Universität zu Köln

Laudenberg, Nils (2023). Colony stimulating factor 1 receptor (CSF1R) blockade of microglia reactivity in the light-damage model of retinal degeneration. PhD thesis, Universität zu Köln.

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Abstract

Reactive microglia are commonly present in retinal degenerative diseases. They can secrete neurotoxic substances, which contribute to photoreceptor cell death, and cause vision loss in the elderly. However, as a fundamental part of the regulatory immune system they also possess supportive effects. In this present study, we aimed at studying the effects of complete microglia depletion and repopulation in a mouse model of acute retinal degeneration that mimics some features of dry AMD using the CSF1R-antagonist PLX3397. Here, we want to elucidate, whether the absence of microglia or repopulated microglia associated with being unprimed would reduce the extend of retinal degeneration. CX3CR1GFP/+ reporter mice that carried the light sensitive RPE65 Leu450 variant received PLX3397 or control diet prior or after white light-exposure to induce retinal degeneration. Microglia were efficiently depleted with PLX3397 under normal and light damage conditions. We demonstrated microglia depletion could stop excessive pro-inflammatory marker expression. However, the extent of retinal degeneration could not be reduced when microglia were absent. In this condition, PLX3397 treatment failed to reduce the rate of photoreceptor loss. Here, we showed that dead cell debris remained in the ONL when microglia where depleted because they were unable to be phagocytosed. Furthermore, the absence of microglia increased the expression of GFAP and genes linked to Müller cells and astrocytes reactivity, like Ccl2 and Il-6. Discontinuation of PLX3397 resulted in rapid renewal of microglia. We demonstrated that the reactivity of newly repopulated microglia could not be dampened in any case. Microglia were instantly reactivated, assumed an amoeboid shape, and migrated into the nuclear layers as they repopulated in an already damaged environment, which was combined with an increased expression of pro-inflammatory markers. In addition, increased astrocyte and Müller cell reactivity was also associated with the newly repopulated microglia. Our study demonstrated that the model of light-induced retinal degeneration does not benefit from microglia depletion and repopulation. In fact, the opposite was true, as the loss of positive effects outweighs the negative effects. Since photoreceptors are on the verge between function and cell survival and dysfunction and death, literally any defect could shift them toward cell death. We assume that one strategy by which microglia might prolong photoreceptor survival is the clearing of dead photoreceptors to prevent bystander cell damage. We demonstrated that astrocytes and Müller cells are likely to become reactive when microglia are absent and contribute to photoreceptor cell death. However, they were unable to constitute for the microglia’s phagocytic activity, which was reflected in increased numbers of TUNEL+ cells. Our findings imply that the development of the pro-inflammatory phenotype of microglia in the condition of retinal degeneration was influenced by the microenvironment. We conclude that the microenvironmental impacts of degenerative diseases are likely to have an impact on the repopulation of microglia in a way that restores their initial over-reactive phenotype.

Item Type:	Thesis (PhD thesis)
Translated title:	Title Language UNSPECIFIED German
Creators:	Creators Email ORCID ORCID Put Code Laudenberg, Nils nils.laudenberg@gmx.net UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-711141
Date:	26 September 2023
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Medicine > Augenheilkunde
Subjects:	Natural sciences and mathematics Life sciences Medical sciences Medicine
Uncontrolled Keywords:	Keywords Language Microglia reactivity English Light-damage model English Microglia depletion PLX3397 English
Date of oral exam:	12 September 2023
Referee:	Name Academic Title Rugarli, Elena Prof.Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/71114