京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第21336号 / 医博第4394号 / 新制||医||1031(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 横出 正之, 教授 岩井 一宏, 教授 戸口田 淳也 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

During embryonic development, adipocytes emerge from microvasculature. Lineage-­‐tracing studies in mice have shown that adipocyte progenitors reside in the adipose tissue capillaries. However, the direct evidence of an association between adipocyte progenitors and vasculature in humans is lacking. A specific class of adipocytes (brown and beige/brite) expresses the uncoupling protein 1 (UCP1), which consumes glucose and fatty acids to generate heat. The abundance of UCP1- containing adipocytes correlates with a lean metabolically healthy phenotype in human. However, a causal relationship between the presence of these cells and metabolic benefits in human is not clear. In this thesis, I report human adipocyte progenitors proliferate in response to pro-angiogenic factors in association with adipose capillary networks in-vitro. The capillary-derived adipocytes transform from being UCP1-negative to positive upon adenylate cyclase activation, a defining feature of the brite/beige phenotype. Activated cells have denser, round mitochondria with UCP1 protein, and display uncoupled respiration. When implanted into NOD-scid IL2rgnull (NSG) mice, the adipocytes can form a vascularized fat pad that induces vascularization and becomes integrated into mouse circulatory system. In normal or high fat diet-fed NSG mice, activated brite/beige adipocytes enhance systemic glucose tolerance and improved hepatic steatosis, thus providing evidence for their potential therapeutic use. The adipocytes also express neuroendocrine and secretory factors such as Interleukin-33, proprotein convertase PCSK1 and proenkephalin PENK, which are correlated with human obesity. Finally, analyses on single-cell clones of capillary-sprout cells reveal the existence of diverse adipogenic progenitor populations. Further characterization of the clones will define the identifying features of the diverse adipocyte progenitor types that exist in human adipose tissue.

No description available.

Enlargement of adipocytes in obesity leads to alteration in adipokine production and these changes are linked to the development of obesity-related cardiovascular diseases. Adipokines specifically associated with obesity-related hypertension include angiotensinogen and adiponectin. Conjugated linoleic acid (CLA) has been reported to reduce blood pressure in obese insulin-resistant rats, but its mechanism of action has not been identified. The objective of this study was to determine whether CLA’s ability to improve obesity-related hypertension involves reducing adipocyte size and altering adipokine production. Fa/fa Zucker rats (6 or 16 week old) were fed diets containing CLA isomers for 8 weeks. The trans(t)10,cis(c)12-CLA isomer reduced adipocyte size in both younger and older rats. Despite beneficial changes in cell size of rats fed the t10,c12-CLA isomer, there were no changes in the renin-angiotensin system or pro-inflammatory cytokines such as tumor necrosis factor (TNF)-alpha and interleukin (IL)-6 or the anti-inflammatory cytokine IL-10. In contrast, the t10,c12-CLA isomer increased adiponectin levels both in the circulation and in adipose tissue. This was associated with increased phosphorylation of endothelial nitric oxide synthase (eNOS) in adipose tissue and aorta. Direct treatment of CLA isomers in cultured endothelial cells did not increase eNOS phosphorylation but increases were observed with adiponectin treatment. In vivo, infusion with adiponectin increased eNOS phosphorylation in adipose of fa/fa Zucker rats in parallel with improvements in blood pressure. Similarly, when circulating levels of adiponectin increased in rats fed the t10,c12-CLA isomer diet, blood pressure was also attenuated. In younger rats, both the t10-c12 and c9,t11-CLA isomers were significantly different from the control group at week 8, however, only the t10,c12-CLA isomer was comparable to the commonly used anti-hypertensive medication captopril. In conclusion, the beneficial effects of the t10,c12-CLA isomer on blood pressure may in part be due to its ability to reduce the number of large adipocytes in vivo, thus increasing the production of adiponectin which subsequently activates vascular eNOS.

Enlargement of adipocytes in obesity leads to alteration in adipokine production and these changes are linked to the development of obesity-related cardiovascular diseases. Adipokines specifically associated with obesity-related hypertension include angiotensinogen and adiponectin. Conjugated linoleic acid (CLA) has been reported to reduce blood pressure in obese insulin-resistant rats, but its mechanism of action has not been identified. The objective of this study was to determine whether CLA’s ability to improve obesity-related hypertension involves reducing adipocyte size and altering adipokine production. Fa/fa Zucker rats (6 or 16 week old) were fed diets containing CLA isomers for 8 weeks. The trans(t)10,cis(c)12-CLA isomer reduced adipocyte size in both younger and older rats. Despite beneficial changes in cell size of rats fed the t10,c12-CLA isomer, there were no changes in the renin-angiotensin system or pro-inflammatory cytokines such as tumor necrosis factor (TNF)-alpha and interleukin (IL)-6 or the anti-inflammatory cytokine IL-10. In contrast, the t10,c12-CLA isomer increased adiponectin levels both in the circulation and in adipose tissue. This was associated with increased phosphorylation of endothelial nitric oxide synthase (eNOS) in adipose tissue and aorta. Direct treatment of CLA isomers in cultured endothelial cells did not increase eNOS phosphorylation but increases were observed with adiponectin treatment. In vivo, infusion with adiponectin increased eNOS phosphorylation in adipose of fa/fa Zucker rats in parallel with improvements in blood pressure. Similarly, when circulating levels of adiponectin increased in rats fed the t10,c12-CLA isomer diet, blood pressure was also attenuated. In younger rats, both the t10-c12 and c9,t11-CLA isomers were significantly different from the control group at week 8, however, only the t10,c12-CLA isomer was comparable to the commonly used anti-hypertensive medication captopril. In conclusion, the beneficial effects of the t10,c12-CLA isomer on blood pressure may in part be due to its ability to reduce the number of large adipocytes in vivo, thus increasing the production of adiponectin which subsequently activates vascular eNOS.

Obesity-related comorbidities, including type 2 diabetes mellitus (T2DM) and nonalcoholic fatty liver disease (NAFLD) have become a major public health concerns. These complications primarily arise in response to cellular changes in white adipose tissue (WAT). In particular, when a majority of fat cells become hypertrophic it promotes a metabolically unhealthy phenotype, which is characterized by chronic low-grade inflammation, insulin resistance, and ectopic lipid accumulation. Research has implicated synthetic (i.e., Bisdehydrodoisynolic acid, BDDA) and natural (i.e., genistein and daidzein) xenoestrogens in the protection against obesity-related pathologies. Bisdehydrodoisynolic acid (BDDA) reduced weight gain and adiposity, as well as improved lipid homeostasis in obese rodents. Alternatively, phytoestrogens, such as genistein and daidzein were reported to induce adipocyte differentiation through potential interactions with PPARγs, canonical WNT proteins, and estrogen receptors (ER) signaling. The current investigation was conducted to test the effects of synthetic and natural estrogenic compounds (BDDA, daidzein, and genistein) for their effects on the induction of adipogenic signaling, which may potentially improve WAT morphology by reducing adipocyte hypertrophy.

No description available.

Obesity is characterized by the accumulation of excess adipose tissue and has become a global health burden as the rates of obesity in both adults and children continue an upward trend year after year. Obesity is an important public health concern as it has been linked to increased prevalence of comorbidities such as type 2 diabetes, fatty liver, cardiovascular complications and cancer. Adipocytes are exquisitely sensitive to energy demands, quickly responding by releasing fatty acids, storing excess calories as triglycerides and/or secreting adipokines. The ability of the adipocyte to carry out its important functions requires perpetual remodeling of the extracellular matrix (ECM) surrounding the adipocyte. Metabolic dysfunction and fibrosis arise when the healthy balance of remodeling becomes dysregulated. The long-term goal of this project was to gain a deeper understanding of the events occurring within an adipocyte in the context of weight gain. I hypothesized that the adipocyte would play an active role in remodeling of the ECM. To test this hypothesis, I fed C57/Bl6 mice either high fat diet (HFD) or chow diet for 8, 20 and 34 weeks, at which time, the perigonadal adipose tissue was digested to isolate the adipocyte fraction and RNA-seq analysis was performed. My data demonstrate that adipocytes responded to their obesogenic, pro-inflammatory environment through upregulation of ECM-related genes after only 8 weeks of HFD coupled with declining expression of mitochondrial genes and increasing genes associated with endoplasmic reticulum (ER) stress after 20 and 34 weeks of HFD. Overall, these data give a novel view into the dysfunctional state of isolated adipocytes over a time course of HFD and response to the changing microenvironment. MICAL2 is an atypical actin-modulating protein that has been shown to be involved in the regulation of MRTFA/SRF signaling and in cancer progression. I demonstrated for the first time that MICAL2 expression is enriched in the stromal vascular fraction of adipose tissue and is upregulated with HFD and pro-fibrotic stimulus, TGF-β1. I also demonstrated that MICAL2 is an anti-adipogenic and pro-fibrogenic protein. Altogether, the novel biology uncovered suggests a role for MICAL2 in adipose tissue remodeling which warrants further investigation. / 2021-06-14T00:00:00Z

Through endocrine and exocrine functioning, physiological needs are communicated to body systems. Physiological need is met through the actions of intracellular signaling cascades and calibrated through an extensive network of regulatory cross talk within the cells of a given tissue. The insulin receptor belongs to a family of perhaps one of the most well studied family of dual receptor and tyrosine kinases (RTK). The signaling cascade downstream of the insulin RTK can be initiated through Insulin or growth factor ligand binding and bears growing relevance to the projected epidemic of obesity related illness and associated cancers. The primary function of the post-prandial insulin response is to support nutrient uptake and storage. Insulin (IS), Insulin-Like Growth Factor (IGF), and Epidermal Growth Factors (EGF) contribute to glucose metabolism, energetic homeostasis, and anabolic applications through effector kinases downstream of activated (phosphorylated) insulin receptor substrates (IRS). Protein Kinase B (AKT) kinase is one such cytosolic effector known to be of critical importance to anabolic metabolism and general cell survival. Under normal circumstances, AKT activity is dependent upon dual phosphorylation events known to occur at the plasma membrane. In an attempt to better understand the mechanism of AKT recruitment to the plasma membrane, earlier experiments reported that IRS stimulation by Insulin-Like Growth Factors (IGF) and Epidermal Growth Factors (EGF) resulted in downstream poly-ubiquitination and subsequent activation of the AKT kinase. This sequence of post-translational modification events suggested that non-proteolytic AKT ubiquitination, accomplished by the E2 Ubiquitin Conjugating enzyme (UBC13), was an important mediator of AKT activation. Through subsequent experimentation, it was determined that non-proteolytic ubiquitination was a necessary step for AKT activation following IRS activation by Insulin. Furthermore, the same two sites previously described in the context of IGF/EGF signaling were exploited through targeted mutagenesis and shown to synergistically regulate AKT translocation to the plasma membrane. Mutant AKT variants with a single mutation to either ubiquitination site resulted in partial knock down of phosphorylated AKT (pAKT), while variants with double mutations resulted in a complete loss of pAKT detection. Under physiologic conditions UBC13 activity can be antagonized by a small multifunctional protein called G-Protein Pathway Suppressor 2 (GPS2). Bearing the kinetics of an endogenous inhibitor, GPS2-mediated regulation directly inhibits the ubiquitin conjugating activity of the enzyme; thereby restricting AKT non-proteolytic poly-ubiquitination and antagonizing the insulin signaling network through a conserved mechanism. In accordance with this role, we have previously shown that GPS2 presence in adipocytes modulates systemic metabolism by restricting the activation of insulin signaling during the fasted state, whereas in absence of GPS2, the adipose tissue is more efficient at lipid storage, and obesity becomes uncoupled from inflammation and insulin resistance. As we are just beginning to unravel the regulatory network governing the cellular response to nutrient excess and pro-growth signaling, it remains unclear whether UBC13 activity is universally engaged in AKT translocation and activation. Here we have focused on the mitochondrial pool of AKT and investigated its regulation. Our findings add to the growing body of knowledge by demonstrating that in pre-adipocytes mitochondrial AKT is activated, in a UBC13-dependent fashion, following insulin stimulation. We also show that GPS2-mediated inhibition of UBC13 equally antagonizes AKT activation in different subcellular compartments, and that mitochondrial AKT activation is partially Phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K) dependent.

No description available.