[The role of SIRT6 in nonalcoholic steatohepatitis].

SIRT6, a member of the silencing information regulatory protein family, is a nicotinamide adenine dinucleotide-dependent histone deacetylase and an ADP-ribose transferase enzyme. It plays an important role in fundamental physiological and pathological processes, including lipid metabolism, inflammation, oxidative stress and fibrosis, and is considered as a potential therapeutic target for metabolic syndrome. SIRT6 knockout mice displayed severe fatty liver, and the expression of SIRT6 in the liver of nonalcoholic steatohepatitis (NASH) mice was significantly lower than that of normal mice. Overexpression of SIRT6 significantly ameliorated NASH-induced liver damage. It is suggested that SIRT6 may play a key role in protecting against NASH. In this paper, we review the important regulatory functions of SIRT6 in the occurrence and development of NASH.

Irisin alleviates pressure overload-induced cardiac hypertrophy by inducing protective autophagy via mTOR-independent activation of the AMPK-ULK1 pathway.

In hypertrophic hearts, autophagic flux insufficiency is recognized as a key pathology leading to maladaptive cardiac remodeling and heart failure. This study aimed to illuminate the cardioprotective role and mechanisms of a new myokine and adipokine, irisin, in cardiac hypertrophy and remodeling. Adult male wild-type, mouse-FNDC5 (irisin-precursor)-knockout and FNDC5 transgenic mice received 4 weeks of transverse aortic constriction (TAC) alone or combined with intraperitoneal injection of chloroquine diphosphate (CQ). Endogenous FNDC5 ablation aggravated and exogenous FNDC5 overexpression attenuated the TAC-induced hypertrophic damage in the heart, which was comparable to the protection of irisin against cardiomyocyte hypertrophy induced by angiotensin II (Ang II) or phenylephrine (PE). Accumulated autophagosome and impaired autophagy flux occurred in the TAC-treated myocardium and Ang II- or PE-insulted cardiomyocytes. Irisin deficiency caused reduced autophagy and aggravated autophagy flux failure, whereas irisin overexpression or supplementation induced protective autophagy and improved autophagy flux, which were reversed by autophagy inhibitors Atg5 siRNA, 3-MA and CQ. Irisin boosted the activity of only AMPK but not Akt and MAPK family members in hypertrophic hearts and cultured cardiomyocytes and further activated ULK1 at Ser555 but not Ser757 and did not affect the mTOR-S6K axis. Blockage of AMPK and ULK1 with compund C and SBI-0206965, respectively, both abrogated irisin's protection against cardiomyocyte hypertrophic injury and reversed its induction of both autophagy and autophagy flux. Our results suggest that irisin protects against pressure overload-induced cardiac hypertrophy by inducing protective autophagy and autophagy flux via activating AMPK-ULK1 signaling.

SIRT6 protects cardiomyocytes against ischemia/reperfusion injury by augmenting FoxO3α-dependent antioxidant defense mechanisms.

SIRT6, a member of the NAD(+)-dependent class III deacetylase sirtuin family, has been revealed to play important roles in promoting cellular resistance against oxidative stress. The formation of reactive oxygen species (ROS) and oxidative stress are the crucial mechanisms underlying cellular damage and dysfunction in cardiac ischemia/reperfusion (I/R) injury, but the role of SIRT6 in I/R-induced ROS and oxidative stress is poorly understood. In this study, by using heterozygous SIRT6 knockout (SIRT6(+/-)) mice and cultured neonatal cardiomyocyte models, we investigated how SIRT6 mediates oxidative stress and myocardial injury during I/R. Partial knockout (KO) of SIRT6 aggravated myocardial damage, ventricular remodeling, and oxidative stress in mice subjected to myocardial I/R, whereas restoration of SIRT6 expression by direct cardiac injection of adenoviral constructs encoding SIRT6 reversed these deleterious effects of SIRT6 KO in the ischemic heart. In addition, partial deletion of the SIRT6 gene decreased myocardial functional recovery following I/R in a Langendorff perfusion model. Similarly, the protective effects of SIRT6 were also observed in cultured cardiomyocytes following hypoxia/reoxygenation. Intriguingly, SIRT6 was noticed to up-regulate AMP/ATP and then activate the adenosine 5'-monophosphate-activated protein kinase (AMPK)-forkhead box O3α (FoxO3α) axis and further initiated the downstream antioxidant-encoding gene expression (manganese superoxide dismutase and catalase), thereby decreasing cellular levels of oxidative stress and mediating cardioprotection in the ischemic heart. These results suggest that SIRT6 protects the heart from I/R injury through FoxO3α activation in the ischemic heart in an AMP/ATP-induced AMPK-dependent way, thus upregulating antioxidants and suppressing oxidative stress.

[The mechanisms of stimulated lipolysis by high concentration of glucose in primary rat adipocytes].

OBJECTIVE: To investigate the cellular mechanisms of adipocyte lipolytic response to a high concentration of glucose, which liberates free fatty acids (FFA) efflux from adipose cells to plasma. METHODS: Adipocytes were isolated from epididymal fat pads of Sprague-Dawley (SD) rats, and were incubated in the presence or absence of excess glucose (25 mmol/L). Glycerol released in the culture medium was determined by use of a colorimetric assay and served as an index of lipolysis. The data are expressed as micromoles glycerol per liter packed cell volume (PCV) of adipocytes. The protein levels of native and phosphorylated perilipin, hormone-sensitive lipase (HSL) and adipose triglyceride lipase (ATGL) were examined by immunoblotting. Adipose lipases activity was determined by performing an enzymatic assay. RESULTS: A high concentration of glucose at 25 mmol/L caused a significant increase in lipolysis in primary rat adipocytes. A 24 h incubation with 25 mmol/L glucose elevated glycerol accumulation from 4.4 mmol/L PCV to 6.4 mmol/L PCV, by 1.5 fold (P<0.01) and promoted glycerol release from 0.11 mmol/L PCV to 0.24 mmol/L PCV, by 2.1 fold (P<0.01). The lipolytic response mediated by high glucose occurred apparently at the end of 16 h and remained high after 24 h incubation. The lipolytic action of glucose at 25 mmol/L was more effective than that at 10 mmol/L. To elucidate the mechanism by which high glucose stimulated lipolysis, we showed that high glucose promoted the phosphorylation of perilipin but did not alter its protein level. Further, we showed that high glucose caused a significant increase in adipose lipases activity by 1.74 fold. The protein level of HSL but not ATGL was significantly upregulated by high glucose. Moreover, the acute lipolytic response to isoproterenol was further enhanced by high glucose. CONCLUSION: High glucose directly stimulates the releases of glycerol and FFA from adipocytes; the cellular mechanisms of this lipolytic action involve promoted perilipin phosphorylation, augmented HSL expression and increased adipose lipases activity under high glucose conditions. These results suggest that a high concentration of glucose alone can directly liberate FFA from adipocyte to plasma, hence increasing systemic FFA levels and impairing insulin sensitivity.

[Perilipin associated with lipid droplets regulates lipolysis].

Perilipins are the proteins associating with the lipid droplets in adipocytes and steroidogenic cells. Unphosphorylated perilipins coat the surface of intracellular lipid droplets to form a barrier that prevents lipase from accessing to triacylglycerol core, thus suppressing lipolysis. Upon activation of protein kinase A (PKA), two proteins, hormone-sensitive lipase (HSL) and perilipins, are phosphorylated. The phosphorylated perilipin is required for inducing the translocation of HSL from the cytosol to the lipid droplets of adipocytes and is essential for the initiation of lipolytic reaction. It is proposed that phosphorylation of perilipin is a key step for the activation of lipolytic cascade via PKA and ERK signaling pathways. Dysregulation of perilipin involves in the pathogenesis of obesity, diabetes and atherosclerosis.

Patients Aged 80 Years or Older are Encountered More Potentially Inappropriate Medication Use.

BACKGROUND: Polypharmacy and potentially inappropriate medications (PIMs) are prominent prescribing issues in elderly patients. This study was to investigate the different prevalence of PIM use in elderly inpatients between 65-79 years of age and 80 years or older, who were discharged from Geriatric Department in West China Hospital. METHODS: A large-scale cohort of 1796 inpatients aged 65 years or over was recruited. Respectively, 618 patients were 65-79 years and 1178 patients were 80 years or older. Updated 2012 Beers Criteria by the American Geriatric Society was applied to assess the use of PIM among the investigated samples. RESULTS: A review of the prescribed medications identified 686 patients aged 80 years or older consumed at least one PIM giving a rate of 58.2%. Conversely, 268 (43.4%) patients aged 65-79 years consumed at least one PIM (χ2 = 40.18, P < 0.001). Patients aged 80 years or older had higher hospitalization expenses, length of stay, co-morbidities, medical prescription, and mortality than patients aged 65-79 years (all with P < 0.001). Patients aged 80 years or older were prescribed with more benzodiazepines, drugs with strong anticholinergic properties, megestrol, antipsychotics, theophylline, and aspirin. In multiple regression analysis, PIM use was significantly associated with female gender, age, number of diagnostic disease, and number of prescribed medication. CONCLUSIONS: The finding from this study revealed that inpatients aged 80 years or older encountered more PIM use than those aged 65-79 years. Anticholinergic properties, megestrol, antipsychotics, theophylline, and aspirin are medications that often prescribed to inpatients aged 80 years or older. Doctors should carefully choose drugs for the elderly, especially the elderly aged 80 years or older.

Ghrelin inhibits doxorubicin cardiotoxicity by inhibiting excessive autophagy through AMPK and p38-MAPK.

Doxorubicin (DOX) is a wide spectrum antitumor drug, but its clinical application is limited by the cardiotoxicity. Ghrelin, a multi-functional peptide hormone with metabolic regulation in energy homeostasis, plays important roles in cardiovascular protection. Now, the underlying mechanisms of ghrelin against DOX-induced cardiomyocyte apoptosis and atrophy are still not clear. In the present study, we revealed an autophagy-dependent mechanism involved in ghrelin's protection against DOX-induced cardiomyocyte death and size decrease. We observed that DOX insult induced remarkable mortality and cardiac dysfunction in mice, and increase in LDH leakage, cardiomyocyte apoptosis and decrease in cell viability and size in mouse hearts and H9c2 cell cultures, which were effectively improved by ghrelin supplement. We further observed that the strong autophagy stirred by DOX exposure was paralleling with the serious apoptosis and size decrease in cardiomyocytes. Ghrelin, like an autophagy inhibitor, 3-MA, inhibited the DOX-induced autophagy and attenuated cardiomyocyte apoptosis and size decrease. Furthermore, ghrelin significantly reduced the intercellular oxidative stress level, a strong autophagy trigger, partly by augmenting the expression and activities of the endogenous anti-oxidative enzymes. After the further investigation in the post signaling pathways of ghrelin receptors in H9c2 cells, including ERK, p38/MAPK, JNK, AMPK and Akt, we observed that ghrelin supplement only reduced the DOX-activated AMPK and augmented the DOX-down regulated p38-MAPK and mTOR phosphorylation. Our results indicated that ghrelin effectively improved the cardiomyocyte survival and size maintenance by suppressing the excessive autophagy through both ROS inhibition and mTOR induction through suppressing AMPK activity and stimulating p38-MAPK activity.