Neural acetylcholinesterase and monoamine oxidase deregulation during streptozotocin-induced behavioral, metabolic and redox modification in Nauphoeta cinerea

Abstract

Genetic and environmental factors have been linked with neurodegeneration, especially in the elderly. Yet, efforts to impede neurodegenerative processes have at best addressed symptoms instead of underlying pathologies. The gap in the understanding of neuro-behavioral plasticity is consistent from insects to mammals, and cockroaches have been proven to be effective models for studying the toxicity mechanisms of various chemicals. We therefore used head injection of 74 and 740 nmol STZ in Nauphoeta cinerea to elucidate the mechanisms of chemical-induced neurotoxicity, as STZ is known to cross the blood-brain barrier. Neurolocomotor assessment was carried out in a new environment, while head homogenate was used to estimate metabolic, neurotransmitter and redox activities, followed by RT-qPCR validation of relevant cellular signaling. STZ treatment reduced the distance and maximum speed travelled by cockroaches, and increased glucose levels while reducing triglyceride levels in neural tissues. The activity of neurotransmitter regulators - AChE and MAO was exacerbated, with concurrent upregulation of glucose sensing and signaling, and increased mRNA levels of redox regulators and inflammation-related genes. Consequently, STZ neurotoxicity is conserved in insects, with possible implications for using N. cinerea to target the multi-faceted mechanisms of neurodegeneration and test potential anti-neurodegenerative agents.

Keywords: 3Rs; Neurodegeneration; Neurotoxicity; Oxidative damage; Redox-inflammation crosstalk.

Fig. 1

7-day Kaplan-Meier survival analysis of cockroaches after single dose head STZ injection (N = 40). Log-rank (Mantel-Cox) test showed significant (P = 0.0003) reduction in survival (increased mortality) of 74 and 740 nM STZ-treated cockroaches compared with control

Fig. 2

Motor and exploratory profile of cockroaches, 7 days after head STZ injection. n = 8. 8-minute video recordings of (A) track plot and (B) heat map were analysed with the ANY-maze (Stoelting CO, USA) software. One-way ANOVA with Tukey’s multiple comparisons test indicated a significant decrease in (C) total distance travelled and (D) maximum speed, as well as a significant increase in (E) total time immobile and (F) total time in periphery in cockroaches exposed to 74 and 740 nmol STZ head injection, compared with cockroaches in the control group. All values are mean ± SD. * indicates a significant difference from control

Fig. 3

Sugar and lipid levels, 7 days after head STZ injection in cockroaches. n = 5. One-way ANOVA with Tukey’s multiple comparisons test indicated a significant increase in (A) Glucose levels, and a significant decrease in (B) Triglyceride levels in neural tissues of cockroaches exposed to 74 and 740 nM STZ head injection, compared with cockroaches in the control group. All values are mean ± SD. * indicates a significant difference from control; # indicates significant differences from 74 nM STZ injection

Fig. 4

Increased neurotransmitter regulator activity, 7 days after head STZ injection in cockroaches. n = 5. One-way ANOVA with Tukey’s multiple comparisons test indicated a significant increase in (A) AChE activity and (B) MAO levels in in neural tissues of cockroaches exposed to 74 and 740 nM STZ head injection, compared with cockroaches in the control group. All values are mean ± SD. * indicates a significant difference from control; # indicates significant differences from 74 nM STZ injection

Fig. 5

Increased oxidative stress, 7 days after head STZ injection in cockroaches. n = 5. One-way ANOVA with Tukey’s multiple comparisons test indicated a significant increase in (A) ROS (B) TBARS, and (C) DCF levels in neural tissues of cockroaches exposed to 74 and 740 nM STZ head injection, compared with cockroaches in the control group. All values are mean ± SD. * indicates a significant difference from control

Fig. 6

Increased antioxidant and detoxification activity, 7 days after head STZ injection in cockroaches. n = 5. One-way ANOVA with Tukey’s multiple comparisons test indicated a significant increase in (A) Total Thiol, and (B) GST activity in neural tissues of cockroaches exposed to 74 and 740 nM STZ head injection, compared with cockroaches in the control group. All values are mean ± SD. * indicates a significant difference from control. # indicates significant differences from 74 nM STZ injection

Fig. 7

Increased glucose transporter (GLUT 1) activity and phosphoinositide 3-kinase (PI3K) signalling cascade, 7 days after head STZ injection in cockroaches. n = 9. One-way ANOVA with Tukey’s multiple comparisons test indicated a significant increase in (A) GLUT 1, and (B) PI3K activity in neural tissues of cockroaches exposed to 74 and 740 nM STZ head injection, compared with cockroaches in the control group. All values are mean ± SD. * indicates a significant difference from control

Fig. 8

Modulated expression of ROS generation regulator —Dual oxidases (DUOX) and antioxidant/detoxification genes, 7 days after head STZ injection in cockroaches. n = 9. One-way ANOVA with Tukey’s multiple comparisons test indicated a significant increase in (A) DUOX, (B) GST Theta, and (C) SOD, as well as significant decrease in (D) Catalase in neural tissues of cockroaches exposed to 74 and 740 nM STZ head injection, compared with cockroaches in the control group. All values are mean ± SD. * indicates a significant difference from control; # indicates significant differences from 74 nM STZ injection

Fig. 9

Increased expression of inflammation-associated genes, 7 days after head STZ injection in cockroaches. n = 9. One-way ANOVA with Tukey’s multiple comparisons test indicated a significant increase in (A) EGR (B) TOLL 1, and (C) UPD3 activity in neural tissues of cockroaches exposed to 74 and 740 nM STZ head injection, compared with cockroaches in the control group. All values are mean ± SD. * indicates a significant difference from control