Depletion of white adipocyte progenitors induces beige adipocyte differentiation and suppresses obesity development

Overgrowth of white adipose tissue (WAT) in obesity occurs as a result of adipocyte hypertrophy and hyperplasia. Expansion and renewal of adipocytes relies on proliferation and differentiation of white adipocyte progenitors (WAP); however, the requirement of WAP for obesity development has not been proven. Here, we investigate whether depletion of WAP can be used to prevent WAT expansion. We test this approach by using a hunter-killer peptide designed to induce apoptosis selectively in WAP. We show that targeted WAP cytoablation results in a long-term WAT growth suppression despite increased caloric intake in a mouse diet-induced obesity model. Our data indicate that WAP depletion results in a compensatory population of adipose tissue with beige adipocytes. Consistent with reported thermogenic capacity of beige adipose tissue, WAP-depleted mice display increased energy expenditure. We conclude that targeting of white adipocyte progenitors could be developed as a strategy to sustained modulation of WAT metabolic activity.Obesity, a medical condition predisposing to diabetes, cardiovascular diseases, cancer, and complicating other life-threatening diseases, is becoming an increasingly important social problem.^{1, 2, 3} Development of pharmacological approaches to reduction of body fat has remained a daunting task.⁴ Approved obesity treatments typically produce only moderate and temporary effects.^2,5 White adipocytes are the differentiated cells of white adipose tissue (WAT) that store triglycerides in lipid droplets.^6,7 In contrast, adipocytes of brown adipose tissue (BAT) dissipate excess energy through adaptive thermogenesis. Under certain conditions, white adipocytes can become partially replaced with brown-like ‘beige'' (‘brite'') adipocytes that simulate the thermogenic function of BAT adipocytes.^7,8 Obesity develops in the context of positive energy balance as a result of hypertrophy and hyperplasia of white adipocytes.⁹Expansion and renewal of the white adipocyte pool in WAT continues in adulthood.^10,11 This process is believed to rely on proliferation and self-renewal of mesenchymal precursor cells¹² that we term white adipocyte progenitors (WAPs). WAPs reside within the population of adipose stromal cells (ASCs)¹³ and are functionally similar to bone marrow mesenchymal stem cells (MSCs).^{14, 15, 16} ASCs can be isolated from the stromal/vascular fraction (SVF) of WAT based on negativity for hematopoietic (CD45) and endothelial (CD31) markers.^17,18 ASCs support vascularization as mural/adventitial cells secreting angiogenic factors^5,19 and, unlike bone marrow MSCs, express CD34.^19,20 WAPs have been identified within the ASC population based on expression of mesenchymal markers, such as platelet-derived growth factor receptor-β (PDGFRβ, aka CD140b) and pericyte markers.^17,18 Recently, a distinct ASC progenitor population capable of differentiating into both white and brown adipocytes has been identified in WAT based on PDGFRα (CD140a) expression and lack of PDGFRβ expression.^21,22 The physiological relevance of the two precursor populations residing in WAT has not been explored.We have previously established an approach to isolate peptide ligands binding to receptors selectively expressed on the surface of cell populations of interest.^{23, 24, 25, 26, 27} Such cell-targeted peptides can be used for targeted delivery of experimental therapeutic agents in vivo. A number of ‘hunter-killer'' peptides²⁸ composed of a cell-homing domain binding to a surface marker and of KLAKLAK₂ (sequence KLAKLAKKLAKLAK), a moiety inducing apoptosis upon receptor-mediated internalization, has been described by our group.^26,29 Such bimodal peptides have been used for depletion of malignant cells and organ-specific endothelial cells in preclinical animal models.^26,30,31 Recently, we isolated a cyclic peptide WAT7 (amino acid sequence CSWKYWFGEC) based on its specific binding to ASCs.²⁰ We identified Δ-decorin (ΔDCN), a proteolytic cleavage fragment of decorin, as the WAT7 receptor specifically expressed on the surface of CD34+PDGFRβ+CD31-CD45- WAPs and absent on MSCs in other organs.²⁰Here, we investigated whether WAPs are required for obesity development in adulthood. By designing a new hunter-killer peptide that directs KLAKLAK₂ to WAPs through WAT7/ΔDCN interaction, we depleted WAP in the mouse diet-induced obesity model. We demonstrate that WAP depletion suppresses WAT growth. We show that, in response to WAP deficiency, WAT becomes populated with beige adipocytes. Consistent with the reported thermogenic function of beige adipocytes,^32,33 the observed WAT remodeling is associated with increased energy expenditure. We identify a population of PDGFRα-positive, PDGFRβ-negative ASCs reported recently²² as a population surviving WAP depletion and responsible for WAT browning.