1. Research Background:

Tauopathies are ageing-related neurodegenerative diseases characterized by accumulation of tau in neurons in neurofibrillary tangles (NFTs). Primary tauopathies like for example Frontotemporal dementia (FTD) can developdue to mutations in the tau gene, which leads to the build-up of tau aggregates in the patient’s brain, loss of brain volume as a result of neuronal cell death and subsequent cognitive decline. Secondary tauopathies do not only contain tau aggregates, but for example additional extracellular aggregates of amyloid-beta (Aβ) in amyloid plaques as seen in Alzheimer’s disease (AD), the most prevalent tauopathy. Due to the increase in life expectancy, the number of people with AD is expected to rise over 100 million by 2050, but to date, no effective treatment not to mention cure does exist for AD or other tauopathies and the underlying mechanisms still remain elusive. One common characteristic of all tauopathies is the chronic neuroinflammation present in the brains of these patients. In the innate immune system of the brain, microglia are the first line of defense. Microglia emerged as central players in the development and progression of tauopathies over the last years when several mutations in microglia-related genes were identified as risk-factors in AD and other diseases. Modifying neuroinflammation could prove a valuable treatment option in the future, but the contribution of the immune system to mechanisms in AD and specifically the effects of microglial cell death and senescence remain poorly understood.

2. Research questions addressed by the group:

While neuroinflammation is widely accepted as a contributor to AD and other tauopathies, microglial cell death in neurodegenerative diseases in general attracted little attention to date. However, work from the past years showed that AD and FTD patients as well as respective mouse models present with activation of the NLRP3 inflammasome in microglia^1–3, a protein complex that induces pyroptotic cell death. The Ising lab is interested in further elucidating the role of pyroptotic cell death in tauopathies by investigating the role of genes that are involved in this regulated cell death pathway. Furthermore, we aim to characterize other types of microglial cell death and investigate theircause and regulation. Finally, we want to elucidate the effects microglial cell death has on intraneuronal tau pathologies, neuronal loss and subsequent memory deficits. Another topic of interest in the lab is (microglial) senescence, a cellular state leading to expression of a distinctive partially pro- inflammatory secretory profile and resistance to cell death. Recently, the occurrence of glial senescence was identified in a tauopathy mouse model and removal of these cells alleviated tau pathology⁴. However, it remains unclear what causes glial senescence and how exactly it affects intraneuronal tauaccumulation. To shed light on these questions, we are interested in the identification of the molecular switch that drives a microglia cell either into senescence or cell death. Further, we investigate how cellular senescence is affected by tau itself and how the senescence-associated secretory profile is involved in the progression of taupathologies.

3. Possible projects:

Project 1: Role of the immunoreceptor CD300lf in tauopathies
Recently, we provided evidence that the assembly and activation of the inflammasome can be induced by tau and that a Nlrp3-knockout reduces progression of tau pathology and improves cognition in tau-transgenic Tau22 mice, a tauopathy model. Interestingly, we found that genetic loss of NLRP3 increased levels of Cd300lf in the brains of Tau22 mice². CD300lf is an inhibitory immunoreceptor present on microglia. CD300lf overexpression was shown to be neuroprotective in a model of acute brain injury⁵ and mice resistant to cerebral malaria had more microglial CD300lf in conjunction with an inhibited inflammatory response⁶. In line with this, Cd300lf-knockout (KO) increased disease severity in an autoimmune demyelination model⁷ and Cd300lf-KO mice showed depressive like-behavior, which was increased after an immune challenge⁸. However, nothing is known about the role of CD300lf in tauopathies, which will therefore be explored in detail in this project with a focus on the receptor’s effects on pyroptotic cell death.

Project 2: Effects of microglial senescence on neurons
One of the main risk factors for late-onset AD is ageing, a process tightly linked to cellular senescence and senescent microglia have been detected in the aged brain and in neurodegenerative diseases. Senescent cells create a pro-inflammatory environment due to the release of the senescence-associated secretory profile (SASP), with which they potentially contribute to the progression of the diseases. Research over the last decades revealed that senescence can be triggered by several stressors including metabolic stress and DNA damage⁹. Chronic stressas it occurs in ageing and neurodegenerative diseases can also be a driver for cellular senescence. However, cellular senescence is a complex process resulting in unique quantitative and qualitative features based on the cell type and senescence-inducer¹⁰. In this project, a disease-specific cellular senescence model for microglia will be used to investigate the involvement of oxidative stress and the role of the SASP in neuronal dysfunction and tau pathology.

4. Applied Methods and model organisms:

In the Ising lab, we combine cell culture work with analyzing tauopathy mouse models. A PhD candidate in the lab can learn how to generate primary microglia cultures from mice as well as techniques to isolate and analyzebrains from adult mice. Furthermore, we aim to establish a brain slice culture model to look at interactions between different cell types. Cells as well as brain tissue are analyzed by Western Blot, ELISA, quantitative PCR (qPCR), flow cytometry, immunostainings and specific cell death assays as well as proteomic approaches. Microglia are isolated from adult animals before analysis by qPCR or flow cytometry. In addition, we will establish a memory test to be used for our tauopathy mouse model.

5. Desirable skills and qualifications:

We are looking for a highly motivated candidate with a scientific interest in neuroinflammation and cell death. The successful applicant should be a team-oriented individual with good written and verbal communication skills in English. The applicant should have experience with cell culture and basic molecular techniques such as PCR and Western Blot. The willingness to work with mice is mandatory and a previous participation in a FELASA-certified course is a plus, but the certificate can also be obtained in the project.

6. References:

1. Heneka, M. T. et al. NLRP3 is activated in Alzheimer’s disease and contributes to pathology in APP/PS1 mice. Nature 493, 674–678 (2013).
2. Ising, C. et al. NLRP3 inflammasome activation drives tau pathology. Nature 575, 669– 673 (2019).
3. Venegas, C. et al. Microglia-derived ASC specks cross-seed amyloid-β in Alzheimer’s disease. Nature 552, 355–361 (2017).
4. Bussian, T. J. et al. Clearance of senescent glial cells prevents tau-dependent pathology and cognitive decline. Nature 562, 578–582 (2018).
5. Peluffo, H. et al. Overexpression of the immunoreceptor CD300f has a neuroprotective role in a model of acute brain injury. Brain Pathol. Zurich Switz. 22, 318–328 (2012).
6. Keswani, T. et al. Expression of CD300lf by microglia contributes to resistance to cerebral malaria by impeding the neuroinflammation. Genes Immun. 21, 45–62 (2020).
7. Xi, H. et al. Negative regulation of autoimmune demyelination by the inhibitory receptor CLM-1. J. Exp. Med. 207, 7–16 (2010).
8. Lago, N. et al. CD300f immunoreceptor is associated with major depressive disorder and decreased microglial metabolic fitness. Proc. Natl. Acad. Sci. U. S. A. 117, 6651–6662 (2020).
9. Wiley, C. D. & Campisi, J. The metabolic roots of senescence: mechanisms and opportunities for intervention. Nat. Metab. 3, 1290–1301 (2021).
10. Coppé, J.-P. et al. Senescence-associated secretory phenotypes reveal cell- nonautonomous functions of oncogenic RAS and the p53 tumor suppressor. PLoS Biol. 6, 2853–2868 (2008).