Inflammation, Sepsis, Epigenetics, miRNAs
Mohamed Elgazzar, PhD
The general theme of my research is basic molecular processes that can be translated to the field of inflammation, with a focus on severe systemic inflammatory processes like sepsis. My specific contributions and emphasis are epigenetic and microRNA based regulation that generates reprogramming of genes linked to inflammation, and posttranscriptional control of inflammatory genes through differential expression and activities of microRNAs.
The general theme of my research is basic molecular processes that can be translated to the field of inflammation, with a focus on severe systemic inflammatory processes like sepsis. My specific contributions and emphasis are epigenetic regulation that generates reprogramming of genes linked to inflammation, and post-transcriptional control of inflammatory genes through differential expression and activities of microRNAs.
Gene reprogramming through epigenetic processes:
Epigenetic gene reprogramming is an emerging concept relevant to human diseases. The general objective of my research is to investigate epigenetics of severe systemic inflammation (SSI), specifically the epigenetic processes that differentially regulate gene transcription in SSI and sepsis. We discovered that SSI blood and tissue leukocytes show gene-specific reprogramming with repressed transcription of acute proinflammatory genes like TNFa, IL-6 and IL-1b and activated transcription of other sets of genes like IkBa, antimicrobial peptides, and anti-inflammatory cytokines. These findings may have clinical relevance since improved outcomes in SSI follow reversal of gene reprogramming. Expression of proinflammatory genes is required for priming and activation of innate immunity cells in order to mount an antimicrobial response. We found that TNFa transcription repression is due to a ‘’histone code’’ shift to histone H3 lysine 9 dimethylation (H3K9me2), H3 serine 10 dephosphorylation (H3S10phos). These results support that epigenetic mechanisms participate in repressing acute inflammatory genes and sustaining often lethal immunosuppression observed in septic patients.
Regulation of posttranscriptional processes by microRNAs in the SSIphenotype:
A second area of my research addresses an unexpected and novel observation that gene-specific regulatory processes for protein production are dissociated from those that regulate the process of transcription. MicroRNAs (miRNAs) appear responsible for gene-specific modifications of mRNA metabolism and translation, which together define protein synthesis. MicroRNAs are an abundant class of endogenous non-coding RNAs of approximately 22-nucleotides in length that regulate gene expression post-transcriptionally by inducing degradation and/or translation repression of target mRNAs. Several hundred miRNAs have been identified in mammals. Bioinformatic predictions indicate that mammalian miRNAs can regulate ~30% of all protein-coding genes. Recent studies have implicated miRNAs in regulating a number of biological pathways, including proliferation, differentiation, apoptosis, and signal transduction, and they suggest that aberrant miRNA expression is a common feature in human diseases such as cancer and some developmental disorders. Our recent work indicates that miRNA expression is differentially regulated in the SSI phenotype. We found that limiting expression of gene-specific miRNAs (miR-221, miR-125b and miR-579) reverses the translational repression of proinflammatory genes like TNF during endotoxin tolerance. This tolerance or hyporesponsiveness to further stimulation with bacterial endotoxin is associated with the immunosuppression that follows SSI.
Innate immunity cell reprogramming in chronic sepsis:
Evidence supports that the pathophysiology of sepsis varies as it moves from an initiating acute hyperinflammatory phase (or SSI) to a chronic hypoinflammatory and immunosuppression phase that sustains chronic infection. Using a mouse model of chronic sepsis, we found that this inflammatory phenotypic switch is initiated in the bone marrow due to inflammatory signals and results in reprogramming of innate cell differentiation and maturation leading to a state of hyporesponsiveness. With this model, we also are studying how miRNAs support the innate immunity cell phenotypic switch to sustain chronic inflammation.
1 R15 GM100322-01 (PI: Elgazzar), 12/01/11–11/30/14, NIH/NIGMS TLR-dependent reprogramming of translation regulates acute systemic inflammation This proposal seeks to identify the posttranscriptional molecular processes that selectively regulate protein synthesis in the severe systemic inflammation phenotype.
R01 AI065791-01A1 (PI: McCall) 02/01/06-01/31/11, NIH/NIAID NF-κB and Chromatin Changes in Human Sepsis This proposal tests that increased expression of RelB acts as a negative feedback mechanism for gene transcription repression in severe systemic inflammation. Role: Co-Investigator
El Mezayen R, El Gazzar M, Seeds MC, McCall CE, Dreskin SC, and Nicolls MR. Endogenous signals released from necrotic cells augment inflammatory responses to bacterial endotoxin. Biochim Biophys Acta 2007; 111:36-44.
El Gazzar M, Yoza B, Hu J, Cousart S, and McCall CE. Epigenetic Silencing of TNFα During Endotoxin Tolerance. J Biol Chem 2007; 282:26857-64.
El Gazzar M, Yoza B, Chen X, Hu J, Hawkins G, and McCall CE. G9a and HP1 couple histone and DNA methylation to TNF transcription silencing during endotoxin tolerance. J Biol Chem 2008; 283:32198-208.
Chen X, Yoza B, El Gazzar M, Hu J, Cousart S, and McCall CE. RelB sustains IkB expression during endotoxin tolerance. Clin Vaccine Immunol 2009; 16:104-10.
El Gazzar M, Yoza B, Chen X, Garcia BA, Young NL, and McCall CE. Chromatin-specific remodeling by HMGB1 and linker histone H1 silence proinflammatory genes during endotoxin tolerance. Mol Cell Biol 2009; 29: 1959-71.
El Mezayen R, El Gazzar M, Rebecca Myer R, and High KP. Aging-dependent upregulation of the IL-23p19 gene expression in dendritic cells is associated with differential transcription factor binding and histone modifications. Aging Cell 2009; 8:553-65.
Chen X, El Gazzar M, Yoza B, and McCall CE. The NF-kappaB factor RelB and histone H3 lysine methyltransferase G9a directly interact to generate epigenetic silencing in endotoxin tolerance. J Biol Chem 2009; 284:27857-65.
El Gazzar M, Liu T, Yoza B, and McCall CE. Dynamic and selective nucleosome repositioning during endotoxin tolerance. J Biol Chem 2010; 285:1259-71.
El Gazzar M and McCall CE. MicroRNAs distinguish translational from transcriptional silencing during endotoxin tolerance. J Biol Chem 2010; 285:20940-51.
McCall CE, Yoza B , Tiefu L, and El Gazzar M. Gene-specific epigenetic regulation in serious infections with systemic inflammation. J Innate Immun 2010; 2:395-405.
Vachharajani V, Wang S, Mishra N, El Gazzar M, Yoza B, and McCall CE. Curcumin modulates leukocyte and platelet adhesion in murine sepsis. Microcirculation 2010; 17:407-16.
Liu T, Yoza BK, El Gazzar M, Vachharajani VT, and McCall CE.NAD +-dependent SIRT1 deacetylase participates in epigenetic reprogramming during endotoxin tolerance. J Biol Chem 2010; 286:9856-64.
El Gazzar, M., Church, A. & McCall, C.E. MiR-146a regulates both transcription silencing and translation disruption during TLR4-induced gene reprogramming. J Leukoc Biol 2011; 90:509-19.
McCall CE, El Gazzar M, Liu T, Vaccharajani V & Yoza BK. Epigenetics, microRNAs, and bioenergy shifts coordinate gene-specific reprogramming during acute systemic inflammation. J Leukoc Biol 2011; 90: 439-46.
El Gazzar M & McCall CE. MicroRNAs and transcription factor regulatory networks in hematopoietic lineage commitment and differentiation: regulators of the regulators. Immunol Cell Biol (Review) 2011; (in press).
Brudecki L, Yin D, Ferguson DA, McCall CE & El Gazzar M. Hematopoietic stem-progenitor cells restore immunoreactivity and improve survival in chronic sepsis. Infect Immun 2011; (submitted).