Takehiro Torisu

Socs3 deficiency in the brain elevates leptin sensitivity and confers resistance to diet-induced obesity.

Leptin is an adipocyte-derived hormone that plays a key role in energy homeostasis, yet resistance to leptin is a feature of most cases of obesity in humans and rodents. In vitro analysis suggested that the suppressor of cytokine signaling-3 (Socs3) is a negative-feedback regulator of leptin signaling involved in leptin resistance. To determine the functional significance of Socs3 in vivo, we generated neural cell–specific SOCS3 conditional knockout mice using the Cre–loxP system. Compared to their wild-type littermates, Socs3-deficient mice showed enhanced leptin-induced hypothalamic Stat3 tyrosine phosphorylation as well as pro-opiomelanocortin (POMC) induction, and this resulted in a greater body weight loss and suppression of food intake. Moreover, the Socs3-deficient mice were resistant to high fat diet–induced weight gain and hyperleptinemia, and insulin-sensitivity was retained. These data indicate that Socs3 is a key regulator of diet-induced leptin as well as insulin resistance. Our study demonstrates the negative regulatory role of Socs3 in leptin signaling in vivo, and thus suppression of Socs3 in the brain is a potential therapy for leptin-resistance in obesity.

Loss of Suppressor of Cytokine Signaling 1 in Helper T Cells Leads to Defective Th17 Differentiation by Enhancing Antagonistic Effects of IFN-γ on STAT3 and Smads

Suppressor of cytokine signaling 1 (SOCS1) is an important negative regulator for cytokines; however, the role of SOCS1 in Th17 differentiation has not been clarified. We generated T cell-specific SOCS1-deficient mice and found that these mice were extremely resistant to a Th17-dependent autoimmune disease model, experimental autoimmune encephalomyelitis. SOCS1-deficient naive CD4+ T cells were predominantly differentiated into Th1 and poorly into Th17 in vitro. These phenotypes were canceled in IFN-γ−/− background, suggesting that a large amount of IFN-γ in SOCS1-deficient T cells suppressed Th17 differentiation. IL-6 plus TGF-β enhanced retinoic acid receptor-related orphan receptor (ROR)-γt expression and suppressed IFN-γ production in wild-type T cells, whereas these effects were severely impaired in SOCS1-deficient T cells. These phenotypes can be partly explained by STAT3 suppression by enhanced SOCS3 induction through hyper-STAT1 activation in SOCS1-deficient T cells. In addition, SOCS1-deficient T cells were much less sensitive to TGF-β. Suppression of Th1 differentiation by TGF-β was impaired in SOCS1-deficient T cells. TGF-β-mediated Smad transcriptional activity was severely inhibited in SOCS1-deficient cells in the presence of IFN-γ. Such impairment of TGF-β functions were not observed in SOCS3-overexpressed cells, indicating that suppression of Smads was independent of SOCS3. Therefore, SOCS1 is necessary for Th17 differentiation by suppressing antagonistic effect of IFN-γ on both STAT3 and Smads. Induction of SOCS3 can partly explain IFN-γ-mediated STAT3 suppression, while other mechanism(s) will be involved in IFN-γ-mediated Smad suppression. SOCS1-deficient T cells will be very useful to investigate the molecular mechanism for the STAT1-mediated suppression of Th17 development.

Autophagy regulates endothelial cell processing, maturation and secretion of von Willebrand factor

Endothelial secretion of von Willebrand factor (VWF) from intracellular organelles known as Weibel-Palade bodies (WPBs) is required for platelet adhesion to the injured vessel wall. Here we demonstrate that WPBs are often found near or within autophagosomes and that endothelial autophagosomes contain abundant VWF protein. Pharmacological inhibitors of autophagy or knockdown of the essential autophagy genes Atg5 or Atg7 inhibits the in vitro secretion of VWF. Furthermore, although mice with endothelial-specific deletion of Atg7 have normal vessel architecture and capillary density, they exhibit impaired epinephrine-stimulated VWF release, reduced levels of high–molecular weight VWF multimers and a corresponding prolongation of bleeding times. Endothelial-specific deletion of Atg5 or pharmacological inhibition of autophagic flux results in a similar in vivo alteration of hemostasis. Thus, autophagy regulates endothelial VWF secretion, and transient pharmacological inhibition of autophagic flux may be a useful strategy to prevent thrombotic events.

The dual function of hepatic SOCS3 in insulin resistance in vivo

Inflammation associates with insulin resistance, which dysregulates nutrient homeostasis and leads to diabetes. The suppressor of cytokine signaling 3 (SOCS3), which is induced by pro‐inflammatory cytokines, such as TNFα and IL‐6, has been implicated in inflammation‐mediated insulin resistance in the liver and adipocytes. However, no genetic evidence has been provided for the involvement of SOCS3 on insulin resistance. Here, we generated hepatocyte‐specific SOCS3‐deficient (L‐SOCS3 cKO) mice and examined insulin sensitivity. Being consistent with a previous idea, the loss of SOCS3 in the liver apparently improved insulin sensitivity. However, unexpectedly, L‐SOCS3 cKO mice exhibited obesity and systemic insulin resistance with age. Insulin signaling was rather suppressed in muscles, suggesting that deletion of the SOCS3 gene in the liver modulates insulin sensitivity in other organs. Anti‐inflammatory reagent, sodium salicylate, partial improved insulin resistance of aged L‐SOCS3 cKO mice, suggesting that enhanced inflammatory status is associated with the phenotype of these mice. STAT3 was hyperactivated and acute‐phase proteins were elevated in L‐SOCS3 cKO mice liver, which were reduced by sodium salicylate treatment. We conclude that hepatic SOCS3 is a mediator of insulin resistance in the liver; however, lack of SOCS3 in the liver promotes systemic insulin resistance by mimicking chronic inflammation.

Quality of life and physical fitness in an 85-year-old population

Since little is known about the very elderly population aged 80 years and older, we evaluated the association of quality of life (QoL) in an 85-year-old population with physical fitness measurements assessed at age 80 and 85 years. Two hundred seven individuals (90 males, 117 females) aged 85 years underwent the Short Form-36 (SF-36) questionnaires for QoL assessment and physical fitness measurements (handgrip strength, leg-extensor strength, one-leg standing time, stepping rate of legs, walking speed). In 85-year-olds, significant associations were found, by multiple regression analysis or logistic regression analysis, with adjustment for various influencing factors in QoL assessed by SF-36 with physical fitness measurements examined at the age of 85 and 80 years. Physical scales and scores in SF-36, such as physical functioning (PF), limitation in role functioning for physical reasons (role physical; RP), bodily pain (BP), and the physical component score (PCS) tended to be more tightly associated with fitness measurements than mental scales and scores such as limitation in role functioning for emotional reasons (role emotional; RE), and emotional well-being (mental health; MH), and mental component score (MCS). Three scales the general health perceptions (GH), the vitality (VT), and the social functioning (SF) consisting of both physical and mental components were associated with fitness, the extent being intermediate between physical scales and mental scales. Of the several physical fitness measurements, leg-extensor strength and the walking speed of 85-year-olds, and the stepping rate of 80-year-olds were most closely associated with QoL. In a very elderly population of 85- and 80-year-olds, significant associations were found between QoL by SF-36 and physical fitness measurements, suggesting that increases in the levels of physical fitness, even in the very elderly, can contribute to improvements in QoL.

Suppressor of cytokine signaling 1 protects mice against concanavalin A-induced hepatitis by inhibiting apoptosis

Acute liver failure is associated with significant mortality. However, the underlying pathophysiological mechanism is not yet fully understood. Suppressor of cytokine signaling‐1 (SOCS1), which is a negative‐feedback molecule for cytokine signaling, has been shown to be rapidly induced during liver injury. Here, using liver‐specific SOCS1‐conditional‐knockout mice, we demonstrated that SOCS1 deletion in hepatocytes enhanced concanavalin A (ConA)–induced hepatitis, which has been shown to be dependent on activated T and natural killer T (NKT) cells. Although serum cytokine level and NKT cell activation were similar in wild‐type (WT) and SOCS1‐deficient mice after ConA treatment, proapoptotic signals, including signal transducers and activators of transcription 1 (STAT1) and Jun‐terminal kinase (JNK) activation, were enhanced in SOCS1‐deficient livers compared with those in WT livers. SOCS1‐deficient hepatocytes had higher expression of Fas antigen and were more sensitive to anti‐Fas antibody–induced apoptosis than were WT hepatocytes. Furthermore, SOCS1‐deficient hepatocytes were more sensitive to tumor necrosis factor (TNF)‐α‐induced JNK activation and apoptosis. These data indicate that SOCS1 is important to the prevention of hepatocyte apoptosis induced by Fas and TNF‐α. In contrast, SOCS1 overexpression in the liver by adenoviral gene transfer prevented ConA‐induced liver injury. Conclusion: These findings indicate that SOCS1 plays important negative roles in fulminant hepatitis and that forced expression of SOCS1 is therapeutic in preventing hepatitis. (HEPATOLOGY 2008.)

Physical Fitness and Cognitive Function in an 85-Year-Old Community-Dwelling Population

Background: Little is known about the association between physical fitness and cognitive function in very elderly people (over 80 years of age). Objectives: To evaluate that relationship in 85-year-old community-dwelling individuals. Methods: Out of 207 participants (90 males, 117 females) who were 85 years old and community-dwelling, 205 completed the Mini-Mental State Examination (MMSE) for evaluating cognitive function. The numbers of subjects who completed physical fitness measurements such as hand-grip strength, isometric leg extensor strength, one-leg standing time, stepping rate, and walking speed were 198, 159, 169, 168, and 151, respectively. Results: There were significant associations in MMSE with hand-grip strength (right or left hand), isometric leg extensor strength, stepping rate, and walking speed by simple regression analysis. MMSE was still significantly associated with hand-grip strength (β = 0.305, p = 0.005 for right side; β = 0.309, p = 0.004 for left side), stepping rate (β = 0.183, p = 0.046), and walking speed (β = –0.222, p = 0.014) by multiple regression analysis after adjustments for the amount of education, gender, smoking, drinking, complication of stroke, body weight, body height, regular medical care, serum albumin, blood HbA1c, and marital status. By logistic regression analysis, the prevalence of a normal MMSE score (MMSE ≧24) was increased by 9% with each 1-kg increase in hand-grip strength of the left hand (OR 1.087, 95% CI 1.003–1.179, p = 0.042), and was increased by 6% with each step per 10 s in stepping rate (OR 1.060, 95% CI 1.000–1.122, p = 0.048). Conclusion: In a very elderly population of 85-year-olds, cognitive function was associated with some physical fitness measurements, independent of confounding factors.

Relationship between tooth loss and mortality in 80-year-old Japanese community-dwelling subjects

BackgroundFindings from several studies suggest associations between tooth loss and health outcomes, including malnutrition, poor quality of life, and mortality, in older individuals. However, limited information is available regarding whether those associations remain true in very elderly subjects after adequately considering confounding factors such as sex and smoking status. Herein, we determined whether the number of teeth in 80-year-old subjects is an independent predictor of mortality.MethodsWe initially contacted 1282 80-year-old community-dwelling individuals born in 1917, of whom 697 responded and participated in a baseline study, with follow-up examinations conducted 4 and 5.5 years later. Data from interviews and medical and oral examinations were obtained, and oral health was determined according to the number of teeth remaining in the oral cavity.ResultsA total of 108 and 157 subjects died in 4 years and 5.5 years, respectively, after the baseline study. Tooth loss was significantly associated with mortality at age 85.5, but not at age 84, after adjusting for potential confounders. When the analysis was stratified by sex, we found a stronger association in females in follow-up examinations conducted at both 4- and 5.5 years. On the other hand, the effect of tooth loss on mortality was not significantly different between smokers and non-smokers.ConclusionTooth loss is a significant predictor of mortality independent of health factors, socio-economic status, and lifestyle in octogenarians, with a stronger association in females.

Relationship between chewing ability and high‐level functional capacity in an 80‐year‐old population in Japan

OBJECTIVES To evaluate the association between high-level functional capacity and chewing in a middle-old community-based population. BACKGROUND Although basic and instrumental activities of daily living are known to be associated with chewing ability in the elderly, an association between higher levels of competence and chewing ability has not been evaluated in the elderly. MATERIALS AND METHODS The association between chewing ability using a number of different foods and high-level functional capacity by the Tokyo Metropolitan Institute of Gerontology was evaluated in 694, 80-year-old people residing in Fukuoka Prefecture, Japan. RESULTS A significant correlation was found, using multiple regression or logistic regression analyses adjusted for various confounding factors, between the number of total chewable foods, hard foods or moderately hard foods, and total functional capacity, instrumental activity, intellectual activity or social role ability. In contrast, the number of slightly hard foods, easily chewable foods and remaining teeth were only partly related to total functional capacity and intellectual activity. CONCLUSION High-level functional capacity including intellectual activity and social role in middle-old elderly was associated with the ability to chew hard foods than to chew easily chewable foods. Maintenance of chewing ability in elderly might result in better intellectual activity and social role.

Intact endothelial autophagy is required to maintain vascular lipid homeostasis

The physiological role of autophagic flux within the vascular endothelial layer remains poorly understood. Here, we show that in primary endothelial cells, oxidized and native LDL stimulates autophagosome formation. Moreover, by both confocal and electron microscopy, excess native or modified LDL appears to be engulfed within autophagic structures. Transient knockdown of the essential autophagy gene ATG7 resulted in higher levels of intracellular 125I‐LDL and oxidized LDL (OxLDL) accumulation, suggesting that in endothelial cells, autophagy may represent an important mechanism to regulate excess, exogenous lipids. The physiological importance of these observations was assessed using mice containing a conditional deletion of ATG7 within the endothelium. Following acute intravenous infusion of fluorescently labeled OxLDL, mice lacking endothelial expression of ATG7 demonstrated prolonged retention of OxLDL within the retinal pigment epithelium (RPE) and choroidal endothelium of the eye. In a chronic model of lipid excess, we analyzed atherosclerotic burden in ApoE−/−mice with or without endothelial autophagic flux. The absence of endothelial autophagy markedly increased atherosclerotic burden. Thus, in both an acute and chronic in vivo model, endothelial autophagy appears critically important in limiting lipid accumulation within the vessel wall. As such, strategies that stimulate autophagy, or prevent the age‐dependent decline in autophagic flux, might be particularly beneficial in treating atherosclerotic vascular disease.