Adipose differentiation-related protein, also known as perilipin 2, ADRP or adipophilin, is a protein which belongs to the perilipin (PAT) family of cytoplasmic lipid droplet (CLD)–binding proteins.[5] In humans it is encoded by the ADFP gene.[6] This protein surrounds the lipid droplet along with phospholipids and is involved in assisting the storage of neutral lipids within the lipid droplets.[7]
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The adipose differentiation related protein (ADRP) was first characterized as an mRNA molecule that express early in adipocyte differentiation.[8] The full length cDNA was cloned by rapid amplification of cDNA ends method and sequence analysis results in a protein with 425 amino acids that is unique and similar sequences had not previously been reported.[8]
In humans, the gene for adipose differentiation related protein is located at short p arm of chromosome 9 at region 22 band 1 from base pair 19108391 to 19127606 (GRCh38.p7) (map).[9]
The proposed models for adipose differentiation related protein (perilipin 2) is maintained by the protein model portal.[10] It is based on homology modelling and no models were found with greater than 90 percent homology. Perlipin 2 has three different functional domains . 1-115 amino acid sequences at N-terminal is highly similar with other perlipin family proteins and is required for stabilization of lipid droplets, 103-215 mid- region is needed for binding at lipid droplets while the C-terminal sequence from 220-437 forms four helix bundles.[11]
Perilipin 2 was thought to be expressed only in adipose tissues previously.[12] However, later on it was found to be expressed in all types of cells including many non-adipose tissues.[12] The function of perilipin 2 involves the formation of lipid droplets, formation of fatty liver by increasing uptake of fatty acids etc. Decreased expression of perilipin 2 decreases the fatty liver while increase expression of perilipin is associated with several metabolic diseases like type 2 diabetes, insulin resistance, heart diseases. Moreover, its expression was also found to be linked with other age related diseases.[7] This protein is associated with the globule surface membrane material and is major constituent of the globule surface. Increase in mRNA levels is one of the earliest indications of adipocyte differentiation.[6]
Pre-adipocytes are undifferentiated fibroblasts that can be stimulated to form adipocytes. Studies have shed light into potential molecular mechanisms in the fate determination of pre-adipocytes although the exact lineage of adipocyte is still unclear.[13]
In humans, a substitution mutation at the C-terminal region of perlipin 2 was shown to affect both the structure and function of the protein.[11] At 251 position , serine residue was substituted by proline which results in the disruption of predicted alpha helical structure of the protein as well as reduction in the plasma triglycerides and lipolysis.[14] Thus, mutation in perlipin 2 may influence the development of different human metabolic diseases.
Conditions like obesity, type 2 diabetes are related with metabolic disorders. It involves increase accumulation of lipid due to impaired fatty acid metabolism. Alcoholic liver diseases and non-alcoholic fatty liver disease are two types of conditions associated with liver lipid accumulation.[15] Obesity is related with increase accumulation of lipid droplets in non-adipose tissues causing lipotoxicity. The expression of perlipin 2 at normal level appears necessary to induce obesity in mouse model. Increased activity of perlipin 2 increases the resistance to insulin thereby promoting type 2 diabetes.[15]
Cardiovascular diseases
Age related diseases like atherosclerosis, hypertension accounts many deaths in elderly people.[16] Accumulation of lipid droplets induce the modification of macrophages to foam cells. Lysis of foam cells resulted in Atherosclerotic plaques and such plaques rupture and blocked the thrombotic vessel.[16] Perlipin 2 protein around the macrophages and foam cells was found to play important role in formation of atheroma. Downregulation of perlipin 2 inhibits the lipid droplet accumulation and decreases the likelihood to convert macrophages to foam cells.[17]
Cancer
Another factor which increases the risk for cancer is aging process.[18] Analysis of body fluids like urine and blood from circulation from different types of cancer for example colorectal cancer, Burkitt cancer, lung adenocarcinoma showed increase level of Perlipin 2.[19] Perlipin 2 can also serve as a biomarker for early detection of some type of cancer.[20]
Sentinelli F, Capoccia D, Incani M, Bertoccini L, Severino A, Pani MG, Manconi E, Cossu E, Leonetti F, Baroni MG (September 2016). "The perilipin 2 (PLIN2) gene Ser251Pro missense mutation is associated with reduced insulin secretion and increased insulin sensitivity in Italian obese subjects". Diabetes Metab. Res. Rev. 32 (6): 550–6. doi:10.1002/dmrr.2751. PMID 26443937. S2CID 5256380. Matsubara J, Honda K, Ono M, Sekine S, Tanaka Y, Kobayashi M, Jung G, Sakuma T, Nakamori S, Sata N, Nagai H, Ioka T, Okusaka T, Kosuge T, Tsuchida A, Shimahara M, Yasunami Y, Chiba T, Yamada T (October 2011). "Identification of adipophilin as a potential plasma biomarker for colorectal cancer using label-free quantitative mass spectrometry and protein microarray". Cancer Epidemiology, Biomarkers & Prevention. 20 (10): 2195–203. doi:10.1158/1055-9965.EPI-11-0400. hdl:2433/197220. PMID 21828233. Prieto DA, Johann DJ, Wei BR, Ye X, Chan KC, Nissley DV, Simpson RM, Citrin DE, Mackall CL, Linehan WM, Blonder J (2014). "Mass spectrometry in cancer biomarker research: a case for immunodepletion of abundant blood-derived proteins from clinical tissue specimens". Biomarkers in Medicine. 8 (2): 269–86. doi:10.2217/bmm.13.101. PMC 4201940. PMID 24521024.
- Bosma M, Hesselink MK, Sparks LM, Timmers S, Ferraz MJ, Mattijssen F, van Beurden D, Schaart G, de Baets MH, Verheyen FK, Kersten S, Schrauwen P (November 2012). "Perilipin 2 improves insulin sensitivity in skeletal muscle despite elevated intramuscular lipid levels". Diabetes. 61 (11): 2679–90. doi:10.2337/db11-1402. PMC 3478528. PMID 22807032.
- Heid HW, Schnölzer M, Keenan TW (December 1996). "Adipocyte differentiation-related protein is secreted into milk as a constituent of milk lipid globule membrane". The Biochemical Journal. 320 (3): 1025–30. doi:10.1042/bj3201025. PMC 1218030. PMID 9003395.
- Heid HW, Moll R, Schwetlick I, Rackwitz HR, Keenan TW (November 1998). "Adipophilin is a specific marker of lipid accumulation in diverse cell types and diseases". Cell and Tissue Research. 294 (2): 309–21. doi:10.1007/s004410051181. PMID 9799447. S2CID 9990761.
- Schultz CJ, Torres E, Londos C, Torday JS (August 2002). "Role of adipocyte differentiation-related protein in surfactant phospholipid synthesis by type II cells". American Journal of Physiology. Lung Cellular and Molecular Physiology. 283 (2): L288–96. doi:10.1152/ajplung.00204.2001. PMID 12114189. S2CID 24026044.
- Saarikoski ST, Rivera SP, Hankinson O (October 2002). "Mitogen-inducible gene 6 (MIG-6), adipophilin and tuftelin are inducible by hypoxia". FEBS Letters. 530 (1–3): 186–90. doi:10.1016/S0014-5793(02)03475-0. PMID 12387890. S2CID 37181106.
- Targett-Adams P, Chambers D, Gledhill S, Hope RG, Coy JF, Girod A, McLauchlan J (May 2003). "Live cell analysis and targeting of the lipid droplet-binding adipocyte differentiation-related protein". The Journal of Biological Chemistry. 278 (18): 15998–6007. doi:10.1074/jbc.M211289200. PMID 12591929.
- Bildirici I, Roh CR, Schaiff WT, Lewkowski BM, Nelson DM, Sadovsky Y (December 2003). "The lipid droplet-associated protein adipophilin is expressed in human trophoblasts and is regulated by peroxisomal proliferator-activated receptor-gamma/retinoid X receptor". The Journal of Clinical Endocrinology and Metabolism. 88 (12): 6056–62. doi:10.1210/jc.2003-030628. PMID 14671211.
- Larigauderie G, Furman C, Jaye M, Lasselin C, Copin C, Fruchart JC, Castro G, Rouis M (March 2004). "Adipophilin enhances lipid accumulation and prevents lipid efflux from THP-1 macrophages: potential role in atherogenesis". Arteriosclerosis, Thrombosis, and Vascular Biology. 24 (3): 504–10. doi:10.1161/01.ATV.0000115638.27381.97. PMID 14707038.
- Nakamura N, Akashi T, Taneda T, Kogo H, Kikuchi A, Fujimoto T (September 2004). "ADRP is dissociated from lipid droplets by ARF1-dependent mechanism". Biochemical and Biophysical Research Communications. 322 (3): 957–65. doi:10.1016/j.bbrc.2004.08.010. PMID 15336557.
- Robenek H, Lorkowski S, Schnoor M, Troyer D (February 2005). "Spatial integration of TIP47 and adipophilin in macrophage lipid bodies". The Journal of Biological Chemistry. 280 (7): 5789–94. doi:10.1074/jbc.M407194200. PMID 15545278.
- Masuda Y, Itabe H, Odaki M, Hama K, Fujimoto Y, Mori M, Sasabe N, Aoki J, Arai H, Takano T (January 2006). "ADRP/adipophilin is degraded through the proteasome-dependent pathway during regression of lipid-storing cells". Journal of Lipid Research. 47 (1): 87–98. doi:10.1194/jlr.M500170-JLR200. PMID 16230742.
- Tobin KA, Harsem NK, Dalen KT, Staff AC, Nebb HI, Duttaroy AK (April 2006). "Regulation of ADRP expression by long-chain polyunsaturated fatty acids in BeWo cells, a human placental choriocarcinoma cell line". Journal of Lipid Research. 47 (4): 815–23. doi:10.1194/jlr.M500527-JLR200. PMID 16391323.
- Dalen KT, Ulven SM, Arntsen BM, Solaas K, Nebb HI (May 2006). "PPARalpha activators and fasting induce the expression of adipose differentiation-related protein in liver". Journal of Lipid Research. 47 (5): 931–43. doi:10.1194/jlr.M500459-JLR200. PMID 16489205.
- Ohsaki Y, Maeda T, Maeda M, Tauchi-Sato K, Fujimoto T (August 2006). "Recruitment of TIP47 to lipid droplets is controlled by the putative hydrophobic cleft". Biochemical and Biophysical Research Communications. 347 (1): 279–87. doi:10.1016/j.bbrc.2006.06.074. PMID 16808905.
- Magra AL, Mertz PS, Torday JS, Londos C (November 2006). "Role of adipose differentiation-related protein in lung surfactant production: a reassessment". Journal of Lipid Research. 47 (11): 2367–73. doi:10.1194/jlr.M600157-JLR200. PMID 16936283.
- Yao M, Huang Y, Shioi K, Hattori K, Murakami T, Nakaigawa N, Kishida T, Nagashima Y, Kubota Y (January 2007). "Expression of adipose differentiation-related protein: a predictor of cancer-specific survival in clear cell renal carcinoma". Clinical Cancer Research. 13 (1): 152–60. doi:10.1158/1078-0432.CCR-06-1877. PMID 17200350.
- Sarov-Blat L, Kiss RS, Haidar B, Kavaslar N, Jaye M, Bertiaux M, Steplewski K, Hurle MR, Sprecher D, McPherson R, Marcel YL (May 2007). "Predominance of a proinflammatory phenotype in monocyte-derived macrophages from subjects with low plasma HDL-cholesterol". Arteriosclerosis, Thrombosis, and Vascular Biology. 27 (5): 1115–22. doi:10.1161/ATVBAHA.106.138990. PMID 17322100.
