The postdoctoral projects within the Postdoc Network RegenerAging focus on aging induced impairments of signaling pathways that control stem cell function and regeneration, involving different stem cells and tissue types and a spectrum of genetic and innovative animal models.
Peripheral nerves (PNs) have a remarkable capacity to regenerate, which depends on both axonal regrowth and dedifferentiation of Schwann cells into remyelinating cells. Aging strongly impairs PN maintenance and regeneration but the molecular causes of this are poorly understood.
We and others showed that the Ras-MAP kinase pathway represents a central component orchestrating PN regeneration. Our work revealed that the actin-cytoskeleton linker protein Ezrin provides a regulatory scaffold for Ras activation. We observed that Schwann cells activate Ezrin during PN regeneration. The main aim of this project is to delineate aging-induced alterations of the Ezrin/Ras pathways and its contribution to aging associated impairments in PN homeostasis and regeneration.
Since bone marrow PN were shown to provide a niche for HSCS, we will collaborate with project 3 (Rudolph/Hochhaus/Passegue) to study whether Schwann cells in PNs of the bone marrow contribute to maintain HSC quiescence. With project 4 (Englert/González-Estévez/Davidson) we will analyze the role of mTOR in Schwann cell behavior and potentially study candidate pathways that are identified on aging in the short lived killifish N. furzeri.
Helen Morrison (FLI)
Christian Hübner, Director of the Institute for Human genetics, Jena University Hospital (UKJ)
Alison Lloyd, University College London (UCL)
The pentameric acetylcholine receptor (AChR) on skeletal muscle fibers decodes the contraction signal from the motor neuron. Our previous work revealed that Rer1 is a sorting receptor of the early secretory pathway assuring that only fully assembled multimeric membrane protein complexes leave the ER. We showed that Rer1 is co-upregulated with AChR subunits during myogenesis and is involved in the assembly of AChR. Reduced Rer1 expression results in reductions in AChR levels, muscle fiber diameters, and neuromuscular junctions. Our preliminary data show that Rer1 expression is reduced in muscles of aging mice.
Our working hypothesis indicates that Rer1 is essential for regeneration of skeletal muscle and its age dependent down-regulation contributes to impairments in skeletal muscle maintenance during aging. The project will pave the way for future analysis, for example compound screens to increase Rer1 protein levels as potential future therapeutic approach against aging-associated muscle decline.
The regulatory genes identified in HSC in project 3 (Rudolph/Hochhaus/Passague) will be tested in muscle regeneration, exploring the hypothesis that common pathways regulate quiescence in both organs. Our project will profit from the work of project 1 (Morrison/Hübner/Lloyd) because of the close relationship and interdependence between muscle and motor neuron. Project 4 (Englert/Gonzalez-Estevez/Davidson) will profit from our expertise on wnt signaling upstream of mTOR. Together with project 5 (Wang/Kestler/Behrens) we will analyze the role of ATR/NBS1 in ER stress in aging neurons.
Christoph Kaether, Julia von Maltzahn (FLI)
Julian Grosskreutz, Jena University Hospital (UKJ)
Markus Rüegg, Biozentrum, University of Basel
Hematopoietic stem cells (HSCs) are maintained in quiescent state, which is required to maintain functional HSCs also during aging. Previous work from our team members revealed that telomere dysfunction induces alteration in the stem cell environment that lead to defects in the maintenance of HSC quiescence resulting in impairments in stem cell functionality with aging.
The main aim of our project is to identify genes that control HSC quiescence using our previously established protocols for in vivo iRNA screens. We will determine the long-term effects of candidate genes on HSCs aging in genetically engineered mouse models and also employ newly established mouse models for the analysis of HSC differentiation during aging. The studies will provide insight into the control of HSC quiescence and its role in aging of the hematopoietic system.
We will collaborate with project 2 (Kaether/von Maltzahn/Grosskreutz/Rüegg) to study the role of quiescence regulating genes in muscle stem cell aging, with project 4 (Englert/González-Estévez/Davidson) to study its role in stem cell maintenance in planarian and regeneration in fish models of aging.
K. Lenhard Rudolph (FLI)
Andreas Hochhaus, Chairman of the Department of Hematology and Oncology, Jena University Hospital (UKJ)
Emmanuelle Passegue, University of California San Francisco (UCSF)
The kinase Target of Rapamycin (mTOR) represents a major signaling hub regulating stem cell maintenance, regeneration, and organismal lifespan by controlling various processes such as protein translation and autophagy among others. It remains incompletely understood which mTOR dependent signals influence the functional decline of stem cells and regeneration during aging.
We and others found that mTOR regulates planarian stem cell function and regeneration. In addition, WT1 was shown to regulate components of the mTOR pathway. A short-lived killifish model (N. furzeri) was developed to study age-dependent impairments in regeneration.
We will use these innovative animal models to conduct in vivo screens to identify mTOR target genes that regulate the maintenance of pluripotent stem cells (planaria) and to determine the influence of candidate genes on aging-associated impairments in regeneration of the fin and/or kidney (N. furzeri).
Together with project 3 (Rudolph/Hochhaus/Passegue) we will study the impact of genes that control stem cell quiescence on aging of N. furzeri. With project 1 (Morrison/Hübner/Lloyd) we will analyze whether components of the mTOR pathway that impair stem cell function and regeneration in planaria also impact axonal regeneration. Together with the bioinformatics expert Hans Kestler, Co-Supervisor of project 5 (Wang/Kestler/Behrens), we will mathematically model aging induced impairments in mTOR signaling that impact regeneration and stem cell maintenance.
Christoph Englert (FLI)
Cristina González-Estévez (FLI)
Alan Davidson, University of Auckland (UoA)
ATR (ATM- and Rad3-related) and NBS (Niemegen Breakage Syndrome) are key enzymes in the DNA damage response (DDR). Mutations in these genes induce degenerative diseases involving different levels of neurological deficits.
We found that while ATR deletion depletes both proliferating and postmitotic cells, NBS1 deletion only caused lethality in replicating progenitors possibly due to the unique function of NBS in repressing replication intermediates. We hypothesize that ATR and NBS1 play a role in regulating expression of genes in non-proliferating cells independent of their function in DDR. To test this hypothesis we focus on following main aims:
- Delineate the involvement of ATR and NBS1 in transcription regulation in Purkinje cells or cortical neurons (bioinformatics analysis of gene arrays of conditional knockout vs. wildtype mice, analysis of transcriptional co-regulators)
- Functional analysis of ATR and/or NBS regulated candidate genes in maintaining adult neurons
Together, these studies will help to understand the function of classical DDR molecules in neurodegeneration and whether these circuits could represent new target for therapies aiming to improve the maintenance of adult neurons.
Rad50 (the NBS1 partner) and ATR have been shown to be important for the development of the hematopoietic system. We will collaborate with project 3 (Rudolph/Hochhaus/Passegue) to study the non-DDR function of NBS1 and ATR in aged HSC cells. We will collaborate with project (Kaether/von Maltzahn/Grosskreutz/Rüegg) to study whether NBS1 and ATR in ER stress response in neural cells during aging.
Zhao-Qi Wang (FLI)
Hans A. Kestler (FLI/Ulm University)
Axel Behrens, Cancer Research UK London Laboratoy (CR-UK)