Gregoire, Francine M., Cynthia M. Smas, and Hei Sook Sul. Understanding Adipocyte Differentiation. Physiol. Rev. 78: 783–809, 1998. — The adipocyte plays a critical role in energy balance. Adipose tissue growth involves an increase in adipocyte size and the formation of new adipocytes from precursor cells. For the last 20 years, the cellular and molecular mechanisms of adipocyte differentiation have been extensively studied using preadipocyte culture systems. Committed preadipocytes undergo growth arrest and subsequent terminal differentiation into adipocytes. This is accompanied by a dramatic increase in expression of adipocyte genes including adipocyte fatty acid binding protein and lipid-metabolizing enzymes. Characterization of regulatory regions of adipose-specific genes has led to the identification of the transcription factors peroxisome proliferator-activated receptor-γ (PPAR-γ) and CCAAT/enhancer binding protein (C/EBP), which play a key role in the complex transcriptional cascade during adipocyt...

Understanding Adipocyte Differentiation

Thyroid hormones (THs) play critical roles in the differentiation, growth, metabolism, and physiological function of virtually all tissues. TH binds to receptors that are ligand-regulatable transcription factors belonging to the nuclear hormone receptor superfamily. Tremendous progress has been made recently in our understanding of the molecular mechanisms that underlie TH action. In this review, we present the major advances in our knowledge of the molecular mechanisms of TH action and their implications for TH action in specific tissues, resistance to thyroid hormone syndrome, and genetically engineered mouse models.

Physiological and molecular basis of thyroid hormone action.

Tissues can be soft like fat, which bears little stress, or stiff like bone, which sustains high stress, but whether there is a systematic relationship between tissue mechanics and differentiation is unknown. Here, proteomics analyses revealed that levels of the nucleoskeletal protein lamin-A scaled with tissue elasticity, E, as did levels of collagens in the extracellular matrix that determine E. Stem cell differentiation into fat on soft matrix was enhanced by low lamin-A levels, whereas differentiation into bone on stiff matrix was enhanced by high lamin-A levels. Matrix stiffness directly influenced lamin-A protein levels, and, although lamin-A transcription was regulated by the vitamin A/retinoic acid (RA) pathway with broad roles in development, nuclear entry of RA receptors was modulated by lamin-A protein. Tissue stiffness and stress thus increase lamin-A levels, which stabilize the nucleus while also contributing to lineage determination.

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Nuclear lamin-A Scales With Tissue Stiffness and Enhances Matrix-Directed Differentiation

Expression of a Constitutively Active Akt Ser/Thr Kinase in 3T3-L1 Adipocytes Stimulates Glucose Uptake and Glucose Transporter 4 Translocation

The metabolic syndrome is a common precursor of cardiovascular disease and type 2 diabetes that is characterized by the clustering of insulin resistance, dyslipidemia, and increased blood pressure. In humans, mutations in the peroxisome proliferator-activated receptor-gamma (PPARgamma) have been reported to cause the full-blown metabolic syndrome, and drugs that activate PPARgamma have proven to be effective agents for the prevention and treatment of insulin resistance and type 2 diabetes. Here we report that telmisartan, a structurally unique angiotensin II receptor antagonist used for the treatment of hypertension, can function as a partial agonist of PPARgamma; influence the expression of PPARgamma target genes involved in carbohydrate and lipid metabolism; and reduce glucose, insulin, and triglyceride levels in rats fed a high-fat, high-carbohydrate diet. None of the other commercially available angiotensin II receptor antagonists appeared to activate PPARgamma when tested at concentrations typically achieved in plasma with conventional oral dosing. In contrast to ordinary antihypertensive and antidiabetic agents, molecules that can simultaneously block the angiotensin II receptor and activate PPARgamma have the potential to treat both hemodynamic and biochemical features of the metabolic syndrome and could provide unique opportunities for the prevention and treatment of diabetes and cardiovascular disease in high-risk populations.

Identification of Telmisartan as a Unique Angiotensin II Receptor Antagonist With Selective PPARγ–Modulating Activity

Cultured 3T3-F442A cells differentiate into adipocytes and accumulate lipid droplets in the cytoplasm. When fat cells are stained with Oil red O, the degree of staining seems to be proportional to the extent of cell differentiation. We report here a fast and simple method to quantitate the extent of adipose conversion by staining the accumulated lipid with Oil red O and determining the amount of extracted dye at 510 nm. The results show that Oil red O specifically stains triglycerides and cholesteryl oleate but no other lipids. This technique is a valuable tool for processing large numbers of cell cultures or samples in which adipose differentiation and/or accumulated triglycerides is to be quantitated.

Quantitation of adipose conversion and triglycerides by staining intracytoplasmic lipids with Oil red O.

The adipose conversion of 3T3-F442A cells depends on an adipogenic factor in serum. In the presence of this factor, cells grown to confluence become spherical, greatly increase the activity of their lipogenic enzymes, and accumulate triglyceride. In the absence of the adipogenic factor, the cells grow normally, but when they reach confluence they do not become spherical, do not accumulate triglyceride, and do not undergo any increase in activity of lipogenic enzymes. In cattle there is a great deal more of the adipogenic factor in the serum before birth than in the serum of grown animals. The nature of the adipogenic factor suggests that it may play an important role in the development of adipose tissue.

Walid Kuri-Harcuch

Papers

Quantitation of adipose conversion and triglycerides by staining intracytoplasmic lipids with Oil red O.

Adipose conversion of 3T3 cells depends on a serum factor.

Differentiation of 3T3-F442A Cells into Adipocytes is Inhibited by Retinoic Acid

Cultivation of adult rat hepatocytes on 3T3 cells: expression of various liver differentiated functions

Extracellular matrix production by mouse 3T3-F442A cells during adipose differentiation in culture.