3T3-L1 is a sub clonal cell line derived from the original 3T3 Swiss albino cell line of 1962. The 3T3 original cell line was isolated from a mouse embryo and propagated for this specific line of 3T3 cells is used to study adipose tissue-related diseases and dysfunctions. The 3T3-L1 Swiss subclone line has been widely utilized, since its development, due to its affinity for lipid droplet deposition in vitro. 3T3-L1 cells have a fibroblast-like morphology, but, under appropriate conditions, the cells differentiate into an adipocyte-like phenotype, providing an exemplar model for white adipocytes. [1] [2] [3] 3T3-L1 cells can be utilized to study a number of cellular and molecular mechanisms related to insulin-resistance, obesity, and diabetes in vitro. [2] Aside from its usages, this cell line is widely developed and can be purchased for continuous propagation for numerous research studies. [4] 3T3-L1 cells of the adipocyte morphology increase the synthesis and accumulation of triglycerides and acquire the signet ring appearance of adipose cells. These cells are also sensitive to lipogenic and lipolytic hormones, as well as drugs, including epinephrine, isoproterenol, and insulin. [5]
The 3T3-L1 cell line is a sub clone that was initially developed from a mouse embryo, from a clonal expansion of Swiss 3T3 cells. [2] [3] In 1962, the original 3T3 cell line that it was established by George Todaro and Howard Green of the New York University School of Medicine. [6] The original cell line was developed through the 3T3 process, which is where the cells derive their naming nomenclature. The 3T3 process began with cultures having 3 days to propagate on a plate (the first "3"), and then a transfer (the "T") of 300,000 cells (second "3") to a new plate to restart the process. These cells will be identified as 3T3 only after they are taken through 20 to 30 passages and have established at a stable growth rate. [7] These cells were originally used to study the properties of transformed cells and the mechanisms of neoplastic transformation. In 1971, Green and Kehinde established a subline of 3T3 cells, called 3T3-L1, which demonstrated a greater propensity for differentiation into adipocytes and a higher affinity for lipid deposition. The cells were cultured in a serum-containing medium and demonstrated a fibroblast-like morphology. In the early 1980s, it was discovered that these cells could be induced to differentiate into adipocytes in response to hormonal stimulation. [2] [5] [8]
3T3-L1 cells, similar to their other 3T3 counterparts, are typically propagated as an adherent monolayer within a culture vessel. Basal cell culture medias for 3T3-L1 cells tends to contain a version of Dubelcco's Modified Eagle's Medium (DMEM), fetal bovine serum (FBS), and an antibiotic at specific levels dependent upon protocol. [9] The DMEM provides essential nutrients, while the FBS provides vital growth factors, and the antibiotic protects against culture contamination. The process of adipogenesis, and the start of differentiation can be induced in 3T3-L1 cells through the addition of compounds such as a synthetic glucocorticoid, a phosphodiesterase inhibitor, and insulin. The most commonly used synthetic glucocorticoid in adipocyte differentiation procedures tends to be dexamethasone and the most commonly used phosphodiesterase inhibitor is 1-methyl-3-isobutyl-xanthine (IBMX). These compounds are usually used in varying combinations and concentrations in differentiation media dependent upon the protocol utilized. [3] [10] [11] [12] [13] 3T3-L1 cells are commonly utilized as an effective model for white adipocytes because of their similar fibroblast-like morphology, lipid accumulation, gene expression, and basal energy exchanges and transformations. [13] Although, some literature suggests that 3T3-L1 adipocytes can possess certain phenotypic signatures similar to other adipocyte lineages aside from white adipocytes. [13]
Adipogenesis can be described as the effective differentiation of preadipocytes into mature adipocytes that can then undergo lipogenesis. During this period, cells can undergo hyperplastic growth until they are differentiated. Since 3T3-L1 cells are an immortalized cell line and require a hormonal differentiation, there has been much debate on their comparability to in vivo studies and primary cell lines. Aside from the synthetic differentiation itself, 3T3-L1 lineages can display low differentiation efficiency when utilizing common differentiation methods. Low differentiation efficiency can change adipogenesis and lipogenesis related experiment results and limit result interpretation. Studies suggest that differentiation efficiency can rely on factors such as culture dish material, culture dish provider, culture dish type, cell confluence at the time of differentiation. [3] [14] Lipogenesis can be described as the biochemical and physical accumulation of triacylglycerides in a differentiated adipocyte. Again, the deposition of adipose tissue relies on the number of adipocytes, their differentiation efficiency and overall lipid accumulation. It is not unrelated that the inhibition of one of these processes could impact others as well.
One advantage of using 3T3-L1 cells is their well-characterized differentiation process, which allows for reproducible experiments and comparison of results across studies. [6] [8] Additionally, the cells can be easily cultured and maintained in the laboratory, and are relatively inexpensive compared to other cell lines or animal models. However, one limitation of using 3T3-L1 cells is that they are derived from mice and may not fully recapitulate human biology. Additionally, 3T3-L1 cells are a homogeneous cell population, which may not fully reflect the heterogeneity of adipose tissue in vivo. [8] These limitations can affect comparability of this particular cell lineage.
While 3T3-L1 gene expression mimics that of a white adipocyte, some literature suggests some phenotypic 3T3-L1 characteristics can resemble that of brown adipocytes. 3T3-L1 cells, when supplemented with catecholamines, utilized UCP-1 to increase oxygen consumption similar to brown adipocytes. This brown adipocyte characteristic was only enhanced with long-term catecholamine supplementation. [13] While the 3T3-L1 lineage can display characteristics similar to both white and brown adipocytes, they have had different results in relation to beige adipocyte phenotype characteristics. When 3T3-L1 cells are differentiated into beige adipocytes, they fail to express any beige phenotypic signatures. [13] The process of differentiation is constantly being re-evaluated in the adipose research sector. While a majority of in vitro experiments utilize the common insulin, dexamethasone, and IBMX combinations, others have found other methods of differentiating and inducing the process of adipogenesis. Other methods can include transfection with a ras oncogene, the combination of dexamethasone and octanoate, and the normal combination with the addition of a peroxisome proliferator-activated receptor y (PPARy) agonist. [3] [12] [15] While some protocols promote the process of adipogenesis in 3T3-L1 cells, others reduce or inhibit the process. In 3T3-L1 adipocytes, oleanolic acid (5umol/L) down regulated the expression of PPARy and cytidine-cytidine-adenosine-adenosine-thymidine (CCAAT) enhancer binding protein a (C/EBPa) during differentiation. Thus, oleanolic acid suppressed adipocyte differentiation and consequential lipid accumulation when applied in differentiation media to 3T3-L1 cells. Berberine impacted GATA-2 and GATA-3 and thus inhibited 3T3-L1 differentiation when applied during differentiation or post-differentiation in vitro. [16] Long term treatment of flavonoid, luteolin, affected PPARy activation and suppressed adipogenesis 3T3-L1 adipocytes. [17] Isopanduratin A also inhibited adipogenesis in 3T3-L1 adipocytes by impacting multiple targets in the adipogenic growth cycle such as PPARy, C/EBPa, sterol regulatory binding protein- 1c (SREB-1c), adiponectin, and lipoprotein lipase(LPL). [18]
Lipolysis is the metabolic pathway through which lipid triglycerides are hydrolyzed into a glycerol and free fatty acids. It is used to mobilize stored energy during fasting or exercise, and usually occurs in fat adipocytes. The most important regulatory hormone in lipolysis is insulin; lipolysis can only occur when insulin action falls to low levels, as occurs during fasting. Other hormones that affect lipolysis include leptin, glucagon, epinephrine, norepinephrine, growth hormone, atrial natriuretic peptide, brain natriuretic peptide, and cortisol.
Adipose tissue is a loose connective tissue composed mostly of adipocytes. It also contains the stromal vascular fraction (SVF) of cells including preadipocytes, fibroblasts, vascular endothelial cells and a variety of immune cells such as adipose tissue macrophages. Its main role is to store energy in the form of lipids, although it also cushions and insulates the body.
Adipocytes, also known as lipocytes and fat cells, are the cells that primarily compose adipose tissue, specialized in storing energy as fat. Adipocytes are derived from mesenchymal stem cells which give rise to adipocytes through adipogenesis. In cell culture, adipocyte progenitors can also form osteoblasts, myocytes and other cell types.
Adiponectin is a protein hormone and adipokine, which is involved in regulating glucose levels and fatty acid breakdown. In humans, it is encoded by the ADIPOQ gene and is produced primarily in adipose tissue, but also in muscle and even in the brain.
In biochemistry, lipogenesis is the conversion of fatty acids and glycerol into fats, or a metabolic process through which acetyl-CoA is converted to triglyceride for storage in fat. Lipogenesis encompasses both fatty acid and triglyceride synthesis, with the latter being the process by which fatty acids are esterified to glycerol before being packaged into very-low-density lipoprotein (VLDL). Fatty acids are produced in the cytoplasm of cells by repeatedly adding two-carbon units to acetyl-CoA. Triacylglycerol synthesis, on the other hand, occurs in the endoplasmic reticulum membrane of cells by bonding three fatty acid molecules to a glycerol molecule. Both processes take place mainly in liver and adipose tissue. Nevertheless, it also occurs to some extent in other tissues such as the gut and kidney. A review on lipogenesis in the brain was published in 2008 by Lopez and Vidal-Puig. After being packaged into VLDL in the liver, the resulting lipoprotein is then secreted directly into the blood for delivery to peripheral tissues.
3T3 cells are several cell lines of mouse embryonic fibroblasts. The original 3T3 cell line was established in 1962 by two scientists then at the Department of Pathology in the New York University School of Medicine, George Todaro and Howard Green. Todaro and Green originally obtained their 3T3 cells from Swiss albino mouse embryo tissue. Later, as a principal investigator position at the National Cancer Institute in Bethesda, Maryland, Todaro repeated the isolation procedure from the NIH Swiss mouse embryo with his students and established NIH-3T3 cell line.
CCAAT-enhancer-binding proteins is a family of transcription factors composed of six members, named from C/EBPα to C/EBPζ. They promote the expression of certain genes through interaction with their promoters. Once bound to DNA, C/EBPs can recruit so-called co-activators that in turn can open up chromatin structure or recruit basal transcription factors.
Sodium pyruvate is a salt of the conjugate anion form of pyruvic acid, known as pyruvate. It is commonly added to cell culture media as an additional source of energy, but may also have protective effects against hydrogen peroxide. This was reported by Giandomenico et al. and has been confirmed by several independent groups.
White adipose tissue or white fat is one of the two types of adipose tissue found in mammals. The other kind is brown adipose tissue. White adipose tissue is composed of monolocular adipocytes.
Peroxisome proliferator-activated receptor gamma, also known as the glitazone reverse insulin resistance receptor, or NR1C3 is a type II nuclear receptor functioning as a transcription factor that in humans is encoded by the PPARG gene.
Obesogens are certain chemical compounds that are hypothesised to disrupt normal development and balance of lipid metabolism, which in some cases, can lead to obesity. Obesogens may be functionally defined as chemicals that inappropriately alter lipid homeostasis and fat storage, change metabolic setpoints, disrupt energy balance or modify the regulation of appetite and satiety to promote fat accumulation and obesity.
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. In humans it is encoded by the ADFP gene. This protein surrounds the lipid droplet along with phospholipids and is involved in assisting the storage of neutral lipids within the lipid droplets.
Insulin induced gene 2, also known as INSIG2, is a protein which in humans is encoded by the INSIG2 gene.
Chemerin, also known as retinoic acid receptor responder protein 2 (RARRES2), tazarotene-induced gene 2 protein (TIG2), or RAR-responsive protein TIG2 is a protein that in humans is encoded by the RARRES2 gene.
Adipogenesis is the formation of adipocytes 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 lipoblasts or 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.
A lipoblast is a precursor cell for an adipocyte.
Krüppel-like factor 15 is a protein that in humans is encoded by the KLF15 gene in the Krüppel-like factor family. Its former designation KKLF stands for kidney-enriched Krüppel-like factor.
Fat storage-inducing transmembrane protein 2 is a protein that in humans is encoded by the FITM2 gene. It plays a role in fat storage. Its location is 20q13.12 and it contains 2 exons. It is also a member of the FIT protein family that has been conserved throughout evolution. Conserved from Saccharomyces cerevisiae to humans is the capability to take fat and store it as cytoplasmic triglyceride droplets. While FIT proteins facilitate the segregation of triglycerides (TGs) into cytosolic lipid droplets, they are not involved in triglyceride biosynthesis. In mammals, both FIT2 and FIT1 from the same family are present, embedded in the wall of the endoplasmic reticulum (ER) where they regulate lipid droplet formation in the cytosol. In S. cerevisiae, it also plays a role in the metabolism of phospholipids. These TGs are in the cytoplasm, encapsulated by a phospholipid monolayer in configurations or organelles that have been given many different names including lipid particles, oil bodies, adiposomes, eicosasomes, and most prevalent in scientific research – lipid droplets.
OP9 cells are a cell line derived from mouse bone marrow stromal cells (mesenchyme). These cells are now characterized as stem cells. When co-cultured with embryonic stem cells (ESC), OP9 cells can induce ESC to differentiate into blood cells by serving as a feeder layer. They have the potential to be used in cell therapy, regenerative medicine and as immunomodulators.
Phosphotyrosine interaction domain containing 1 is a protein that in humans is encoded by the PID1 gene.