|
Research Interests:
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-ranscriptional control of inflammatory genes through differential expression and activities of microRNAs.
Current Research:
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 severe systemic inflammation.
We discovered that SSI blood and tissue leukocytes show gene-specific reprogramming with repressed transcription of acute proinflammatory genes like TNFa 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. I found that TNFa transcription repression is due to a ‘’histone code’’ shift to histone H3 lysine 9 dimethylation (H3K9me2), H3 serine 10 dephosphorylation (H3S10p0) and repressor heterochromatin protein 1 (HP1) promoter binding in an SSI cell model. These results support that epigenetic mechanisms participates in repressing acute inflammatory genes and sustaining often lethal immunosuppression observed in SSI patients. This novel paradigm supports that gene-specific switches generate silenced facultative heterochromatin that can alternate between its state and that of transcriptionally responsive euchromatin changes from euchromatin characteristics (expressed) to that of heterochromatin (repressed).
Data in an SSI cell model identify candidate nucleosomes modifying proteins at the TNFa promoter with binding of G9a and SUV39h H3 methyltransferases, LSD1 demethylase, and heterochromatin adapter protein1 (HP1) in the transcription repressed state. Conversely, association of MSK1 and Aurora B histone H3 kinases in the transcription activated state suggests a reciprocal relationship between methylated and phosphorylated H3. Preliminary data also support CpG hypermethylation of the TNFa promoter in the repressed transcription state with concomitant binding of DNA methyltransferases Dnmt3a and 3b and adapter proteins MeCP2 and MBD1. This work has resulted in three publications in highly regarded journals: two in the Journal of Biological Chemistry (2007 and 2008) and one in Molecular and Cellular Biology (2009)
Regulation of post transcriptional processes by microRNAs in the SSI phenotype. 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. Thus, the two processes are dissociated. MicroRNAs (miRNAs) and mRNA-binding proteins 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 controlling degradation and/or translation of target mRNAs. miRNAs act as adapters that employ a silencing complex to target mRNAs by base-pairing with sequences within the 3` untranslated region (3`UTR) of target mRNA. Several hundred miRNAs have been identified in mammals, and the list is expected to grow. 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 suggested that abnormal miRNA expression was a common feature in human diseases such as cancer and some developmental disorders. My recent work indicates that miRNA expression is differentially regulated in SSI phenotype. Limiting expression of specific miRNAs reverses the translational repression of proinflammatory genes like TNFa during endotoxin tolerance.
Together, the studies of dissociated epigenetic and post-transcriptional processes guide therapeutic interventions based on this novel paradigm in a murine model of SSI, which I am working on. The work is underway to identify the mechanisms of miRNA-mediated translational repression of acute proinflammatory genes in SSI.
Recent Publications:
El Gazzar M, Yoza B, Chen X, Garcia BA, Young NL, and McCall CE. HMGB1 interacts with the linker histone H1 to repress TNFα transcription during endotoxin-mediated epigenetic silencing.Mol Cell Biol.2009 Apr; 29(7):1959-71.
El Gazzar M, Yoza B, Chen X, Hu J, Hawkins G, and McCall CE. G9a and HP1 couple histone and DNA methylation to TNFa transcription silencing during endotoxin tolerance. J Biol Chem. 2008 Nov; 283(47):32198-208.
Chen X, Yoza B, El Gazzar M, Hu J, Cousart S, and McCall CE. RelB sustains IkBa expression during endotoxin tolerance. Clin Vaccine Immunol. 2009 Jan; 16(1):104-10.
El Gazzar M, Yoza BK, Hu JY, Cousart SL, McCall CE. Epigenetic silencing of tumor necrosis factor alpha during endotoxin tolerance. J Biol Chem. 2007 Sep 14;282(37):26857-64.
El Gazzar M, El Mezayen R, Nicolls MR, Dreskin SC. Thymoquinone attenuates proinflammatory responses in lipopolysaccharide-activated mast cells by modulating NF-kappaB nuclear transactivation. Biochim Biophys Acta. 2007 Apr;1770(4):556-64.
Publications:
For a listing of additional publications, refer to PubMed, a service provided by the National Library of Medicine |