Dysregulated growth and loss of podocytes are important features of HIV-associated nephropathy. Recently, HIV was reported to induce a new type of programed cell death, pyroptosis, in T lymphocytes through induction of Nod-like receptor protein 3 (NLRP3) inflammasome complexes. We evaluated the role of HIV in podocyte NLRP3 inflammasome formation both in vivo and in vitro. Renal cortical sections of HIV-transgenic mice (Tg26) displayed increased expression of NLRP3, ASC (a CARD protein), caspase-1, and IL-1b proteins, confirming NLRP3 inflammasome complex formation in podocytes of Tg26 mice. Renal tissues of Tg26 mice also displayed enhanced mRNA levels and protein expressions of inflammasome markers (NLRP3, ASC, and caspase-1, and IL-1b). Serum of Tg26 mice also showed elevated concentrations of IL-1b cytokine compared with FVBN mice. HIV induced pyroptosis in a dose-and time-dependent manner within podocytes, a phenotype of inflammasome activation. Caspase-1 inhibitor not only attenuated podocyte expression of caspase-1 and IL-1b but also provided protection against pyroptosis, suggesting that HIV-induced podocyte injury was mediated by caspase-1 activation. Interestingly, HIV-induced podocyte pyroptosis could be partially inhibited by Tempol (a superoxide dismutase-mimetic agent) and by glyburide (an inhibitor of potassium efflux). These findings suggest that generation of reactive oxygen species and potassium efflux contribute to HIV-induced pyroptosis and NLRP3 inflammasome activation in podocytes.
Within inflammatory environments, B cells encountering foreign or self-Ag can develop tertiary lymphoid tissue expressing activation-induced cytosine deaminase (AID). Recently, this DNA-modifying enzyme was detected in nonlymphoid cells within several inflamed tissues and strongly implicated in malignant transformation. This study examines whether a cyclooxygenase 2 (COX-2) pathway, often linked to inflammation, influences AID expression in activated B lymphocytes. In this paper, we report that dividing human B cells responding to surrogate C3d-coated Ag, IL-4, and BAFF express AID, as well as COX-2. A progressive increase in AID with each division was paralleled by a division-related increase in a COX-2–linked enzyme, microsomal PGE2 synthase-1, and the PGE2R, EP2. Cells with the greatest expression of AID expressed the highest levels of EP2. Although COX-2 inhibitors diminished both AID expression and IgG class switching, exogenous PGE2 and butaprost, a selective EP2 agonist, augmented AID mRNA/protein and increased the numbers of IgG+ progeny. Despite the latter, the proportion of IgG+ cells within viable progeny generally declined with PGE2 supplementation. This was not due to PGE2-promoted differentiation to plasma cells or to greater downstream switching. Rather, because phosphorylated ataxia telangiectasia mutated levels were increased in progeny of PGE2-supplemented cultures, it appears more likely that PGE2 facilitates AID-dependent DNA double-strand breaks that block B cell cycle progression or promote activation-induced cell death, or both. Taken together, the results suggest that a PGE2 feed-forward mechanism for augmenting COX-2 pathway proteins promotes progressively increased levels of AID mRNA, protein, and function.
Resting mature human B cells undergo a dynamic process of clonal expansion, followed by clonal contraction, during an in vitro response to surrogate C3d-coated antigen and innate immune system cytokines, IL-4 and BAFF. We here explore the mechanism for clonal contraction through following the time- and division-influenced expression of several pro- and anti-apoptotic proteins within CFSE-labeled cultures. Several findings, involving both human and mouse B cells, show that a mitochondria-dependent apoptotic pathway involving p53 contributes to the high AICD susceptibility of replicating blasts. Activated B cell clones exhibit elevated p53 protein and elevated mRNA/protein of pro-apoptotic molecules known to be under direct p53 transcriptional control, Bax, Bad, Puma, Bid, and pro-caspase 6, accompanied by reduced anti-apoptotic Bcl-2. Under these conditions, Bim levels were not increased. Findings that full length Bid protein significantly declines in AICD-susceptible replicating blasts, while Bid mRNA does not, suggests that Bid is actively cleaved to short-lived, pro-apoptotic tBid. AICD was diminished, albeit not eliminated, by p53 siRNA transfection, genetic deletion of p53, or Bcl-2 overexpression. DNA damage is a likely trigger for p53-dependent AICD since susceptible lymphoblasts expressed significantly elevated levels of both phospho-ATMser1980 and phospho-H2AXser139. Deficiency in activation-induced cytosine deaminase (AID) diminishes but does not ablate murine B cell AICD, indicating that AID-induced DNA damage is only in part responsible. Evidence for p53-influenced AICD during this route of TI clonal expansion raises the possibility that progeny bearing p53 mutations might undergo positive selection in peripherally inflamed tissues with elevated levels of IL-4 and BAFF.
Exosomes are cell-generated nano-vesicles found in most biological fluids. Major components of their cargo are lipids, proteins, RNA, DNA, and non-coding RNAs. The miRNAs carried within exosomes reveal real-time information regarding disease status in leukemia and other cancers, and therefore exosomes have been studied as novel biomarkers for cancer. We investigated the impact of exosomes on cell proliferation in pediatric acute lymphocytic leukemia (PALL) and its reversal by silencing of exo-miR-181a. We isolated exosomes from the serum of PALL patients (Exo-PALL) and conditioned medium of leukemic cell lines (Exo-CM). We found that Exo-PALL promotes cell proliferation in leukemic B cell lines by gene regulation. This exosome-induced cell proliferation is a precise event with the up-regulation of proliferative (PCNA, Ki-67) and pro-survival genes (MCL-1, and BCL2) and suppression of pro-apoptotic genes (BAD, BAX). Exo-PALL and Exo-CM both show over expression of miR-181a compared to healthy donor control exosomes (Exo-HD). Specific silencing of exosomal miR-181a using a miR-181a inhibitor confirms that miR-181a inhibitor treatment reverses Exo-PALL/Exo-CM-induced leukemic cell proliferation in vitro. Altogether, this study suggests that exosomal miR-181a inhibition can be a novel target for growth suppression in pediatric lymphatic leukemia.
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