Biology subjects

Jens Rolff

Publications and source records attributed to Jens Rolff.

3 recordsLinked to original sources

bioRxiv2016

EARLY INFLAMMATION, IMMUNOPATHOLOGY AND AGING

Age-related diseases are often attributed to immunopathology, which results in self-damage caused by an inappropriate inflammatory response. Immunopathology associated with early-life inflammation also appears to cause faster ageing, although we lack direct experimental evidence for this association. To understand the interactions between ageing, inflammation and immunopathology, we used the mealworm beetle Tenebrio molitor as a study organism. We hypothesized that phenoloxidase (PO), an important immune effector in insect defence, may impose substantial immunopathological costs by causing tissue damage, in turn accelerating aging. In support of this hypothesis, we found that RNAi knockdown of PO transcripts in young adults reduced inflammation-induced autoreactive tissue damage to Malpighian tubules, and increased adult lifespan. Our work thus provides empirical evidence for a causative link between immunopathological costs of early life inflammation and faster ageing. We also reasoned that if natural selection weakens with age, older individuals should display increased immunopathological costs associated with an immune response. Indeed, we found that while old infected individuals cleared infection faster than young individuals, they displayed exacerbated immunopathological costs and higher post-infection mortality. RNAi-mediated knockdown of PO response reduced immunopathology in older beetles and increased their lifespan after infection. This is the first demonstration of a direct role of immunopathological consequences of immune response during ageing in insects. Our work is also the first report that highlights the pervasive role of immunopathology under diverse contexts of aging and immune response.

Evolutionary Biology↗

bioRxiv2015

Cationic Peptides Facilitate Iron-induced Mutagenesis in Bacteria

Pseudomonas aeruginosa is the causative agent of chronic respiratory infections and is an important pathogen of cystic fibrosis patients. Adaptive mutations play an essential role for antimicrobial resistance and persistence. The factors that contribute to bacterial mutagenesis in this environment are not clear. Recently it has been proposed that cationic antimicrobial peptides such as LL-37 could act as a mutagen in P. aeruginosa. Here we provide experimental evidence that mutagenesis is the product of a joint action of LL-37 and free iron. By estimating mutation rate, mutant frequencies and assessing mutational spectra in P. aeruginosa treated either with LL-37, iron or a combination of both we demonstrate that mutation rate and mutant frequency were increased only when free iron and LL-37 were present simultaneously. The addition of an iron chelator completely abolished this mutagenic effect, suggesting that LL-37 enables iron to enter the cells resulting in DNA damage by Fenton reactions. This was also supported by the observation that the mutational spectrum of the bacteria under LL-37-iron regime showed one of the characteristic Fenton reaction fingerprints: C to T transitions. Free iron concentration in nature and within hosts is kept at a very low level, but the situation in infected lungs of cystic fibrosis patients is different. Intermittent bleeding and damage to the epithelial cells in lungs may contribute to the release of free iron that in turn leads to generation of reactive oxygen species and deterioration of the respiratory tract, making it more susceptible to the infection.\n\nAuthor SummaryCationic antimicrobial peptides (cAMPs) are small proteins naturally produced by the immune system to limit bacterial growth mainly through pore formation in the membrane. It has recently been suggested that sub-inhibitory concentrations of cAMPs promote bacterial mutagenesis, similarly to antibiotics. However, we previously reported that cAMPs do not increase mutation rate and do not activate bacterial stress responses. Here we resolve this contradiction. We report that free iron in the culture medium increases mutagenesis in the presence of cAMPs. We show that sub-inhibitory concentrations of cAMPs facilitate entry of free iron into bacterial cells, where it interacts with hydrogen peroxide, thereby resulting in production of DNA-damaging reactive oxygen species and increased mutagenesis. Moreover, these results may have clinically-relevant implications: while very little free iron is normally present in healthy individuals, this is not the case in patients suffering from cystic fibrosis, where elevated bacterial mutagenesis promotes antibiotic resistance and contributes to persistence and severity of infection. Thus, an intervention aimed at reduction of free iron in the lungs could reduce the cAMPs-facilitation of iron-mediated mutagenesis; hence antibiotic resistance and pathoadaptation.

Microbiology↗

bioRxiv2015

Genomic signatures of experimental adaptation to antimicrobial peptides in Staphylococcus aureus

ObjectivesThe evolution of resistance against antimicrobial peptides has long been considered unlikely due to their mechanism of action, yet experimental selection with AMPs results in rapid evolution of resistance in several species of bacteria. Although numerous studies have utilized mutant screens to identify loci that determine AMP susceptibility, there is a dearth of data concerning the genomic changes which accompany experimental evolution of AMP resistance.\n\nMethodsUsing genome re-sequencing we analysed the mutations which arise during experimental evolution of resistance to the cationic AMPs iseganan, melittin and pexiganan, as well as to a combination of melittin and pexiganan, or to the aminoglycoside antibiotic streptomycin.\n\nResultsAnalysis of 17 independently replicated Staphylococcus aureus selection lines, including unselected controls, showed that each AMP selected for mutations at distinct loci. We identify mutations in genes involved in the synthesis and maintenance of the cell envelope. This includes genes previously identified from mutant screens for AMP resistance, and genes involved in the response to AMPs and cell-wall-active antibiotics. Furthermore, transposon insertion mutants were used to verify that a number of the identified genes are directly involved in determining AMP susceptibility.\n\nConclusionsStrains selected for AMP resistance under controlled experimental evolution displayed consistent AMP-specific mutations in genes which determine AMP susceptibility. This suggests that different routes to evolve resistance are favored within a controlled genetic background.

Microbiology↗