CDFD :: Fungal pathogenesis

marked increase in the number of patients with AIDS and other immuno-compromise in recent years has resulted in the emergence of fungi as predominant human pathogens all over the world. Candida spp. are the leading cause of disseminated fungal infections in neonates (premature infants), immune-compromised patients, diabetic and post-operative patients. Although Candida albicans is still the major culprit responsible for about 60% of these infections, systemic infections due to the non-albicans species of Candida such as C. glabrata, C. krusei, C. tropicalis etc. have increased significantly in the last two decades. In fact C. glabrata is now the second most common yeast pathogen found in BSI after C. albicans accounting for about 16% of total Candida BSIs. C. glabrata is a haploid budding yeast and is closely related to the model yeast Saccharomyces cerevisiae. Long-term goals of our laboratory are aimed towards the better understanding of the pathogenesis of C. glabrata. Despite its similarity to S. cerevisiae and the lack of common virulence traits such as hyphae formation and secretion of proteolytic activity, C. glabrata can establish itself as a successful pathogen under appropriate host conditions. Although some pre-disposition in the patients appears to be an important factor in most of the Candida infections reported to date, questions remain unanswered regarding the intrinsic properties that make commensal yeasts potential pathogens. Survival in-vivo is a complex multifactorial process requiring the co-ordination of several responses such as the ability to survive the nutrient poor host environment, the ability to evade the host immune response, the ability to develop resistance to anti-fungal drugs etc. Our lab is trying to better understand the pathogenesis of C. glabrata, by focusing on some of these responses using a combination of genetics, molecular biology and cell culture screens. Our immediate interests lie mainly in three different areas of C. glabrata biology. The first involved the study of host-pathogen interactions using mammalian macrophage cell lines and the second is to understand the intrinsic resistance of C. glabrata towards the most widely used anti-fungal drug, fluconazole. Thirdly, we are trying to decipher the role of a family of aspartyl proteases in the patho-biology of C. glabrata.

Project 1: Functional genomic analysis of C. glabrata-macrophage interactions
To study the molecular interactions of C. glabrata with macrophages which constitute the first line of host defense against this pathogenic yeast, we are using an in-vitro system comprised of murine macrophage like cell line J774A.1. One of the current projects involves the identification and characterization of the factors that are required for survival in-vivo using a combination of mutant screens, transcriptional profiling analysis and cell biology approaches

Project 2: Innate resistance of C. glabrata towards fluconazole
The second aspect of our research involves the study of fluconazole resistance in C. glabrata. A major clinical challenge in treating C. glabrata infections is the high innate resistance of this yeast towards the most commonly used anti-fungal drug, fluconazole. One of the first steps towards developing new combinatorial anti-fungal agents is a better understanding of C. glabrata's response to fluconazole. Keeping this in mind, a project in the lab is focused on a genome-wide screen for mutants with altered fluconazole susceptibility profiles using a high throughput strategy whereby pools of 96 mutants will be screened at once.

Project 3: Role of aspartyl proteases in the patho-biology of C. glabrata
Our recent transcriptional profiling analysis of macrophage internalized C. glabrata cells in an in-vitro system shows an up-regulation of seven members of a multi-gene family that codes for a family of cell-surface associated, glycosylphosphatidylinositol-linked aspartyl proteases (yapsins). A part of our research is centered around a comprehensive analysis of the role of this yapsin gene family in the pathogenesis of C. glabrata via a combination of molecular biology, genetics and biochemical approaches.