The Unique Metabolic Characteristics of Bone Marrow Adipose Tissue

Abstract

Bone marrow adipose tissue (MAT) is distinct from white adipose tissue (WAT) or brown adipose tissue (BAT) for its location, feature and function. As a largely ignored adipose depot, it is situated in bone marrow space and resided with bone tissue side-by-side. MAT is considered not only as a regulator of bone metabolism through paracrine, but also as a functionally particular adipose tissue that may contribute to global metabolism. Adipokines, inflammatory factors and other molecules derived from bone marrow adipocytes may exert systematic effects. In this review, we summary the evidence from several aspects including development, distribution, histological features and phenotype to elaborate the basic characteristics of MAT. We discuss the association between bone metabolism and MAT, and highlight our current understanding of this special adipose tissue. We further demonstrate the probable relationship between MAT and energy metabolism, as well as glucose metabolism. On the basis of preliminary results from animal model and clinical studies, we propose that MAT has its unique secretory and metabolic function, although there is no in-depth study at present.

Keywords: adipokine; bone marrow; bone mesenchymal stem cell; endocrine; marrow adipose tissue.

Figure 1

(A) Comparison of rMAT and cMAT. (B,C) Regulatory factors of MAT.

Figure 2

Secretion of MAT as well as adipocyte-derived molecules in the regulation of bone metabolism in the bone marrow cavity. MAT could secrete EVs, leptin, adiponectin, inflammatory factors, RANKL, and DPP4. These factors regulate bone metabolism from different aspects. Among them, adiponectin has been confirmed to enter into the circulation. EVs cause a phenotypic transformation of osteoblast to adipocyte. Leptin regulates bone metabolism in three ways (①-③). Moreover, Adiponectin regulates bone metabolism through four pathways (I-IV). Inflammatory cytokines promote osteoclast formation and adipocyte differentiation. RANKL promote osteoclast formation. The role of DPP4 in bone marrow cavity remains unclear.