Moderate aerobic training enhances the effectiveness of insulin therapy through hypothalamic IGF1 signaling in rat model of Alzheimer's disease

Abstract

Alzheimer's disease (AD) is a neurological condition that is connected with a decline in a person's memory as well as their cognitive ability. One of the key topics of AD research has been the exploration of metabolic causes. We investigated the effects of treadmill exercise and intranasal insulin on learning and memory impairment and the expression of IGF1, BDNF, and GLUT4 in hypothalamus. The animals were put into 9 groups at random. In this study, we examined the impact of insulin on spatial memory in male Wistar rats and analyzed the effects of a 4-week pretreatment of moderate treadmill exercise and insulin on the mechanisms of improved hypothalamic glucose metabolism through changes in gene and protein expression of IGF1, BDNF, and GLUT4. We discovered that rat given Aβ_25-35 had impaired spatial learning and memory, which was accompanied by higher levels of Aβ plaque burden in the hippocampus and lower levels of IGF1, BDNF, and GLUT4 mRNA and protein expression in the hypothalamus. Additionally, the administration of exercise training and intranasal insulin results in the enhancement of spatial learning and memory impairments, the reduction of plaque burden in the hippocampus, and the enhancement of the expression of IGF1, BDNF, and GLUT4 in the hypothalamus of rats that were treated with Aβ_25-35. Our results show that the improvement of learning and spatial memory due to the improvement of metabolism and upregulation of the IGF1, BDNF, and GLUT4 pathways can be affected by pretreatment exercise and intranasal insulin.

Keywords: Alzheimer’s disease; Insulin; Metabolism; Spatial learning and memory; Treadmill exercise.

Figure 1

Schematic diagram of the experimental protocol. Aβ (10 µg/rat)/saline were administered bilaterally Intra-cerebroventricular to the animals. Each group received its own training and treatment protocol. And 21 days after the Aβ injection in all groups, learning and spatial memory were evaluated with the MWM test, thioflavin-S, real-time PCR, and ELISA tests.

Figure 2

Hippocampal Thioflavin S staining. Using thioflavin S, the hippocampus tissue from the control, Aβ group, and treatment groups was stained. Magnification 400 ×; scale bars 200 µm.

Figure 3

Hippocampal Thioflavin S staining. The control group's results revealed no amyloid deposits. In the Aβ, Aβ + EXE, Aβ + PIN, Aβ + INT, Aβ + EXE + PIN, Aβ + EXE + INT, and Aβ + EXE + PIN + INT groups, the Aβ deposits were visible in the images. The results were presented as the mean ± SEM (n = 3 in each group).

Figure 4

By using optical fluorescence imaging, one can observe the INS being taken in by Rat's nose. A) Shaved control rat, FITC-IN. B) Fluorescence images of the Brain, 15 min (top left row), 1 h (top right row), 3 h (bottom left row), and 5 h (bottom right row) after intranasal administration of FITC- IN suspension are shown. C) Optical imaging of the organs (5 h after injection, rats were slaughtered, and the organs were taken out). The images that were produced matched the outcomes of in vivo imaging.

Figure 5

Blood glucose levels. According to the collected data, there were significant differences between the groups in the level of glucose in time3. The results were presented as the mean ± SEM (n = 16 in each group).

Figure 6

Test of MWM. Nine groups of adult Wistar rats were created at random. Spatial memory effects of ICV-Aβ/Saline dosing The MWM parameters for the several groups on the probing day were displayed in order from A to D. (A) Traveled distance: Rats receiving insulin and EXE showed a shorter travel distance to the hidden platform than rats receiving Aβ (P < 0.0001). (B) Escape Latency: The infusion of Aβ substantially reduced brain function. The EXE and IN therapy groups saw a considerable improvement in this condition (P < 0.001). (C) Velocity in the training phase, there was no significant difference in swimming speed during training between groups (p > 0.05). (D) Probe trial: In comparison to the group serving as the control, the A group's performance was subpar. In spite of this, the amount of time spent in the target zone significantly increased in the Aβ + EXE, Aβ + EXE + PIN, and Aβ + EX + PIN + INT groups (P < 0.0001). The Aβ impact appears to have been reversed by intranasal EXE and IN therapy. Results are shown as mean ± SEM (n = 8 in each group).

Figure 7

Gene expression of IGF1, BDNF, and GLUT4 in the hypothalamus. Aβ decreased the expression of IGF1, BDNF, and GLUT4 genes in the hypothalamus. Moderate training exercise along with receiving insulin as treatment and pretreatment significantly increased the mRNA levels of IGF1, BDNF, and GLUT4 in the hypothalamus of rats. Results are shown as mean ± SEM (n = 3 in each group).

Figure 8

ELISA analysis of IGF1, BDNF, and GLUT4 in the hypothalamus. Aβ decreased levels of IGF1, BDNF, and GLUT4 in the hypothalamus of a rat model of AD. Rat treated with moderate training exercise and insulin treatment showed a higher level of IGF1, BDNF, and GLUT4 proteins in the hypothalamus. Measured by the ELISA kit. Moderate training exercise and insulin treatment significantly increased the level of IGF1 (F_{(8, 18)} = 7.72, P = 0.009), BDNF (F_{(8, 18)} = 11.20, P = 0.008), and GLUT4 (F_{(8, 18)} = 5.59, P = 0.02) proteins in the hypothalamus of group B rats. Results are shown as mean ± SEM (n = 3 in each group).