CSMD1 regulates brain complement activity and circuit development

• Published in: Brain, behavior, and immunity Vol. 119; pp. 317 - 332
• Main Authors: Baum, Matthew L., Wilton, Daniel K., Fox, Rachel G., Carey, Alanna, Hsu, Yu-Han H., Hu, Ruilong, Jäntti, Henna J., Fahey, Jaclyn B., Muthukumar, Allie K., Salla, Nikkita, Crotty, William, Scott-Hewitt, Nicole, Bien, Elizabeth, Sabatini, David A., Lanser, Toby B., Frouin, Arnaud, Gergits, Frederick, Håvik, Bjarte, Gialeli, Chrysostomi, Nacu, Eugene, Lage, Kasper, Blom, Anna M., Eggan, Kevin, McCarroll, Steven A., Johnson, Matthew B., Stevens, Beth
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Inc 01.07.2024
• Subjects: Animals; Basic Medicine; Brain - metabolism; Cells, Cultured; Complement C3 - metabolism; Complement cascade; Complement control protein; Complement System Proteins - metabolism; Humans; Medical and Health Sciences; Medicin och hälsovetenskap; Medicinska och farmaceutiska grundvetenskaper; Membrane Proteins - genetics; Membrane Proteins - metabolism; Mice; Mice, Inbred C57BL; Mice, Knockout; Microglia - metabolism; Neural circuits; Neurons - metabolism; Neurosciences; Neurovetenskaper; Schizophrenia; Synapses - metabolism; Synaptic pruning; Thalamus - metabolism; Synaptic pruning; Schizophrenia; Complement cascade; Neural circuits; Complement control protein
• ISSN: 0889-1591; 1090-2139; 1090-2139
• DOI: 10.1016/j.bbi.2024.03.041

Our findings support a model in which CSMD1 opposes actions of the complement cascade in neural tissues (top left). We investigated two models in which CSMD1/Csmd1 was genetically ablated: human cortical neurons derived from embryonic stem cells, and a back-crossed C57bl6-Tac mouse line (top right). CSMD1 is normally expressed by neurons and present at synapses where it can protect them from complement (bottom left); in the absence of CSMD1 (bottom right), we find more deposition of complement (on cultured human cortical neurons and in the mouse visual system), reduced numbers of synapses (in the mouse visual system), and synaptosomes that are more readily engulfed by microglia (in vitro). Created with BioRender.com. [Display omitted] •CSMD1, genetically associated with schizophrenia, localizes to synapses and interacts with complement in the brain.•CSMD1 KO mice have increased complement C3 at synapses and disrupted development of the retinogeniculate circuit.•Microglia show greater engulfment of CSMD1 KO synaptosomes in vitro, which is blocked by inhibition of complement receptor.•Human stem cell-derived neurons lacking CSMD1 were more vulnerable to complement deposition.•CSMD1 may function as a regulator of complement-mediated synapse elimination during brain development. Complement proteins facilitate synaptic elimination during neurodevelopmental pruning, but neural complement regulation is not well understood. CUB and Sushi Multiple Domains 1 (CSMD1) can regulate complement activity in vitro, is expressed in the brain, and is associated with increased schizophrenia risk. Beyond this, little is known about CSMD1 including whether it regulates complement activity in the brain or otherwise plays a role in neurodevelopment. We used biochemical, immunohistochemical, and proteomic techniques to examine the regional, cellular, and subcellular distribution as well as protein interactions of CSMD1 in the brain. To evaluate whether CSMD1 is involved in complement-mediated synapse elimination, we examined Csmd1-knockout mice and CSMD1-knockout human stem cell-derived neurons. We interrogated synapse and circuit development of the mouse visual thalamus, a process that involves complement pathway activity. We also quantified complement deposition on synapses in mouse visual thalamus and on cultured human neurons. Finally, we assessed uptake of synaptosomes by cultured microglia. We found that CSMD1 is present at synapses and interacts with complement proteins in the brain. Mice lacking Csmd1 displayed increased levels of complement component C3, an increased colocalization of C3 with presynaptic terminals, fewer retinogeniculate synapses, and aberrant segregation of eye-specific retinal inputs to the visual thalamus during the critical period of complement-dependent refinement of this circuit. Loss of CSMD1 in vivo enhanced synaptosome engulfment by microglia in vitro, and this effect was dependent on activity of the microglial complement receptor, CR3. Finally, human stem cell-derived neurons lacking CSMD1 were more vulnerable to complement deposition. These data suggest that CSMD1 can function as a regulator of complement-mediated synapse elimination in the brain during development.