Rewiring Fragile X: Targeting glial pruning deficits to rescue hippocampal circuit function

• Applicants: Professor Dr. Martin Korte; Dr. Kristin Michaelsen-Preusse
• Subject Area: Developmental Neurobiology
• Term: since 2013
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 244181329

Fragile X syndrome (FXS), the most common inherited form of intellectual disability and a leading monogenic cause of autism, is characterized by abnormal synaptic development, including an excess of immature dendritic spines and altered excitation/inhibition (E/I) balance in the hippocampus and cortex. While neuronal consequences of FMRP loss are well studied, growing evidence suggests that glial dysfunction—particularly impaired microglia-mediated synaptic pruning—plays a causal role in shaping these circuit abnormalities. Our recent findings demonstrate persistent spine immaturity in the CA3 region of adult Fmr1 knockout mice, accompanied by behavioral deficits in hippocampus-dependent pattern completion. Preliminary data further suggest aberrant microglial morphology and pruning function in CA3, implicating microglial dysfunction in the pathogenesis of FXS. This project aims to uncover the developmental trajectory, molecular mechanisms, and therapeutic potential of targeting glial pruning deficits in FXS. It is structured into three interrelated work packages. In Work Package 1, we will define when and where microglial and astrocytic pruning deficits emerge using super-resolution (STED) and two-photon imaging, cell type–specific TRAP transcriptomics, and synaptic and electrophysiological profiling across development, with a focus on CA3. In Work Package 2, we will dissect the molecular underpinnings of these pruning impairments. Candidate pathways—such as the complement system, CX3CL1–CX3CR1 signaling, and TREM2—will be tested in vivo and in a newly established physiologically relevant neuron–astrocyte–microglia co-culture model to reduce animal use and establish mechanistic causality. Building on these insights, Work Package 3 will evaluate whether therapeutic modulation of pruning pathways can rescue synaptic and behavioral phenotypes in Fmr1 KO mice. We will administer minocycline, CX3CR1 agonists, TREM2 activators, or complement modulators during critical developmental windows identified in WP1. Outcome measures will include microglial morphology, synaptic engulfment, dendritic spine density, E/I balance, and hippocampus-dependent behavior (e.g., pattern completion). Together, this proposal will clarify the role of glial pruning dysfunction in FXS, define critical windows for therapeutic intervention, and establish whether targeting glial pathways can recalibrate neural circuits and improve behavioral outcomes. The results will provide a mechanistic and translational framework for future glia-based therapies in FXS and related neurodevelopmental disorders.

• DFG Programme: Research Grants