Universität zu Köln

Kinuthia, Urbanus Muthai (2024). Pharmacological modulation of inflammation in mouse models of experimental diabetic retinopathy. PhD thesis, Universität zu Köln.

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Abstract

Microglia are the immune sentinels of the central nervous system including the retina, where they play crucial roles in innate immunity and maintenance of retina CNS tissue homeostasis. Mild reactivity of microglia is important in mounting an inflammatory response, termed parainflammation, which is an important function of tissue macrophages. However, chronic activation of microglia due to sustained tissue stress leads to dysfunction of microglia-specific immune checkpoints, which aggravates cell reactivity with increased secretion of cytokines and chemokines. The overt activation of microglia is a key feature of retinal degenerative diseases and ocular retinopathies including diabetic retinopathy (DR). Indeed, mounting evidence in mice and human patients has shown that neuroinflammation precedes the clinically detectable microvascular complications of DR. This highlights microglia, resident immune macrophages of the retina, not only as drivers of inflammation but also as targets for therapeutic intervention. Indeed, immunomodulation of microglia reactivity has been studied in various degenerative diseases of the eye and showed improved disease outcomes. However, immunomodulation had not been studied in the models of neural and vascular complications reminiscent of human DR where loss of pericytes is associated with breakdown of the blood retina barrier. The PDGFB/PDGFRβ signalling is vital for adequate pericyte coverage of endothelial cells, proper retention of PDGFB in retinal endothelium. However, the lack of adequate disease models that recapitulate key features of human disease has precluded understanding of the cellular and molecular factors of DR. Therefore, the aim of the present study was to investigate whether pharmacological modulation of inflammation with minocycline limits disease progression and confers protection to the retina. Minocycline is a second-generation tetracycline that has anti-inflammatory effects besides its use as a bacteriostatic drug. Moreover, this thesis aimed at identifying the cellular and molecular phenotype of activated microglia and its response to minocycline during disease pathogenesis. By using mouse models of attenuation of the PDGFB/PDGFRβ signalling in the postnatal retina, we show that microglia reactivity is an early feature of the disease and it was sustained in the mature mouse retina. The early activation of microglia was associated with an inflammatory gene signature marked by CCL2, TSPO, LGALS3, AIF-1 and morphological changes reflecting an inflammatory state. Minocycline effectively downregulated the expression of microglia activation factors and angiogenic factors including VEGFA, ICAM-1 and PGF. Transcriptomic analyses of the mature retina of the pericyte inhibition model revealed FGF2, EDN2, GLYCAM-1, AIF-1 and CASP-1 as key inflammatory factors in the late stage of disease. In the mature retinas of the PDGFB depletion model, we observed an upregulation of VEGFA, FGF2, TSPO, LGALS3 and VWF. Besides reactive gliosis, leaky vasculature was observed in the mature mouse retinas. Notably, minocycline suppressed the expression of the inflammatory and angiogenic factors, reduced reactive gliosis and limited microglia activation and migration into the nuclear layers and subretinal space. Furthermore, we show that minocycline mediates its protective effect, at least in part, at a transcriptional level by downregulation of STAT3. Taken together, the present findings show that treatment with minocycline dampened microglia reactivity attenuated retinal inflammation and microvascular abnormalities in mice with an ocular phenotype reminiscent of diabetic retinopathy.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Kinuthia, Urbanus Muthai muthaiurbanus@gmail.com UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-727240
Date:	2024
Place of Publication:	Cologne
Language:	English
Faculty:	Faculty of Medicine
Divisions:	Unspecified
Subjects:	Medical sciences Medicine
Uncontrolled Keywords:	Keywords Language diabetic retinopathy, retina, microglia, vasculature, Blood retina barrier UNSPECIFIED
Date of oral exam:	15 April 2024
Referee:	Name Academic Title Langmann, Thomas Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/72724