1. The average birth weight in the FGR group was significantly lower than in the control group.
Currently, there are many methods to establish the FGR rat model, such as 50% energy restriction, uterine artery ligation, pharmacological method, chronic nitric oxide synthase inhibition-induced method, and so on[20–22]. The 50% diet restriction method is widely used, but maternal rats are prone to mania in the state of hunger. The incidence of abortion, stillbirth, and postpartum feeding would increase. Yue Jing et al. adopted an 8% low protein diet combined with 75% diet restriction modeling and achieved an excellent modeling success rate. In this experiment, we successfully established the FGR rat model by75% energy restriction combined with 8% low protein fed. The average success rate of modeling was 83.5%.
The birth weight of rat offspring we used in the subsequent analyses in the FGR group was significantly lower than that in the control group (P < 0.05) (Table 1). The birth weight in the FGR group met the diagnosis criteria of FGR as it was lower than the average birth weight of the control group by 2 SD.
Table 1
Comparison of birth weight between FGR and control group (x̄± s, g)
‾
|
|
FGR
|
Control
|
P
|
|
n = 12
|
n = 12
|
|
E18
|
1.28 ± 0.05
|
1.72 ± 0.07
|
<0.001
|
P1
|
5.22 ± 0.21
|
7.48 ± 0.22
|
<0.001
|
E18: Embryonic day 18th ; P1: Postnatal day 1st. FGR: fetal growth restriction.
|
2. The expression of NPY in the hypothalamus of FGR offspring increased.
In rats, the peak of neurogenesis is on gestational day 10.5th to 16.5th. NPY can be detected for the first time on day E14.5. Embryo day 18th and postnatal day 1st rat offspring were chosen as study subjects to confirm the expression difference of NPY and consistency of the difference in or out-utero.
We used IF to detect NPY expression qualitatively and positionally. As is shown in Fig. 1, green fluorescence is the expression part of NPY; Blue fluorescence is the nuclear expression part. NPY was mainly distributed around the third ventricle. Compared with the control group, the fluorescence intensity of NPY in the FGR group was brighter.
3. The protein and mRNA expression of DNMT1 decreased in the FGR group, while that of Bsx and NPY increased.
Hypothalamus tissues were used to detect the expression of DNMT1, Bsx, and NPY by RT-qPCR and WB. Results are shown in Fig. 2 and Fig. 3. Compared with the control group, the DNMT1 protein expression in the FGR group decreased. both in the E18 and P1 cohort (Fig. 2a). On the contrary, the Bsx and NPY protein expression increased (Fig. 2b, Fig. 2c). Besides, the result also displayed a decreased trend of DNMT1 protein expression from E18 to P1, while Bsx and NPY exhibited the opposite trend.
The DNMT1 mRNA expression in the FGR group, either the E18 cohort or the P1 cohort, was significantly lower than that in the control group (P < 0.05). The difference was much apparent in the E18 cohort(Fig. 3A). The Bsx and NPY mRNA expression in the FGR group, both the E18 cohort and P1 cohort, were significantly higher than that in the control group (Fig. 3B and Fig. 3C) (P < 0.05). Besides, the result also suggested a decreased trend of DNMT1 mRNA expression from E18 to P1, while NPY exhibited the opposite trend.
4. The methylation level of the Bsx promoter in the hypothalamus decreased in the FGR group.
To clarify whether there is a methylation change on Bsx, we detected the methylation level of Bsx by MSP. The result is shown in Fig. 4. The methylation level of Bsx promoter region in FGR group was lower than that in the control group, while the un-methylation level was higher (Fig. 4).
5. The expression of Bsx and NPY increased in NPCs cultured in vitro with DNMT1 specific inhibitor.
To clarify whether DNMT1 can regulate the expression of Bsx and NPY, we cultured NPCs in a differentiation medium with or without DNMT1 specific inhibitor. 5-AZA, a kind of DNMT1-specific enzyme activity inhibitor, was used in this experiment.
As shown in Fig. 5A, the DNMT1 mRNA expression in the FGR group was lower than in the control group (P < 0.05). In the groups that NPCs were cultured in vitro with 5-AZA, the expression of DNMT1 was inhibited (P < 0.05). There was no significant difference between groups cultured with 5-AZA.
In Fig. 5B, compared with the control group, the mRNA expression of Bsx in the FGR group increased with statistical significance (P < 0.05). The Bsx expression in groups cultured with 5-AZA was much higher than that cultured without 5-AZA (P < 0.05). NPY displayed the same expression mode as Bsx (Fig. 5C).
6. The methylation level in the Bsx promotor region decreased in NPCs cultured in vitro with DNMT1 specific inhibitor.
We also tested Bsx methylation levels among groups. The result is shown in Fig. 6. Compared with the control group, the methylation level in the Bsx promoter region in the FGR group decreased. Meanwhile, the methylation level decreased in NPCs cultured in vitro with 5-AZA compared with those cultured without the inhibitor. The inhibit phenomenon was much more evident in the P1 cohort than in the E18 cohort (Fig. 6).