Project description:The mitogen-activated protein kinase (MAPK) p38 pathway is reported to regulate macrophage responses to lipopolysaccharide (LPS) at least partly via the phosphorylation of the mRNA-destabilizing factor tristetraprolin (TTP). LPS-activated MAPK p38 phosphorylates and activates the downstream kinase MAPK-activated protein kinase 2 (MK2), which then phosphorylates serines 52 and 178 of TTP, resulting in loss of mRNA-destabilizing activity. As a consequence, mRNAs that contain binding sites for TTP are stabilized in a manner that is acutely sensitive to the activity of the MAPK p38 pathway. Dual specificity phosphatase 1 (DUSP1) dephosphorylates and inactivates MAPK p38. Dusp1-/- macrophages overexpress a number of pro-inflammatory mediators, but their genome-wide responses to LPS have not yet been described in detail. Dusp1-/- mice are exceptionally sensitive to a wide variety of inflammatory challenges, including experimental models of endotoxemia or sepsis. It has been suggested (but not yet proven) that DUSP1 controls the inflammatory response of macrophages in part via the regulation of MAPK p38 activity and TTP phosphorylation status. We generated a mouse knock-in strain, in which codons 52 and 178 of the endogenous Zfp36 gene (which encodes TTP) were mutated to alanine codons. The mutation gives rise to a constitutively active form of TTP, which cannot be inactivated via the p38 MAPK pathway. The Zfp36aa/aa strain was back-crossed against C57/BL6 for > 10 generations. We also generated a double-targeted strain in which the Zfp36 mutation was combined with disruption of the Dusp1 gene. This expression array describes LPS responses of primary mouse bone marrow-derived macrophages of four genotypes, and closely matched genetic background: wild type (Dusp1+/+ : Zfp36+/+); TTP mutant (Zfp36aa/aa); DUSP1 knock out (Dusp1-/-); and double targeted (Dusp1-/- : Zfp36aa/aa). The data provide a comprehensive picture of the impact of Dusp1 deletion or TTP mutation on the responses of primary macrophages to LPS. They also demonstrate that the excessive inflammatory responses of Dusp1-/- macrophages are largely a consequence of the phosphorylation and inactivation of TTP. Genome wide expression profiles of wild type, Dusp1-/-, Zfp36aa/aa and Dusp1-/-/Zfp36aa/aa M-CSF derived macrophages, stimulated with LPS for 1 or 4 hours

Project description:Radiation biodosimetry based on transcriptomic analysis of peripheral blood is a valuable tool to detect radiation exposure after a radiological/nuclear event and obtain useful biological information that could predict tissue and organismal injury. However, confounding factors, including inflammation, can potentially obscure the predictive power of the method. The mitogen-activated protein kinase (MAPK) p38 is normally regulated by the MAP3K-MAP2K pathway in mammalian cells. Members of the p38 MAPK family respond to pro-inflammatory signals and environmental stresses. However, in T cells there is an alternative pathway for p38MAPK activation. This pathway has been shown to play an important role in antigen-receptor-activated T cells and participate in immune and inflammatory responses. Radiation is known to induce a pro-inflammatory response. To examine the role of p38MAPK in response to radiation, we used two mouse models expressing either a p38αMAPK dominant negative (DN) mutation that would be expected to globally suppress p38MAPK signaling or a double knock-in (DKI) mutant, which would be expected to inhibit specifically T cell receptor activation. We exposed wild-type and p38MAPK mutant mice to 7 Gy x-rays and 24 h later we isolated whole blood and performed genome microarray and gene ontology analysis. Comparison between the two mutants (DN, DKI) suggest that the alternative p38MAPK pathway may have wider functions in the response to radiation exposure beyond its well established role as a downstream effector of activated T-cell receptor. Among the differentially enriched pathways, irradiation leads to a significant overrepresentation of pathways associated with morbidity and mortality as well as organismal cell death. In contrast, these pathways were significantly underrepresented in p38MAPKDN and p38MAPKDKI mutant mice, implying that p38MAPK suppression protects mice from the deleterious effects of radiation. Furthermore, radiation exposure resulted in an enrichment of a small number of phagocytosis-related pathways; however, considerably more phagocytosis-related pathways were overrepresented in the p38MAPK mutant mice, implying that p38MAPK signaling, normally, restricts phagocytosis of apoptotic cells after radiation and may, thus, contribute to persistent inflammation. Finally, despite the significant changes in gene expression, we were still able to identify a panel of genes that could accurately distinguish between irradiated and control mice, irrespective of p38MAPK status.

Project description:The mitogen-activated protein kinase (MAPK) p38 pathway is reported to regulate macrophage responses to lipopolysaccharide (LPS) at least partly via the phosphorylation of the mRNA-destabilizing factor tristetraprolin (TTP). LPS-activated MAPK p38 phosphorylates and activates the downstream kinase MAPK-activated protein kinase 2 (MK2), which then phosphorylates serines 52 and 178 of TTP, resulting in loss of mRNA-destabilizing activity. As a consequence, mRNAs that contain binding sites for TTP are stabilized in a manner that is acutely sensitive to the activity of the MAPK p38 pathway. Dual specificity phosphatase 1 (DUSP1) dephosphorylates and inactivates MAPK p38. Dusp1-/- macrophages overexpress a number of pro-inflammatory mediators, but their genome-wide responses to LPS have not yet been described in detail. Dusp1-/- mice are exceptionally sensitive to a wide variety of inflammatory challenges, including experimental models of endotoxemia or sepsis. It has been suggested (but not yet proven) that DUSP1 controls the inflammatory response of macrophages in part via the regulation of MAPK p38 activity and TTP phosphorylation status. We generated a mouse knock-in strain, in which codons 52 and 178 of the endogenous Zfp36 gene (which encodes TTP) were mutated to alanine codons. The mutation gives rise to a constitutively active form of TTP, which cannot be inactivated via the p38 MAPK pathway. The Zfp36aa/aa strain was back-crossed against C57/BL6 for > 10 generations. We also generated a double-targeted strain in which the Zfp36 mutation was combined with disruption of the Dusp1 gene. This expression array describes LPS responses of primary mouse bone marrow-derived macrophages of four genotypes, and closely matched genetic background: wild type (Dusp1+/+ : Zfp36+/+); TTP mutant (Zfp36aa/aa); DUSP1 knock out (Dusp1-/-); and double targeted (Dusp1-/- : Zfp36aa/aa). The data provide a comprehensive picture of the impact of Dusp1 deletion or TTP mutation on the responses of primary macrophages to LPS. They also demonstrate that the excessive inflammatory responses of Dusp1-/- macrophages are largely a consequence of the phosphorylation and inactivation of TTP.

Project description:Background: Evidence has recently accumulated suggesting that mature hepatocytes have the unique capacity to autonomously decide their replication fate. The molecular mechanism by which hepatocytes switch from an essentially quiescent state to rapidly proliferation after liver injury is not fully understood. To provide molecular insights into the self-renewal of mature hepatocytes, we have applied an ex vivo liver slice culture system. Results: After liver injury, activation of p38 and Erk1/2 began in mature hepatocytes within 5 min. Erk1/2 was activated at the edge of the cut as well as on the surface of liver slices. The number of hepatocytes that contain activated Erk1/2 increased within 1 h and then decreased. Concomitantly, immediate early genes (IEGs), such as Jun, early gene response 1 (Egr1) and Myc were induced and Ki67 positive hepatocytes appeared 24 h after liver injury in the slices. In agreement with in vivo studies, transcriptome analysis using 2 h slice culture reveals that 63% of upregulated genes were downstream of lipopolysaccharide (LPS) stimulation which induces interleukin 6 (IL 6) or tumor necrosis factor (TNF) alpha pathways. Furthermore, circadian clock regulator, such as members of the basic helix-loop-helix family, Bhlhe40 and Bhlhe41, were highly upregulated for 4 h after injury. Although upon injury Jun or Egr1 were induced in liver slices from proliferation-defective liver, no circadian clock regulator genes were upregulated. Moreover, using an in vitro cell culture system we show that Bhlhe40 is required for the G0-G1 transition. Conclusion: Our data suggest that the circadian clock regulator, Bhlhe40, is involved in the G0-G1 transition. An ex vivo system using normal and proliferation defective KO liver is a useful tool for identification of genes that trigger cell proliferation shortly after liver injury. This method may also be applied for measurement of the liver regeneration potential of individual livers at the priming phase. In one dual-color microarray hybridization, mRNA expression changes after 2h ex vivo incubation of liver slices were examined.

Dataset Information

Extracellular-signal regulated kinase (Erk1/2), mitogen-activated protein kinase-activated protein kinase 2 (MK2) and tristetraprolin (TTP) comprehensively regulate injury-induced immediate early gene (IEG) response in in vitro liver organ culture.

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