Biology:Adipogenesis

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Histology features of a lipoblast, also known as an adipocyte precursor cell or preadipocyte.

Adipogenesis is the formation of adipocytes (fat cells) from stem cells.[1] It involves 2 phases, determination, and terminal differentiation. Determination is mesenchymal stem cells committing to the adipocyte precursor cells, also known as lipoblasts or preadipocytes which lose the potential to differentiate to other types of cells such as chondrocytes, myocytes, and osteoblasts.[2] 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.[3]

Differentiated Adipocyte stained with Oil Red O

Introduction

Adipocytes play a vital role in energy homeostasis and process the largest energy reserve as triglycerol in the body of animals.[4] 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.[5] 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.

Differentiation

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.[6] 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.[7]

Models of in vitro differentiation

Cell Line Origin Differentiation Protocol
Committed Pre-adipocytes
3T3-L1 Sub-clone of Swiss 3T3[8] FBS+ I+ D+ M
3T3-F442A Sub-clone of Swiss 3T3[9] FBS + I
Ob17 Differentiated adipocyte from epididymal fat pad of C57BL/6J ob/ob mice[10] FBS+ I+ T3
TA1 Subclone of C3H10T1/2 [11] FBS + D + I
30A5 Subclone of C3H10T1/2[12] FBS + D + M + I
1246 Adipogenic Subclone of CH3 mouse teratocarcinoma cell line T984[13] D + M + I
Non-committed with adipogenic potential
NIH3T3 NIH Swiss mouse embryo cells[14] Ectopic expression of PPAR-gamma, C/EBP-alpha or C/EBP-beta + D+ M+ I
Swiss 3T3 Swiss mouse embryo cells[15] Ectopic expression of C/EBP-alpha
Balb/3T3 Balb/c mouse embryo cells[16] Ectopic expression of C/EBP-alpha
C3H 10T1/2 C3H mouse embryo cells[17] PPAR-gamma ligand
Kusa 4b10 mouse bone marrow stromal cell line[18] FBS + I + D + M
C2C12 Thigh muscles of C3H mice[19] Thiazolidinediones
G8 Hind limb muscles of fetal Swiss webster mouse[20] Ectopic expression of PPAR-gamma + CEBP/alpha +D + I
FBS = Fetal Bovine Serum, D = Dexamethasone, I = Insulin, M = Methylisobutylxanthine T3 = Triiodothyronine

Transcriptional regulations

PPARγ

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.[21] PPARγ is necessary and sufficient to promote fat cell differentiation. PPARγ is required for embryonic stem cells (ES cells) differentiation to adipocytes.[22] The expression of PPARγ itself is sufficient to convert fibroblast into adipocytes in vitro.[23] 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.[24] Thiazolidinediones (TZDs), antidiabetic agents which well used differentiation cocktail in vitro, promoting the activity of PPARγ.

C/EBPs

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.[25] 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.[26] C/EBPα also plays an important role in the insulin sensitivity of adipocytes.[27] However, C/EBPγ suppresses differentiation which might due to inactivation by C/EBPβ.

Transcriptional cascade

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),[28] GATA2/3,[29] retinoic acid receptor α,[30] and SMAD6/7[31] don't affect the expression of C/EBPβ and C/EBPδ but inhibit the induction of PPARγ and C/EBPα.

Other regulations

Products of endocrine system such as insulin, IGF-1, cAMP, glucocorticoid, and triiodothyronine effectively induce adipogenesis in preadipocytes.[32][33][34]

Insulin and IGF1

Insulin regulates adipogenesis through insulin-like growth factor 1 (IGF1) receptor signaling. Insulin/IGF1 promotes the induction transcription factors regulating terminal differentiation.

Wnt signaling

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.[35] Wnt/β-catenin inhibits the differentiation of preadipocytes by inhibiting the induction of PPARγ and C/EBPα.

BMPs

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.[36] BMPs also promotes the differentiation of preadipocytes.

Senescent cells

Senescent adipose progenitor cells in subcutaneous adipose tissue has been shown to suppress adipogenic differentiation.[37] Reduced adipogenesis in obese persons is due to increased senescent cells in adipose tissue rather than reduced numbers of stem/progenitor cells.[38]

References

  1. ↑ "Adipogenesis". https://www.merriam-webster.com/dictionary/adipogenesis. 
  2. ↑ "Understanding adipocyte differentiation". Physiological Reviews 78 (3): 783–809. July 1998. doi:10.1152/physrev.1998.78.3.783. PMID 9674695. 
  3. ↑ "Search for the preadipocyte progenitor cell". Journal of Clinical Investigation 116 (12): 3103–3106. 2006. doi:10.1172/JCI30666. PMID 17143324. 
  4. ↑ "Regulation of adipocyte development". Annual Review of Nutrition 14: 99–129. 1994. doi:10.1146/annurev.nu.14.070194.000531. PMID 7946535. 
  5. ↑ "Adipocyte differentiation from the inside out". Nature Reviews. Molecular Cell Biology 7 (12): 885–96. December 2006. doi:10.1038/nrm2066. PMID 17139329. 
  6. ↑ "Transcriptional regulation of adipogenesis". Genes & Development 14 (11): 1293–307. June 2000. doi:10.1101/gad.14.11.1293. PMID 10837022. 
  7. ↑ "Identification of white adipocyte progenitor cells in vivo". Cell 135 (2): 240–9. October 2008. doi:10.1016/j.cell.2008.09.036. PMID 18835024. 
  8. ↑ "Sublines of mouse 3T3 cells that accumulate lipid". Cell 1 (3): 113–116. 28 February 1974. doi:10.1016/0092-8674(74)90126-3. 
  9. ↑ "Spontaneous heritable changes leading to increased adipose conversion in 3T3 cells". Cell 7 (1): 105–13. January 1976. doi:10.1016/0092-8674(76)90260-9. PMID 949738. 
  10. ↑ "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. December 1978. doi:10.1073/pnas.75.12.6054. PMID 216011. Bibcode: 1978PNAS...75.6054N. 
  11. ↑ "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. December 1984. doi:10.1016/S0021-9258(17)42583-X. PMID 6392298. 
  12. ↑ "Effect of tumor necrosis factor on acetyl-coenzyme A carboxylase gene expression and preadipocyte differentiation". Molecular Endocrinology 2 (5): 395–403. May 1988. doi:10.1210/mend-2-5-395. PMID 2901666. 
  13. ↑ "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. April 1981. doi:10.1016/0014-4827(81)90107-5. PMID 7215448. 
  14. ↑ "Murine sarcoma and leukemia viruses: assay using clonal lines of contact-inhibited mouse cells". Journal of Virology 4 (5): 549–53. November 1969. doi:10.1128/jvi.4.5.549-553.1969. PMID 4311790. 
  15. ↑ "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. May 1963. doi:10.1083/jcb.17.2.299. PMID 13985244. 
  16. ↑ "Development of 3T3-like lines from Balb-c mouse embryo cultures: transformation susceptibility to SV40". Journal of Cellular Physiology 72 (2): 141–8. October 1968. doi:10.1002/jcp.1040720208. PMID 4301006. 
  17. ↑ "Establishment and characterization of a cloned line of C3H mouse embryo cells sensitive to postconfluence inhibition of division". Cancer Research 33 (12): 3231–8. December 1973. PMID 4357355. 
  18. ↑ "EphrinB2 regulation by PTH and PTHrP revealed by molecular profiling in differentiating osteoblasts". Journal of Bone and Mineral Research 23 (8): 1170–81. August 2008. doi:10.1359/jbmr.080324. PMID 18627264. 
  19. ↑ "Serial passaging and differentiation of myogenic cells isolated from dystrophic mouse muscle". Nature 270 (5639): 725–7. Dec 22–29, 1977. doi:10.1038/270725a0. PMID 563524. Bibcode: 1977Natur.270..725Y. 
  20. ↑ "Synapse formation between two clonal cell lines". Science 196 (4293): 995–8. May 1977. doi:10.1126/science.193191. PMID 193191. Bibcode: 1977Sci...196..995C. 
  21. ↑ "Transcriptional Regulation of Adipogenesis". Comprehensive Physiology 7 (2): 635–674. March 2017. doi:10.1002/cphy.c160022. ISBN 9780470650714. PMID 28333384. 
  22. ↑ "PPAR gamma is required for the differentiation of adipose tissue in vivo and in vitro". Molecular Cell 4 (4): 611–7. October 1999. doi:10.1016/s1097-2765(00)80211-7. PMID 10549292. 
  23. ↑ "Stimulation of adipogenesis in fibroblasts by PPAR gamma 2, a lipid-activated transcription factor". Cell 79 (7): 1147–56. December 1994. doi:10.1016/0092-8674(94)90006-x. PMID 8001151. 
  24. ↑ "Role of peroxisome proliferator-activated receptor-gamma in maintenance of the characteristics of mature 3T3-L1 adipocytes". Diabetes 51 (7): 2045–55. July 2002. doi:10.2337/diabetes.51.7.2045. PMID 12086932. 
  25. ↑ "Regulated expression of three C/EBP isoforms during adipose conversion of 3T3-L1 cells". Genes & Development 5 (9): 1538–52. September 1991. doi:10.1101/gad.5.9.1538. PMID 1840554. 
  26. ↑ "Adipogenesis: forces that tip the scales". Trends in Endocrinology and Metabolism 13 (1): 5–11. January 2002. doi:10.1016/s1043-2760(01)00517-3. PMID 11750856. 
  27. ↑ "Cross-regulation of C/EBP alpha and PPAR gamma controls the transcriptional pathway of adipogenesis and insulin sensitivity". Molecular Cell 3 (2): 151–8. February 1999. doi:10.1016/s1097-2765(00)80306-8. PMID 10078198. 
  28. ↑ "Inhibition of adipogenesis by Wnt signaling". Science 289 (5481): 950–3. August 2000. doi:10.1126/science.289.5481.950. PMID 10937998. Bibcode: 2000Sci...289..950R. 
  29. ↑ "Function of GATA transcription factors in preadipocyte-adipocyte transition". Science 290 (5489): 134–8. October 2000. doi:10.1126/science.290.5489.134. PMID 11021798. Bibcode: 2000Sci...290..134T. 
  30. ↑ "Retinoic acid blocks adipogenesis by inhibiting C/EBPbeta-mediated transcription". Molecular and Cellular Biology 17 (3): 1552–61. March 1997. doi:10.1128/mcb.17.3.1552. PMID 9032283. 
  31. ↑ "Roles of autocrine TGF-beta receptor and Smad signaling in adipocyte differentiation". The Journal of Cell Biology 149 (3): 667–82. May 2000. doi:10.1083/jcb.149.3.667. PMID 10791980. 
  32. ↑ "Induction of fatty acid synthetase synthesis in differentiating 3T3-L1 preadipocytes". The Journal of Biological Chemistry 255 (10): 4745–50. May 1980. doi:10.1016/S0021-9258(19)85559-X. PMID 7372608. 
  33. ↑ "Control of specific protein biosynthesis during the adipose conversion of 3T3 cells". The Journal of Biological Chemistry 255 (18): 8811–18. September 1980. doi:10.1016/S0021-9258(18)43575-2. PMID 6773950. 
  34. ↑ "Adipose cell differentiation: evidence for a two-step process in the polyamine-dependent Ob1754 clonal line". The Biochemical Journal 238 (1): 115–22. August 1986. doi:10.1042/bj2380115. PMID 3800927. 
  35. ↑ "Adipogenesis and WNT signalling". Trends in Endocrinology and Metabolism 20 (1): 16–24. January 2009. doi:10.1016/j.tem.2008.09.002. PMID 19008118. 
  36. ↑ "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. July 1998. doi:10.1083/jcb.142.1.295. PMID 9660882. 
  37. ↑ "Adipose Stromal Cell Expansion and Exhaustion: Mechanisms and Consequences". Cells 9 (4): 863. 2020. doi:10.3390/cells9040863. PMID 32252348. 
  38. ↑ "Reduced subcutaneous adipogenesis in human hypertrophic obesity is linked to senescent precursor cells". Nature Communications 10 (1): 2757. 2019. doi:10.1038/s41467-019-10688-x. PMID 31227697. Bibcode: 2019NatCo..10.2757G. 



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