Irisin injected mice display increased tibial cortical mineral density and polar moment of inertia

It has been recently reported that, after physical activity, the skeletal muscle releases Irisin, the newly identified myokine able of driving transition of white adipocytes into brown [1]. This result supported the role of skeletal muscle as endocrine organ, suggesting that it could target other tissues besides adipose tissue. In our previous work, we demonstrated that conditioned media collected from primary myoblasts of exercised mice were able to increase OB differentiation and this effect was Irisinmediated [2]. Here we show that Irisin has positive effect on cortical mineral density and geometry in vivo. Young male mice were injected with r-Irisin and cortical bone adaptation was analyzed by micro-CT at tibial midshaft. Our results show that cortical tissue mineral density is significantly increased in Irisin-injected mice compared to vehicle-injected littermates (+7.15%; p<0.01). Furthermore, this higher density of calcium hydroxyapatite at cortical site is accompanied by increase in periosteal circumference (+7.5%; p<0.03) and polar moment of Inertia (pMOI +19,21%; p<0,01). A greater pMOI indicates stronger resistance of a long bone to torsion and, together with higher bone mineral density, suggests higher protection against fracture. The effect of Irisin is fully comparable to the effect of physical activity that is widely accepted method for increasing bone mineral density and bone size in healthy populations. In view of further proving the involvement of Irisin in bone metabolism, we validate its direct effect on osteoblasts in vitro. Phosphorylation of the MAP kinase ERK and the expression of Atf4 were significantly increased after Irisin treatment, as well as ALP and pro-Collagen I mRNA expression. Our data highlight a novel link in muscle-fat-bone axis demonstrating that Irisin targets bone tissue directly, driving positive effects on cortical mineral density and geometry in vivo. These findings would expand the research of exercise-mimetic drugs that might be widely used to treat osteoporotic patients who are suffering from immobilization and cannot perform physical activity

Studio comparativo sullo sviluppo dell'Organo Adiposo nell'uomo e nel topo. Potenziali correlazioni morfo-funzionali

I tessuti principali che costituiscono l’organo adiposo sono due: il tessuto adiposo bianco (WAT) e il tessuto adiposo bruno (BAT). Essi sono costituiti da cellule assai differenti per caratteristiche morfologiche, biochimiche e funzionali; tuttavia sono entrambi presenti nello stesso organo all’interno del quale cooperano funzionalmente per il mantenimento dell’omeostasi energetica. Si trovano inoltre zone miste nelle quali si è identificato un terzo tipo cellulare chiamato pauciloculare o brite/beige. Gli adipociti in questione presentano caratteristiche morfologiche e funzionali intermedie tra i tipici adipociti bianchi e quelli bruni, risultando scarsamente positivi per l’UCP1 e con una morfologia multiloculare ma con una goccia lipidica prevalente nel citoplasma. Il presente studio ha lo scopo di caratterizzare i modelli di sviluppo del BAT e del WAT in specifiche sedi anatomiche, confrontando i depositi di grasso umano fetali con gli stessi dei soggetti umani adulti. A tal fine sono stati analizzati diversi depositi in sedi anatomiche dei compartimenti sottocutanei e viscerali prelevati in 12 soggetti umani durante lo sviluppo fetale (da 16 fino a 39 settimane) utilizzando tecniche di immunoistologia e la TEM. I primi accumuli lipidici si riscontrano nelle isole vascolo-adipocitiche localizzate nella parte superiore del tronco a livello sottocutaneo. In particolare abbiamo studiato il deposito cervicale che mostra una struttura a strati dove la stragrande maggioranza degli adipociti presenti nei livelli superficiali così come in quelli profondi, è caratterizzata da un chiaro aspetto multiloculare e UCP1-positivo. Anche il deposito interscapolare di BAT è visualizzabile in fasi precosi di sviluppo e comunque prima degli accumuli di grasso viscerale presi in esame come il peri-renale ed il para-aortico (mediastinico). In tutti i depositi analizzati, le fibre adrenergiche appaiono nelle isole adipocitiche solo nella fase finale dello sviluppo e solo dopo l’espressione della proteina UCP1. Nei depositi presi in considerazione, in corrispondenza di diversi momenti dello sviluppo, è stato testato lo Zic1, un marker del fenotipo bruno. I risultati suggeriscono che la conversione fenotipica e/o altri meccanismi possono guidare il "whitening” di alcuni depositi, che porta alla scomparsa del BAT negli esseri umani adulti. Scoprire i meccanismi coinvolti nel reclutamento degli adipociti bruni / Brite e il loro mantenimento negli esseri umani adulti avrebbe il potenziale per ispirare strategie terapeutiche che aumentano la spesa energetica nonché per frenare l'obesità e le malattie metaboliche.The main tissues forming the parenchyma of the Adipose Organ are White Adipose Tissue (WAT) and Brown Adipose Tissue (BAT). Both white and brown adipocytes are found together at discrete anatomical locations and they cooperate functionally to maintain energy homeostasis. The multilocular UCP1-positive adipocytes that are interspersed among white adipocytes, are also known as brite or beige adipocytes. This study aims to characterize developmental patterns of BAT and WAT in specific anatomical locations by comparing fetal and adult human fat depots. Several anatomical locations of the subcutaneous and visceral compartments were evaluated in 12 human subjects during fetal development (from 16 up to 39 weeks) using immunohistology and TEM. Lipid accumulation was first detected in the vasculo-adipocytic anlages in the upper portion of the subcutaneous area. In particular, the cervical depot had a layered structure where the vast majority of adipocytes in deep as well as superficial layers, had a clear multilocular UCP1-positive aspects. Interscapular BAT was also detected quite early in development before the accumulation of the visceral fat depots such as the peri-renal and the mediastinal (para-aortic) fat. IN all the depots analyzed, adrenergic fibers appeared in the fat anlages only in the final stage of development and after UCP1 protein expression. Zic1, used as brown adipocyte marker, have been tested in different depots and at different time points of development. Findings suggest that phenotypic conversion and/or other mechanisms may drive the “whitening” of some depots, leading to BAT disappearance in adult humans. Uncovering the mechanisms involved in brown/brite adipocyte recruitment and maintenance in adult humans, would have the potential to inspire therapeutic strategies that increase energy expenditure and to curb obesity and metabolic diseases.

Developmental aspects of the adipose tissue. From fetal to adult humans

Brown and white adipocytes are found together at discrete anatomical locations; the multilocular UCP1-positive adipocytes that are interspersed among white adi- pocytes are also known as brite or beige adipocytes (1). Brown adipose tissue (BAT) undergoes a significant reduction in the course of human life. This study aims to characterize developmental patterns of BAT and white AT in specific anatomical locations by comparing fetal and adult human fat depots. Several depots of the subcutaneous and visceral compartments were evaluated in 12 subjects during fetal development (from 16 up to 39 weeks) using immunohistology, morphometry and TEM. Comparison with the corresponding fat depot found in adults was then performed. Fat tissue was first detected in the vasculo-adipocytic anlages in the upper portion of the subcutaneous area. In particular, the cervical depot had a layered structure where the vast majority of adipocytes in deep as well as superficial layers had a clear multilocular UCP1-positive aspects. Adrenergic fibers appear in the fat anlages only in the final stage of development and after UCP1 protein expression. Zic1 (brown) and Hoxc8 (white/brite) adipocytes markers have been tested in different depots and at different time points of development (2). Findings suggest that phenotypic conver- sion and/or other mechanisms may drive the “whitening” of some depots, leading to BAT disappearance in adult humans. Uncovering the mechanisms involved in brown/brite adipocyte recruitment and maintenance in adult humans would have the potential to inspire therapeutic strategies that increase energy expenditure and to curb obesity and metabolic diseases

Adipose-Specific Deficiency of Fumarate Hydratase in Mice Protects Against Obesity, Hepatic Steatosis and Insulin Resistance

Obesity and type 2 diabetes are associated with impaired mitochondrial function in adipose tissue. To study the effects of primary deficiency of mitochondrial energy metabolism in fat, we generated mice with adipose-specific deficiency of fumarate hydratase (FH), an integral Krebs cycle enzyme (AFHKO mice). AFHKO mice have severe ultrastructural abnormalities of mitochondria, ATP depletion in white and brown adipose tissues (WAT, BAT), low WAT mass with small adipocytes and impaired thermogenesis with large unilocular brown adipocytes. AFHKO mice are strongly protected against obesity, insulin resistance and fatty liver despite aging and high fat feeding. AFHKO white adipocytes showed normal lipolysis but low triglyceride synthesis. ATP depletion in normal white adipocytes by mitochondrial toxins also decreased triglyceride synthesis, proportionally to ATP depletion, suggesting that reduced triglyceride synthesis may result nonspecifically from adipocyte energy deficiency. At thermoneutrality, protection from insulin resistance and hepatic steatosis was diminished. Taken together, our results show that, under the cold stress of regular animal room conditions, adipocyte-specific FH deficiency in mice causes mitochondrial energy depletion in adipose tissues and protects from obesity, hepatic steatosis and insulin resistance, suggesting that in cold-stressed animals, mitochondrial function in adipose tissue is a determinant of fat mass and insulin sensitivity

Fat-specific Dicer deficiency accelerates aging and mitigates several effects of dietary restriction in mice

Aging increases the risk of type 2 diabetes, and this can be prevented by dietary restriction (DR). We have previously shown that DR inhibits the downregulation of miRNAs and their processing enzymes - mainly Dicer - that occurs with aging in mouse white adipose tissue (WAT). Here we used fat-specific Dicer knockout mice (AdicerKO) to understand the contributions of adipose tissue Dicer to the metabolic effects of aging and DR. Metabolomic data uncovered a clear distinction between the serum metabolite profiles of Lox control and AdicerKO mice, with a notable elevation of branched-chain amino acids (BCAA) in AdicerKO. These profiles were associated with reduced oxidative metabolism and increased lactate in WAT of AdicerKO mice and were accompanied by structural and functional changes in mitochondria, particularly under DR. AdicerKO mice displayed increased mTORC1 activation in WAT and skeletal muscle, where Dicer expression is not affected. This was accompanied by accelerated age-associated insulin resistance and premature mortality. Moreover, DR-induced insulin sensitivity was abrogated in AdicerKO mice. This was reverted by rapamycin injection, demonstrating that insulin resistance in AdicerKO mice is caused by mTORC1 hyperactivation. Our study evidences a DR-modulated role for WAT Dicer in controlling metabolism and insulin resistance

Lack of NLRP3-inflammasome leads to gut-liver axis derangement, gut dysbiosis and a worsened phenotype in a mouse model of NAFLD.

Abstract Non-Alcoholic Fatty Liver Disease (NAFLD) represents the most common form of chronic liver injury and can progress to cirrhosis and hepatocellular carcinoma. A “multi-hit” theory, involving high fat diet and signals from the gut-liver axis, has been hypothesized. The role of the NLRP3-inflammasome, which senses dangerous signals, is controversial. Nlrp3−/− and wild-type mice were fed a Western-lifestyle diet with fructose in drinking water (HFHC) or a chow diet. Nlrp3−/−-HFHC showed higher hepatic expression of PPAR γ2 (that regulates lipid uptake and storage) and triglyceride content, histological score of liver injury and greater adipose tissue inflammation. In Nlrp3−/−-HFHC, dysregulation of gut immune response with impaired antimicrobial peptides expression, increased intestinal permeability and the occurrence of a dysbiotic microbiota led to bacterial translocation, associated with higher hepatic expression of TLR4 (an LPS receptor) and TLR9 (a receptor for double-stranded bacterial DNA). After antibiotic treatment, gram-negative species and bacterial translocation were reduced, and adverse effects restored both in liver and adipose tissue. In conclusion, the combination of a Western-lifestyle diet with innate immune dysfunction leads to NAFLD progression, mediated at least in part by dysbiosis and bacterial translocation, thus identifying new specific targets for NAFLD therapy

Overexpression of cyclooxygenase-2 in adipocytes reduces fat accumulation in inguinal white adipose tissue and hepatic steatosis in high-fat fed mice

Cyclooxygenases are known as important regulators of metabolism and immune processes via conversion of C20 fatty acids into various regulatory lipid mediators, and cyclooxygenase activity has been implicated in browning of white adipose tissues. We generated transgenic (TG) C57BL/6 mice expressing the Ptgs2 gene encoding cyclooxygenase-2 (COX-2) in mature adipocytes. TG mice fed a high-fat diet displayed marginally lower weight gain with less hepatic steatosis and a slight improvement in insulin sensitivity, but no difference in glucose tolerance. Compared to littermate wildtype mice, TG mice selectively reduced inguinal white adipose tissue (iWAT) mass and fat cell size, whereas the epididymal (eWAT) fat depot remained unchanged. The changes in iWAT were accompanied by increased levels of specific COX-derived lipid mediators and increased mRNA levels of interleukin-33, interleukin-4 and arginase-1, but not increased expression of uncoupling protein 1 or increased energy expenditure. Epididymal WAT (eWAT) in TG mice exhibited few changes except from increased infiltration with eosinophils. Our findings suggest a role for COX-2-derived lipid mediators from adipocytes in mediating type 2 immunity cues in subcutaneous WAT associated with decreased hepatic steatosis, but with no accompanying induction of browning and increased energy expenditure.ISSN:2045-232

Overexpression of cyclooxygenase-2 in adipocytes reduces fat accumulation in inguinal white adipose tissue and hepatic steatosis in high-fat fed mice

Cyclooxygenases are known as important regulators of metabolism and immune processes via conversion of C20 fatty acids into various regulatory lipid mediators, and cyclooxygenase activity has been implicated in browning of white adipose tissues. We generated transgenic (TG) C57BL/6 mice expressing the Ptgs2 gene encoding cyclooxygenase-2 (COX-2) in mature adipocytes. TG mice fed a high-fat diet displayed marginally lower weight gain with less hepatic steatosis and a slight improvement in insulin sensitivity, but no difference in glucose tolerance. Compared to littermate wildtype mice, TG mice selectively reduced inguinal white adipose tissue (iWAT) mass and fat cell size, whereas the epididymal (eWAT) fat depot remained unchanged. The changes in iWAT were accompanied by increased levels of specific COX-derived lipid mediators and increased mRNA levels of interleukin-33, interleukin-4 and arginase-1, but not increased expression of uncoupling protein 1 or increased energy expenditure. Epididymal WAT (eWAT) in TG mice exhibited few changes except from increased infiltration with eosinophils. Our findings suggest a role for COX-2-derived lipid mediators from adipocytes in mediating type 2 immunity cues in subcutaneous WAT associated with decreased hepatic steatosis, but with no accompanying induction of browning and increased energy expenditure