AAV-mediated delivery of a proliferation inducing ligand (APRIL) to cortical neurons limits inflammation and demyelination in the corpus callosum of the cuprizone mouse model

BACKGROUND: A Proliferation-Inducing Ligand (APRIL) is a tumour necrosis factor superfamily member with multiple effector roles in the peripheral and central nervous system (CNS). In the CNS, APRIL helps maintain immune homeostasis and supports neuronal survival, yet whether it can therapeutically modulate acute neuro-inflammatory and neurodegenerative processes is unclear. To investigate this in a severe neuro-inflammatory context, we tested whether local APRIL delivery can influence microglial/astrocytic responses and demyelination in the cuprizone (CPZ) mouse model of neuro-inflammation and demyelination. METHODS: We applied adeno-associated virus (AAV)-mediated gene transfer to drive APRIL expression by cortical neurons positioned directly above the splenium of the corpus callosum. Following CPZ intoxication, we evaluated microglial and astrocytic activation and myelin content by in vivo T2 and diffusion magnetic resonance imaging (MRI), and validated them by post-mortem quantitative immunohistochemistry (IHC) and bulk transcriptomic and proteomic profiling. RESULTS: T2 and diffusion MRI, corroborated by quantitative IHC, demonstrated that secretion of APRIL by cortical neurons attenuated CPZ-induced microglial recruitment and demyelination in the splenium, but not in the cortex. Integrated transcriptome-proteome analysis of splenium and cortex, further supported by IHC, highlighted astroglial lipid-metabolic circuitry - marked by the astrocytic fatty-acid-binding protein 7 (Fabp7) - as a candidate axis underlying APRIL's effects to reduce inflammatory cell recruitment and myelin preservation. CONCLUSIONS: AAV-mediated expression of APRIL by cortical neuron counteracted microglial recruitment and demyelination in the splenium of CPZ-treated mice. Our multi-omics integration analysis nominated several pathways, including Fabp7-linked astrocytic lipid metabolism, to elucidate APRIL's mechanism of action. Together, these findings provide a framework for the mechanistic dissection of APRIL's therapeutic potential and further translational evaluation in CNS pathologies characterised by acute neuro-inflammatory responses.