Hyphae are the invasive forms of filamentous fungi such as Aspergillus spp. and are the reason for the clinical disease we see in patients. The exact molecular mechanism of hyphal development, beginning from condial germination to hyphal extension and invasion, is not completely understood. All antifungals that have activity against A. fumigatus ultimately function to limit hyphal growth. We have shown through countless studies that the calcineurin pathway, a conserved cell signaling system present in all eukaryotes, is a central regulator of hyphal growth. Our work in this area focuses on the specific molecular mechanisms and downstream effectors that calcineurin controls in order to regulate hyphal growth and disease.
Calcineurin control over hyphal septation and cell wall biosynthesis
Septa are crucial in hyphal growth as they are the natural dividers in the growing hyphae, critical for continued growth and compartmentalization of cellular function. We were the first group to establish that both calcineurin subunits are stably present in the developing A. fumigatus hyphal septum, sitting as disks on each side of the septum. Calcineurin deletion mutants create septal defects and miscues in cellular metabolism. The hyphal septa is also a prime example of how important cell wall biosynthesis is for the organism. The cell wall serves as the leading point for the growing and invading hyphae as well as the first contact point with the host. The cell wall functions as both a structural component to hold the cell together as well as a scaffold for countless cellular functions. We have shown that calcineurin controls cell wall metabolism, and now we are working on uncovering the exact molecular mechanisms of regulation.
Hsp90 regulation over hyphal growth
Heat-shock protein 90 (Hsp90) is a molecular chaperone in eukaryotes and calcineurin is a major client protein of this chaperone. We have demonstrated the importance of Hsp90 control related to A. fumigatus antifungal resistance as well as stress response following antifungal exposure. Understanding the exact links between Hsp90 and calcineurin will be helpful to fully comprehend the wealth of interactions and functions these two pathways play in A. fumigatus growth and disease.
The currently available calcineurin inhibitors (FK506, Cyclosporine A) are extremely active against A. fumigatus, yet immunosuppressive in the host as they were designed to suppress IL-2 secretion to prevent graft rejection in patients. We are working on novel targeting regions and chemical approaches to develop fungal-specific calcineurin inhibitors that still inhibit fungal calcineurin, but have limited or no effect on mammalian (especially human) calcineurin.
Newer molecular methods to diagnose invasive aspergillosis
The timely and accurate diagnosis of invasive aspergillosis is complicated and often delayed. While the current best approach, the galactomannan double-sandwich ELISA assay, has greatly helped clinicians with a non-invasive assay, it has several critical sensitivity as well as specificity deficits. Our laboratory, in collaboration with several different colleagues, are working on novel molecular diagnostic tools harnessing single-chain antibodies as well as a secondary methodology using chromatography. To test this we utilize several different animal models of invasive aspergillosis.
The Steinbach lab has several main areas of research focus, each encompassing multiple projects and funded studies. The lab is extensively funded through numerous NIH grants (three R01s, two R21s, and a P01) as well as several foundation and philanthropic grants.
Duke University Medical Center
Department of Pediatrics - Infectious Diseases Department of Molecular Genetics & Microbiology
427 Jones Building, Research Drive, Duke University Medical Center, Durham, NC 27710 | Tel: 919 681 2613