Schultz C J, Blanchette-Mackie E J, Scow R O
Laboratory of Cellular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
J Lipid Res. 2000 Feb;41(2):214-25.
Combined lipase deficiency (cld) is a recessive mutation in mice that causes a severe lack of lipoprotein lipase (LPL) and hepatic lipase (HL) activities, hyperlipemia, and death within 3 days after birth. Earlier studies showed that inactive LPL and HL were synthesized by cld/cld tissues and that LPL synthesized by cld/cld brown adipocytes was retained in their ER. We report here a study of HL in liver, adrenal, and plasma of normal newborn and cld/cld mice. Immunofluorescence studies showed HL was present in extracellular space, but not in cells, in liver and adrenal of both normal and cld/cld mice. When protein secretion was blocked with monensin, HL was retained intracellularly in liver cell cultures and in incubated adrenal tissues of both groups of mice. These findings demonstrated that HL was synthesized and secreted by liver and adrenal cells in normal newborn and cld/cld mice. HL activities in liver, adrenal, and plasma in cld/cld mice were very low, <8% of that in normal newborn mice, indicating that HL synthesized and secreted by cld/cld cells was inactive. Livers of both normal newborn and cld/cld mice synthesized LPL, but the level of LPL activity in cld/cld liver was very low, <9% of that in normal liver. Immunofluorescence studies showed that LPL was present intracellularly in liver of cld/cld mice, indicating that LPL was synthesized but not secreted by cld/cld liver cells. Immunofluorescent LPL was not found in normal newborn liver cells unless the cells were treated with monensin, thus demonstrating that normal liver cells synthesized and secreted LPL. Livers of both groups of mice contained an unidentified alkaline lipase activity which accounted for 34-54% of alkaline lipase activity in normal and 65% of that in cld/cld livers. Our findings indicate that liver and adrenal cells synthesized and secreted HL in both normal newborn and cld/cld mice, but the lipase was inactive in cld/cld mice. That cld/cld liver cells secreted inactive HL while retaining inactive LPL indicates that these closely related lipases were processed differently.
联合脂肪酶缺乏症（cld）是小鼠中的一种隐性突变，会导致严重缺乏脂蛋白脂肪酶（LPL）和肝脂肪酶（HL）活性、高脂血症，并在出生后3天内死亡。早期研究表明，无活性的LPL和HL由cld/cld组织合成，且cld/cld棕色脂肪细胞合成的LPL保留在其内质网中。我们在此报告一项对正常新生小鼠和cld/cld小鼠的肝脏、肾上腺及血浆中HL的研究。免疫荧光研究表明，在正常和cld/cld小鼠的肝脏和肾上腺中，HL存在于细胞外空间而非细胞内。当用莫能菌素阻断蛋白质分泌时，HL在两组小鼠的肝细胞培养物和孵育的肾上腺组织中均保留在细胞内。这些发现表明，正常新生小鼠和cld/cld小鼠的肝脏和肾上腺细胞合成并分泌HL。cld/cld小鼠肝脏、肾上腺及血浆中的HL活性非常低，不到正常新生小鼠的8%，表明cld/cld细胞合成并分泌的HL无活性。正常新生小鼠和cld/cld小鼠的肝脏均合成LPL，但cld/cld肝脏中LPL活性水平非常低，不到正常肝脏的9%。免疫荧光研究表明，LPL存在于cld/cld小鼠肝脏的细胞内，表明LPL由cld/cld肝细胞合成但未分泌。在正常新生肝细胞中未发现免疫荧光LPL，除非细胞用莫能菌素处理，从而证明正常肝细胞合成并分泌LPL。两组小鼠的肝脏均含有一种未鉴定的碱性脂肪酶活性，其在正常肝脏中占碱性脂肪酶活性的34 - 54%，在cld/cld肝脏中占65%。我们的发现表明，正常新生小鼠和cld/cld小鼠的肝脏和肾上腺细胞均合成并分泌HL，但该脂肪酶在cld/cld小鼠中无活性。cld/cld肝细胞分泌无活性的HL同时保留无活性的LPL，表明这些密切相关的脂肪酶加工方式不同。
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