A comparative study of the timecourse of the expression of the thermo-inducible HSP70 gene in clinical and environmental isolates of Aspergillus fumigatus

Abstract

The internal environment within animals or humans provides different conditions to invading saprophytic fungal pathogens, requiring the differential regulation of genes in comparison to environmental conditions. Understanding the mechanisms by which pathogens regulate genes within the host may be key in determining pathogen behavior within the host and may additionally facilitate further investigation into novel therapeutic agents. The heat shock protein (HSP) 70 gene and its associated proteins have been frequently reported to be among the most highly expressed and dominant proteins present within various locations at physiological temperatures. The present study examined relative gene expression levels of the HSP70 gene in Aspergillus fumigatus isolates from both clinical and environmental origins, at a range of temperature points (20, 30, 37 and 42 degrees C) over five days, using reverse transcriptionquan-titative polymerase chain reaction, comparing with a standard A. fumigatus strain incubated at 25 degrees C. The results indicated a differential gene expression pattern for the environmental and clinical isolates. During the five days, the HSP70 expression levels in the clinical samples were higher than in the environmental samples. However, the difference in the expression levels between the two groups at 42 degrees C was reduced. The mean HSP70 expression level over the five incubation days demonstrated a gradual and continual increasing trend by temperature elevation in both groups at 30, 37 and 42 degrees C, however, at 20 degrees C both groups demonstrated reduced expression. The temperature shift from 20 to 42 degrees C resulted in HSP70 induction and up to a 10- and 8.6-fold change in HSP70 expression levels on the fifth day of incubation in the clinical and environmental groups, respectively. In conclusion, incubation at 37 and 42 degrees C resulted in the highest expression levels in both experimental groups, with these temperature points important for the induction of HSP70 expression in A. fumigatus.