Department of Basic Pharmaceutical Sciences, College of Pharmacy, The University Louisiana at Monroe, Monroe, Louisiana 71209, USA.
J Neurosci Res. 2011 Jul;89(7):1114-24. doi: 10.1002/jnr.22632. Epub 2011 Apr 12.
Cellular metabolic stasis is monitored in discrete brain sites, including the dorsal vagal complex (DVC), where A2 noradrenergic neurons perform this sensory function. Single-cell qPCR and high-sensitivity immunoblotting were used to determine if A2 neurons adapt to chronic hypoglycemia by increasing substrate fuel transporter expression, and whether such adjustments coincide with decreased cellular energy instability during this systemic metabolic stress. Tyrosine hydroxylase-immunolabeled neurons were laser-microdissected from the caudal DVC 2 hr after single or serial neutral protamine Hagedorn insulin (NPH) dosing. Preceding hypoglycemia suppressed basal A2 MCT2, GLUT3, and GLUT4 profiles and diminished MCT2, GLUT4, and glucokinase responses to recurring hypoglycemia. Acute NPH caused a robust increase in A2 phospho-AMPK protein levels; baseline phospho-AMPK expression was elevated after 3 days of insulin treatment but only slight augmented after a fourth NPH injection. Transcripts encoding the catecholamine biosynthetic enzyme dopamine-β-hydroxylase were unaffected by acute NPH but were diminished by serial insulin dosing. This evidence for diminished basal A2 glucose and lactate uptake and attenuated phospho-AMPK-mediated detection of hypoglycemia-associated energy deficits suggests that these cells acclimate to chronic hypoglycemia by adopting a new metabolic steady state characterized by energy paucity and reduced sensitivity to hypoglycemia. Because dopamine-β-hydroxylase mRNA was reduced after serial, but not single NPH dosing, A2 neurotransmitter biosynthesis may be impervious to acute hypoglycemia but inhibited when posthypoglycemic metabolic deficiency is exacerbated by recurring hypoglycemia. This research suggests that chronic hypoglycemia-associated adjustments in A2-sensory neurotransmission may reflect cellular energetic debilitation rather than adaptive attenuation of cellular metabolic imbalance.
细胞代谢停滞在离散的脑区受到监测，包括背侧迷走复合体（DVC），其中 A2 去甲肾上腺素能神经元执行这种感觉功能。单细胞 qPCR 和高灵敏度免疫印迹用于确定 A2 神经元是否通过增加底物燃料转运蛋白的表达来适应慢性低血糖，以及在这种系统性代谢应激期间，这种调整是否与细胞能量不稳定性的降低相吻合。在单次或连续中性鱼精蛋白 Hagedorn 胰岛素（NPH）给药后 2 小时，用酪氨酸羟化酶免疫标记的神经元从 DVC 的尾部进行激光微切割。低血糖抑制了基础 A2 MCT2、GLUT3 和 GLUT4 谱，并减弱了 MCT2、GLUT4 和葡萄糖激酶对反复低血糖的反应。急性 NPH 引起 A2 磷酸 AMPK 蛋白水平的强烈增加；胰岛素治疗 3 天后基础磷酸 AMPK 表达升高，但第四次 NPH 注射后仅略有增加。急性 NPH 对编码儿茶酚胺生物合成酶多巴胺-β-羟化酶的转录本没有影响，但连续胰岛素给药后减少。这些证据表明，基础 A2 葡萄糖和乳酸摄取减少，磷酸 AMPK 介导的低血糖相关能量缺陷检测减弱，表明这些细胞通过采用新的代谢稳态来适应慢性低血糖，其特征是能量匮乏和对低血糖的敏感性降低。由于连续而不是单次 NPH 给药后多巴胺-β-羟化酶 mRNA 减少，A2 神经递质生物合成可能对急性低血糖不敏感，但在反复低血糖加剧低血糖后代谢缺陷时受到抑制。这项研究表明，与慢性低血糖相关的 A2 感觉神经传递的调整可能反映了细胞能量衰弱，而不是细胞代谢失衡的适应性减弱。
