Fighting obesity: When muscle meets fat

Figures & data

Figure 1. Origin of brown, white and beige adipocytes. Two types of common precursors of muscle/fat lineage are derived from mesenchymal stem cells. These 2 types of common precursors are distinguished by Myf5, Pax7, Pax3 and PDGFRα expression. Myf5⁺, Pax7⁺ and Pax3⁺ common precursors give rise to specified muscle or brown adipose precursors that differentiate into either mature myocytes (Myf5⁺, MyoD⁺, Myogenin⁺) or brown adipocytes (UCP1⁺), respectively. Myf5-, Pax3-, Pax7- and PDGFRα+ common precursors give rise to specified beige or white adipose precursors that differentiate into either mature beige adipocytes (Tnfrnfs9⁺, Tmem26⁺, Tbx1⁺) or white adipocytes (Eva1⁺, Hspb7⁺, Pdk4⁺), respectively. The interconversion of mature beige and white adipocytes may occur under environmental stimulus.

Figure 2. Distribution of various adipose depots Adipose tissues are generally divided into brown adipose depots and white adipose depots. Brown adipose depots include interscapular BAT (isBAT), subscapular BAT (sBAT), cervical BAT (cBAT), peri-aortic BAT (paBAT) and renal BAT (rBAT). White adipose depots include anteriorsubcutaneous WAT (asWAT), inguinal WAT (inWAT), retroperitoneal WAT (rWAT), gonadal WAT (gWAT), mesenteric WAT (mWAT), and intramuscular fat (IMAT).

Table 1. Potential myokines, their secretion and target sites, and functions

	Production site	Target site	Function
BDNF	muscle, brain, gastrointestinal sites, others	muscle, brain	fatty acid oxidation, cognition
FGF2	various	muscle-bone interphase, central nervous system, heart, blood vessels	muscle-bone interaction, neurogenesis
FGF21	muscle, liver, others	muscle, adipose tissue	anti-obese, browning of WAT
Fstl	Liver, muscle	muscle, liver	Antagonizes myostatin
IL4	muscle, mast cells, Th2 cells, eosinophils, and basophils	muscle, leukocytes and other immune cells, brain	immunity regulation, satellite cell proliferation, muscle hypertrophy and myogenesis, cognition
IL6	muscle, adipose, liver, pancreas	muscle, adipose, liver, pancreas	glucose production, fatty acid oxidation, hepatic glucose production, anti-inflammation
IL7	muscle	muscle, immune cells	satellite cell differentiation, T/B cell development
IL8	muscle, liver	muscle, liver	chemokine, angiogenic factor
IL15	muscle	muscle	fat metabolism, muscle-fat interaction
Irisin/Fndc5	muscle, brain, liver, heart, intracranial artery, tongue, and nerve	muscle, brain	oxidative metabolism, browning of WAT
LIFs	various	muscle, blood, bone, liver, nerve	cell proliferation, muscle hypertrophy and regeneration
MCP1	Muscle, adipose, blood and etc.	various	recruiting monocytes, neutrophils, lymphocytes, and inducing chemotaxis
Mstn	muscle, adipose, bone	muscle, adipose	muscle mass, fatty acid oxidation, browning of WAT
Myonectin	muscle	muscle, adipose	metabolic control