Novel Dual Mechanism GRT-X Agonist Acting on Kv7 Potassium Channel/Translocator Protein Receptor Prevents Motoneuron Degeneration Following Exposure to Mouse and Human Amyotrophic Lateral Sclerosis/Frontotemporal Dementia Astrocyte-Conditioned Media

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) form a continuous spectrum of aggressive neurodegenerative diseases affecting primarily motoneurons (MNs) and cortical frontotemporal neurons. Noncell autonomous mechanisms contribute to ALS/FTD, wherein astrocytes release toxic factor(s) detrimental to MNs. Because of the multifactorial nature of ALS, single-pathway-focused therapies have limited effectiveness in improving ALS. Therefore, novel combinatorial therapies are currently being pursued. Here, we evaluated whether the simultaneous activation of two complementary targets, the voltage-gated potassium channels 7.2/3 (Kv7.2/3) and the mitochondrial translocator protein (TSPO), by a novel synthesized compound (GRT-X) is an effective neuroprotective treatment in ALS in vitro models. We exposed primary rat ventral spinal cord neuronal cultures and rat spinal cord organotypic cultures to astrocyte-conditioned medium derived from primary mouse ALS astrocytes expressing mutant human SOD1 (SOD1^G93A-ACM) or from human-induced pluripotent stem cell (iPSC)-derived astrocytes carrying an ALS-causing mutation in SOD1 (SOD1^D90A-ACM) or an ALS/FTD-causing mutation in TDP-43 (TDP43^{A90 V}-ACM). We report that the diverse human and mouse ALS/FTD-ACMs compromise the MN viability. Remarkably, GRT-X led to consistent protection of MNs. Moreover, ALS/FTD-ACM increases oxidative stress levels, which are prevented with GRT-X treatment. Together, we show that the complementary activation of TSPO and Kv7.2/3 may offer a novel therapeutic strategy for ALS/FTD due to its capacity to protect MNs from noncell-autonomous toxicity induced by diseased astrocytes.

GRT-X; amyotrophic lateral sclerosis; astrocyte conditioned medium; frontotemporal dementia; motoneuron death; oxidative and excitotoxity stress.