Langfort J, Donsmark M, Ploug T, Holm C, Galbo H
Copenhagen Muscle Research Centre, Department of Medical Physiology, The Panum Institute, University of Copenhagen, Denmark.
Acta Physiol Scand. 2003 Aug;178(4):397-403. doi: 10.1046/j.1365-201X.2003.01155.x.
The enzymatic regulation of intramuscular triacylglycerol (TG) breakdown has until recently not been well understood. Our aim was to elucidate the role of hormone-sensitive lipase (HSL), which controls TG breakdown in adipose tissue.
Isolated rat muscle as well as exercising humans were studied.
The presence of HSL was demonstrated in all muscle fibre types by Western blotting of muscle fibres isolated by collagenase treatment or after freeze-drying. The content of HSL varies between fibre types, being higher in oxidative than in glycolytic fibres. Analysed under conditions optimal for HSL, neutral lipase activity in muscle can be stimulated by adrenaline as well as by contractions. These increases are abolished by presence of anti-HSL antibody during analysis. Moreover, immunoprecipitation with affinity-purified anti-HSL antibody causes similar reductions in muscle HSL protein concentration and in measured neutral lipase responses to contractions. The immunoreactive HSL in muscle is stimulated by adrenaline via beta-adrenergic activation of protein kinase A (PKA). From findings in adipocytes it is likely that PKA phosphorylates HSL at residues Ser563, Ser659 and Ser660. Contraction probably also enhances muscle-HSL activity by phosphorylation, because the contraction-induced increase in HSL activity is increased by the protein phosphatase inhibitor okadaic acid and reversed by alkaline phosphatase. A novel signalling pathway in muscle by which HSL activity may be stimulated by protein kinase C (PKC) via extracellular signal regulated kinase (ERK) has been demonstrated. In contrast to previous findings in adipocytes, in muscle activation of ERK is not necessary for stimulation of HSL by adrenaline. However, contraction-induced HSL activation is mediated by PKC, at least partly via the ERK pathway. In fat cells ERK is known to phosphorylate HSL at Ser600. So, phosphorylation of different sites may explain that in muscle the effects of contractions and adrenaline on HSL activity are partially additive. In line with the view that the two stimuli act by different mechanisms, training increases the contraction-mediated, but diminishes the adrenaline mediated HSL activation in muscle.
The existence and regulation of HSL in skeletal muscle indicate a role of HSL in muscle TG metabolism.
直到最近，人们对肌肉内三酰甘油（TG）分解的酶促调节仍未完全理解。我们的目的是阐明激素敏感性脂肪酶（HSL）的作用，该酶控制脂肪组织中的TG分解。
对分离的大鼠肌肉以及运动中的人类进行了研究。
通过对经胶原酶处理或冷冻干燥后分离的肌纤维进行蛋白质印迹分析，证实在所有肌纤维类型中均存在HSL。HSL的含量在不同纤维类型之间有所差异，在氧化型纤维中比在糖酵解型纤维中更高。在最适合HSL的条件下进行分析时，肌肉中的中性脂肪酶活性可被肾上腺素以及收缩所刺激。在分析过程中，抗HSL抗体的存在会消除这些增加。此外，用亲和纯化的抗HSL抗体进行免疫沉淀会导致肌肉中HSL蛋白浓度以及测得的对收缩的中性脂肪酶反应出现类似程度的降低。肌肉中的免疫反应性HSL通过蛋白激酶A（PKA）的β-肾上腺素能激活而被肾上腺素刺激。从脂肪细胞的研究结果来看，PKA可能在丝氨酸563、丝氨酸659和丝氨酸660位点使HSL磷酸化。收缩可能也通过磷酸化增强肌肉HSL活性，因为收缩诱导的HSL活性增加会被蛋白磷酸酶抑制剂冈田酸增强，并被碱性磷酸酶逆转。已证明在肌肉中存在一种新的信号通路，通过该通路蛋白激酶C（PKC）可经由细胞外信号调节激酶（ERK）刺激HSL活性。与之前在脂肪细胞中的发现不同，在肌肉中，ERK的激活对于肾上腺素刺激HSL并非必需。然而，收缩诱导的HSL激活至少部分是由PKC介导的，通过ERK途径。已知在脂肪细胞中ERK会在丝氨酸600位点使HSL磷酸化。因此，不同位点的磷酸化可能解释了在肌肉中收缩和肾上腺素对HSL活性的影响部分是相加的。与这两种刺激通过不同机制起作用的观点一致，训练会增加收缩介导的，但会减少肾上腺素介导的肌肉中HSL激活。
骨骼肌中HSL的存在及其调节表明HSL在肌肉TG代谢中发挥作用。
