We have long thought that remnant lipoproteins (RLP) in plasma are significantly increased as the result of disturbed lipoprotein metabolism followed by obesity and insulin resistance. Therefore, it w Show more
We have long thought that remnant lipoproteins (RLP) in plasma are significantly increased as the result of disturbed lipoprotein metabolism followed by obesity and insulin resistance. Therefore, it was believed that insulin resistance causes and enhances RLP formation. In contrast, this hypothesis states that RLP induces insulin resistance as the result of obesity associated with the excessive fat intake. The majority of plasma TG increased after fat intake is TG in RLP (RLP-TG) and the majority of postprandial RLP is VLDL remnants, not CM remnants. RLP is newly formed lipoproteins primarily for energy supply against starvation, like blood sugar after carbohydrate intake. Since RLP bearing apoE, LPL and Lp(a) function as ligands for the VLDL receptor, RLP interacts with the VLDL receptor in visceral fat adipocytes and stored as TG similar to excessive blood sugar. However, the excessive VLDL remnants induces obesity and its associated insulin resistance, which plays a major role as the initiator of metabolic domino effects, similar to blood sugar primarily serving as an energy supply to protect against starvation. Show less
G-protein-coupled receptors (GPCRs) constitute the largest family of transmembrane receptors and regulate a variety of physiological and disease processes. Although the roles of many non-odorant GPCRs Show more
G-protein-coupled receptors (GPCRs) constitute the largest family of transmembrane receptors and regulate a variety of physiological and disease processes. Although the roles of many non-odorant GPCRs have been identified in vivo, several GPCRs remain orphans (oGPCRs). The gastrointestinal (GI) tract is the largest endocrine organ and is a promising target for drug discovery. Given their close link to physiological function, the anatomical and histological expression profiles of benchmark GI-related GPCRs, such as the cholecystokinin-1 receptor and GPR120, and 106 oGPCRs were investigated in the mucosal and muscle-myenteric nerve layers in the GI tract of C57BL/6J mice by quantitative real-time polymerase chain reaction. The mRNA expression patterns of these benchmark molecules were consistent with previous in situ hybridization and immunohistochemical studies, validating the experimental protocols in this study. Of 96 oGPCRs with significant mRNA expression in the GI tract, several oGPCRs showed unique expression patterns. GPR85, GPR37, GPR37L1, brain-specific angiogenesis inhibitor (BAI) 1, BAI2, BAI3, and GPRC5B mRNAs were preferentially expressed in the muscle-myenteric nerve layer, similar to GPCRs that are expressed in both the central and enteric nerve systems and that play multiple regulatory roles throughout the gut-brain axis. In contrast, GPR112, trace amine-associated receptor (TAAR) 1, TAAR2, and GPRC5A mRNAs were preferentially expressed in the mucosal layer, suggesting their potential roles in the regulation of secretion, immunity, and epithelial homeostasis. These anatomical and histological mRNA expression profiles of oGPCRs provide useful clues about the physiological roles of oGPCRs in the GI tract. Show less