H. Innate immune responses to DNA damage in aging-associated vascular disease

Professor Björn Schumacher

Rationale and aims

DNA damage accumulation causally contributes to the functional decline associated with aging. Congenital defects in nucleotide excision repair (NER) lead to highly skin cancer prone Xeroderma pigmentosum (XP) or accelerated aging in Cockayne syndrome (CS) patients when global-genome (GG-) NER or transcription-coupled (TC-) NER is affected, respectively (Edifizi & Schumacher, 2015). CS patients display growth retardation and premature aging, and typically die between the ages of 12 and 16 from atherosclerosis.

Current state of research and own preliminary work

Figure 1: In C. elegans, persistent CpG-rich DNA induces an innate immune response that, when chronic, causes loss of proteostasis in the endoplasmic reticulum. This dysfunction ultimately leads to tissue degeneration, similar to the outcomes of chronic inflammation in higher organisms. Treatment with low doses of tunicamycin and N-acetylglucosamine (box – Therapeutic Interventions), both of which promote proteostasis, alleviate the stress on the endoplasmic reticulum leading to tissue maintenance – even during the ongoing immune response.

A better understanding of the pathomechanisms triggering such premature functional deterioration has been severely impeded by the vast complexity of NER syndromes in humans and the respective mammalian models. Therefore, to advance our current rudimentary understanding of the underlying molecular and cellular mechanisms of DNA damage-driven atherosclerosis, and potentially, other vascular pathologies, we have established the genetically traceable nematode C. elegans as a model system reflecting the distinct outcomes of NER mutations (Lans et al, 2010; Mueller et al, 2014). Importantly, we have previously determined that CS mouse models show inflammatory signaling reminiscent of natural aging (Schumacher et al, 2008). Inflammatory responses to DNA damage have been increasingly recognized as important patho-mechanisms of tissue damage, resulting from DNA damage accumulation in premature and normal aging. We have also determined that similar to mammals, DNA damage in C. elegans triggers innate immune responses and uncovered that these responses orchestrate systemic adaptations to genome instability (Ermolaeva et al, 2013).

Experimental approach and work program

Given the strong link between NER defects and premature aging, the prevalence of atherosclerosis in CS patients, and the inflammatory signature in (premature) aging mouse models, we propose that better understanding the underlying mechanisms through which DNA damage leads to inflammation will provide new insights into future therapeutic strategies to combat vascular pathologies. To this end, we will employ C. elegans to ascertain how innate immune signaling is activated upon the presence of DNA damage. We will specifically investigate MAPK signaling pathways as evolutionary conserved immune signaling activators. We have recently uncovered how innate immune signaling leads to an inflammation-like phenotype in C. elegans that is reminiscent of tissue damage observed in mammals (Williams and Schumacher, unpublished). We will now determine how chronic DNA damage in NER-deficient nematodes triggers tissue degeneration and will assess the role of innate immune signaling by employing available genetic mutants in MAPK signaling components that allow us to genetically activate and inactive innate immune signaling.

We recently determined that the inflammation-like tissue degeneration upon chronic innate immune activation leads to protein folding stress in the endoplasmic reticulum (ER), likely due to the chronic production of secreted innate immune peptides that are produced in the ER before they are passaged through the Golgi apparatus for secretion. The chronic innate immunity fails to induce the ER unfolded protein response (UPRER). In contrast, when we apply low dose tunicamycin that induces the UPRER or treat the animals with hexosamine that leads to augmented ER protein folding activity (Denzel et al, 2014), we could systemically alleviate the inflammation-associated tissue disruption. We propose that UPRER activation could resolve inflammation-associated protein folding stress and thus antagonize the detrimental consequences of chronic inflammation. We will determine the mechanistic links between innate immune activity and ER stress by genetic analysis following of UPRER and the production of innate immune peptides upon DNA damage as well as upon cytosolic detection of CpG-rich DNA that we established to trigger an innate immune response in C. elegans. Within the consortium, we will validate whether low dose tunicamycin or hexosamine treatment might resolve the chronic inflammation associated with mammalian vascular disease models. We will systematically test hypotheses and validate our findings in mammalian disease models, thus directly benefitting from the synergisms of this consortium, to explore functional conservation of innate immune responses to DNA damage and assess their role in vascular remodeling.

Potential future therapeutic implications

Our project will open new opportunities for therapeutic targeting of DNA damage driven inflammatory signaling with the aim to prevent aging-associated vascular dysfunction.

Added value through collaborations within the CCRC

This project will provide further profound insights into the fundamental mechanisms of inflammatory responses that are driven by the gradual accumulation of DNA damage with aging. Given the nuclear affinity of leukocyte peroxidases and DNA damage by reactive oxygen species, the current project will link the research projects of the Papantonis (nuclear translocation) and Baldus (MPO) groups. We will test the connection between DNA damage signaling and glomeruli dysfunction together with the Benzing group and validate links to inflammatory signaling with the Pasparakis group. Together with the Rosenkranz group, we will investigate DNA damage signaling in macrophages and during inflammation and with the Rudolph group we will assess MAPK signaling in inflammatory responses. Proteomics of the DNA damage response and genomics for detecting innate immune gene expression will be performed with the core facilities (C. Freese / M. Krüger and P. Nürnberg). PhD / MD students will gain access to model system genetics and their relevance for understanding the biology of aging-associated inflammation.