Studies of replicative and chronological lifespan in Saccharomyces cerevisiae have advanced understanding of longevity in all eukaryotes. Chronological lifespan in this species is defined as the age-dependent viability of nondividing cells. To date this parameter has only been estimated under calorie restriction, mimicked by starvation. Because postmitotic cells in higher eukaryotes often do not starve, we developed a model yeast system to study cells as they age in the absence of calorie restriction. Yeast cells were encapsulated in a matrix consisting of calcium alginate to form ?3 mm beads that were packed into bioreactors and fed ad libitum. Under these conditions cells ceased to divide, became heat shock and zymolyase resistant, yet retained high fermentative capacity. Over the course of 17 d, immobilized yeast cells maintained >95% viability, whereas the viability of starving, freely suspended (planktonic) cells decreased to <10%. Immobilized cells exhibited a stable pattern of gene expression that differed markedly from growing or starving planktonic cells, highly expressing genes in glycolysis, cell wall remodeling, and stress resistance, but decreasing transcription of genes in the tricarboxylic acid cycle, and genes that regulate the cell cycle, including master cyclins CDC28 and CLN1. Stress resistance transcription factor MSN4 and its upstream effector RIM15 are conspicuously up-regulated in the immobilized state, and an immobilized rim15 knockout strain fails to exhibit the long-lived, growth-arrested phenotype, suggesting that altered regulation of the Rim15-mediated nutrient-sensing pathway plays an important role in extending yeast chronological lifespan under calorie-unrestricted conditions.
Bile salts exhibit potent antibacterial properties, acting as detergents to disrupt cell membranes and as DNA-damaging agents. Although bacteria inhabiting the intestinal tract are able to resist biles antimicrobial effects, relatively little is known about how bile influences virulence of enteric pathogens. Escherichia coli O157:H7 is an important pathogen of humans, capable of causing severe diarrhea and more serious sequelae. In this study, the transcriptome response of E. coli O157:H7 to bile was determined. Bile exposure induced significant changes in mRNA levels of genes related to virulence potential, including a reduction of mRNA for the 41 genes making up the locus of enterocyte effacement (LEE) pathogenicity island. Bile treatment had an unusual effect on mRNA levels for the entire flagella-chemotaxis regulon, resulting in two- to four-fold increases in mRNA levels for genes associated with the flagella hook-basal body structure, but a two-fold decrease for "late" flagella genes associated with the flagella filament, stator motor, and chemotaxis. Bile salts also caused increased mRNA levels for seventeen genes associated with iron scavenging and metabolism, and counteracted the inhibitory effect of the iron chelating agent 2,2-dipyridyl on growth of E. coli O157:H7. These findings suggest that E. coli O157:H7 may use bile as an environmental signal to adapt to changing conditions associated with the small intestine, including adaptation to an iron-scarce environment.
It is widely held that exposure to pathogens such as fungi can be an agent of comorbidity, such as exacerbation of asthma or chronic obstructive pulmonary disease. Although many studies have examined allergic responses to fungi and their effects on pulmonary function, the possible pathologic implications of the early innate responses to fungal pathogens have not been explored. We examined early responses to the atypical fungus Pneumocystis in two common strains of mice in terms of overall immunological response and related pathology, such as cell damage and airway hyperresponsiveness (AHR). We found a strong strain-specific response in BALB/c mice that included recruitment of neutrophils, NK, NKT, and CD4 T cells. This response was accompanied by elevated indicators of lung damage (bronchoalveolar lavage fluid albumin and LDH) and profound AHR. This early response was absent in C57BL/6 mice, although both strains exhibited a later response associated with the clearance of Pneumocystis. We found that this AHR could not be attributed exclusively to the presence of recruited neutrophils, NKT, NK, or CD4 cells or to the actions of IFN-? or IL-4. However, in the absence of STAT6 signaling, AHR and inflammatory cell recruitment were virtually absent. Gene expression analysis indicated that this early response included activation of several transcription factors that could be involved in pulmonary remodeling. These results show that exposure to a fungus such as Pneumocystis can elicit pulmonary responses that may contribute to morbidity, even without prior sensitization, in the context of certain genetic backgrounds.
Many chronic diseases, such as non-healing wounds are characterized by prolonged inflammation and respond poorly to conventional treatment. Bacterial biofilms are a major impediment to wound healing. Persistent infection of the skin allows the formation of complex bacterial communities termed biofilm. Bacteria living in biofilms are phenotypically distinct from their planktonic counterparts and are orders of magnitude more resistant to antibiotics, host immune response, and environmental stress. Staphylococcus aureus is prevalent in cutaneous infections such as chronic wounds and is an important human pathogen.
Immune-reconstitution after highly active antiretroviral therapy (HAART) is often incomplete, and some HIV-infected individuals fail to regenerate type-I interferon (IFN)-producing pDCs. We recently demonstrated that during Pneumocystis (PC) infection in CD4 T cell-competent mice the absence of type-I IFN signaling results in chronic pulmonary inflammation and fibrosis despite clearance. Because the mechanisms involved are poorly understood, we further characterized the role of type-I IFN signaling in immune responses to PC. We show that type-I IFN signaling around day 7 postinfection is critical to the outcome of inflammation. Microarray analysis of pulmonary CD11c(+) cells revealed that at day 7 post infection, wild-type cells up-regulated type-I IFN-responsive genes as well as SOCS1, which is a critical negative-regulator of type-I IFN and IFN-gamma signaling. This was associated with an eosinophilic lung inflammation, PC clearance, and complete restitution. However, pulmonary CD11c(+) cells from IFNAR(-/-) mice demonstrated increased tumor necrosis factor (TNF)-alpha production and lacked SOCS1-induction at day 7. This was followed by a transient lymphocytic and IFN-gamma response before switching to a chronic eosinophilic inflammation of the lung. Early neutralization of TNF-alpha did not prevent chronic inflammation in IFNAR(-/-) mice, but treatment with an anti-IFN-gamma antibody did. We propose that during PC lung infection type-I IFNs induce SOCS1-associated regulatory mechanisms, which prevent excessive IFN-gamma-mediated responses that cause chronic lung damage. Therefore, partial immune-reconstitution in AIDS, attributable to reduced type-I IFN actions, might disrupt regulatory aspects of inflammation, causing unexplained chronic pulmonary complications as seen in some patients during HAART.
We have developed a method for preparing high-quality total RNA from Ca-alginate-encapsulated Saccharomyces cerevisiae that is suitable for microarray analysis. Encapsulated cells were harvested from immobilized cell reactors and flash-frozen in liquid nitrogen. Following low-temperature mechanical disruption, cells were freed from Ca-alginate by reverse ionotropic gelation and purified by centrifugation, and then total RNA was extracted using hot acid phenol. The yield and quality of the RNA were consistently high; the RNA was free of contaminating alginate, and in microarray analysis it performed as well as RNA isolated from planktonic cells.
Staphylococcus aureus biofilms are associated with chronic skin infections and are orders of magnitude more resistant to antimicrobials and host responses. S. aureus contains conserved nonribosomal peptide synthetases that produce the cyclic dipeptides tyrvalin and phevalin (aureusimine A and B, respectively). The biological function of these compounds has been speculated to be involved in virulence factor gene expression in S. aureus, protease inhibition in eukaryotic cells, and interspecies bacterial communication. However, the exact biological role of these compounds is unknown. Here, we report that S. aureus biofilms produce greater amounts of phevalin than their planktonic counterparts. Phevalin had no obvious impact on the extracellular metabolome of S. aureus as measured by high-performance liquid chromatography-mass spectrometry and nuclear magnetic resonance. When administered to human keratinocytes, phevalin had a modest effect on gene expression. However, conditioned medium from S. aureus spiked with phevalin amplified differences in keratinocyte gene expression compared to conditioned medium alone. Phevalin may be exploited as potential biomarker and/or therapeutic target for chronic, S. aureus biofilm-based infections.
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