Modulation of microglial function by neuronal expression of the Alzheimer multifactorial therapeutic agent E2F4DN is mediated by a soluble factor

Abstract

AbstractBackgroundAlzheimer’s disease (AD) is a neurodegenerative disorder in which altered immune response is an important etiological factor (Cell Rep. 2019;27:1293.e6‐1306.e6, Nature 2019;575:669‐673). The transcription factor E2F4 regulates gene networks affected in AD (Interdiscip. Sci. 2019;11:226‐236), thus constituting a potential target for intervention. Neuronal expression of a dominant negative form of E2F4 (E2F4DN), which cannot be phosphorylated in two conserved Thr residues, can attenuate microgliosis in a mouse model of AD (Neurotherapeutics 2021;18:2484‐2503, Mol. Neurobiol. 2022;59:3016‐30392), as evidenced by the reduction of area occupied by microglia (i.e. Iba1‐positive cells). Communication between neurons and microglia is essential to regulate microglial activation and neuroprotection. The loss of this communication can cause microglia overactivation and produce persistent inflammation, finally resulting in the exacerbation of the neuropathology (Neural Regen. Res. 2019;14:1499‐1502).MethodMouse cortical neurons were cultured and maintained for 9 days in vitro (DIV) for maturation. Neurons were then transfected with an E2F4DN adenoviral (Ad5) vector, or a control EGFP Ad5 vector. After 48 h, rat microglia were treated for 24 hours with the conditioned media, and then fixed and immunostained with the microglia marker Iba1. The size of these cells was analyzed as a readout of the glial inflammatory activity (Sci. Rep. 2017;7:1576).ResultMicroglial cell size was analyzed from images obtained in the fluorescence microscope. This would determine if any soluble factor secreted by neurons that express E2F4DN, but not by neurons that express EGFP, is capable of inducing morphological changes that may reflect functional changes in this cell type. A reduction in the size of microglia was observed when the conditioned medium came from neurons expressing E2F4DN. These results show the existence of a differential communication mechanism between neurons and microglia depending on the expression of E2F4DN.ConclusionWe suggest that there is an E2F4DN‐dependent neuron‐microglia communication based on soluble factors such as those described by Simon et al. (Neuroscience 2019;405:24‐34). Altogether, our data are consistent with a beneficial immune response elicited by neurons expressing E2F4DN, a molecule proposed as a multifactorial therapeutic agent against AD.