Bruce Beutler - Scientific Contributions

Scientific Contributions

Beutler is best known for his pioneering molecular and genetic studies of inflammation and innate immunity. He was the first to isolate mouse tumor necrosis factor-alpha (TNF), and to demonstrate the inflammatory potential of this cytokine, proving its important role in endotoxin-induced shock. Subsequently, he invented recombinant molecules expressly designed to neutralize TNF, fusing the binding portion of TNF receptor proteins to the heavy chain of an immunoglobulin molecule to force receptor dimerization. These molecules were later used extensively as the drug Etanercept in the treatment of rheumatoid arthritis, Crohn's disease, psoriasis, and other forms of inflammation.

Interested in the mechanism by which LPS activates mammalian immune cells, Beutler used TNF production as a phenotypic endpoint to identify the LPS receptor. Identification of the receptor hinged on the positional cloning of the mammalian Lps locus, which had been known since the 1960s as a key genetic determinant of all biological responses to LPS. Beutler thus discovered the key sensors of microbial infection in mammals, demonstrating that one of the mammalian Toll-like receptors, TLR4, acts as the membrane-spanning component of the mammalian LPS receptor complex. The TLRs (of which ten are now known to exist in humans) are now widely known to function in the perception of microbes, each detecting signature molecules that herald infection. These receptors also mediate severe illness, including shock and systemic inflammation as it occurs in the course of an infection. They are central to the pathogenesis of sterile inflammatory and autoimmune diseases such as systemic lupus erythematosus. The research on TLRs won him the Nobel Prize in 2011.

The positional cloning of Lps was completed in 1998. Beutler thereafter continued to apply a forward genetic approach to the analysis of immunity in mammals. In this process, germline mutations that alter immune function are created through a random process using the alkylating agent ENU, detected by their phenotypic effects, and then isolated by positional cloning. His work disclosed numerous essential signaling molecules required for the innate immune response, and helped to delineate the biochemistry of innate immunity.

ENU mutagenesis was also used by Beutler and colleagues to study the global response to a defined infectious agent. By screening mutant mice for susceptibility to mouse cytomegalovirus (MCMV), they identified a large number of genes that make a life-or-death difference during infection, and termed this set of genes the MCMV "resistome". These genes fall into "sensing," "signaling," "effector," "homeostatic," and "developmental" categories, and some of them were wholly unexpected. For example, K_ir6.1 ATP-sensitive potassium channels in the smooth muscle of the coronary arteries serve an essential homeostatic role during infection by this microbe, and mutations that affect them cause sudden death during infection.

In the course of their work, Beutler and his colleagues identified genes required for other important biological processes, including the regulation of iron absorption, hearing, and embryonic development, since their disruption by ENU created strikingly abnormal visible phenotypes.