Marrow Adipose Tissue: Trimming the Fat

Marrow adipose tissue (MAT) is a unique fat depot, located in the skeleton, that has the potential to contribute to both local and systemic metabolic processes. In this review we highlight several recent conceptual developments pertaining to the origin and function of MAT adipocytes; consider the relationship of MAT to beige, brown, and white adipose depots; explore MAT expansion and turnover in humans and rodents; and discuss future directions for MAT research in the context of endocrine function and metabolic disease. MAT has the potential to exert both local and systemic effects on metabolic homeostasis, skeletal remodeling, hematopoiesis, and the development of bone metastases. The diversity of these functions highlights the breadth of the potential impact of MAT on health and disease. MAT is dynamically regulated in metabolic diseases including diabetes, obesity, and anorexia, and by pharmacotherapies including estrogen, growth hormone, and glucocorticoids.MAT is an endocrine organ that during caloric restriction can contribute to circulating adipokines, such as adiponectin.MAT exists in two forms, regulated and constitutive. Regulated and constitutive marrow adipocytes are defined based on their surrounding microenvironment and response to external stimuli. They have distinct developmental patterns, adipocyte size, lipid saturation, and transcription factor expression.The fold-increase of MAT in rodent models of metabolic diseases such as diabetes and obesity exceeds that observed in humans. The persistence of MAT adipocytes after their formation is also significantly reduced in mice.