Adipogenesis is the formation of adipocytes (fat cells) from stem cells. It involves 2 phases, determination, and terminal differentiation. Determination is mesenchymal stem cells committing to the adipocyte precursor cells, also known as preadipocytes which lose the potential to differentiate to other types of cells such as chondrocytes, myocytes, and osteoblasts. Terminal differentiation is that preadipocytes differentiate into mature adipocytes. Adipocytes can arise either from preadipocytes resident in adipose tissue, or from bone-marrow derived progenitor cells that migrate to adipose tissue.
Adipocytes play a vital role in energy homeostasis and process the largest energy reserve as triglycerol in the body of animals. Adipocytes stay in a dynamic state, they start expanding when the energy intake is higher than the expenditure and undergo mobilization when the energy expenditure exceeds the intake. This process is highly regulated by counter regulatory hormones to which these cells are very sensitive. The hormone insulin promotes expansion whereas the counter hormones epinephrine, glucagon, and ACTH promote mobilization. Adipogenesis is a tightly regulated cellular differentiation process, in which mesenchymal stem cells committing to preadipocytes and preadipocytes differentiating into adipocytes. Cellular differentiation is a change of gene expression patterns which multipotent gene expression alters to cell type specific gene expression. Therefore, transcription factors are crucial for adipogenesis. Transcription factors, peroxis proliferator-activated receptor γ (PPARγ) and CCAAT enhancer-binding proteins (C/EBPs) are main regulators of adipogenesis. Comparing with cells from other lineage, the in vitro differentiation of fat cells is authentic and recapitulates most of the characteristic feature of in vivo differentiation. The key features of differentiated adipocytes are growth arrest, morphological change, high expression of lipogenic genes and production of adipokines like adiponectin, leptin, resistin (in the mouse, not in humans) and TNF-alpha.
In vitro studies on differentiation have used the pre-committed preadipocyte lineage, such as 3T3-L1 and 3T3-F442A cell line, or preadipocytes isolated from the stromal-vascular fraction of white adipose tissue. In vitro differentiation is a highly ordered process. Firstly, proliferating preadipocytes arrest growth usually by contact inhibition. The growth arrest followed by the earliest events, including a morphological change of preadipocyte from the fibroblast-shape to the round-shape and the induction of transcription factors C/EBPβ, and C/EBPδ. The second phase of growth arrest is the expression of two key transcription factors PPARγ and C/EBPα which promote expression of genes that confer the characteristics of mature adipocytes. These genes include adipocyte protein (aP2), insulin receptor, glycerophosphate dehydrogenase, fatty acid synthase, acetyl CoA carboxylase, glucose transporter type 4 (Glut 4) and so on. Through this process, lipid droplets accumulate in the adipocyte. However, preadipocytes cell lines have difficult to different to differentiate into adipocytes. Preadipocytes display CD45− CD31− CD34+ CD29+ SCA1+ CD24+ surface markers can proliferate and differentiate to adipocytes in vivo.
Models of in vitro differentiation
|Cell Line||Origin||Differentiation Protocol|
|3T3-L1||Sub-clone of Swiss 3T3||FBS+ I+ D+ M|
|3T3-F442A||Sub-clone of Swiss 3T3||FBS + I|
|Ob17||Differentiated adipocyte from epididymal fat pad of C57BL/6J ob/ob mice||FBS+ I+ T3|
|TA1||Subclone of C3H10T1/2 ||FBS + D + I|
|30A5||Subclone of C3H10T1/2||FBS + D + M + I|
|1246||Adipogenic Subclone of CH3 mouse teratocarcinoma cell line T984||D + M + I|
|Non-committed with adipogenic potential|
|NIH3T3||NIH Swiss mouse embryo cells||Ectopic expression of PPAR-gamma, C/EBP-alpha or C/EBP-beta + D+ M+ I|
|Swiss 3T3||Swiss mouse embryo cells||Ectopic expression of C/EBP-alpha|
|Balb/3T3||Balb/c mouse embryo cells||Ectopic expression of C/EBP-alpha|
|C3H 10T1/2||C3H mouse embryo cells||PPAR-gamma ligand|
|Kusa 4b10||mouse bone marrow stromal cell line||FBS + I + D + M|
|C2C12||Thigh muscles of C3H mice||Thiazolidinediones|
|G8||Hind limb muscles of fetal Swiss webster mouse||Ectopic expression of PPAR-gamma + CEBP/alpha +D + I|
|FBS = Fetal Bovine Serum, D = Dexamethasone, I = Insulin, M = Methylisobutylxanthine T3 = Triiodothyronine|
PPARγ is a member of the nuclear-receptor superfamily and is the master regulator of adipogenesis. PPARγ heterodimerizes with retinoid X receptor (RXR) and then binds to DNA, which activates the promoters of the downstream genes. PPARγ induces fat-cell specific genes, including aP2, adiponectin and phosphoenolpyruvate carboxykinase (PEPCK). PPARg activation has effects on several aspects of the mature adipocyte characteristics such as morphological changes, lipid accumulation, and the acquisition of insulin sensitivity. PPARγ is necessary and sufficient to promote fat cell differentiation. PPARγ is required for embryonic stem cells (ES cells) differentiation to adipocytes. The expression of PPARγ itself is sufficient to convert fibroblast into adipocytes in vitro. Other pro-adipogenic factors like C/EBPs and Krüppel-like factors (KLFs) have been shown to induce the PPARγ promoter. Moreover, PPARγ is also required to maintain the expression of genes that characterize the mature adipocyte. Thiazolidinediones (TZDs), antidiabetic agents which well used differentiation cocktail in vitro, promoting the activity of PPARγ.
C/EBPs, transcription factors, are members of the basic-leucine zipper class. cAMP, an inducer of adipogenesis, can promote expression of C/EBPβ and C/EBPδ. At the early stage of differentiation, the transient increase of C/EBPβ and C/EBPδ mRNA and protein levels are thought to activate the adipogenic transcription factors, PPARγ and C/EBPα. PPARγ and C/EBPα can feedback to induce the expression of each other as well as their downstream genes. C/EBPα also plays an important role in the insulin sensitivity of adipocytes. However, C/EBPγ suppresses differentiation which might due to inactivation by C/EBPβ.
Although PPARγ and C/EBPα are master regulators of adipogenesis, other transcription factors function in the progression of differentiation. Adipocyte determination and differentiation factor 1 (ADD1) and sterol regulatory element binding protein 1 (SREBP1) can activate PPARγ by the production of an endogenous PPARγ ligand or directly promote the expression of PPARγ. cAMP-responsive element binding protein promotes differentiation, while the activation of PPARγ and C/EBPα is also responsive to negative regulation. T-cell factor/lymphoid enhancer-binding factor (TCF/LEF), GATA2/3, retinoic acid receptor α, and SMAD6/7 don't affect the expression of C/EBPβ and C/EBPδ but inhibit the induction of PPARγ and C/EBPα.
Insulin and IGF1
Wnt/β-catenin signaling suppresses adipogenesis, by promoting the differentiation of mesenchymal stem cells into myocytes and osteocytes but blocking the commitment to the adipocytic lineage. Wnt/β-catenin inhibits the differentiation of preadipocytes by inhibiting the induction of PPARγ and C/EBPα.
Bone morphogenetic proteins (BMPs) are transforming growth factor β (TGFβ) superfamily members. BMP2 can either stimulates the determination of multipotent cells or induce osteogenesis through different receptor heteromers. BMPs also promotes the differentiation of preadipocytes.
Senescent adipose progenitor cells in subcutaneous adipose tissue has been shown to suppress adipogenic differentiation. Reduced adipogenesis in obese persons is due to increased senescent cells in adipose tissue rather than reduced numbers of stem/progenitor cells.
- "Adipogenesis". Merriam-Webster. Retrieved 3 January 2020.
- Gregoire FM, Smas CM, Sul HS (July 1998). "Understanding adipocyte differentiation". Physiological Reviews. 78 (3): 783–809. doi:10.1152/physrev.1922.214.171.1243. PMID 9674695. S2CID 1538359.
- Hausman GJ, Hausman DB (2006). "Search for the preadipocyte progenitor cell". Journal of Clinical Investigation. 116 (12): 3103–3106. doi:10.1172/JCI30666. PMC 1679717. PMID 17143324.
- Cornelius P, MacDougald OA, Lane MD (1994). "Regulation of adipocyte development". Annual Review of Nutrition. 14: 99–129. doi:10.1146/annurev.nu.14.070194.000531. PMID 7946535.
- Rosen ED, MacDougald OA (December 2006). "Adipocyte differentiation from the inside out". Nature Reviews. Molecular Cell Biology. 7 (12): 885–96. doi:10.1038/nrm2066. PMID 17139329.
- Rosen ED, Walkey CJ, Puigserver P, Spiegelman BM (June 2000). "Transcriptional regulation of adipogenesis". Genes & Development. 14 (11): 1293–307. PMID 10837022.
- Rodeheffer MS, Birsoy K, Friedman JM (October 2008). "Identification of white adipocyte progenitor cells in vivo". Cell. 135 (2): 240–9. doi:10.1016/j.cell.2008.09.036. PMID 18835024.
- Green H, Kehinde O (28 February 1974). "Sublines of mouse 3T3 cells that accumulate lipid". Cell. 1 (3): 113–116. doi:10.1016/0092-8674(74)90126-3.
- Green H, Kehinde O (January 1976). "Spontaneous heritable changes leading to increased adipose conversion in 3T3 cells". Cell. 7 (1): 105–13. doi:10.1016/0092-8674(76)90260-9. PMID 949738.
- Négrel R, Grimaldi P, Ailhaud G (December 1978). "Establishment of preadipocyte clonal line from epididymal fat pad of ob/ob mouse that responds to insulin and to lipolytic hormones". Proceedings of the National Academy of Sciences of the United States of America. 75 (12): 6054–8. Bibcode:1978PNAS...75.6054N. doi:10.1073/pnas.75.12.6054. PMC 393116. PMID 216011.
- Chapman AB, Knight DM, Dieckmann BS, Ringold GM (December 1984). "Analysis of gene expression during differentiation of adipogenic cells in culture and hormonal control of the developmental program". The Journal of Biological Chemistry. 259 (24): 15548–55. PMID 6392298.
- Pape ME, Kim KH (May 1988). "Effect of tumor necrosis factor on acetyl-coenzyme A carboxylase gene expression and preadipocyte differentiation". Molecular Endocrinology. 2 (5): 395–403. doi:10.1210/mend-2-5-395. PMID 2901666.
- Darmon M, Serrero G, Rizzino A, Sato G (April 1981). "Isolation of myoblastic, fibro-adipogenic, and fibroblastic clonal cell lines from a common precursor and study of their requirements for growth and differentiation". Experimental Cell Research. 132 (2): 313–27. doi:10.1016/0014-4827(81)90107-5. PMID 7215448.
- Jainchill JL, Aaronson SA, Todaro GJ (November 1969). "Murine sarcoma and leukemia viruses: assay using clonal lines of contact-inhibited mouse cells". Journal of Virology. 4 (5): 549–53. doi:10.1128/jvi.4.5.549-553.1969. PMC 375908. PMID 4311790.
- Todaro GJ, Green H (May 1963). "Quantitative studies of the growth of mouse embryo cells in culture and their development into established lines". The Journal of Cell Biology. 17 (2): 299–313. doi:10.1083/jcb.17.2.299. PMC 2106200. PMID 13985244.
- Aaronson SA, Todaro GJ (October 1968). "Development of 3T3-like lines from Balb-c mouse embryo cultures: transformation susceptibility to SV40". Journal of Cellular Physiology. 72 (2): 141–8. doi:10.1002/jcp.1040720208. PMID 4301006.
- Reznikoff CA, Brankow DW, Heidelberger C (December 1973). "Establishment and characterization of a cloned line of C3H mouse embryo cells sensitive to postconfluence inhibition of division". Cancer Research. 33 (12): 3231–8. PMID 4357355.
- Allan EH, Häusler KD, Wei T, Gooi JH, Quinn JM, Crimeen-Irwin B, et al. (August 2008). "EphrinB2 regulation by PTH and PTHrP revealed by molecular profiling in differentiating osteoblasts". Journal of Bone and Mineral Research. 23 (8): 1170–81. doi:10.1359/jbmr.080324. PMID 18627264.
- Yaffe D, Saxel O (Dec 22–29, 1977). "Serial passaging and differentiation of myogenic cells isolated from dystrophic mouse muscle". Nature. 270 (5639): 725–7. Bibcode:1977Natur.270..725Y. doi:10.1038/270725a0. PMID 563524.
- Christian CN, Nelson PG, Peacock J, Nirenberg M (May 1977). "Synapse formation between two clonal cell lines". Science. 196 (4293): 995–8. Bibcode:1977Sci...196..995C. doi:10.1126/science.193191. PMID 193191.
- Mota de Sá P, Richard AJ, Hang H, Stephens JM (March 2017). "Transcriptional Regulation of Adipogenesis". Comprehensive Physiology. 7 (2): 635–674. doi:10.1002/cphy.c160022. ISBN 9780470650714. PMID 28333384.
- Rosen ED, Sarraf P, Troy AE, Bradwin G, Moore K, Milstone DS, et al. (October 1999). "PPAR gamma is required for the differentiation of adipose tissue in vivo and in vitro". Molecular Cell. 4 (4): 611–7. doi:10.1016/s1097-2765(00)80211-7. PMID 10549292.
- Tontonoz P, Hu E, Spiegelman BM (December 1994). "Stimulation of adipogenesis in fibroblasts by PPAR gamma 2, a lipid-activated transcription factor". Cell. 79 (7): 1147–56. doi:10.1016/0092-8674(94)90006-x. PMID 8001151.
- Tamori Y, Masugi J, Nishino N, Kasuga M (July 2002). "Role of peroxisome proliferator-activated receptor-gamma in maintenance of the characteristics of mature 3T3-L1 adipocytes". Diabetes. 51 (7): 2045–55. doi:10.2337/diabetes.51.7.2045. PMID 12086932.
- Cao Z, Umek RM, McKnight SL (September 1991). "Regulated expression of three C/EBP isoforms during adipose conversion of 3T3-L1 cells". Genes & Development. 5 (9): 1538–52. doi:10.1101/gad.5.9.1538. PMID 1840554.
- MacDougald OA, Mandrup S (January 2002). "Adipogenesis: forces that tip the scales". Trends in Endocrinology and Metabolism. 13 (1): 5–11. doi:10.1016/s1043-2760(01)00517-3. PMID 11750856.
- Wu Z, Rosen ED, Brun R, Hauser S, Adelmant G, Troy AE, et al. (February 1999). "Cross-regulation of C/EBP alpha and PPAR gamma controls the transcriptional pathway of adipogenesis and insulin sensitivity". Molecular Cell. 3 (2): 151–8. doi:10.1016/s1097-2765(00)80306-8. PMID 10078198.
- Ross SE, Hemati N, Longo KA, Bennett CN, Lucas PC, Erickson RL, MacDougald OA (August 2000). "Inhibition of adipogenesis by Wnt signaling". Science. 289 (5481): 950–3. Bibcode:2000Sci...289..950R. doi:10.1126/science.289.5481.950. PMID 10937998.
- Tong Q, Dalgin G, Xu H, Ting CN, Leiden JM, Hotamisligil GS (October 2000). "Function of GATA transcription factors in preadipocyte-adipocyte transition". Science. 290 (5489): 134–8. Bibcode:2000Sci...290..134T. doi:10.1126/science.290.5489.134. PMID 11021798. S2CID 8445774.
- Schwarz EJ, Reginato MJ, Shao D, Krakow SL, Lazar MA (March 1997). "Retinoic acid blocks adipogenesis by inhibiting C/EBPbeta-mediated transcription". Molecular and Cellular Biology. 17 (3): 1552–61. doi:10.1128/mcb.17.3.1552. PMC 231881. PMID 9032283.
- Choy L, Skillington J, Derynck R (May 2000). "Roles of autocrine TGF-beta receptor and Smad signaling in adipocyte differentiation". The Journal of Cell Biology. 149 (3): 667–82. doi:10.1083/jcb.149.3.667. PMC 2174852. PMID 10791980.
- Student AK, Hsu RY, Lane MD (May 1980). "Induction of fatty acid synthetase synthesis in differentiating 3T3-L1 preadipocytes". The Journal of Biological Chemistry. 255 (10): 4745–50. PMID 7372608.
- Spiegelman BM, Green H (September 1980). "Control of specific protein biosynthesis during the adipose conversion of 3T3 cells". The Journal of Biological Chemistry. 255 (18): 8811–18. PMID 6773950.
- Amri EZ, Dani C, Doglio A, Etienne J, Grimaldi P, Ailhaud G (August 1986). "Adipose cell differentiation: evidence for a two-step process in the polyamine-dependent Ob1754 clonal line". The Biochemical Journal. 238 (1): 115–22. doi:10.1042/bj2380115. PMC 1147104. PMID 3800927.
- Christodoulides C, Lagathu C, Sethi JK, Vidal-Puig A (January 2009). "Adipogenesis and WNT signalling". Trends in Endocrinology and Metabolism. 20 (1): 16–24. doi:10.1016/j.tem.2008.09.002. PMC 4304002. PMID 19008118.
- Chen D, Ji X, Harris MA, Feng JQ, Karsenty G, Celeste AJ, et al. (July 1998). "Differential roles for bone morphogenetic protein (BMP) receptor type IB and IA in differentiation and specification of mesenchymal precursor cells to osteoblast and adipocyte lineages". The Journal of Cell Biology. 142 (1): 295–305. doi:10.1083/jcb.142.1.295. PMC 2133031. PMID 9660882.
- Eckel-Mahan K, Latre AR, Kolonin MG (2020). "Adipose Stromal Cell Expansion and Exhaustion: Mechanisms and Consequences". Cells. 9 (4): 863. doi:10.3390/cells9040863. PMC 7226766. PMID 32252348.
- Gustafson B, Nerstedt A, Smith U (2019). "Reduced subcutaneous adipogenesis in human hypertrophic obesity is linked to senescent precursor cells". Nature Communications. 10 (1): 2757. doi:10.1038/s41467-019-10688-x. PMC 6588633. PMID 31227697.