diet and regulation of innate immunity
We are interested in the Western Diet, a diet that arose nearly 10,000 years ago post-Neolithic period that is high in saturated fats and sugar and low in fiber, is one of the most prevalent diets in Westernized nations, and is associated with obesity. It is known that the Western Diet can influence susceptibility to infections and severity of inflammatory diseases; thus, we are investigating the role of the Western Diet in regulating innate immunity and outcome of infectious disease.
Cell Death and sepsis projects
As a post-doctoral fellow my research has been focused on understanding the contribution of cell death during sepsis in order to identify novel diagnostic and therapeutic targets. Sepsis is defined as the presence of systemic inflammatory response syndrome due to infection and is one of the leading causes of death in intensive care units. Cell death and release of proinflammatory mediators contribute to mortality during sepsis. Specifically, caspase-11-dependent cell death contributes to pathology and decreases in survival time in sepsis models. I used a myriad of techniques, including a genome-wide CRISPR screen, to identify new proteins and pathways that contribute to caspase-11-dependent cell death. I found a novel role for complement in enhancing this cell death pathway during sepsis, thus exacerbating pathologies and increasing mortality. We have targeted the complement pathway with an existing inhibitor and have shown it’s a viable candidate for a novel sepsis therapeutic. Additionally, we found that complement and caspase-11 human ortholog caspase-5 transcripts can be used as early diagnostic markers for septic patients. My techniques built to look for novel regulators of cell death and sepsis will continue to be fruitful as I validate more hits from my screens. In addition to this project, I am currently elucidating the role of environmental factors, such as diet, on the basal immune state of the host and how this affects susceptibility-to and severity-of sepsis.
Napier BA, Brubaker SW, Sweeney T, Gertsvolf NA, Monnett P, Rothmeier GH, Puschnik A, Carette JE, Khatri P, Monack DM. (2016) Complement pathway enhances caspase-11-dependent cell death and sepsis severity. J Ex Med. 2016. Oct 3. pil. jem.20160027.
Napier BA and Monack DM (2017) Generating a RAW264.7 CRISPR-Cas9 genome-wide library. Bio-protoc. In preparation.
Napier BA. (2017) Editorial: The sum of all defenses: Tolerance + Resistance. Pathog Dis. In press.
Liddelow SA, Guttenplan KA, Clarke LE, Bennett FC, Bohlen CJ, Schirmer L, Bennett ML, Munch AE, Chung WS, Peterson TC, Wilton DK, Frouin A, Napier BA, Panicker N, Kumer M, Buckwalter MS, Rowitch D, Dawson VL, Dawson TM, Stevens B, Barres BA. (2017) Neurotoxic reactive astrocytes are induced by activated microglia. Nature. 2017 Jan 18. doi: 10.1038/nature21029.
Napier BA and Monack DM. (2016). A lipid arsenal to control inflammation. Science. 352(6290):1173-4.
bacterial bioweapon pathogenesis
My early graduate work focused on elucidating the dynamic relationship between the cytosolic intracellular bacterial pathogen Francisella and its host during infection. To prevent infection with pathogenic organisms, humans and other mammals restrict access to essential nutrients in a process termed nutritional immunity. I found that the limited availability of one metabolite, biotin, in the bacteria-containing phagosome, restricted the bacteria to a non-replicative niche, inhibiting bacterial replication and subsequent disease. These results have proven to be a paradigm for other cytosolic bacterial pathogens that require various host-derived nutrients during replication. Additionally, I contributed to multiple projects that elucidated virulence functions in Francisella, including: CRISPR-Cas9 mediates Francisella virulence through regulation of essential bacterial lipoproteins, tyrosine-kinase inhibitor imatinib can clear Francisella infection, lipid A modifications affects Francisella pathogenesis, and hydroperoxide resistance determines Francisella virulence. Together, my work has not only contributed to understanding the relationship between intracellular bacterial pathogens and their host, but also has identified novel therapeutics and antimicrobial targets.
Napier BA, Meyer L, Bina JE, Miller MA, Sjöstedt A, Weiss DS. (2012). A link between biotin and rapid phagosomal escape in Francisella. Proc Natl Acad Sci USA. 109(44):1804-89.
Feng Y, Napier BA, Manandhar M, Henke SK, Weiss DS, Cronan JE. (2014). A Francisella virulence factor catalyzes an essential reaction of biotin biosynthesis. Mol Microbiol. 91(2):300-14.
Sampson TR, Napier BA, Schroeder MR, Jones CL, Weiss DS. (2014) Enhancement of envelope integrity by a CRISPR/Cas system promotes evasion of the inflammasome. Proc Natl Acad Sci USA. 111(30):11163-8.
Napier RJ, Norris BA, Swimm A, Giver CR, Harris WAC, Laval J, Napier BA, Patel G, Crump R, Peng Z, Bornmann W, Pulendra B, Buller RM, Weiss DS, Tirouvanziam R, Waller EK, Kalman D. (2015) Low doses of Imatinib induce myelopoiesis and enhance host antimicrobial immunity. PLoS Pathogens. 11(3):e1004770.
antibiotic resistance mechanisms
The second portion of my graduate work focused on understanding antibiotic failure in the clinic for treating pan- or multi-drug resistant Acinetobacter baumannii and Enterobacter cloacae infections. Antibiotic resistance threatens the delivery of safe and effective healthcare and is projected to lead to 10 million annual deaths worldwide by 2050. We identified the over-looked risk of inducing cross-resistance to host antimicrobials when treating patients with cationic microbial peptide colistin as a last-line antibiotic. Our work suggests the possible future use of an array of cationic antimicrobial peptides in development as therapeutics may have unintended negative consequences, eventually leading to the generation of hypervirulent strains that are resistant to innate host defenses.
We also identified clinical isolates of E. cloacae that harbored low-frequency bacterial subpopulations resistant to colistin, but were misclassified as susceptible by current diagnostics. We show that during murine infection, in the absence of colistin, innate immune defenses led to an increased frequency of the resistant subpopulation, leading to inefficacy of subsequent colistin therapy. Thus, we demonstrated that the ability of low-frequency bacterial subpopulations contribute to clinically relevant antibiotic resistance, elucidating an enigmatic cause of antibiotic treatment failure and highlighting the critical need for more sensitive diagnostics.
Napier BA, Burd EM, Satola SW, Cagle SM, Ray SM, McGann P, Pohl J, Lesho EP, Weiss DS. (2013). Clinical use of colistin induces cross-resistance to host antimicrobials in Acinetobacter baumannii. mBio. 4(3):e00021-13. Recommended by Faculty of 1000
Napier BA, Band VI, Burd EM*, Weiss DS* (2014). Colistin heteroresistance in Enterobacter cloacae is associated with cross-resistance to host antimicrobial lysozyme. Antimicrob Agents Chemother. 58(9):5594-7. *, co-corresponding authors.
Band VI*, Crispell EK*, Napier BA, Herrera CM, Tharp GK, Vavikolanu K, Pohl J, Read TD, Bosinger SE, Trent MS, Burd EM, Weiss DS. (2016). Antibiotic failure mediated by a resistant subpopulation in Enterobacter cloacae. Nature Microbio. DOI: 10.1038/NMICROBIOL.2016.53. *, authors contributed equally.
Chin CY, Gregg KA, Napier BA, Ernst RK, Weiss DS. (2015) A PmrB-regulated deacetylase required for lipid A modification and polymyxin resistance in Acinetobacter baumannii. Antimicrob Agents Chemother. 00515-15.