IL-4 shaping glutamatergic synapse like structures for more mature iPSC derived neuron phenotypes

The prototypical pleiotropic anti-inflammatory cytokine IL-4 not only acts on immune cells but also has important roles in the nervous system mediating antinociception and neuroregeneration. Therefore, we explored the expression of IL-4, its receptors IL4RA and IL13RA1 and downstream signaling components together with morphological and functional assays as well as transcriptomic profiling in human nociceptors differentiating from induced pluripotent stem cells (iNocs). IL-4 induced de novo formation of synaptic boutons immunoreactive for vesicular glutamate transporter vGLUT1 in iNocs which express both, components of the IL-4 receptor complex (IL-4RA and IL-13RA1) and signaling machinery (Jak1/2, STAT6, PKC isoforms, translation factor EiF4E) during differentiation. Pharmacological inhibition of these translational or cellular signaling components reduced the synaptogenic effect. IL-4 induced distinct transcriptomic changes associated with biological process ontologies for "neuron projection development", "axonogenesis" and "synapse", "cellular process involved in reproduction in multicellular organism", "regulation of membrane potential" and "calcium ion transmembrane transport". This partially reflected injury-induced transcriptional changes of mouse nerve injury models which contribute to regenerative processes in peripheral nerve but possibly also to reconnecting primary afferent neurons to their projections in the spinal dorsal horn and indicates a critical role for IL-4 in the control of developing and established neuronal networks.