Intercellular communication between neurons and astrocytes by leukemia inhibitory factors (LIF)

Abstract

Astrocytes have traditionally been regarded as supportive cells, but their crucial roles in synaptic formation, modulation of synaptic transmission, and brain function have been increasingly recognized in recent decades. They enable bidirectional communication with neurons by receiving neuronal signals and eliciting intracellular calcium responses, subsequently releasing gliotransmitters to feedback neurons to influence neuronal functions. In previous studies, we elucidated the G_q signaling pathway-mediated secretion of LIF, a member of the interleukin-6 (IL-6) family, in HEK293 cells. Given the neuroprotective and anti-inflammatory role of LIF in the CNS as well as its secretion from astrocytes, this study aims to investigate the potential of neurotransmitters or neuromodulators to induce LIF secretion in astrocytes, and further elucidate the involvement of LIF in astrocyte-neuron communication. Upon screening a panel of cell lines, the astrocytic cell line U-87 MG and neuronal cell line SK-N-MC were selected based on their established calcium profiles for common neurotransmitters and neuromodulators. The release of LIF from U-87 MG cells, triggered by neurotransmitters and neuromodulators that stimulate intracellular Ca²⁺ mobilization in U-87 MG cells, was detected. Meanwhile, the calcium profiles were also characterized in primary astrocytes and neurons from mice. In both U-87 MG and primary astrocytes, neuromodulator bradykinin (BK) was observed to induce Ca²⁺ mobilization and secretion of LIF. LIF effectively induced phosphorylation of STAT3 (P-STAT3) in SK-N-MC and neurons. The ability of IL-6 to induce the P-STAT3 in both cells was also demonstrated. Moreover, it was shown that LIF exhibited a neuroprotective effect against glutamate-induced excitotoxicity. Co-culturing of astrocytic U-87 MG and neuronal SK-N-MC cells, or primary astrocytes and neurons showed increased levels of P-STAT3 in SK-N-MC cells and neurons. The elevation of P-STAT3 could be attenuated by neutralizing antibody of LIF in the co-culture system. Additionally, the conditioned medium derived from U-87 MG cells was found to stimulate autocrine activation of P-STAT3 on the same cells. The conditioned-medium derived from SK-N-MC cells and primary neurons stimulated Ca²⁺ mobilization and ERK phosphorylation in the astrocytic recipient cells and could be reduced by the antagonist of BK receptor. Collectively, this study indicates the involvement of LIF and IL-6 in intercellular communication between astrocytes and neurons, with BK capable of inducing the secretion of LIF in astrocytic cells.

Date of Award	2024
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Yung Hou WONG (Supervisor)