RIPK1 and RIPK3 kinases promote cell death independent inflammation by TLR4-TRIF.
Abstract: The innate
immune response is an essential first line of defense against bacterial and viral
infection. Myeloid-derived cells, such as macrophages, function as crucial components of
the innate immune system in recognizing pathogen-associated molecular patterns. Cell
death and inflammation are the main innate immune processes contributing to eliminate
pathogen proliferation. RIPK1 ... read moreand RIPK3-dependnet necrotic cell death has been
previously linked to the signaling by innate immune Toll-like receptors (TLRs). In this
work, I describe a previously unappreciated role the kinase activities of RIPK1 and
RIPK3 in primary macrophages in directing inflammatory gene expression downstream from
TLR4 that manifest independently of cell death. I found that upon the loss of caspase-8
in vitro, RIPK1 kinase activity is markedly elevated in primary macrophages in response
to TLR4 agonist lipopolysaccharide (LPS). Using this in vitro system, I further
established that kinase activities of RIPK1 and RIPK3 induce acute inflammatory cytokine
mRNA expression and protein release. This regulation requires the TLR4 adapter, TRIF, in
addition to, MAP kinases, Erk1/2. The transcription factors, cFos and NF-κB are
also required for RIPK1 and RIPK3 dependent inflammatory responses. Importantly, using
genetic and pharmacologic tools, I found that RIPK1 and RIPK3 account for the major
fraction of the acute inflammatory responses elicited by LPS in vivo even in the absence
of exogenous inhibition of caspase-8. Overall, these findings provide new insights into
RIPK1 and RIPK3 kinase functions in the context of innate immune responses and identify
new drug-targetable activities that may be highly relevant to the mechanisms of
RIPK1/3-dependent inflammatory pathologies.
Thesis (Ph.D.)--Tufts University, 2016.
Submitted to the Dept. of Pharmacology & Experimental Therapeutics.
Advisor: Alexei Degterev.
Committee: Theoharis Theoharides, Alexander Poltorak, Martin Beinborn, and Nikoli Slavov.
Keyword: Pharmacology.read less