Unleashing the potential of adipose organoids: A revolutionary approach to combat obesity-related metabolic diseases

Abstract

Obesity-related metabolic diseases, including obesity, diabetes, hyperlipidemia, and non-alcoholic fatty liver diseases pose a significant threat to health. However, comprehensive pathogenesis exploration and effective therapy development are impeded by the limited availability of human models. Notably, advances in organoid technology enable the generation of adipose organoids that recapitulate structures and functions of native human adipose tissues to investigate mechanisms and develop corresponding treatments for obesity-related metabolic diseases. Here, we review the general principles, sources, and three-dimensional techniques for engineering adipose organoids, along with strategies to promote maturation. We also outline the application of white adipose organoids, primarily for disease modeling and drug screening, and highlight the therapeutic potential of thermogenic beige and brown adipose organoids in promoting weight loss and glucose and lipid metabolic homeostasis. We also discuss the challenges and prospects in the establishment and bench-to-bedside of adipose organoids, as well as their potential applications.

Keywords: Adipose organoid; Brown adipose tissue; Metabolic disease; Obesity; Type 2 diabetes mellitus.

Figure 1

General principles to generate adipose organoids in vitro based on the in vivo development of adipose tissues. Based on the understanding of the development in vivo, by modulating WNT and BMP signaling pathways, brown and white adipocyte progenitors going through paraxial and splanchnic mesoderm, respectively, are induced from pluripotency stem cells (PSCs). Brown adipocyte progenitors from PSCs and stromal vascular fragments from brown adipose tissues correspond to the brown adipocyte progenitor stage in vivo which are fate-determined to brown adipocytes. Therefore, brown adipose organoids can be derived in the basic adipogenic differentiation medium through activation of PPARγ and C/EBPα, key factors of adipogenesis; while supplementation of browning compounds that mimic the EBF2 and PRDM16 activation in vivo can further enhance the differentiation efficiency. White adipocyte progenitors from PSCs, adipose-derived stem cells, stromal vascular fragments from white adipose tissues, and micro white adipose tissues correspond to the white adipocyte progenitor stage in vivo which is bipotent. Therefore, white adipose organoids can be derived in the basic adipogenic differentiation medium. With additional genetic engineering techniques to introduce thermogenic genes and/or supplementation of browning compounds to mimic the cold exposure or β-adrenergic stimuli that activate EBF2 and PRDM16 in vivo, beige adipose organoids can be successfully induced from these bipotent sources. ADSC: adipose-derived stem cell; BeAO: beige adipose organoid; BeAP: beige adipocyte progenitors; BrAO: brown adipose organoid; BrAP: brown adipocyte progenitor; Micro-WAT: micro white adipose tissue; PSC: pluripotent stem cell; SVF-BAT: stromal vascular fragment from brown adipose tissue; SVF-WAT: stromal vascular fragment from white adipose tissue; WAO: white adipose organoid; WAP: white adipocyte progenitor.

Figure 2

Scaffold-free and scaffold-based strategies to establish 3D adipose organoids. Through three-dimensional (3D) techniques including scaffold-free and scaffold-based techniques, 3D adipose organoids can be fabricated from various sources. The ultra-low attachment technique is the most widely used scaffold-free technique due to its automation, simplicity, and high throughput. The hanging drop technique enables precise size control, but is challenging to replenish the low-volume culture medium. Cell-sheet engineering enables the generation of adipose organoids through superposition. Microwell arrays perform well in precisely controlling the diameters of adipose organoids by limiting seeded cell numbers. The magnetic levitation technique also enables the establishment of adipose organoids composed of more than one cellular component through positive or negative magnetophoresis. The microfluidic device provides a chance to recapitulate the communication between adipose tissues and other organs. Scaffold-based techniques include synthetic, natural polymer, and decellularized matrices that can be used alone or in combination with 3D bioprinting and microfluidic systems. Scaffolds promote cell attachment and migration and inhibit excessive cell aggregation. They also promote sprouting, adipogenesis, maintenance of depot-specific and subject-specific characteristics, and long-term preservation of viability and function of adipose organoids. BeAO: beige adipose organoid; BrAO: brown adipose organoid; Col I: type I collagen; dECM: decellularized extracellular matrix; GelMA: methacrylate gelatin; HAMA: hyaluronic acid; PEG: poly(ethylene-glycol); PLGA: poly(lactic-co-glycolic acid); PNIPAAm: poly(N-isopropylacrylamide); PSC: pluripotent stem cells; WAO: white adipose organoid; 3D: three dimensional.

Figure 3

Promoting vascularization and incorporating immune cells to facilitate maturation of adipose organoids. Considering the native adipose tissue niche, both vascularization and immune cell incorporation are crucial for the maturation of adipose organoids. Regarding research intensity, vascularization has been predominantly investigated in brown adipose organoids and beige adipose organoids to promote browning. Although incorporating immune cells is essential for all types of adipose organoids, currently only mice macrophages were successfully incorporated into white adipose organoids for disease modeling and drug screening. No studies have generated brown or beige adipose organoids with macrophages incorporated yet. By incorporating exogenous human microvascular endothelial cells and human umbilical vein endothelial cells (a), or using stromal vascular fragments, microvascular fragments, and adipose tissue explants with endogenous endothelial cells (b), well-vascularized adipose organoids can be successfully generated. (c) The supplementation of angiogenic compounds such as VEGF, IL-6, KITLG, and FLT3LG, along with endothelial growth medium further promotes vascularization, beige preadipocyte proliferation, and ex vivo browning. (d) By co-culturing mice macrophages, RAW264.7, with mice 3T3-L1 preadipocytes or human adipose-derived stem cells in alginate hydrogel mixture by three-dimensional bioprinting, inflamed white adipose organoids with insulin-resistance were successfully generated. (e) By directly inducing the adipogenic differentiation of stromal vascular fragments, adipose organoids with resident CD45⁺ CD31^- immune cells preserved such as macrophages and mast cells were generated. BeAO: beige adipose organoid; BrAO: brown adipose organoid; EC: endothelial cell; EGM2-MV: endothelial cell growth medium 2-microvascular; Mø: macrophage; WAO: white adipose organoid.

Figure 4

Application of adipose organoids in disease modeling, drug screening, and regenerative medicine. (a) White adipose organoids can model obesity through exposure to fatty acids or TNF-α, or co-culture with immune cells under lipopolysaccharide stimuli. Disease modeling of type 2 diabetes mellitus (T2DM) can be established through co-culture adipose organoids with macrophages, or from patient-derived adipose organoids. Besides, a microfluid system is applied to investigate the role of adipose tissues in the progression of non-alcoholic fatty liver disease (NAFLD) by mimicking healthy, obese, diabetic, and pro-inflammatory plasma conditions. (b) By assessing the effects of compounds on lipid accumulation, adipogenic gene expression, pro-inflammatory cytokine secretion, and metabolism such as glucose uptake, white adipose organoids can be applied to high throughput drug screening and personalized precision medicine in obeisity, T2DM, and NAFLD. (c) Brown adipose organoids reduce body weight and fat mass as well as relieve inflammation after transplantation. Transplantation also shows therapeutic potential in T2DM by reducing glucose levels and improving glucose intolerance and insulin-resistance. Besides, it regulates dyslipidemia, relieves inflammation and fibrosis in livers, and improves liver function. (d) Beige adipose organoid transplantation shows potential for treating obesity. Additionally, it also reduces glucose levels and improves glucose tolerance and turnover. Alb: albumin; AST: aspartate transaminase; BeAO: beige adipose organoid; BrAO: brown adipose organoid; Core T: core temperature; EE: energy expenditure; GPT: glutamate pyruvate transaminase; hADSC: human adipose-derived stem cells; HDL/TC: the ration of high-density lipoprotein to total cholesterol; LDL: low-density lipoprotein; LPS: lipopolysaccharide; mMø: mice macrophage; m3T3-L1: mice preadipocytes; NAFLD: non-alcoholic fatty liver disease; TC: total cholesterol; TG: triglyceride; T2DM: type 2 diabetes mellitus; VO2: maximum volume of oxygen; WAO: white adipose organoid.