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The Effect of Exercise Intensity on Changes in Neuronal Nitric Oxide Synthase Expression in the Hippocampus and Cerebral Cortex of Obese Mice

고지방식이로 유도된 비만 마우스의 해마 및 대뇌피질에서 운동강도에 따른 nNOS 발현의 변화

  • 백경완 (부산대학교 스포츠과학부)
  • Received : 2018.09.19
  • Accepted : 2018.11.26
  • Published : 2019.01.30

Abstract

Recent studies reported that obesity upregulated the expression of neuronal nitric oxide synthase (nNOS) and regulated particular behavior patterns in animal models. They also reported that ameliorated the increase in nNOS expression and decreased depression and anxiolytic effects. Thus, exercise seems to be an effective strategy for improving brain function by downregulating nNOS. However, the immune response differs greatly, depending on the exercise intensity. The aim of the present study was to investigate differences in brain nNOS expression in obese C57BL/6 mice that performed exercise of different intensities. Obesity was induced in 6-wks-old mice (n=35) by feeding a 60%-fat diet for 6-wks. A control (CON) group (n=14) was fed a normal diet. At the end of the induction 6-wks period of obesity, seven animals in the CON group and obesity-induced group were sacrificed to confirm obesity induction (preliminary experiments and confirmation of visceral fat accumulation). The remaining animals were then used in an 8-wks exercise intervention. Other than the CON (n=7), the obesity-induced animals were divided into the following groups: high-fat diet (HFD, n=7), HFD-low intensity (HFD-LI, n=7, 12 m/min for 75 min), HFD-moderate intensity (HFD-MI, n=7, 15 m/min for 60 min), and HFD-high intensity (HFD-HI, n=7, 18 m/min for 50 min). The exercise was performed on an animal treadmill. The expression of the nNOS protein in the hippocampus was significantly higher in the HFD group as compared with that in the CON group (p<0.01). However, there was no difference in the hippocampal expression of the nNOS protein in the other exercise groups as compared with that in the CON group. In contrast, nNOS expression in the HFD-HI group was significantly lower than that in the HFD-LI group (p<0.05). The expression of phosphorylated Akt (pAkt) was significantly higher in all the exercise groups as compared with that in the CON and HFD groups. There was no difference in the expression of pAkt in the cerebral cortex among groups, and the expression of pAkt in the cerebellum was significantly higher in the HFD-HI group as compared with that in the CON group (p<0.05). There were also no between-group differences in pAkt expression in the cerebellum among the various exercise groups. In conclusion, nNOS seems to be overexpressed in response to obesity, and it appears to be downregulated by exercise. Relatively high-intensity exercise may be effective in improving brain function by downregulating nNOS.

최근 비만에 의해 과발현된 신경세포형 산화질소 생성효소(neuronal nitric oxide synthase, nNOS)가 정서적 행동을 조절하는 중요한 인자라는 보고되었다. 이와 관련한 최근의 연구에서 운동이 비만에 의해 과발현된 nNOS를 억제하고 정서적 우울감과 항불안 효과를 감소시켰다는 연구결과가 보고되었다. 운동은 nNOS를 억제하여 뇌의 기능을 향상시킬 수 있는 효과적인 전략으로 보이지만 운동은 강도에 따라 면역 반응에 큰 차이가 있다. 따라서 본 연구에서는 고지방식이(high-fat diet, HFD)로 유도된 비만 마우스에서 다른 강도의 운동을 실시하여 해마의 nNOS 발현의 차이를 분석하고자 하였다. 실험동물은 C57BL/6 마우스를 사용하였다. 대조군(CON, n=14)을 제외한 마우스(n=35)에게 6주 동안 60%의 고지방식이를 섭취시켜 비만을 유도하였다. 6주간의 비만유도 기간이 종료된 후 CON과 비만이 유도된 동물 각각 7마리씩 희생하여 비만유도를 확인하는데 사용되었다. 나머지 동물은 8주간의 운동중재 연구에 이용되었다. 이 때 CON을 제외하고 비만이 유도된 동물들은 고지방대조군(HFD) 그리고 저강도운동군(HFD-LI, n=7) 중강도운동군(HFD-MI, n=7) 그리고 HFD-고강도(HFD-HI, n=7)로 나누어졌다. HFD-LI는 12 m/min으로 75분, HFD-MI는 15 m/min으로 60분 그리고 HFD-HI는 18 m/min으로 50분 동안 동물용 트레드밀에서 운동이 수행되었다(동등한 운동량, 900 m). 해마(hippocampus)의 nNOS 단백질의 발현은 CON에 비해 HFD에서 유의하게 높았고(p<0.01), CON과 운동을 실시한 모든 그룹과 차이가 없었다. 하지만 HFD-LI에 비해 HFD-HI가 유의하게 nNOS 발현이 낮았다(p<0.05). 대뇌피질에서는 CON에 비해 HFD에서 유의하게 높았으나(p<0.01), 다른 그룹 간에 차이는 없었다. nNOS의 생성을 조절할 수 있는 인산화된 Akt (pAkt)의 발현이 CON과 HFD에 비해 운동을 실시한 나머지 그룹 모두에서 유의하게 높았다. 대뇌피질에서의 pAkt의 발현에서는 차이가 모든 그룹 간에 차이가 없었고, 소뇌에서는 CON에 비해 HFD-HI에서 유의하게 높았다(p<0.05). 소뇌에서는 각 그룹 간에 차이가 없었다. 결론적으로 nNOS는 고지방식이와 비만에 의해 과발현된 것으로 보여지고 이를 운동을 통하여 낮출 수 있는 것으로 보여지며, 이 때 운동량이 같다는 가정하에 상대적으로 높은 강도가 효과적일 가능성이 있다.

Keywords

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Fig. 1. Experimental design.

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Fig. 2. A. Body weight change during the total experiment period in the total group. B. Body weight change during the induction of obesity phase in the normal diet-fed group and high-fat diet-fed group. C. Body weight change during the intervention phase in the exercised group. D. Food efficiency ratio.

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Fig. 3. Western blot showing nNOS protein in the hippocampus (A), cerebral cortex (B), and cerebellum (C) of all groups (1:CON; 2:HFD; 3:HFD-LI; 4;HFD-MI; 5:HFD-HI).

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Fig. 4. nNOS gene expression levels in the cerebral cortex (A) and cerebellum (B) of all groups.

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Fig. 5. Western blot showing pAktSer473 protein in the hippocampus (A), cerebral cortex (B), and cerebellum (C) of all groups (1:CON; 2:HFD; 3:HFD-LI; 4;HFD-MI; 5:HFD-HI).

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