Neurocellular stress response to Mojave Type A Rattlesnake venom: A study of molecular mechanisms using a human iPSC-derived neural stem cell model
The Mojave rattlesnake (Crotalus scutulatus scutulatus) is classified as the “highest medically important” snake in the risk categories in the United States. Although responsible for fewer snakebite envenomations and deaths compared to other species, Mojave rattlesnake venom is poorly characterized and shows significant geographical variability. The venom of Type A animals primarily contains the ß-neurotoxin referred to as Mojave Toxin (MTX), which is responsible for the neurotoxic effects that make bites from this snake particularly feared. Previous studies have shown that ß-neurotoxin from different snake species produced similar but complex effects by mechanisms that are not fully understood. We performed a genome-wide transcriptomic analysis of the neurocellular response to Mojave Type A rattlesnake venom using induced pluripotent stem cell (iPSC) -derived human neural stem cells (NSCs) to unveil the molecular mechanisms underlying the damage caused by this snake's envenomation. Our results suggest that snake venom metalloproteases (svMPs), although have a limited repertoire in type A animal venom, facilitate venom spread by digesting tissue's extracellular matrix. The MTX, which is composed of heterodimers of basic and acidic phospholipase A2 (PLA2) and is the dominant constituent of this venom, co-opts the host arachidonic acid and Ca2+ second messenger mechanisms in a dose- and time-dependent escalating venom damage. The release of arachidonic acid and the rapid increase in intracellular Ca2+ caused by the PLA2 activity of MTX triggers multiple signaling cascades. The activation of MAPKs and NF-?B regulated proinflammatory cascades were the top enriched pathways in the shorter 4-hour NSC response to venom challenge and suggest a significant role of PKC-d in the activation of MAPKs. The rapid increase in intercellular Ca2+ and resulting cellular depolarization plausibly have a role in neurotransmitter overload in the cholinergic and glutamatergic excitatory synapses and MTX-induced presynaptic blockade of nerve signals. The expression of the acetylcholinesterase gene (ACHE), which degrades acetylcholine, and the downregulation of GRIK1 and GRIK3 genes, which encode KA-iGluRs proteins suggest a cellular response to neurotransmitter overload in the excitatory synapses. Our results also show that the MTX/svPLA2 mediated dysregulation of Ca2+ homeostasis, particularly depletion from the endoplasmic reticulum (ER), causes ER stress and upregulation of unfolded protein response (UPR). The UPR and the oxidative stress caused by ROS generated in CYP1A1-mediated hydroxylation of arachidonic acid, contribute to mitochondrial membrane permeabilization. The activation of UPR, mitochondrial toxicity, and oxidative stress, constitute the degenerative phase of the venom challenge in NSCs and synergistically contribute to apoptotic and ferroptotic programmed cell death. Overall design: Well-characterized, low-passage human NSCs generated from validated iPSCs of four different individuals were challenged with vehicle control, and 10 µg/mL and 30 µg/mL Mojave Type A rattlesnake venom and then analyzed at 4- and 24-hour by deep mRNA sequencing.