Robert A. Heinzen, Ph.D.

Head, Coxiella Pathogenesis Section 

Dr. Heinzen received his Ph.D. in microbiology from Washington State University in 1991. After completing an Intramural Research Training Award fellowship in the Laboratory of Intracellular Parasites at the NIH in 1996, Dr. Heinzen joined the faculty of the University of Wyoming as an assistant professor of molecular biology where he was awarded tenure and promoted to associate professor in 2002. Dr. Heinzen was recruited to the NIH in 2003 as head of the new Coxiella Pathogenesis Section in the Laboratory of Intracellular Parasites.

Description of Research Program

We are investigating the pathophysiology and molecular basis of virulence of Coxiella burnetii, an obligate intracellular bacterium and the cause of human acute and chronic Q fever. This category B potential agent of bioterrorism has pronounced environmental stability and a very low infectious dose. The in vivo target of Coxiella is the macrophage where the organism replicates in a parasitophorous vacuole (PV) with lysosomal characteristics.

Major Areas of Research

Host interactions
Coxiella has the extraordinary ability to replicate within a PV having the harsh characteristics of a lysosome. Our results indicate that Coxiella proteins remodel the PV to make it amenable for growth. The biochemical nature of the Coxiella PV and the pathogen and host molecules that regulate its biogenesis are ill-defined. Using a variety of contemporary cell biology techniques, we are characterizing the Coxiella PV to define both Coxiella and host factors that mediate its formation.

Coxiella can establish a persistent infection that can reactivate months or years after initial exposure. Mechanisms by which Coxiella evades clearance by the host immune response during persistence are unknown. Dendritic cells (DC) are exceptional antigen presenting cells that bridge the innate and adaptive immune responses; however, their roles in controlling Coxiella infection are unknown. To improve our understanding of DC involvement in the pathogenesis of human Q fever, we are investigating human DC responses to infection by diverse strains of Coxiella.

(A and B). A mouse bone marrow-derived macrophage containing a Coxiella PV heavily stained with the acidotropic base acridine orange. (C). Coxiella (red) are bounded by a PV membrane in Vero cells that labels with antibody directed against Flottilin-1 (green), a host protein associated with plasma membrane cholesterol-rich lipid rafts.

Developmental biology

Scanning and transmission electron micrographs showing PV harboring Coxiella developmental forms.

The impressive environmental stability of Coxiella is due to biogenesis of a highly resistant cell form termed the small cell variant (SCV) that arises during a biphasic developmental cycle that includes a replicatively active large cell variant (LCV). The transcriptome and proteome of purified SCV and LCV are being characterized to define the program of gene expression associated with Coxiella morphological differentiation. Moreover, the biological and resistance properties of SCV and LCV are being defined. In addition to gaining a clearer understanding of the biological relevance of Coxiella development forms and the proteins that confer their unique properties, this study may identify cell form-specific antigens that provide the basis of rationally designed subunit vaccines and new diagnostics.

Genomics and genetic systems
Considerable genomic DNA heterogeneity exists among Coxiella strains isolated from environmental sources and human acute or chronic disease patients. Using high-density DNA arrays, we are conducting a comparative genomics analysis of Coxiella strains to better understand the degree and significance of genetic variation. These studies are aimed at identifying correlations between genetic polymorphisms and human disease potential. To date, this study has revealed genetic mechanisms of Coxiella LPS phase variation, the conserved plasmid content of the organism, and possible pathogenomic determinants of virulence. Moreover, this study describes a forensic tool for identification and grouping of strains from disparate sources. Identification of Coxiella virulence factors has been thwarted because the organism lacks a system of genetic manipulation. To this end, we are using a multifaceted approach to genetically transform the organism.

Hierarchical clustering of 22 C. burnetii isolates based on the number of partially or fully deleted genes relative to the reference Nine Mile isolate. Genomic DNA was hybridized to an Affymetrix Genechip containing probe pairs to each open reading frame of C. burnetii Nine Mile.

Research Group Members

Left to right: Paul Beare, Anders Omsland, Dale Howe, Bob Heinzen, Diane Cockrell, Stacey Gilk, Dan Voth, Jeff Shannon.

Selected Publications

View list in PubMed.

Voth DE, Howe D, Heinzen RA. Coxiella burnetii inhibits apoptosis in human THP-1 cells and monkey primary alveolar macrophages. Infect Immun. 2007 Sep;75(9):4263-71.

Coleman SA, Fischer ER, Cockrell DC, Voth DE, Howe D, Mead DJ, Samuel JE, Heinzen RA. Proteome and antigen profiling of Coxiella burnetii developmental forms. Infect Immun. 2007 Jan;75(1):290-8.

Beare PA, Samuel JE, Howe D, Virtaneva K, Porcella SF, Heinzen RA. Genetic diversity of the Q fever agent, Coxiella burnetii, assessed by microarray-based whole-genome comparisons. J Bacteriol. 2006 Apr;188(7):2309-24.

Howe D, Heinzen RA. Coxiella burnetii inhabits a cholesterol-rich vacuole and influences cellular cholesterol metabolism. Cell Microbiol. 2006 Mar;8(3):496-507.

Shannon JG, Howe D, Heinzen RA. Virulent Coxiella burnetii does not activate human dendritic cells: role of lipopolysaccharide as a shielding molecule. Proc Natl Acad Sci U S A. 2005 Jun 14;102(24):8722-7.

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