Effects of 2D-Shear Wave Elastography on Brain-Derived Neurotrophic Factor (BDNF) in the Brains of Neonatal Mice and Exploration of the Mechanism

Abstract

BACKGROUND The aim of this study was to explore the effect and duration of 2-dimensional shear wave elastography (2D-SWE) irradiation on the expression of brain-derived neurotrophic factor (BDNF) in the brains of neonatal mice and to preliminarily investigate whether its mechanism is neuronal apoptosis. MATERIAL AND METHODS Neonatal mice (within 48 hours of birth) were subjected to 2D-SWE irradiation of the brain for 10 minutes (group S1), 20 minutes (group S2), and 30 minutes (group S3). The mice were sacrificed immediately after irradiation or 24 hours after irradiation. Brains were collected for real-time polymerase chain reaction (RT-PCR) and western blot experiments to determine the expression of BDNF in each group. TdT-mediated dUTP nick-end labeling (TUNEL) was performed to observe neuronal apoptosis in the brain. RESULTS The results of PCR and western blots from the brains of neonatal mice that were sacrificed immediately after irradiation show that S1, S2, and S3 were significantly different from those in the control group. The PCR and western blot results of brain tissues from neonatal mice sacrificed at 24 hours after irradiation showed that there was no significant difference between the S1, S2, S3, and control groups. The results of TUNEL experiments showed that there was no statistically significant difference in the number of apoptotic neurons between the S1, S2, S3, and control groups. CONCLUSIONS 2D-SWE irradiation of neonatal mice for more than 10 minutes downregulated the expression of BDNF. This effect disappeared within 24 hours after the irradiation, and the 2D-SWE scan seemed not to induce neuronal apoptosis.

Figure 1

Preparation of animal models. (A) Schematic of neonatal rats exposed to 2D-SWE. (B) The standard image of neonatal rats subjected to 2D-SWE. 2D-SWE – 2-dimensional shear wave elastography.

Figure 2

The expression of BDNF in the brains of mice sacrificed immediately after exposure to 2D-SWE. The relative mRNA expression of BDNF qRT-PCR (A). The protein levels of BDNF were assessed by western blot (B). The densitometric analysis of each band was performed using Image-Pro Plus 6.0, and protein expression levels were normalized to actin. Data are presented as the mean±SD from 3 independent experiments. Differences in measurement data were compared with one-way ANOVA. * P<0.05; ** P<0.01, and NS – no significance (P>0.05). BDNF – brain-derived neurotrophic factor; 2D-SWE – 2-dimensional shear wave elastography; mRNA – messenger RNA; qRT-PCR – quantitative real-time polymerase chain reaction; SD – standard deviation.

Figure 3

The expression of BDNF in the brains of mice sacrificed 24 hours after exposure to 2D-SWE. The relative mRNA expression levels of BDNF was detected by qRT-PCR (A). The protein expression levels of BDNF were quantified by western blots (B). The densitometric analysis of each band was performed using Image-Pro Plus 6.0, and the protein expression levels were normalized to those of actin. Data are presented as the mean±SD from 3 independent experiments. Differences in measurement data were compared with one-way ANOVA method. * P<0.05; ** P<0.01, and NS – no significance (P>0.05). BDNF – brain-derived neurotrophic factor; 2D-SWE – 2-dimensional shear wave elastography; mRNA – messenger RNA; qRT-PCR – quantitative real-time polymerase chain reaction; SD – standard deviation.

Figure 4

Image of the TUNEL test. The control group (A), Group S1 (B), Group S2 (C), and Group S3 (D). TUNEL – TdT-mediated dUTP nick-end labeling.