Combined loss of proapoptotic genes Bak or Bax with Bim synergizes to cause defects in hematopoiesis and in thymocyte apoptosis

The proapoptotic members of the Bcl-2 family can be subdivided into members that contain several Bcl-2 homology (BH) domains and those that contain only the BH3 domain. Although it is known that BH3-only proteins and the multi-BH domain proteins, Bak and Bax, are essential for programmed cell death, the overlapping role of these two subgroups has not been examined in vivo. To investigate this, we generated Bak/Bim and Bax/Bim double deficient mice. We found that although Bax−/−Bim−/−, but not Bak−/−Bim−/−, mice display webbed hind and front paws and malocclusion of the incisors, both groups of mice present with dysregulated hematopoiesis. Combined loss of Bak and Bim or Bax and Bim causes defects in myeloid and B-lymphoid development that are more severe than those found in the single knock-out mice. Bak−/−Bim−/− mice have a complement of thymocytes that resembles those in control mice, whereas Bax−/−Bim−/− mice are more similar to Bim−/− mice. However, thymocytes isolated from Bak−/−Bim−/− or Bax−/−Bim−/− mice are markedly more resistant to apoptotic stimuli mediated by the intrinsic pathway as compared with thymocytes from single-knockout mice. These data suggest an essential overlapping role for Bak or Bax and Bim in the intrinsic apoptotic pathway

Systemic Autoimmunity and Lymphoproliferation Are Associated with Excess IL-7 and Inhibited by IL-7Rα Blockade

Lupus is characterized by disturbances in lymphocyte homeostasis, as demonstrated by the marked accumulation of activated/memory T cells. Here, we provide evidence that proliferation of the CD8+ precursors for the accumulating CD4–CD8– T cells in MRL-Faslpr lupus-predisposed mice is, in part, driven by commensal antigens. The ensuing lymphadenopathy is associated with increased production of IL-7 due to expansion of fibroblastic reticular cells, the primary source of this cytokine. The excess IL-7 is not, however, consumed by CD4–CD8– T cells due to permanent down-regulation of IL-7Rα (CD127), but instead supports proliferation of autoreactive T cells and progression of autoimmunity. Accordingly, IL-7R blockade reduced T cell activation and autoimmune manifestations even when applied at advanced disease stage. These findings indicate that an imbalance favoring production over consumption of IL-7 may contribute to systemic autoimmunity, and correction of this imbalance may be a novel therapeutic approach in lymphoproliferative and autoimmune syndromes

A cell-cycle independent role for p21 in regulating synovial fibroblast migration in rheumatoid arthritis

Rheumatoid arthritis (RA) is characterized by synovial hyperplasia and destruction of cartilage and bone. The fibroblast-like synoviocyte (FLS) population is central to the development of pannus by migrating into cartilage and bone. We demonstrated previously that expression of the cell cycle inhibitor p21 is significantly reduced in RA synovial lining, particularly in the FLS. The aim of this study was to determine whether reduced expression of p21 in FLS could alter the migratory behavior of these cells. FLS were isolated from mice deficient in p21 (p21((-/-))) and were examined with respect to growth and migration. p21((-/-) )and wild-type (WT) FLS were compared with respect to migration towards chemoattractants found in RA synovial fluid in the presence and absence of cell cycle inhibitors. Restoration of p21 expression was accomplished using adenoviral infection. As anticipated from the loss of a cell cycle inhibitor, p21((-/-) )FLS grow more rapidly than WT FLS. In examining migration towards biologically relevant RA synovial fluid, p21((-/-) )FLS display a marked increase (3.1-fold; p < 0.05) in migration compared to WT cells. Moreover, this effect is independent of the cell cycle since chemical inhibitors that block the cell cycle have no effect on migration. In contrast, p21 is required to repress migration as restoration of p21 expression in p21((-/-) )FLS reverses this effect. Taken together, these data suggest that p21 plays a novel role in normal FLS, namely to repress migration. Loss of p21 expression that occurs in RA FLS may contribute to excessive invasion and subsequent joint destruction

Pro-apoptotic Bid is required for the resolution of the effector phase of inflammatory arthritis

Rheumatoid arthritis is an autoimmune disease characterized by hyperplasia of the synovial lining and destruction of cartilage and bone. Recent studies have suggested that a lack of apoptosis contributes to the hyperplasia of the synovial lining and to the failure in eliminating autoreactive cells. Mice lacking Fas or Bim, two pro-apoptotic proteins that mediate the extrinsic and intrinsic death cascades, respectively, develop enhanced K/BxN serum transfer-induced arthritis. Since the pro-apoptotic protein Bid functions as an intermediate between the extrinsic and intrinsic apoptotic pathways, we examined the role that it plays in inflammatory arthritis. Mice deficient in Bid (Bid-/-) show a delay in the resolution of K/BxN serum transfer-induced arthritis. Bid-/- mice display increased inflammation, bone destruction, and pannus formation compared to wild-type mice. Furthermore, Bid-/- mice have elevated levels of CXC chemokine and IL-1β in serum, which are associated with more inflammatory cells throughout the arthritic joint. In addition, there are fewer apoptotic cells in the synovium of Bid-/- compared to Wt mice. These data suggest that extrinsic and intrinsic apoptotic pathways cooperate through Bid to limit development of inflammatory arthritis

Loss of Bid does not alter the cytokine and chemokine milieu of the joint

<p><b>Copyright information:</b></p><p>Taken from "Pro-apoptotic Bid is required for the resolution of the effector phase of inflammatory arthritis"</p><p>http://arthritis-research.com/content/9/3/R49</p><p>Arthritis Research & Therapy 2007;9(3):R49-R49.</p><p>Published online 17 May 2007</p><p>PMCID:PMC2206343.</p><p></p> Pro-inflammatory cytokine production in ankle joints following transfer of K/BxN serum. Untreated wild-type (Wt) and Bid-/- mice were euthanized at three, five, or seven days post-serum transfer. Ankles from each mouse (days 3, = 6 (Wt) and n= 8 (Bid-/-); day 5, = 10; day 7, = 12 (Wt) and = 8 (Bid-/-)) were isolated, snap frozen, ground into a fine powder, lysed, and examined for production of tumor necrosis factor (TNF)α and IL-1β using sandwich ELISAs. Chemokine production in ankle joints following transfer of K/BxN serum. Ankles lysates as described above were examined for production of CXC chemokine (KC) and monocyte chemoattractant protein (MCP)-1 using ELISA. Data are shown as μg/μl per joint. Values represent the mean ± standard error, which were compared by Student's -test

Histological scores of ankle sections from wild-type (Wt) and Bid-/- mice

<p><b>Copyright information:</b></p><p>Taken from "Pro-apoptotic Bid is required for the resolution of the effector phase of inflammatory arthritis"</p><p>http://arthritis-research.com/content/9/3/R49</p><p>Arthritis Research & Therapy 2007;9(3):R49-R49.</p><p>Published online 17 May 2007</p><p>PMCID:PMC2206343.</p><p></p> Bid-/- mice have increased inflammation and joint destruction compared to Wt mice. Ankles isolated from mice (Wt, = 9; Bid-/- = 7) were prepared as described in Figure 2. Ankle sections were evaluated and scored by a pathologist blinded to the study as described in the Materials and methods section. Values represent the mean ± standard error of ankles/time point, which were compared by Student's -test. Increased numbers of lymphocytes and polymorphonuclear (PMNs) cells in inflamed Bid-/- joints. Ankles were prepared as described above. Values represent the mean ± standard error of ankles/time point, which were compared by Student's -test. Arthritic Bid-/- mice have more macrophages in the pannus and in the whole joint. Ankles were examined for F4/80 antigen as described in Materials and methods. The number of positive cells for F4/80 in pannus, synovial lining, and whole joint was determined by a pathologist blinded to the study. Values represent the mean ± standard error of ankles/time point, which were compared by Student's -test