SIRT7 suppresses energy expenditure and thermogenesis by regulating brown adipose tissue functions in mice.

Brown adipose tissue plays a central role in the regulation of the energy balance by expending energy to produce heat. NAD+-dependent deacylase sirtuins have widely been recognized as positive regulators of brown adipose tissue thermogenesis. However, here we reveal that SIRT7, one of seven mammalian sirtuins, suppresses energy expenditure and thermogenesis by regulating brown adipose tissue functions. Whole-body and brown adipose tissue-specific Sirt7 knockout mice have higher body temperature and energy expenditure. SIRT7 deficiency increases the protein level of UCP1, a key regulator of brown adipose tissue thermogenesis. Mechanistically, we found that SIRT7 deacetylates insulin-like growth factor 2 mRNA-binding protein 2, an RNA-binding protein that inhibits the translation of Ucp1 mRNA, thereby enhancing its inhibitory action on Ucp1. Furthermore, SIRT7 attenuates the expression of batokine genes, such as fibroblast growth factor 21. In conclusion, we propose that SIRT7 serves as an energy-saving factor by suppressing brown adipose tissue functions.

Structural analysis of the catalytic domain of Artemis endonuclease/SNM1C reveals distinct structural features.

The endonuclease Artemis is responsible for opening DNA hairpins during V(D)J recombination and for processing a subset of pathological DNA double-strand breaks. Artemis is an attractive target for the development of therapeutics to manage various B cell and T cell tumors, because failure to open DNA hairpins and accumulation of chromosomal breaks may reduce the proliferation and viability of pre-T and pre-B cell derivatives. However, structure-based drug discovery of specific Artemis inhibitors has been hampered by a lack of crystal structures. Here, we report the structure of the catalytic domain of recombinant human Artemis. The catalytic domain displayed a polypeptide fold similar overall to those of other members in the DNA cross-link repair gene SNM1 family and in mRNA 3'-end-processing endonuclease CPSF-73, containing metallo-ß-lactamase and ß-CASP domains and a cluster of conserved histidine and aspartate residues capable of binding two metal atoms in the catalytic site. As in SNM1A, only one zinc ion was located in the Artemis active site. However, Artemis displayed several unique features. Unlike in other members of this enzyme class, a second zinc ion was present in the ß-CASP domain that leads to structural reorientation of the putative DNA-binding surface and extends the substrate-binding pocket to a new pocket, pocket III. Moreover, the substrate-binding surface exhibited a dominant and extensive positive charge distribution compared with that in the structures of SNM1A and SNM1B, presumably because of the structurally distinct DNA substrate of Artemis. The structural features identified here may provide opportunities for designing selective Artemis inhibitors.

SIRT7 has a critical role in bone formation by regulating lysine acylation of SP7/Osterix.

SP7/Osterix (OSX) is a master regulatory transcription factor that activates a variety of genes during differentiation of osteoblasts. However, the influence of post-translational modifications on the regulation of its transactivation activity is largely unknown. Here, we report that sirtuins, which are NAD(+)-dependent deacylases, regulate lysine deacylation-mediated transactivation of OSX. Germline Sirt7 knockout mice develop severe osteopenia characterized by decreased bone formation and an increase of osteoclasts. Similarly, osteoblast-specific Sirt7 knockout mice showed attenuated bone formation. Interaction of SIRT7 with OSX leads to the activation of transactivation by OSX without altering its protein expression. Deacylation of lysine (K) 368 in the C-terminal region of OSX by SIRT7 promote its N-terminal transactivation activity. In addition, SIRT7-mediated deacylation of K368 also facilitates depropionylation of OSX by SIRT1, thereby increasing OSX transactivation activity. In conclusion, our findings suggest that SIRT7 has a critical role in bone formation by regulating acylation of OSX.

SIRT7 is an important regulator of cartilage homeostasis and osteoarthritis development.

Sirtuins (SIRT1-7) are NAD+-dependent deacetylase/deacylases that regulate a wide variety of biological functions. Although the roles of sirtuins in cartilage homeostasis and cartilage diseases have been well studied, there is no information on the contribution of SIRT7 to cartilage homeostasis and osteoarthritis (OA) pathologies. Here, we demonstrate that Sirt7 knockout mice are resistant to the development of aging-associated OA and forced exercise-induced OA. Attenuation of Sirt7 in the murine chondrogenic cell line ATDC5 increased the deposition of a glycosaminoglycan-rich extracellular matrix and the mRNA expression of extracellular matrix components such as Col2a1 and Acan. Mechanistically, we found that SIRT7 suppressed the transcriptional activity of SOX9, which is an important transcription factor in chondrocytes, and that the enzymatic activity of SIRT7 was required for its function. Our results indicate that SIRT7 is a novel important regulator of cartilage homeostasis and OA development.

Does patchouli oil change blood platelet monoamine oxidase-A activity of adult mammals?

Patchouli oil, an essential aroma oil extracted from patchouli leaf during short-term exposure with five and ten drops either inhibited (at 1 or 2 h) or stimulated (at 4 h) the platelet MAO-A activity depending on the dosages of the aroma oil mainly due to inhibition or stimulation of its K m. The long-term 15 consecutive days exposure (with two or five drops) of patchouli oil, on the other hand, maximally stimulated the platelet MAO-A activity with five drops patchouli oil for 1 h exposure, but further continuation of its exposure with same doses (two or five drops) for 30 consecutive days significantly stimulated (with two drops) and inhibited (with five drops) the platelet MAO-A activity due to stimulation and inhibition respectively of its corresponding both K m and V max. These results thus suggest that this aroma oil exposure may modulate the blood platelet serotonergic regulation depending on the dose, duration, and conditions of exposure.

Sirtuin 7-dependent deacetylation of DDB1 regulates the expression of nuclear receptor TR4.

Sirtuin 7 (SIRT7) is an NAD+-dependent deacetylase/deacylase, but only a limited number of SIRT7 substrates have been identified. Recently, we found that Sirt7 knockout mice are resistant to high-fat diet-induced fatty liver, and that SIRT7 positively regulates the protein level of TR4, a nuclear receptor involved in lipid metabolism, by inhibiting the CUL4B/DDB1/DCAF1 E3 ubiquitin ligase complex. However, the mechanism by which SIRT7 inhibits the E3 ubiquitin ligase complex was not identified. Here, we demonstrate that SIRT7 binds directly to DDB1 and deacetylates DDB1 at Lys1121. K1121R-DDB1 (a deacetylation-mimicking mutant) displayed reduced binding with DCAF1. The expression of TR4 protein and TR4 target genes, including Cd36, Cidea, Cidec and Pparg1, was increased in K1121R-DDB1-overexpressing Hepa1-6 cells compared to WT-DDB1-overexpressing cells. Our results indicate that the SIRT7-mediated deacetylation of K1121 attenuates the activity of the CUL4B/DDB1/DCAF1 E3 ubiquitin ligase complex by reducing binding between DDB1 and DCAF1, leading to the increased expression of TR4.

Hypoxia reduces HNF4α/MODY1 protein expression in pancreatic ß-cells by activating AMP-activated protein kinase.

Hypoxia plays a role in the deterioration of ß-cell function. Hepatocyte nuclear factor 4α (HNF4α) has an important role in pancreatic ß-cells, and mutations of the human HNF4A gene cause a type of maturity-onset diabetes of the young (MODY1). However, it remains unclear whether hypoxia affects the expression of HNF4α in ß-cells. Here, we report that hypoxia reduces HNF4α protein expression in ß-cells. Hypoxia-inducible factor was not involved in the down-regulation of HNF4α under hypoxic conditions. The down-regulation of HNF4α was dependent on the activation of AMP-activated protein kinase (AMPK), and the reduction of HNF4α protein expression by metformin, an AMPK activator, and hypoxia was inhibited by the overexpression of a kinase-dead (KD) form of AMPKα2. In addition, hypoxia decreased the stability of the HNF4α protein, and the down-regulation of HNF4α was sensitive to proteasome inhibitors. Adenovirus-mediated overexpression of KD-AMPKα2 improved insulin secretion in metformin-treated islets, hypoxic islets, and ob/ob mouse islets. These results suggest that down-regulation of HNF4α could be of importance in ß-cell dysfunction by hypoxia.

Hematological and biochemical status of Beta-thalassemia major patients in Bangladesh: A comparative analysis.

BACKGROUND: Thalassemia is one of the most common hereditary disorders and Beta-thalassemia major is its severe form. The present study is concerned with the analysis of liver function, thyroid function and estimation of critical serum ions as well as hematological characteristics in beta-thalassemia patients and controls. SUBJECTS AND METHODS: The study included 54 patients with beta-thalassemia major and 54 healthy individuals matched by sex and age. The activity of Alanine transaminase (ALT), Alkaline phosphatase (ALP) and Aspartate transaminase (AST) were assessed in order to evaluate the liver function. Serum content of iron (Fe), calcium (Ca), magnesium (Mg), sodium (Na) and potassium (K) were also estimated. Tri iodothyronine (T3), Thyroxin (T4) and Thyroid-stimulating hormone (TSH) levels were assessed in order to evaluate the thyroid function. Hemoglobin (Hb), ferritin, hematocrit (HCT), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration(MCHC), total iron binding capacity (TIBC) and creatinine level were also measured. RESULTS: Significantly, higher ALT (P< 0.001), AST (P< 0.05), ALP (P< 0.001) activities and lower creatinine (P< 0.001) level in beta-thalassemia patients were found in comparison to healthy individuals. Lower serum level of calcium (P< 0.05), magnesium (P< 0.05) and higher level of iron (P> 0.05), sodium (P> 0.05) and potassium (P > 0.05) have been found in patients in comparison to healthy individuals. Hematological parameters like Hb (P< 0.001), ferritin (P< 0.05), HCT (P< 0.001), MCV (P< 0.05) and MCH (P< 0.05) have been significantly reduced in patients except MCHC (P> 0.05). No significant difference was observed in thyroid function between patients and control group. CONCLUSIONS: Our study demonstrates that beta-thalassemia patients and controls have difference in liver function, thyroid function, serum contents of ions and hematological characteristics.

Low serum level of high-sensitivity C-reactive protein in a Japanese patient with maturity-onset diabetes of the young type 3 (MODY3).

High-sensitivity C-reactive protein (hs-CRP) levels in European populations are lower in patients with maturity-onset diabetes of the young type 3 (MODY3) than in those with type 2 diabetes. hs-CRP levels have been suggested to be useful for discriminating MODY3 from type 2 diabetes. As hs-CRP levels are influenced by various factors including race and body mass index, it is worthwhile to examine whether hs-CRP can serve as a biomarker for MODY3 in Japanese. Here we describe the case of a Japanese MODY3 patient with a nonsense mutation in the HNF1A gene. Two measurements showed consistently lower hs-CRP levels (<0.05 and 0.09 mg/L) than in Japanese patients with type 1 and type 2 diabetes. Hepatic expression of Crp messenger ribonucleic acid was significantly decreased in Hnf1a knockout mice. The hs-CRP level might be a useful biomarker for MODY3 in both Japanese and European populations.

SIRT7 controls hepatic lipid metabolism by regulating the ubiquitin-proteasome pathway.

Sirtuins (SIRT1-7) have attracted considerable attention as regulators of metabolism over the past decade. However, the physiological functions and molecular mechanisms of SIRT7 are poorly understood. Here we demonstrate that Sirt7 knockout mice were resistant to high-fat diet-induced fatty liver, obesity, and glucose intolerance, and that hepatic triglyceride accumulation was also attenuated in liver-specific Sirt7 knockout mice. Hepatic SIRT7 positively regulated the protein level of TR4/TAK1, a nuclear receptor involved in lipid metabolism, and as a consequence activated TR4 target genes to increase fatty acid uptake and triglyceride synthesis/storage. Biochemical studies revealed that the DDB1-CUL4-associated factor 1 (DCAF1)/damage-specific DNA binding protein 1 (DDB1)/cullin 4B (CUL4B) E3 ubiquitin ligase complex interacted with TR4, leading to its degradation, while binding of SIRT7 to the DCAF1/DDB1/CUL4B complex inhibited the degradation of TR4. In conclusion, we propose that hepatic SIRT7 controls lipid metabolism in liver by regulating the ubiquitin-proteasome pathway.

Inhibition of H3K18 deacetylation of Sirt7 by Myb-binding protein 1a (Mybbp1a).

Sirt7 localizes in the nucleus (enriched in the nucleolus) and is an NAD(+)-dependent deacetylase with high selectivity for the acetylated lysine 18 of histone H3 (H3K18Ac). It has been reported that Sirt7 is necessary for maintaining the fundamental properties of the cancer cell phenotype and stabilizing the tumorigenicity of human cancer via deacetylation of H3K18Ac. However, the regulators of Sirt7 deacetylase activity are unknown. Myb-binding protein 1a (Mybbp1a) is reported to interact with and regulate the function of a number of transcription factors. In the present study, we demonstrated that Mybbp1a binds to Sirt7 in vitro and in vivo. Serial deletion studies indicated that N- and C-terminal regions of Sirt7 and C-terminal region of Mybbp1a are important for the binding. Furthermore, transfection experiments showed that Mybbp1a is capable of inhibiting the deacetylation activity of H3K18Ac by Sirt7. Our findings demonstrate that Mybbp1a is a novel negative regulator of Sirt7.

Anks4b, a novel target of HNF4α protein, interacts with GRP78 protein and regulates endoplasmic reticulum stress-induced apoptosis in pancreatic ß-cells.

Mutations of the HNF4A gene cause a form of maturity-onset diabetes of the young (MODY1) that is characterized by impairment of pancreatic ß-cell function. HNF4α is a transcription factor belonging to the nuclear receptor superfamily (NR2A1), but its target genes in pancreatic ß-cells are largely unknown. Here, we report that ankyrin repeat and sterile α motif domain containing 4b (Anks4b) is a target of HNF4α in pancreatic ß-cells. Expression of Anks4b was decreased in both ßHNF4α KO islets and HNF4α knockdown MIN6 ß-cells, and HNF4α activated Anks4b promoter activity. Anks4b bound to glucose-regulated protein 78 (GRP78), a major endoplasmic reticulum (ER) chaperone protein, and overexpression of Anks4b enhanced the ER stress response and ER stress-associated apoptosis of MIN6 cells. Conversely, suppression of Anks4b reduced ß-cell susceptibility to ER stress-induced apoptosis. These results indicate that Anks4b is a HNF4α target gene that regulates ER stress in ß-cells by interacting with GRP78, thus suggesting that HNF4α is involved in maintenance of the ER.