The loss of α2ß1 integrin suppresses joint inflammation and cartilage destruction in mouse models of rheumatoid arthritis.

OBJECTIVE: Integrin α2ß1 functions as a major receptor for type I collagen on different cell types, including fibroblasts and inflammatory cells. Although in vitro data suggest a role for α2ß1 integrin in regulating both cell attachment and expression of matrix-degrading enzymes such as matrix metalloproteinases (MMPs), mice that lack the α2 integrin subunit (Itga2(-/-) mice) develop normally and are fertile. We undertook this study to investigate the effect of Itga2 deficiency in 2 different mouse models of destructive arthritis: the antigen-induced arthritis (AIA) mouse model and the human tumor necrosis factor α (TNFα)-transgenic mouse model. METHODS: AIA was induced in the knee joints of Itga2(-/-) mice and wild-type controls. Human TNF-transgenic mice were crossed with Itga2(-/-) mice and were assessed clinically and histopathologically for signs of arthritis, inflammation, bone erosion, and cartilage damage. MMP expression, proliferation, fibroblast attachment, and ERK activation were determined. RESULTS: Under arthritic conditions, Itga2 deficiency led to decreased severity of joint pathology. Specifically, Itga2(-/-) mice showed less severe clinical symptoms and dramatically reduced pannus formation and cartilage erosion. Mice lacking α2ß1 integrin exhibited reduced MMP-3 expression, both in their sera and in fibroblast-like synoviocytes (FLS), due to impaired ERK activation. Further, both the proliferation and attachment of FLS to cartilage were partially dependent on α2ß1 integrin in vitro and in vivo. CONCLUSION: Our findings suggest that α2ß1 integrin contributes significantly to inflammatory cartilage destruction by promoting fibroblast proliferation and attachment and MMP expression.

Establishment of a matrix-associated transepithelial resistance invasion assay to precisely measure the invasive potential of synovial fibroblasts.

OBJECTIVE: Synovial fibroblasts (SFs) contribute to several aspects of the pathogenesis of rheumatoid arthritis (RA) and have been implicated most prominently in the progressive destruction of articular cartilage. Targeting the invasive phenotype of RASFs has therefore gained increasing attention, but the precise measurement of their invasive capacity and the evaluation of potential treatment effects constitute a challenge that needs to be addressed. This study used a novel in vitro invasion assay based on the breakdown of transepithelial electrical resistance to determine the course of fibroblast invasion into extracellular matrix. METHODS: A matrix-associated transepithelial resistance invasion (MATRIN) assay was used to assess SFs from patients with RA in comparison with SFs from patients with osteoarthritis (OA). The SFs were grown on a commercially available collagen mix that was placed onto the upper side of a Transwell polycarbonate membrane. In addition, freshly isolated cartilage extracts were studied to assess the conditions in vivo. Under this membrane, a monolayer of MDCK-C7 cells was seeded to create a high electrical resistance. RESULTS: Invasion of fibroblasts into the matrix affected the integrity of the MDCK-C7 monolayer and led to a measurable decrease and subsequent breakdown of electrical resistance. Unlike in the assay with OASFs, which did not achieve a breakdown of resistance up to 72 hours, RASFs exhibited a pronounced invasiveness in this assay, with a 50% breakdown after 42 hours. Treatment of fibroblasts with either a matrix metalloproteinase inhibitor or antibodies against beta1 integrin significantly reduced the invasiveness of RASFs. CONCLUSION: The MATRIN assay is a valuable and sensitive biologic assay system that can be used to determine precisely the invasive potential of RASFs in vitro, and thus would be suitable for screening anti-invasion compounds.

ProSAP-interacting protein 1 (ProSAPiP1), a novel protein of the postsynaptic density that links the spine-associated Rap-Gap (SPAR) to the scaffolding protein ProSAP2/Shank3.

ProSAPs/Shanks are a family of proteins that have a major scaffolding function for components of the postsynaptic density (PSD) of excitatory brain synapses. Members of the family harbor a variety of domains for protein-protein interactions, one of which is a unique PDZ domain that differs significantly from those of other proteins. We have identified a novel binding partner for this PDZ domain, termed ProSAPiP1, that is highly enriched in the PSD and shares significant sequence homology with the PSD protein PSD-Zip70. Both molecules code for a Fez1 domain that can be found in a total of four related proteins. ProSAPiP1 is widely expressed in rat brain and co-localizes with ProSAP2/Shank3 in excitatory spines and synapses. ProSAP2/Shank3 co-immunoprecipitates with ProSAPiP1 but not with PSD-Zip70. Both proteins, however, bind and recruit SPAR to synapses with a central coiled-coil region that harbors a leucine zipper motif. This region is also responsible for homo- and heteromultimerization of ProSAPiP1 and PSD-Zip70. Thus, ProSAPiP1 and PSD-Zip70 are founders of a novel family of scaffolding proteins, the "Fezzins," which adds further complexity to the organization of the PSD protein network.

Bradykinin-induced pulmonary vasoconstriction is time and inducible nitric oxide synthase dependent in a peritonitis sepsis model.

In an isolated perfused lung model, bradykinin induced pulmonary vasoconstriction in rats made septic by the injection of lipopolysaccharide (LPS). To mimic the pathophysiology of sepsis in humans more closely, we investigated pulmonary endothelial injury in a peritonitis model (cecal ligation and perforation; CLP). Male Sprague-Dawley rats were randomly divided into nine groups (n = 6-8). LPS and CLP rats were compared after 6 h with and without treatment with a selective inhibitor of inducible nitric oxide synthase (iNOS), L-N(6)-(1-iminoethyl)-lysine. Time dependency was investigated in CLP-treated rats at 24 h. The pulmonary circulation was isolated and perfused with a constant flow after the rats' tracheas were intubated and ventilated. Bradykinin (1, 3, and 6 microg) was injected, and changes in perfusion pressure were measured. Lungs were harvested for Western blot analysis to determine the role of iNOS in pulmonary endothelial dysfunction. In contrast to CLP 24 h rats, dose-dependent bradykinin-induced pulmonary vasoconstriction was observed in LPS and CLP 6 h rats. Concomitant administration of L-N(6)-(1-iminoethyl)-lysine significantly attenuated this vasoconstriction in both groups. The iNOS protein was expressed in lung homogenates from LPS 6 h and CLP 6 h but not from CLP 24 h rats. Both sepsis models caused bradykinin-induced pulmonary vasoconstriction, with the CLP groups demonstrating a time dependency of this effect. In conjunction with the time-dependent decrease in iNOS protein, the attenuated bradykinin-induced vasoconstriction due to selective iNOS inhibition suggests an important role for iNOS in pulmonary endothelial injury for both sepsis models.

Brain-specific splicing of alpha-actinin 1 (ACTN1) mRNA.

Two isoforms of alpha-actinin 1 (ACTN1) known to be generated by tissue-specific alternative splicing of mutually exclusive exons have been described. Muscle cells express ACTN1 containing the smooth muscle exon (SM), while other (non-muscle) cells contain the non-muscle exon (NM). In this report, we describe the characterization of a novel ACTN1 isoform in adult rat brain in which both exons (NM + SM) are combined in the same transcript to give a brain-specific sequence domain (BS). Reverse transcriptase polymerase chain reaction (RT-PCR) demonstrated that expression of the BS exon was restricted to the brain. During development, weak expression of the BS exon was observed at early postnatal stages whereas in adult brain, it represented the predominant isoform of ACTN1. In situ hybridization analysis revealed that BS expression was highest in neurons of the hippocampus, cortex, and caudate putamen while the cerebellum and other subcortical structures showed only weak labeling.

Insulin-induced expression of the activity-regulated cytoskeleton-associated gene (ARC) in human neuroblastoma cells requires p21(ras), mitogen-activated protein kinase/extracellular regulated kinase and src tyrosine kinases but is protein kinase C-independent.

We examined the effect of insulin on the expression of the activity-regulated cytoskeleton-associated gene (ARC), an effector immediate early gene with a proposed role in memory formation. In human SH-SY5Y neuroblastoma cells, application of insulin leads to dramatic increase in ARC mRNA and protein levels. Inhibition experiments reveal, that p21(ras), mitogen-activated protein kinase/extracellular regulated kinase and tyrosine kinase (src) activity are required for the insulin-induced ARC expression in SH-SY5Y cells, whereas protein kinase C is not involved in the signal transduction pathway. Our data indicated for the first time a correlation of the insulin-controlled signal cascade and the induction of synaptic plasticity-associated immediate early genes.