While cognitive impairment is common in peripheral diseases such as chronic kidney disease (CKD), mechanistic insights and effective therapies are lacking. Multiple toxins accumulating as a consequence of CKD have been identified, yet the consequences for cellular crosstalk in the brain and the mechanisms underlying the associated neuronal dysfunction remain largely elusive. In the case of CKD, more than 100 uremic toxins have been identified. Renal transplantation largely reverses the cognitive impairment associated with CKD, demonstrating that cognitive impairment in CKD can be reversed. This indicates that pharmaceutical approaches to target cognitive impairment in association with CKD may be feasible. However, it is unlikely that targeting a single toxin will be sufficient to combat neuronal dysfunction associated with peripheral diseases such as CKD, given the large number of toxins involved and since the pattern of accumulating toxins varies among affected patients. Rather than identifying single toxins, identifying a common mechanism inducing neuronal dysfunction and thus impairing cognition may identify new and feasible therapeutic approaches. One commonality of peripheral diseases such as liver or renal failure is sterile inflammation. Sterile inflammation has been linked with neurodegenerative diseases and associated cognitive impairment and inflammasome activation is one hallmark of chronic pathologies in the brain. Mutations in the
inflammasome component NLRP3 show clinical manifestations of cryopyrin- associated periodic syndromes (CAPS), which are characterized by skin rash, fever and joint pain. Further, abnormal and constant NLRP3 signaling has been associated with some chronic and degenerative diseases such as Alzheimer’s disease (AD), atherosclerosis, arthritis or cancer. A causative function of the NLRP3 inflammasome for neurodegenerative processes is supported by preclinical studies. These pre-clinical studies used whole body knock out mice to demonstrate that deficiencies of NLRP3, caspase-1 or the primary receptor for IL-1β, IL-1R1, protect mice from
neurodegenerative processes. While providing important insights into the role of the NLRP3-inflammasome in neurodegenerative processes, these studies did not identify the relevant cell types in which the inflammasome is activated, the mechanisms underlying inflammasome activation and the consequences thereof, e.g. for intracerebral cross-talk. In addition, whether sterile inflammation triggered by the NLRP3 inflammasome impairs cognition in the setting of primarily peripheral diseases
such as CKD remains unknown. To address these open questions, I used a mouse model of CKD, in which I detected NLRP3 inflammasome in brains. Interestingly, despite inflammasome activation in the brain, microglial caspase-1 deficiency did not improve cerebral inflammation and cognition in CKD mice. I identified noncanonical IL-1β maturation in microglia in CKD conditions, which was cathepsin c – caspase-8
mediated. Restoring K+ homeostasis in microglia or genetic inhibition of neuronal IL-1R1 signaling abolished CKD-induced cognitive impairment. Mechanistically, noncanonical IL-1β maturation and secretion from microglia promotes via IL-1R signaling cognitive impairment in neurons. This identifies a molecular mechanism of sterile CNS inflammation and the associated intercellular signaling pathway, which may be therapeutically amendable. Microglial K+ dyshomeostasis and
noncanonical microglial IL-1β maturation may be druggable targets in some forms of cognitive impairment.:Content 2
List of abbreviations 5
Graphical abstract 8
2 Introduction 9
2.1 Chronic kidney disease and cognition 11
2.2 Microglia cells 13
2.3 The inflammasome, potassium dyshomeostasis in brain cells and thallium autometallography 15
2.4 Sterile inflammation in neurodegenerative diseases 17
3 Aims of the study 19
4 Materials and Methods 20
4.1 Reagents 20
4.2 Mice 27
4.3 CKD mouse model (5/6 nephrectomy model) 30
4.4 Evans Blue extravasation assay 32
4.5 2-photon microscopy 32
4.6 Analysis of mice 33
4.7 In vivo interventions 33
4.8 Histology and immunohistochemical analysis 34
4.9 Cell culture 34
4.10 Dextran permeability assay 35
4.11 Thallium-AMG (TlAMG), ex vivo and in vitro 36
4.12 Protein extraction and Western blotting 38
4.13 IL-1β ELISA 38
4.14 Reverse Transcriptase Polymerase Chain Reaction (RT–PCR) 38
4.15 Proximity ligation assay (PLA) 39
4.16 Behavioral analysis 39
4.17 Cathepsin c substrate assay 40
4.18 snRNA-Seq 41
4.19 Statistical Analysis 42
5 Results 43
5.1 Chronically impaired renal function leads to cognitive decline 43
5.2 Blood brain barrier (BBB) disruption in chronic kidney disease 44
5.3 Potassium dyshomeostasis in brain cells in CKD 45
5.4 CKD leads to microglia activation 46
5.5 Priming of microglia in CKD depends on potassium dyshomeostasis and its restoration improves cognition in CKD 49
5.6 TRAM34 ameliorates potassium dyshomeostasis and behavior in CKD 51
5.7 Uremia-induced cognitive impairment depends on microglia- neuron crosstalk via IL-1R1 52
5.8 Deciphering the microglial molecular pathway in CKD 56
5.9 Microglia activation in CKD is independent of NLRP3 56
5.10 Microglial IL-1β maturation occurs independently of the NLRP3-Caspase-1 inflammasome in CKD 57
5.11 The role of caspase- 8 in microglia activation in CKD 60
5.12 Lysosomal cathepsin c promotes microglia activation pivotal for caspase-8 activation 62
5.13 Broader implication of the pathway in other chronic peripheric diseases 63
5.14 Microglia inflammasome activation and IL-1β release is sufficient to induce cognitive impairment 64
5.15 Tables 66
6 Discussion 69
7 Summary 75
8 Zusammenfassung 80
9 References 86
10 Declaration about the independent preparation of the work 97
11 Presentation of own contribution 98
12 Curriculum vitae 99
13 Publications 104
14 Acknowledgments 106
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:88444 |
| Date | 05 December 2023 |
| Creators | Zimmermann, Silke |
| Contributors | Universität Leipzig |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/acceptedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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