Tissue factor pathway inhibitor-2 is a novel inhibitor of matrix metalloproteinases with implications for atherosclerosis

Degradation of ECM, particularly interstitial collagen, promotes plaque instability, rendering atheroma prone to rupture. Previous studies implicated matrix metalloproteinases (MMPs) in these processes, suggesting that dysregulated MMP activity, probably due to imbalance with endogenous inhibitors, promotes complications of atherosclerosis. We report here that the serine proteinase inhibitor tissue factor pathway inhibitor-2 (TFPI-2) can function as an MMP inhibitor. TFPI-2 diminished the ability of the interstitial collagenases MMP-1 and MMP-13 to degrade triple-helical collagen, the primary load-bearing molecule of the ECM within human atheroma. In addition, TFPI-2 also reduced the activity of the gelatinases MMP-2 and MMP-9. In contrast to the "classical" tissue inhibitors of MMPs (TIMPs), TFPI-2 expression in situ correlated inversely with MMP levels in human atheroma. TFPI-2 colocalized primarily with smooth muscle cells in the normal media as well as the plaque's fibrous cap. Conversely, the macrophage-enriched shoulder region, the prototypical site of matrix degradation and plaque rupture, stained only weakly for TFPI-2 but intensely for gelatinases and interstitial collagenases. Evidently, human mononuclear phagocytes, an abundant source of MMPs within human atheroma, lost their ability to express this inhibitor during differentiation in vitro. These findings establish a new, anti-inflammatory function of TFPI-2 of potential pathophysiological significance for human diseases, including atherosclerosis

Gαq-containing G proteins regulate B cell selection and survival and are required to prevent B cell–dependent autoimmunity

Survival of mature B cells is regulated by B cell receptor and BAFFR-dependent signals. We show that B cells from mice lacking the Gαq subunit of trimeric G proteins (Gnaq−/− mice) have an intrinsic survival advantage over normal B cells, even in the absence of BAFF. Gnaq−/− B cells develop normally in the bone marrow but inappropriately survive peripheral tolerance checkpoints, leading to the accumulation of transitional, marginal zone, and follicular B cells, many of which are autoreactive. Gnaq−/− chimeric mice rapidly develop arthritis as well as other manifestations of systemic autoimmune disease. Importantly, we demonstrate that the development of the autoreactive B cell compartment is the result of an intrinsic defect in Gnaq−/− B cells, resulting in the aberrant activation of the prosurvival factor Akt. Together, these data show for the first time that signaling through trimeric G proteins is critically important for maintaining control of peripheral B cell tolerance induction and repressing autoimmunity

B cells from p50/NF-κB knockout mice have selective defects in proliferation, differentiation, germ-line C_H transcription, and Ig class switching

To better understand the role of NF-κB in normal B cell physiology, we used a purified population of resting B cells from p50/NF-κ B knockout (p50^(-/-)) mice to determine their ability to proliferate, secrete Ig, express germ-line C_H RNA, and undergo Ig isotype switching in vitro in response to a number of distinct stimuli. p50^(-/-) B cells proliferated normally in response to dextran-anti-IgD Abs (αδ-dex) and membrane-bound, but not soluble, CD40 ligand (CD40), and they were virtually unresponsive to LPS when compared with control B cells. p50^(-/-) B cells secreted markedly reduced Ig in response to αδ-dex or mCD40L in the presence of IL-4 + IL-5, despite their relatively normal proliferative rates, whereas normal Ig secretion was restored by the combination of αδ-dex and CD40L. p50^(-/-) B cells expressed normal steady-state levels of germ-line C_Hγ1 and C_Hα RNA but markedly reduced germ-line C_Hγ3 and C_Hϵ RNA upon appropriate stimulation. Although p50^(-/-) B cells underwent substantial switching to IgG1, a marked reduction in the switch to IgG3 and IgE, as IgA, was observed. These data are the first to demonstrate key, independent roles for p50/NF-κB in normal B cell maturation to Ig secretion, germ-line CH gene activation, and Ig class switching, as well as mitogenesis, and provide a powerful and well-defined in vitro model system for studying the role of p50/NF-κB in a wide range of normal cellular functions