two of five rabbits in the superoxide dismutase-polyethylene glycol group did not have an early or late phase asthmatic response, while all rabbits in the control group had an asthmatic response. There was no significant difference in lung histology between both groups.

CONCLUSION

A rabbit model of chronic allergic asthma treated with superoxide dismutase-polyethylene glycol showed a trend of improvement in airway responsiveness but no significant effect on airway inflammation.

Fibroblast growth factor 2 control of vascular tone

Vascular tone control is essential in blood pressure regulation, shock, ischemia-reperfusion, inflammation, vessel injury/repair, wound healing, temperature regulation, digestion, exercise physiology, and metabolism. Here we show that a well-known growth factor, FGF2, long thought to be involved in many developmental and homeostatic processes, including growth of the tissue layers of vessel walls, functions in vascular tone control. Fgf2 knockout mice are morphologically normal and display decreased vascular smooth muscle contractility, low blood pressure and thrombocytosis. Following intra-arterial mechanical injury, FGF2-deficient vessels undergo a normal hyperplastic response. These results force us to reconsider the function of FGF2 in vascular development and homeostasis in terms of vascular tone control.

Transgenic Galphaq overexpression induces cardiac contractile failure in mice

The critical cell signals that trigger cardiac hypertrophy and regulate the transition to heart failure are not known. To determine the role of Galphaq-mediated signaling pathways in these events, transgenic mice were constructed that overexpressed wild-type Galphaq in the heart using the alpha-myosin heavy chain promoter. Two-fold overexpression of Galphaq showed no detectable effects, whereas 4-fold overexpression resulted in increased heart weight and myocyte size along with marked increases in atrial naturietic factor ( approximately 55-fold), beta-myosin heavy chain ( approximately 8-fold), and alpha-skeletal actin ( approximately 8-fold) expression, and decreased ( approximately 3-fold) beta-adrenergic receptor-stimulated adenylyl cyclase activity. All of these signals have been considered markers of hypertrophy or failure in other experimental systems or human heart failure. Echocardiography and in vivo cardiac hemodynamic studies indeed revealed impaired intrinsic contractility manifested as decreased fractional shortening (19 +/- 2% vs. 41 +/- 3%), dP/dt max, a negative force-frequency response, an altered Starling relationship, and blunted contractile responses to the beta-adrenergic agonist dobutamine. At higher levels of Galphaq overexpression, frank cardiac decompensation occurred in 3 of 6 animals with development of biventricular failure, pulmonary congestion, and death. The element within the pathway that appeared to be critical for these events was activation of protein kinase Cepsilon. Interestingly, mitogen-activated protein kinase, which is postulated by some to be important in the hypertrophy program, was not activated. The Galphaq overexpressor exhibits a biochemical and physiologic phenotype resembling both the compensated and decompensated phases of human cardiac hypertrophy and suggests a common mechanism for their pathogenesis.

Anti-T cell receptor antibody prolongs transgene expression and reduces lung inflammation after adenovirus-mediated gene transfer

Replication-deficient delta E1a-E3 adenovirus mediates efficient gene transfer to the mouse lung; however it induces a host immune response mediated, in part, by T cells. This immune response is associated with loss of transgene expression. Monoclonal antibodies (mAb) against the T cell receptor (TCR) complex can inhibit both CD4+ and CD8+ T cell responses in vivo and are the most potent anti-T cell agents in clinical use. To determine whether such mAbs can be used to prolong adenovirus-mediated transgene expression, the vector Av1Luc1 (delta E1a-E3 recombinant adenovirus encoding the firefly luciferase gene) was administered intratracheally to C57BL/6 mice on day 0. Three days prior to adenovirus administration (day -3), mice were treated with a single i.p. injection of the anti-TCR mAb H57. Controls received phosphate-buffered saline. Animals were sacrificed on days 3, 14, 28, and 56 and lungs were assessed for transgene expression and histopathology. Luciferase activity decreased markedly in the controls by day 14, but was maintained at high levels in animals receiving anti-TCR mAb. A mild, focal, predominantly neutrophilic inflammation was observed in the alveoli of all mice 3 days after virus administration. In PBS-treated controls, this inflammation progressed to a moderate to severe multifocal, perivascular and peribronchiolar lymphoid infiltration at 14 days. B cells and T cells were present in approximately equal numbers, with CD4+ T cells predominating over CD8+ T cells by 3- to 28-fold. Treatment with H57 resulted in near-complete prevention of the lymphocytic inflammatory infiltrate and increased luciferase activity throughout the 56-day study period, in association with TCR modulation and T cell depletion. Thus, anti-TCR mAb decreases inflammation and prolongs gene expression following adenovirus-mediated gene transfer.

Germ-free and barrier-raised TGF beta 1-deficient mice have similar inflammatory lesions

Barrier-raised transforming growth factor beta 1 (TGF beta 1)-deficient mice consistently die before 35 days of age of a severe multiorgan inflammatory disease that can affect the skeletal muscle, heart, liver, pancreas, salivary gland, lung, oesophagus and stomach. The underlying cause of this disease is not known. To determine whether abnormal responsiveness of the immune system to the presence of enteric flora plays a causative role, a colony of TGF beta 1-deficient and wild-type mice were raised in a sterile environment. Seven germ-free TGF beta 1-deficient and 5 germ-free TGF beta 1 wild-type mice were examined. Lesion development was analysed and compared with historical data on 50 barrier-raised TGF beta 1 mutant mice and 32 barrier-raised wild-type mice. All germ-free TGF beta 1-deficient mice died shortly after weaning, as do their barrier-raised counterparts. There was a significant delay in death in germ-free TGF beta 1-deficient mice compared with barrier-raised mutant mice. However, there was no difference in the type, severity or incidence of lesions between TGF beta 1 mutant mice raised under germ-free or barrier conditions. Germ-free wild-type mice had no lesions. It is concluded that microorganisms play a minimal role in disease induction in TGF beta 1-deficient mice.

Rescue of cardiac alpha-actin-deficient mice by enteric smooth muscle gamma-actin

The muscle actins in higher vertebrates display highly conserved amino acid sequences, yet they show distinct expression patterns. Thus, cardiac alpha-actin, skeletal alpha-actin, vascular smooth muscle alpha-actin, and enteric smooth muscle gamma-actin comprise the major actins in their respective tissues. To assess the functional and developmental significance of cardiac alpha-actin, the murine (129/SvJ) cardiac alpha-actin gene was disrupted by homologous recombination. The majority ( approximately 56%) of the mice lacking cardiac alpha-actin do not survive to term, and the remainder generally die within 2 weeks of birth. Increased expression of vascular smooth muscle and skeletal alpha-actins is observed in the hearts of newborn homozygous mutants and also heterozygotes but apparently is insufficient to maintain myofibrillar integrity in the homozygous mutants. Mice lacking cardiac alpha-actin can be rescued to adulthood by the ectopic expression of enteric smooth muscle gamma-actin using the cardiac alpha-myosin heavy chain promoter. However, the hearts of such rescued cardiac alpha-actin-deficient mice are extremely hypodynamic, considerably enlarged, and hypertrophied. Furthermore, the transgenically expressed enteric smooth muscle gamma-actin reduces cardiac contractility in wild-type and heterozygous mice. These results demonstrate that alterations in actin composition in the fetal and adult heart are associated with severe structural and functional perturbations.

Compensatory mechanisms associated with the hyperdynamic function of phospholamban-deficient mouse hearts

Phospholamban ablation is associated with significant increases in the sarcoplasmic reticulum Ca(2+)-ATPase activity and the basal cardiac contractile parameters. To determine whether the observed phenotype is due to loss of phospholamban alone or to accompanying compensatory mechanisms, hearts from phospholamban-deficient and age-matched wild-type mice were characterized in parallel. There were no morphological alterations detected at the light microscope level. Assessment of the protein levels of the cardiac sarcoplasmic reticulum Ca(2+)-ATPase, calsequestrin, myosin, actin, troponin I, and troponin T revealed no significant differences between phospholamban-deficient and wild-type hearts. However, the ryanodine receptor protein levels were significantly decreased (25%) upon ablation of phospholamban, probably in an attempt to regulate the release of Ca2+ from the sarcoplasmic reticulum, which had a significantly higher diastolic Ca2+ content in phospholamban-deficient compared with wild-type hearts (16.0 +/- 2.2 versus 8.6 +/- 1.0 mmol Ca2+/kg dry wt, respectively). The increases in Ca2+ content were specific to junctional sarcoplasmic reticulum stores, as there were no alterations in the Ca2+ content of the mitochondria or A band. Assessment of ATP levels revealed no alterations, although oxygen consumption increased (1.6-fold) to meet the increased ATP utilization in the hyperdynamic phospholamban-deficient hearts. The increases in oxygen consumption were associated with increases (2.2-fold) in the active fraction of the mitochondrial pyruvate dehydrogenase, suggesting increased tricarboxylic acid cycle turnover and ATP synthesis. 31P nuclear magnetic resonance studies demonstrated decreases in phosphocreatine levels and increases in ADP and AMP levels in phospholamban-deficient compared with wild-type hearts. However, the creatine kinase activity and the creatine kinase reaction velocity were not different between phospholamban-deficient and wild-type hearts. These findings indicate that ablation of phospholamban is associated with downregulation of the ryanodine receptor to compensate for the increased Ca2+ content in the sarcoplasmic reticulum store and metabolic adaptations to establish a new energetic steady state to meet the increased ATP demand in the hyperdynamic phospholamban-deficient hearts.

Anti-T cell receptor monoclonal antibody prolongs transgene expression following adenovirus-mediated in vivo gene transfer to mouse synovium

There are no cures for rheumatoid arthritis (RA) or other inflammatory autoimmune arthropathies. Gene transfer to the synovium would allow administration of anti-inflammatory gene products directly to the articular space where they could exert a local down-regulatory effect on the autoimmune process. Several well-characterized murine models of arthritis closely resemble RA immunologically, genetically, and histopathologically. To determine whether the mouse could serve as a model for gene transfer to the synovium, a methodology was developed to reproducibly inject a 5-microliter volume into the articular space of the mouse knee. Using this approach, Av1LacZ4, an E1a-E3-deleted adenoviral (Ad5) vector expressing the lacZ transgene, was delivered intra-articularly (5 x 10(8) pfu). lacZ expression was observed in the articular synovium for at least 14 days. Biochemical quantitation demonstrated a gradual loss of transgene expression, associated with an early, predominantly neutrophilic, inflammatory response that progressed to a lymphocytic infiltrate, followed by gradual resolution over a 3-week period. Pretreatment with the anti-TCR monoclonal antibody (mAb) H57 resulted in a significant reduction in lymphocytic infiltration and a prolongation of transgene expression. These data demonstrate that transgenes can be delivered to the mouse knee joint space, affording a powerful tool to test the potential of gene therapy as a therapeutic modality for RA. As in other systems, the immune response against recombinant adenoviral vectors may limit the extent and duration of gene expression in the synovium. Anti-T cell mAbs may be useful in inhibiting this immune response.

Annexin VI overexpression targeted to heart alters cardiomyocyte function in transgenic mice

Annexin VI is a member of a family of Ca(2+)-dependent phospholipid-binding proteins that is expressed in many tissues, including the heart. It is a regulator of membrane-associated events, including the skeletal muscle ryanodine-sensitive Ca2+ release channel and the cardiac Na+/Ca2+ exchanger. The potential roles of annexin VI in Ca2+ signaling in cardiac myocytes were evaluated by targeting its overexpression to the hearts of transgenic mice. Expression of full-length human annexin VI cDNA was targeted to the heart using the alpha-myosin heavy chain gene promoter (Subramaniam, A., W. K. Jones, J. Gulick, S. Wert, J. Neumann, and J. Robbins. J. Biol. Chem. 266: 24613-24620, 1991). Five transgenic lines exhibited at least 10-fold overexpression of annexin VI protein in both atria and ventricles. Pathological evaluation indicated mice overexpressing annexin VI had enlarged dilated hearts, acute diffuse myocarditis, lymphocytic infiltration, moderate to severe fibrosis throughout the heart, and mild fibrosis around the pulmonary veins of the lungs. Contractile mechanics of cardiomyocytes isolated from hearts of transgenic animals showed frequency-dependent reduced percent shortening and decreased rates of contraction and relaxation compared with control animals. Cardiomyocytes isolated from transgenic animals had lower basal levels of intracellular free Ca2+ and a reduced rise in free Ca2+ following depolarization. After stimulation, intracellular free Ca2+ returned to basal levels faster in transgenic cells than in cells from control animals. These data demonstrate that the overexpression of annexin VI in the heart disrupts normal Ca2+ homeostasis and suggests that this dysfunction may be due to annexin VI regulation of pumps and/or exchangers in the membranes of cardiomyocytes.

Safety of adenovirus-mediated transfer of the human cystic fibrosis transmembrane conductance regulator cDNA to the lungs of nonhuman primates

To define the toxicity of cystic fibrosis transmembrane conductance regulator gene (CFTR) gene therapy with a replication-deficient recombinant adenovirus (Av1Cf2) in a nonhuman primate model, 10(10) plaque forming units (pfu) were instilled directly through a bronchoscope into the right lung of 5 macaques, and a lower dose of 4 x 10(6) pfu was administered to the right lung of 1 macaque. One sham-treated control received phosphate-buffered saline (PBS). The macaques were evaluated sequentially by clinical examination, vital signs, weight, hematology, blood chemistry, chest radiography, pulse oximetry, and bronchoalveolar lavage (BAL) at baseline and 3-28 days post-treatment. After the period of observation, macaques were sacrificed for autopsy and histological examination. The macaques tolerated the experimental therapy clinically with no changes in body temperature, oxygen saturation, heart rate, body weight, or blood pressure. However, 1 macaque with visible evidence of aspiration at the time of initial bronchoscopy developed tachypnea with right lower lobe (RLL) pneumonia on chest radiograph and by histology. There were no changes in Hgb, Wbc, BUN, plasma electrolytes, bilirubin, or hepatic transaminases. In the macaques that received 10(10) pfu, there was a progressive increase in the number of CD8+ lymphocytes in BAL that was maximal at 28 days. Histological examination of the treated lungs of the high-dose macaques at 3 days showed marked peribronchial and perivascular cuffing by inflammatory cells and alveolar accumulation of neutrophils and macrophages. The alveolitis appeared to be resolving at 28 days, although the perivascular and peribronchial aggregates of mononuclear cells were still present. In the high-dose macaques, BAL interleukin-8 (IL-8) was increased at all time points (256-388 pg/ml versus 1-84 pg/ml at baseline and in control), whereas IL-1 beta was increased only at days 21 and 28 (341-852 pg/ml versus 30-92 pg/ml at baseline and in control). There were no increases in BAL cell counts, IL-1 beta or IL-8, and histological changes were mild in the macaque that received 4 x 10(6) pfu. Evaluation for Av1Cf2-derived human CFTR expression using RS-PCR demonstrated expression at 3, 10, and 21, but not 28 days in macaques treated with 10(10) pfu of Av1Cf2. In situ hybridization analysis demonstrated human CFTR mRNA in the alveolar regions of the lobes that received the vector at 10 and 21 days. There was no evidence of expression after treatment with 4 x 10(6) pfu. This study showed that high-dose adenoviral vector administration to the lung achieved CFTR gene transfer and expression but was associated with increased concentrations of cytokines in BAL and alveolar inflammation. A low dose, equivalent to the maximum clinical dose currently proposed for phase I trials in human subjects, was not associated with cellular or cytokine evidence of inflammation, and histological abnormalities were mild.

Gastric lesions in transforming growth factor beta-1 heterozygous mice

Transforming growth factor beta-1 (TGF beta 1) is known to inhibit the growth of many epithelial cell types in culture. Consequently, it is important to determine whether it has any tumor suppressor activity in vitro. Fifteen heterozygous and eight wild type TGF beta 1-deficient mice were examined to determine if there was a difference in lifespan or lesion development due to the loss of one TGF beta 1 allele. Mice were killed when there was evidence of neoplasia or severe illness. There was no significant difference in the lifespan of the two groups. Hyperplastic lesions in the glandular mucosa were seen in 10 TGF beta 1 (+/-) mice. These lesions were localized to the lesser curvature of the stomach, extending from the limiting ridge to the pylorus. Seven of the 10 glandular hyperplastic lesions in the TGF beta 1 (+/-) mice had features similar to human gastritis cystica profunda. Associated with the glandular invasion of the muscularis were a mixed inflammatory infiltration of the surrounding muscular wall and mucosa with chronic vasculitis in the tissues adjacent to these lesions. In contrast to the distinct genotypic differences in lesion incidence observed in the glandular stomach, there was no significant difference in lesion incidence in other organs. The increased incidence of the hyperplastic lesions in the TGF beta 1 (+/-) mice is highly suggestive that allelic loss of TGF beta 1 plays an important role in the genesis of these lesions. However, allelic loss of TGF beta 1 does not cause alterations in the incidence of neoplasia.

Molecular and physiological effects of overexpressing striated muscle beta-tropomyosin in the adult murine heart

Tropomyosins comprise a family of actin-binding proteins that are central to the control of calcium-regulated striated muscle contraction. To understand the functional role of tropomyosin isoform differences in cardiac muscle, we generated transgenic mice that overexpress striated muscle-specific beta-tropomyosin in the adult heart. Nine transgenic lines show a 150-fold increase in beta-tropomyosin mRNA expression in the heart, along with a 34-fold increase in the associated protein. This increase in beta-tropomyosin message and protein causes a concomitant decrease in the level of alpha-tropomyosin transcripts and their associated protein. There is a preferential formation of the alpha beta-heterodimer in the transgenic mouse myofibrils, and there are no detectable alterations in the expression of other contractile protein genes, including the endogenous beta-tropomyosin isoform. When expression from the beta-tropomyosin transgene is terminated, alpha-tropomyosin expression returns to normal levels. No structural changes were observed in these transgenic hearts nor in the associated sarcomeres. Interestingly, physiological analyses of these hearts using a work-performing model reveal a significant effect on diastolic function. As such, this study demonstrates that a coordinate regulatory mechanism exists between alpha- and beta-tropomyosin gene expression in the murine heart, which results in a functional correlation between alpha- and beta-tropomyosin isoform content and cardiac performance.