載脂蛋白J（apoJ），是具有多種功能的分泌性醣蛋白。 ApoJ在內質網（ER）以前體形式形成，並且在高基氏體中經由弗林蛋白酶切成α-和β-亞基後形成成熟的apoJ。在其他研究中已經發現apoJ與調節人類疾病相關，包括衰老，神經退行性疾病，癌症和代謝/心血管疾病。在之前的研究，我們已經發現apoJ會作為宿主蛋白促進傳染性丙型肝炎病毒（HCV）顆粒的產生，並且穩定了在ER及高基氏體膜接觸位的油滴與HCV病毒蛋白之間的相互作用。我們推測apoJ可能與HCV誘導的脂質累積有關。然而，apoJ在致病性脂質累積中的分子機制仍然不清楚。因此，我們的目的是要探討apoJ調節細胞內脂質累積的作用機制。在本研究中，我們使用游離脂肪酸，包括棕櫚酸（PA）和油酸（OA）去誘導肝細胞（Huh7和HepG2）和巨噬細胞（U937和THP-1）中的脂質累積。結果顯示，PA和OA除了誘導肝細胞脂質累積也會使apoJ的表現量增加。ApoJ減少後也會阻斷Huh7細胞中PA和OA誘導的脂質累積。此外，apoJ在游離脂肪酸處理後會和游離膽固醇，膽固醇酯位在相同位置。這些結果顯示了apoJ在肝臟異常脂質累積中扮演重要作用。我們接下來透過免疫螢光法得知游離脂肪酸處理後apoJ會與固醇酰基轉移酶（SOAT）在一起，SOAT是將細胞內游離膽固醇酯化成膽固醇酯的酵素。 根據以上的實驗結果顯示apoJ透過與SOAT相互作用調節細胞內脂質累積。 因此，在未來apoJ和SOAT可以做為與異常脂質累積相關疾病的治療目標。

Apolipoprotein J (apoJ), also known as clusterin, is a secretory glycoprotein with multiple functions. ApoJ is synthesized in the endoplasmic reticulum (ER) as a precursor form and maturated in the Golgi after cleavage into α- and β-subunits by furin. Several human diseases, including aging, neurodegenerative disorders, cancers, and metabolic/cardiovascular diseases have been found to be correlated with the regulation of apoJ. Previously, our group had identified apoJ as a host protein which facilitated infectious hepatitis C virus (HCV) particle production and stabilized the interaction between lipid droplet (LD) and HCV viral proteins at the ER-Golgi membrane contact site. We speculated that apoJ might be associated with HCV-induced lipid accumulation. However, the molecular mechanism of apoJ in pathogenic lipid accumulation is still elusive. Therefore, the mechanism of apoJ in regulation of intracellular lipid accumulation was addressed. In the present study, the free fatty acids, including palmitic acid (PA) and oleic acid (OA), were applied to induce intracellular lipid accumulation in hepatocytes (Huh7 and HepG2) and macrophages (U937 and THP-1). The results showed that PA and OA induced lipid accumulation in hepatocytes parallel with increasing level of apoJ. Knockdown of apoJ blocked PA and OA-induced lipid accumulation, and meanwhile apoJ was colocalized with free cholesterol and cholesteryl ester after free fatty acids treatment, suggesting the crucial role of apoJ in hepatic aberrant lipid accumulation. Furthermore, apoJ was colocalized with sterol O-acyltransferase (SOAT), the enzyme responsible for the biosynthesis of intracellular cholesteryl ester after free fatty acids treatment by immunofluorescence. Together, the results suggested that apoJ might modulate intracellular lipid accumulation by interacting with SOAT, providing prospective therapeutic targets for metabolic diseases related to aberrant lipid accumulation.

Alger, H. M., J. M. Brown, J. K. Sawyer, K. L. Kelley, R. Shah, M. D. Wilson, M. C. Willingham and L. L. Rudel (2010). "Inhibition of acyl-coenzyme A:cholesterol acyltransferase 2 (ACAT2) prevents dietary cholesterol-associated steatosis by enhancing hepatic triglyceride mobilization." J Biol Chem 285(19): 14267-14274.

Chang, N. Y., Y. J. Chan, S. T. Ding, Y. H. Lee, W. C. HuangFu and I. H. Liu (2016). "Sterol O-Acyltransferase 2 Contributes to the Yolk Cholesterol Trafficking during Zebrafish Embryogenesis." PLoS One 11(12): e0167644.

Chu, B. B., Y. C. Liao, W. Qi, C. Xie, X. Du, J. Wang, H. Yang, H. H. Miao, B. L. Li and B. L. Song (2015). "Cholesterol transport through lysosome-peroxisome membrane contacts." Cell 161(2): 291-306.

Cooper, A. D. (1997). "Hepatic uptake of chylomicron remnants." Journal of lipid research 38(11): 2173-2192.

Dai, Z., W. Qi, C. Li, J. Lu, Y. Mao, Y. Yao, L. Li, T. Zhang, H. Hong, S. Li, T. Zhou, Z. Yang, X. Yang, G. Gao and W. Cai (2013). "Dual regulation of adipose triglyceride lipase by pigment epithelium-derived factor: a novel mechanistic insight into progressive obesity." Mol Cell Endocrinol 377(1-2): 123-134.

Gibson, J. H., B. Slobedman, K. Harikrishnan, S. L. Williamson, D. Minchenko, A. El-Osta, J. L. Stern and J. Christodoulou (2010). "Downstream targets of methyl CpG binding protein 2 and their abnormal expression in the frontal cortex of the human Rett syndrome brain." BMC neuroscience 11(1): 53.

Gluchowski, N. L., M. Becuwe, T. C. Walther and R. V. Farese, Jr. (2017). "Lipid droplets and liver disease: from basic biology to clinical implications." Nat Rev Gastroenterol Hepatol 14(6): 343-355.

Goo, Y. H., S. H. Son and A. Paul (2017). "Lipid Droplet-Associated Hydrolase Promotes Lipid Droplet Fusion and Enhances ATGL Degradation and Triglyceride Accumulation." Sci Rep 7(1): 2743.

Green, C. J., C. Pramfalk, K. J. Morten and L. Hodson (2015). "From whole body to cellular models of hepatic triglyceride metabolism: man has got to know his limitations." Am J Physiol Endocrinol Metab 308(1): E1-20.

Hsu, S., E. Koren, Y. Chan, M. Koscec, A. Sheehy, F. Kolodgie, R. Virmani and D. Feder (2014). "Effects of everolimus on macrophage-derived foam cell behavior." Cardiovasc Revasc Med 15(5): 269-277.

Khor, V. K., W. J. Shen and F. B. Kraemer (2013). "Lipid droplet metabolism." Curr Opin Clin Nutr Metab Care 16(6): 632-637.

Koltai, T. (2014). "Clusterin: a key player in cancer chemoresistance and its inhibition." Onco Targets Ther 7: 447-456.

Lada, A. T., M. Davis, C. Kent, J. Chapman, H. Tomoda, S. Omura and L. L. Rudel (2004). "Identification of ACAT1- and ACAT2-specific inhibitors using a novel, cell-based fluorescence assay: individual ACAT uniqueness." J Lipid Res 45(2): 378-386.

Lee, R. G., M. C. Willingham, M. A. Davis, K. A. Skinner and L. L. Rudel (2000). "Differential expression of ACAT1 and ACAT2 among cells within liver, intestine, kidney, and adrenal of nonhuman primates." Journal of lipid research 41(12): 1991-2001.

Lin, C. C., P. Tsai, H. Y. Sun, M. C. Hsu, J. C. Lee, I. C. Wu, C. W. Tsao, T. T. Chang and K. C. Young (2014). "Apolipoprotein J, a glucose-upregulated molecular chaperone, stabilizes core and NS5A to promote infectious hepatitis C virus virion production." J Hepatol 61(5): 984-993.

Loizides-Mangold, U., S. Clement, A. Alfonso-Garcia, E. Branche, S. Conzelmann, C. Parisot, E. O. Potma, H. Riezman and F. Negro (2014). "HCV 3a core protein increases lipid droplet cholesteryl ester content via a mechanism dependent on sphingolipid biosynthesis." PLoS One 9(12): e115309.

Materia, S., M. A. Cater, L. W. J. Klomp, J. F. B. Mercer and S. La Fontaine (2012). "Clusterin and COMMD1 Independently Regulate Degradation of the Mammalian Copper ATPases ATP7A and ATP7B." Journal of Biological Chemistry 287(4): 2485-2499.

Ohshiro, T., K. Kobayashi, M. Ohba, D. Matsuda, L. L. Rudel, T. Takahashi, T. Doi and H. Tomoda (2017). "Selective inhibition of sterolO-acyltransferase 1 isozyme by beauveriolide III in intact cells." Sci Rep 7(1): 4163.

Onal, G., O. Kutlu, D. Gozuacik and S. Dokmeci Emre (2017). "Lipid Droplets in Health and Disease." Lipids Health Dis 16(1): 128.

Park, S., K. W. Mathis and I. K. Lee (2014). "The physiological roles of apolipoprotein J/clusterin in metabolic and cardiovascular diseases." Rev Endocr Metab Disord 15(1): 45-53.

Plakkal Ayyappan, J., A. Paul and Y. H. Goo (2016). "Lipid droplet-associated proteins in atherosclerosis (Review)." Mol Med Rep 13(6): 4527-4534.

Rawson, R. B. (2003). "The SREBP pathway--insights from Insigs and insects." Nat Rev Mol Cell Biol 4(8): 631-640.

Sansanwal, P., L. Li and M. M. Sarwal (2015). "Inhibition of intracellular clusterin attenuates cell death in nephropathic cystinosis." J Am Soc Nephrol 26(3): 612-625.

Shim, Y. J., B. H. Kang, H. S. Jeon, I. S. Park, K. U. Lee, I. K. Lee, G. H. Park, K. M. Lee, P. Schedin and B. H. Min (2011). "Clusterin induces matrix metalloproteinase-9 expression via ERK1/2 and PI3K/Akt/NF-kappaB pathways in monocytes/macrophages." J Leukoc Biol 90(4): 761-769.

Trougakos, I. P. (2013). "The molecular chaperone apolipoprotein J/clusterin as a sensor of oxidative stress: implications in therapeutic approaches - a mini-review." Gerontology 59(6): 514-523.
Trougakos, I. P. and E. S. Gonos (2002). "Clusterin/apolipoprotein J in human aging and cancer." The international journal of biochemistry & cell biology 34(11): 1430-1448.

Wu, N., R. Q. Li and L. Li (2018). "SOAT1 deficiency attenuates atherosclerosis by regulating inflammation and cholesterol transportation via HO-1 pathway." Biochem Biophys Res Commun 501(2): 343-350.

Yang, N. and Q. Qin (2015). "Apolipoprotein J: A New Predictor and Therapeutic Target in Cardiovascular Disease?" Chin Med J (Engl) 128(18): 2530-2534.

Zeituni, E. M., M. H. Wilson, X. Zheng, P. A. Iglesias, M. A. Sepanski, M. A. Siddiqi, J. L. Anderson, Y. Zheng and S. A. Farber (2016). "Endoplasmic Reticulum Lipid Flux Influences Enterocyte Nuclear Morphology and Lipid-dependent Transcriptional Responses." J Biol Chem 291(45): 23804-23816.

Zhang, F., M. Kumano, E. Beraldi, L. Fazli, C. Du, S. Moore, P. Sorensen, A. Zoubeidi and M. E. Gleave (2014). "Clusterin facilitates stress-induced lipidation of LC3 and autophagosome biogenesis to enhance cancer cell survival." Nat Commun 5: 5775.

Zhao, K. and N. D. Ridgway (2017). "Oxysterol-Binding Protein-Related Protein 1L Regulates Cholesterol Egress from the Endo-Lysosomal System." Cell Rep 19(9): 1807-1818.