Inhibition of RORγT Skews TCRα Gene Rearrangement and Limits T Cell Repertoire Diversity

Recent studies have elucidated the molecular mechanism of RORγT transcriptional regulation of Th17 differentiation and function. RORγT was initially identified as a transcription factor required for thymopoiesis by maintaining survival of CD4⁺CD8⁺ (DP) thymocytes. While RORγ antagonists are currently being developed to treat autoimmunity, it remains unclear how RORγT inhibition may impact thymocyte development. In this study, we show that in addition to regulating DP thymocytes survival, RORγT also controls genes that regulate thymocyte migration, proliferation, and T cell receptor (TCR)α selection. Strikingly, pharmacological inhibition of RORγ skews TCRα gene rearrangement, limits T cell repertoire diversity, and inhibits development of autoimmune encephalomyelitis. Thus, targeting RORγT not only inhibits Th17 cell development and function but also fundamentally alters thymic-emigrant recognition of self and foreign antigens. The analysis of RORγ inhibitors has allowed us to gain a broader perspective of the diverse function of RORγT and its impact on T cell biology.

Physiological Expression of AMPKγ2RG Mutation Causes Wolff-Parkinson-White Syndrome and Induces Kidney Injury in Mice

Mutations of the AMP-activated kinase gamma 2 subunit (AMPKγ2), N488I (AMPKγ2^NI) and R531G (AMPKγ2^RG), are associated with Wolff-Parkinson-White (WPW) syndrome, a cardiac disorder characterized by ventricular pre-excitation in humans. Cardiac-specific transgenic overexpression of human AMPKγ2^NI or AMPKγ2^RG leads to constitutive AMPK activation and the WPW phenotype in mice. However, overexpression of these mutant proteins also caused profound, non-physiological increase in cardiac glycogen, which might abnormally alter the true phenotype. To investigate whether physiological levels of AMPKγ2^NI or AMPKγ2^RG mutation cause WPW syndrome and metabolic changes in other organs, we generated two knock-in mouse lines on the C57BL/6N background harboring mutations of human AMPKγ2^NI and AMPKγ2^RG, respectively. Similar to the reported phenotypes of mice overexpressing AMPKγ2^NI or AMPKγ2^RG in the heart, both lines developed WPW syndrome and cardiac hypertrophy; however, these effects were independent of cardiac glycogen accumulation. Compared with AMPKγ2^WT mice, AMPKγ2^NI and AMPKγ2^RG mice exhibited reduced body weight, fat mass, and liver steatosis when fed with a high fat diet (HFD). Surprisingly, AMPKγ2^RG but not AMPKγ2^NI mice fed with an HFD exhibited severe kidney injury characterized by glycogen accumulation, inflammation, apoptosis, cyst formation, and impaired renal function. These results demonstrate that expression of AMPKγ2^NI and AMPKγ2^RG mutations at physiological levels can induce beneficial metabolic effects but that this is accompanied by WPW syndrome. Our data also reveal an unexpected effect of AMPKγ2^RG in the kidney, linking lifelong constitutive activation of AMPK to a potential risk for kidney dysfunction in the context of an HFD.

Altered lipoprotein metabolism in P2Y(13) knockout mice

The purinergic receptor P2Y(13) has been shown to play a role in the uptake of holo-HDL particles in in vitro hepatocyte experiments. In order to determine the role of P2Y(13) in lipoprotein metabolism in vivo, we ablated the expression of this gene in mice. Here we show that P2Y(13) knockout mice have lower fecal concentrations of neutral sterols (-27%±2.1% in males) as well as small decreases in plasma HDL (-13.1%±3.2% in males; -17.5%±4.0% in females) levels. In addition, significant decreases were detected in serum levels of fatty acids and glycerol in female P2Y(13) knockout mice. Hepatic mRNA profiling analyses showed increased expression of SREBP-regulated cholesterol and fatty acid biosynthesis genes, while fatty acid β-oxidation genes were significantly decreased. Liver gene signatures also identified changes in PPARα-regulated transcript levels. With the exception of a small increase in bone area, P2Y(13) knockout mice do not show any additional major abnormalities, and display normal body weight, fat mass and lean body mass. No changes in insulin sensitivity and oral glucose tolerance could be detected. Taken together, our experiments assess a role for the purinergic receptor P2Y(13) in the regulation of lipoprotein metabolism and demonstrate that modulating its activity could be of benefit to the treatment of dyslipidemia in people.

Diet induction of monocyte chemoattractant protein-1 and its impact on obesity

OBJECTIVE

To examine the effect of a high-fat diet on gene expression in adipose tissues and to determine induction kinetics of adipose monocyte chemoattractant protein-1 and -3 (MCP-1 and MCP-3) in diet-induced obesity (DIO) and the effect of a lack of MCP-1 signaling on DIO susceptibility and macrophage recruitment into adipose tissue.

RESEARCH METHODS AND PROCEDURES

Obese and lean adipose tissues were profiled for expression changes. The time-course of MCP-1 and MCP-3 expression was examined by reverse transcriptase-polymerase chain reaction. Plasma MCP-1 levels were determined by enzyme-linked immunosorbent assay (ELISA). Chemokine receptor-2 (CCR2) knockout mice were placed on the high-fat diet to determine DIO susceptibility. Macrophage infiltration in adipose tissue was examined by immunohistochemistry with F4/80 antibody.

RESULTS

DIO elevated adipose expression of many inflammatory genes, including MCP-1 and MCP-3. Adipose MCP-1 and MCP-3 mRNA levels increased within 7 days of starting a high-fat diet, with elevation of plasma MCP-1 detected after 4 weeks on the diet. The induction of MCP-1 and MCP-3 expression preceded that of tumor necrosis factor-alpha. The elevated plasma MCP-1 concentration in obese mice was partially reversed by treatment with AM251. No change in DIO susceptibility and macrophage accumulation in adipose tissue were observed in CCR2 knockout mice, which lack the MCP-1 receptor CCR2.

DISCUSSION

A high-fat diet elevated adipose expression of inflammatory genes, including early induction of MCP-1 and MCP-3, supporting the view that obese adipose tissues contribute to systemic inflammation. However, despite increased MCP-1 in obesity, disruption of MCP-1 signaling did not confer resistance to DIO in mice or reduce adipose tissue macrophage infiltration.

A Protective Role for Matrix Metalloproteinase-3 in Squamous Cell Carcinoma

Elevated expression of matrix metalloproteinase-3 (MMP-3/stromelysin-1) is associated with a variety of tumor types, although its in vivo functional role remains unclear. In human and murine squamous cell carcinoma (SCC), MMP-3 is expressed in the stromal compartment at all of the stages of tumor progression and is expressed by the malignant epithelial cells in late-stage, highly invasive tumors. To elucidate whether MMP-3 plays a causal role during SCC, wild-type and MMP-3 null mice were subjected to chemical carcinogenesis procedures by topical application of either the complete carcinogen 1-methyl-3-nitro-1-nitroso-guanidine or two-stage initiation and promotion with 7,12-dimethylbenz[a]anthracene and 12-O-tetradecanoylphorbol-13-acetate. Contrasting with our expectations, tumors originating on MMP-3 null mice had enhanced initial tumor growth rates as compared with control animals, although there was no difference in tumor onset or incidence. This elevated rate in growth was coupled with an elevated proliferative index and a reduced vasculature density but with no significant effect on apoptosis. Tumors from MMP-3 null mice had a prevalence of undifferentiated spindle tumors as compared with controls, which was concomitant with a higher percentage of MMP-3 null mice evidencing surface lung metastases. Tumor progression in MMP-3 null mice was inversely associated with leukocyte infiltration, in which an overall reduction in tumor-associated macrophages and neutrophils was evident. We propose that MMP-3 is expressed as a protective response and plays an important role in host defense during SCC tumorigenesis.

Antibody-mediated blockade of the CXCR3 chemokine receptor results in diminished recruitment of T helper 1 cells into sites of inflammation

Naïve T cells, when activated by specific antigen and cytokines, up-regulate adhesion molecules as well as chemokine receptors on their surface, which allows them to migrate to inflamed tissues. Human studies have shown that CXCR3 is one of the chemokine receptors that is induced during T cell activation. Moreover, CXCR3-positive T cells are enriched at inflammatory sites in patients with autoimmune diseases such as rheumatoid arthritis and multiple sclerosis. In this study, we use a mouse model of inflammation to demonstrate that CXCR3 is required for activated T cell transmigration to inflamed tissue. Using an anti- mCXCR3 antibody, we have shown that in vitro-differentiated T helper (Th) 1 and Th2 cells up-regulated CXCR3 upon stimulation with specific antigen/major histocompatibility complex. However, only Th1 cells, when adoptively transferred to syngeneic recipients, are efficiently recruited to the peritoneum in an adjuvant-induced peritonitis model. Furthermore, the neutralizing anti-mCXCR3 antibody profoundly inhibits the recruitment of Th1 cells to the inflamed peritoneum. Real-time, quantitative reverse transcriptase-polymerase chain reaction analysis demonstrates that the CXCR3 ligands, interferon (IFN)-inducible protein 10 (CXCL10) and IFN-inducible T cell alpha chemoattractant (CXCL11), are among the many chemokines induced in the adjuvant-treated peritoneum. The anti-mCXCR3 antibody is also effective in inhibiting a delayed-type hypersensitivity response, which is largely mediated by enhanced trafficking of activated T cells to peripheral inflammatory sites. Collectively, our results suggest that CXCR3 has a critical role in T cell transmigration to sites of inflammation and thus, may serve as a molecular target for anti-inflammatory therapies.

Stromelysin-1 regulates adipogenesis during mammary gland involution

The matrix metalloproteinase MMP-3/stromelysin-1 (Str1) is highly expressed during mammary gland involution induced by weaning. During involution, programmed cell death of the secretory epithelium takes place concomitant with the repopulation of the mammary fat pad with adipocytes. In this study, we have used a genetic approach to determine the role of Str1 during mammary involution. Although Str1 has been shown to induce unscheduled apoptosis when expressed ectopically during late pregnancy (Alexander, C.M., E.W. Howard, M.J. Bissell, and Z. Werb. 1996. J. Cell Biol. 135:1669-1677), we found that during post-lactational involution, mammary glands from transgenic mice that overexpress the tissue inhibitor of metalloproteinases, TIMP-1 (TO), or mice carrying a targeted mutation in Str1 showed accelerated differentiation and hypertrophy of adipocytes, while epithelial apoptosis was unaffected. These data suggest that matrix metalloproteinases (MMPs) do not induce unscheduled epithelial cell death after weaning, but instead alter the stromal microenvironment. We used adipogenic 3T3-L1 cells as a cell culture model to test the function of MMPs during adipocyte differentiation. Fibroblastic 3T3-L1 progenitor cells expressed very low levels of MMPs or TIMPs. The transcription of a number of MMP and TIMP mRNAs [Str1, MT1-MMP, (MMP-14) collagenase-3 (MMP-13), gelatinase A (MMP-2), and TIMP-1, -2 and -3] was induced in committed preadipocytes, but only differentiated adipocytes expressed an activated MMP, gelatinase A. The addition of MMP inhibitors (GM 6001 and TIMP-1) dramatically accelerated the accumulation of lipid during differentiation. We conclude that MMPs, especially Str1, determine the rate of adipocyte differentiation during involutive mammary gland remodeling.

Deficiency in inducible nitric oxide synthase results in reduced atherosclerosis in apolipoprotein E-deficient mice

Inducible NO synthase (iNOS) present in human atherosclerotic plaques could contribute to the inflammatory process of plaque development. The role of iNOS in atherosclerosis was tested directly by evaluating the development of lesions in atherosclerosis-susceptible apolipoprotein E (apoE)-/- mice that were also deficient in iNOS. ApoE-/- and iNOS-/- mice were cross-bred to produce apoE-/-/iNOS-/- mice and apoE-/-/iNOS+/+ controls. Males and females were placed on a high fat diet at the time of weaning, and atherosclerosis was evaluated at two time points by different methods. The deficiency in iNOS had no effect on plasma cholesterol, triglyceride, or nitrate levels. Morphometric measurement of lesion area in the aortic root at 16 wk showed a 30-50% reduction in apoE-/-/iNOS-/- mice compared with apoE-/-/iNOS+/+ mice. Although the size of the lesions in apoE-/-/iNOS-/- mice was reduced, the lesions maintained a ratio of fibrotic:foam cell-rich:necrotic areas that was similar to controls. Biochemical measurements of aortic cholesterol in additional groups of mice at 22 wk revealed significant 45-70% reductions in both male and female apoE-/-/iNOS-/- mice compared with control mice. The results indicate that iNOS contributes to the size of atherosclerotic lesions in apoE-deficient mice, perhaps through a direct effect at the site of the lesion.

Cleavage of aggrecan at the Asn341-Phe342 site coincides with the initiation of collagen damage in murine antigen-induced arthritis: a pivotal role for stromelysin 1 in matrix metalloproteinase activity

OBJECTIVE

The destruction of articular cartilage during arthritis is due to proteolytic cleavage of the extracellular matrix components. This study investigates the kinetic involvement of metalloproteinases (MMPs) in the degradation of the 2 major cartilage components, aggrecan and type II collagen, during murine antigen-induced arthritis (AIA). In addition, the role of stromelysin 1 (SLN-1) induction of MMP-induced neoepitopes was studied.

METHODS

VDIPEN neoepitopes in aggrecan and collagenase-induced COL2-3/4C neoepitopes in type II collagen were identified by immunolocalization. Stromelysin 1-deficient knockout (SLN1-KO) mice were used to study SLN-1 involvement.

RESULTS

In AIA, the VDIPEN epitopes in aggrecan appeared after initial proteoglycan (PG) depletion. The collagenase-induced type II collagen neoepitopes colocalized with VDIPEN epitopes. Remarkably, cartilage from arthritic SLN1-KO mice showed neither the induction of VDIPEN nor collagen cleavage-site neoepitopes during AIA, suggesting that stromelysin is a pivotal mediator in this process. PG depletion, as measured by the loss of Safranin O staining, was similar in SLN1-KO mice and wild-type strains. Furthermore, in vitro induction of VDIPEN epitopes in aggrecan and COL2-3/4C epitopes in type II collagen, on exposure of cartilage to interleukin-1, could not be accomplished in SLN1-KO mice, whereas intense staining was achieved for both epitopes in cartilage of wild-type strains.

CONCLUSION

This study emphasizes that SLN-1 is essential in the induction of MMP-specific aggrecan and collagen cleavage sites during AIA. It suggests that SLN-1 is not a dominant enzyme in PG breakdown, but that it activates procollagenases and is crucial in the initiation of collagen damage.

Stromelysin-1-deficient fibroblasts display impaired contraction in vitro

Targeted disruption of the stromelysin-1 gene in mice causes a delay in excisional wound healing due to a failure in wound contraction. Therefore, we postulated that stromelysin-1 activity is responsible for initiating contraction. To test this hypothesis, we compared the contractile capacity of fibroblasts from stromelysin-1 knockout mice (strom-1 KO) with that of normal fibroblasts using a collagen gel contraction model. Fibroblast cultures were established from explants of skin and lung parenchyma from strom-1 KO and wild-type mice, then transferred to the surface of collagen gels. The extent of contraction was determined by measuring greatest gel diameter. Results demonstrated that (1) all fibroblasts contracted collagen gels in a uniform concentric fashion, (2) skin fibroblasts from both sets of mice exhibited greater gel contraction than did lung fibroblasts, and (3) strom-1 KO fibroblasts demonstrated significantly less contraction (21-23%) than wild-type fibroblasts. These data support the hypothesis that absence of stromelysin-1 results in defective fibroblast contraction that may contribute to delayed wound healing.

Coordinate expression of matrix metalloproteinase family members in the uterus of normal, matrilysin-deficient, and stromelysin-1-deficient mice

The expression patterns of matrix metalloproteinase (MMP) family members during the murine estrous cycle and postpartum uterine involution were analyzed, and the consequence of removing specific MMPs during uterine functions was determined using mice deficient in either matrilysin (MAT) or stromelysin-1 (STR-1). In wild-type animals, MAT, STR-1, STR-2, STR-3, and gelatinase A were consistently expressed during the most active phases of the estrous cycle, estrus and proestrus. The messenger RNA for these MMPs as well as collagenase-3 and the tissue inhibitors of metalloproteinases were also expressed during uterine involution, as determined by Northern analysis and in situ hybridization. Notably, MAT, STR-2, and collagenase-3 messenger RNA levels were elevated at early times of involution and rapidly decreased with time, whereas the transcripts for other MMPs remained elevated throughout the involution process. Involution proceeded normally in mice lacking MAT or STR-1; however, the expression of STR-1 and STR-2 was dramatically up-regulated in MAT nullizygous mice, and the expression of MAT and STR-2 was moderately up-regulated in STR-1-deficient animals. We conclude that the concerted action of several MMPs is likely to play an important role in the remodeling of the postpartum uterus, and that mechanisms that compensate for the loss of a specific MMP during this process appear to exist.

A natural disruption of the secretory group II phospholipase A2 gene in inbred mouse strains

The synovial fluid or group II secretory phospholipase A2 (sPLA2) has been implicated as an important agent involved in a number of inflammatory processes. In an attempt to determine the role of sPLA2 in inflammation, we set out to generate sPLA2-deficient mice. During this investigation, we observed that in a number of inbred mouse strains, the sPLA2 gene was already disrupted by a frameshift mutation in exon 3. This mutation, a T insertion at position 166 from the ATG of the cDNA, terminates out of frame in exon 4, resulting in the disruption of the calcium binding domain in exon 3 and loss of both activity domains coded by exons 4 and 5. The mouse strains C57BL/6, 129/Sv, and B10.RIII were found to be homozygous for the defective sPLA2 gene, whereas outbred CD-1:SW mice had variable genotype at this locus. BALB/c, C3H/HE, DBA/1, DBA/2, NZB/BIN, and MRL lpr/lpr mice had a normal sPLA2 genotype. The sPLA2 mRNA was expressed at very high levels in the BALB/c mouse small intestine, whereas in the small intestine of the sPLA2 mutant mouse strains, sPLA2 mRNA was undetectable. In addition, PLA2 activity in acid extracts of the small intestine were approximately 40 times higher in BALB/c than in the mutant mice. Transcription of the mutant sPLA2 gene resulted in multiple transcripts due to exon skipping. None of the resulting mutant mRNAs encoded an active product. The identification of this mutation should not only help define the physiological role of sPLA2 but also has important implications in mouse inflammatory models developed by targeted mutagenesis.