https://hdl.handle.net/20.500.11811/925 Wed, 15 Apr 2026 06:19:31 GMT 2026-04-15T06:19:31Z https://hdl.handle.net/20.500.11811/13648 Sialylation as a checkpoint for inflammatory and complement-related retinal diseases Min, Yiduo; Cuevas-Rios, German; Langmann, Thomas; Neumann, Harald Sialylation is a modification process involving the addition of sialic acid residues to the termini of glycoproteins and glycolipids in mammalian cells. Sialylation serves as a crucial checkpoint inhibitor of the complement and immune systems, particularly within the central nervous system (CNS), including the retina. Complement factor H (FH), complement factor properdin (FP), and sialic acid-binding immunoglobulin-like lectin (SIGLEC) receptors of retinal mononuclear phagocytes are key players in regulating the complement and innate immune systems in the retina by recognizing sialic acid (Sia) residues. Intact retinal sialylation prevents any long-lasting and excessive complement or immune activation in the retina. However, sialylated glycolipids are reduced in the CNS with aging, potentially contributing to chronic inflammatory processes in the retina. Particularly, genetically induced hyposialylation in mice leads to age-related, complement factor C3-mediated retinal inflammation and bipolar cell loss. Notably, most of the gene transcript pathways enriched in the mouse retina, following genetically induced hyposialylation, are also involved in age-related macular degeneration (AMD). Interestingly, intravitreal application of polysialic acid (polySia) controlled the innate immune responses in the mouse retina by blocking mononuclear phagocyte reactivity, inhibiting complement activation, and protecting against vascular damage in two different humanized SIGLEC-11 animal models. Accordingly, a polySia polymer conjugate has entered clinical phase II/III testing in patients with geographic atrophy secondary to AMD. Thus, hyposialylation or dysfunctional sialylation should be considered as an age-related contributor to inflammatory retinal diseases, such as AMD. Consequently, sialic acid-based biologics could provide novel therapies for complement-related retinal diseases. Fri, 27 Jun 2025 00:00:00 GMT https://hdl.handle.net/20.500.11811/13648 2025-06-27T00:00:00Z https://hdl.handle.net/20.500.11811/13596 Alterations in dopaminergic innervation and receptors in focal cortical dysplasia Meli, Norisa; Sheran, Katherine; Pitsch, Julika; Krabbe, Sabine; Borger, Valeri; Baumgartner, Tobias; Becker, Albert; Blaess, Sandra Focal cortical dysplasia (FCD) type 2 is the most common malformation of cortical development associated with pharmaco-resistant focal epilepsy and frequently located in the frontal cortex. Neuropathological hallmarks comprise abnormal cortical layering and enlarged, dysmorphic neuronal elements. Fundamentally altered local neuronal activity has been reported in human FCD type 2 epilepsy surgical biopsies. Of note, FCD type 2 emerges during brain development and forms complex connectivity architectures with surrounding neuronal networks. Local cortical microcir-cuits, particularly in frontal localization, are extensively modulated by monoaminergic axonal projections originating from the brainstem. Previous analysis of monoaminergic modulatory inputs in human FCD type 2 biopsies suggested altered density and distribution of these monoaminergic axons; however, a systematic investigation is still pending.<br /> Here, we perform a comprehensive analysis of dopaminergic (DA) innervation, in human FCD type 2 biopsies and in the medial prefrontal cortex (mPFC) of an FCD type 2 mouse model [mechanistic target of rapamyin (mTOR) hyperactivation model] during adolescent and adult stages. In addition, we analyse the expression of dopamine receptor transcripts via multiplex fluorescent RNA in situ hybridization in human specimens and the mPFC of this mouse model. In the mTOR hyperactivation mouse model, we observe a transient alteration of DA innervation density during adolescence and a trend towards decreased innervation in adulthood. In human FCD type 2 areas, the overall DA innervation density is decreased in adult patients compared with control areas from these patients. Moreover, the DA innervation shows an altered lamination pattern in the FCD type 2 area compared with the control area. Dopamine receptors 1 and 2 appear to be differentially expressed in the dysmorphic neurons in human samples and mTOR-mutant cells in mice compared with normally developed neurons.<br /> Intriguingly, our results suggest complex molecular and structural alterations putatively inducing impaired DA neurotransmission in FCD type 2. We hypothesize that this may have important implications for the development of these malformations and the manifestation of seizures. Wed, 16 Apr 2025 00:00:00 GMT https://hdl.handle.net/20.500.11811/13596 2025-04-16T00:00:00Z https://hdl.handle.net/20.500.11811/13561 Aberrant hippocampal Ca²⁺ microwaves following synapsin-dependent adeno-associated viral expression of Ca²⁺ indicators Masala, Nicola; Mittag, Manuel; Ambrad Giovannetti, Eleonora; O'Neil, Darik A.; Distler, Fabian J.; Rupprecht, Peter; Helmchen, Fritjof; Yuste, Rafael; Fuhrmann, Martin; Beck, Heinz; Wenzel, Michael; Kelly, Tony Genetically encoded calcium indicators (GECIs) such as GCaMP are invaluable tools in neuroscience to monitor neuronal activity using optical imaging. The viral transduction of GECIs is commonly used to target expression to specific brain regions, can be conveniently used with any mouse strain of interest without the need for prior crossing with a GECI mouse line, and avoids potential hazards due to the chronic expression of GECIs during development. A key requirement for monitoring neuronal activity with an indicator is that the indicator itself minimally affects activity. Here, using common adeno-associated viral (AAV) transduction procedures, we describe spatially confined aberrant Ca²⁺ microwaves slowly travelling through the hippocampus following expression of GCaMP6, GCaMP7, or R-CaMP1.07 driven by the synapsin promoter with AAV-dependent gene transfer in a titre-dependent fashion. Ca²⁺ microwaves developed in hippocampal CA1 and CA3, but not dentate gyrus nor neocortex, were typically first observed at 4 wk after viral transduction, and persisted up to at least 8 wk. The phenomenon was robust and observed across laboratories with various experimenters and setups. Our results indicate that aberrant hippocampal Ca²⁺ microwaves depend on the promoter and viral titre of the GECI, density of expression, as well as the targeted brain region. We used an alternative viral transduction method of GCaMP which avoids this artefact. The results show that commonly used Ca²⁺ - indicator AAV transduction procedures can produce artefactual Ca²⁺ responses. Our aim is to raise awareness in the field of these artefactual transduction-induced Ca²⁺ microwaves, and we provide a potential solution. Tue, 23 Jul 2024 00:00:00 GMT https://hdl.handle.net/20.500.11811/13561 2024-07-23T00:00:00Z https://hdl.handle.net/20.500.11811/13255 The impact of the mesoprefrontal dopaminergic system on the maturation of interneurons in the murine prefrontal cortex Islam, K. Ushna S.; Blaess, Sandra The prefrontal cortex (PFC) undergoes a protracted maturation process. This is true both for local interneurons and for innervation from midbrain dopaminergic (mDA) neurons. In the striatum, dopaminergic (DA) neurotransmission is required for the maturation of medium spiny neurons during a critical developmental period. To investigate whether DA innervation influences the maturation of interneurons in the PFC, we used a conditional knockout (cKO) mouse model in which innervation from mDA neurons to the mPFC (mesoprefrontal innnervation) is not established during development. In this mouse model, the maturation of parvalbumin (PV) and calbindin (CB) interneuron populations in the PFC is dysregulated during a critical period in adolescence with changes persisting into adulthood. PV interneurons are particularly vulnerable to lack of mesoprefrontal input, showing an inability to maintain adequate PV expression with a concomitant decrease in <em>Gad1</em> expression levels. Interestingly, lack of mesoprefrontal innervation does not appear to induce compensatory changes such as upregulation of DA receptor expression in PFC neurons or increased innervation density of other neuromodulatory (serotonergic and noradrenergic) innervation. In conclusion, our study shows that adolescence is a sensitive period during which mesoprefrontal input plays a critical role in promoting the maturation of specific interneuron subgroups. The results of this study will help to understand how a dysregulated mesoprefrontal DA system contributes to the pathophysiology of neurodevelopmental disorders. Fri, 05 Jul 2024 00:00:00 GMT https://hdl.handle.net/20.500.11811/13255 2024-07-05T00:00:00Z