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Autophagy in peripheral blood mononuclear cells is associated with body fat percentage
Abstract
Context
Numerous chronic conditions including obesity exhibit autophagic dysfunction. Association of immune cell autophagic marker regulation by body fat percentage (%BF) is unknown.
Objective
Investigate autophagy activity in peripheral blood mononuclear cells (PBMCs) of adults with distinct %BFs and obesity-related circulating inflammatory markers.
Materials and methods
Sixteen individuals (eight males) with %BF above (n = 8, 36.9 ± 3.6 years, 27.1 ± 8.1%BF) and below (n = 8, 37.1 ± 3.7 years, 13.3 ± 3.7%BF) their age- and sex-specific 50th percentile value based on the American College Sports Medicine guidelines participated. Body fat percentage was calculated from hydrostatic weighing. PBMCs were isolated from venous blood, and PBMC autophagic flux markers (LC3-I, LC3-II, and p62) were measured via Western blot. CRP, resistin, leptin, and adiponectin were measured via ELISA.
Results
LC3-II/LC3-I ratio correlated with %BF (r=–0.56, p=.023). Insulin (p=.05) and CRP (p=.018) were higher in high %BF participants.
Discussion and conclusions
Autophagic activity markers in PBMCs correlate with %BF, but are not different between %BF groups.
... A variety of proteins are involved in the regulation of autophagy, of which LC3 and p62/SQSTM1 (hereafter referred to as p62) are typical. Autophagy levels can be assessed by the expression of p62, LC3-II/LC3-I (Amorim et al. 2023;Jamali-Raeufy et al. 2021) and GFP-LC3 proteins (Bai et al. 2021). The LC3 protein exists in two forms: LC3-I and LC3-II. ...
Depressive symptoms are common in Parkinson’s disease (PD). The relationships between autophagy and PD or depression have been documented. However, no studies explored the role of autophagy markers associated with depressive symptoms in PD. Our study aimed to investigate the relationships between autophagy markers, cognitive impairments and depressive symptoms in PD patients. A total of 163 PD patients aged 50–80 years were recruited. Plasma concentrations of autophagy markers (LC3-I, LC3-II and p62/SQSTM1) and glycolipid parameters were measured. Depressive symptoms, cognitive impairments, and motor function were assessed using the Hamilton Depression Rating Scale-17 (HAMD-17), the Montreal Cognitive Assessment (MoCA), and the Movement Disorders Society Unified Parkinson's Rating Scale Part III (MDS-UPDRS-III), respectively. There were no significant differences between depressed and non-depressed PD patients for LC3-I, LC3-II, LC3-II/LC3-I and p62/SQSTM1. After controlling confounding variables, LC3-II/LC3-I showed an independent relationship with depressive symptoms in PD patients (Beta = 10.082, t = 2.483, p = 0.014). Moreover, in depressive PD patients, p62/SQSTM1 was associated with MoCA score (Beta = – 0.002, t = − 2.380, p = 0.020); Further, p62/SQSTM1 was related to naming ability; in addition, p62/SQSTM1 was independently associated with delayed recall (Beta = − 0.001, t = − 2.452, p = 0.017). LC3-II/LC3-I was related to depressive symptoms in PD patients. In depressive PD patients, p62/SQSTM1 was associated with cognitive function, especially naming ability and delayed recall.
... Furthermore, obesity is associated with systemic inflammation and immune cell recruitment to metabolic tissues (6,7). The autophagic activity of PBMCs is known to correlate as well with obesity-related body fat percentage (8). In adipose tissue, increased abundances of proinflammatory immune cells such as M1 macrophages and CD8 1 T cells have been observed, which secrete proinflammatory cytokines such as IL-1b, IL-6, IL-17, and IFN-g (9). ...
Obesity is a dramatically increasing disease, accompanied with comorbidities such as cardiovascular disease and obstructive sleep apnea syndrome (OSAS). Both obesity and OSAS per se are associated with systemic inflammation. However, the multifactorial impact of obesity, OSAS, and its concomitant diseases on the immunological characteristics of circulating monocytes has not yet been fully resolved. Monocyte subsets of 82 patients with obesity were analyzed in whole blood measurements in terms of the CD14/CD16 cell surface expression patterns and different monocytic adhesion molecules using flow cytometry. Plasma levels of adipokines adiponectin and leptin of all patients were evaluated and correlated with accompanying cellular and clinical values. Whole blood measurements revealed a significant overall redistribution of CD14/CD16 monocyte subsets in patients with obesity. Monocytic adhesion molecules CD11a, CD11b, and CX3CR1 were significantly elevated. The observed alterations significantly correlated with plasma leptin levels and diabetes status as crucial amplifying factors. The additive impact of obesity, diabetes, and OSAS on the immunological balance of peripheral blood monocytes requires a coordinated regimen in terms of therapeutic treatment, respiratory support, and weight loss to improve the systemic immunity in these patients.
Autophagy is one of the major degradative mechanisms that can eliminate excessive nutrients, toxic protein aggregates, damaged organelles and invading microorganisms. In response to obesity and obesity-associated lipotoxic, proteotoxic and oxidative stresses, autophagy plays an essential role in maintaining physiological homeostasis. However, obesity and its associated stress insults can often interfere with the autophagic process through various mechanisms, which result in further aggravation of obesity-related metabolic pathologies in multiple metabolic organs. Paradoxically, inhibition of autophagy, within specific contexts, indirectly produces beneficial effects that can alleviate several detrimental consequences of obesity. In this minireview, we will provide a brief discussion about our current understanding of the impact of obesity on autophagy and the role of autophagy dysregulation in modulating obesity-associated pathological outcomes.
The growing concern about the impact of overweight on health has led to studies that shed light on types of obesity other than the classic model based on body mass index. Normal-weight obesity syndrome is characterized by excess body fat in individuals with adequate body mass index (18.5-24.9 kg/m(2)). This condition increases the risk of cardiovascular morbidity and mortality and other conditions associated with chronic diseases, such as insulin resistance, hypertension, and dyslipidemia. The aims of this review are to define the diagnostic criteria for normal-weight obesity syndrome and to examine the risks associated with this condition in order to promote preventive measures and early treatment for affected individuals.
The United States (US) Equal Employment Opportunity Commission has proposed rules allowing employers to penalize employees up to 30% of health insurance costs if they fail to meet 'health' criteria such as reaching a specified Body Mass Index (BMI). Our objective was to examine cardiometabolic health misclassifications given standard BMI categories. Participants (N=40 420) were individuals aged 18+ in the nationally representative 2005-2012 National Health and Nutrition Examination Survey (NHANES). Using blood pressure, triglyceride, cholesterol, glucose, insulin resistance, and C-reactive protein data, population frequencies/percentages of metabolically healthy versus unhealthy individuals were stratified by BMI. Nearly half of overweight individuals, 29% of obese individuals, and even 16% of obesity type II/III individuals were metabolically healthy. Moreover, over 30% of normal weight individuals were cardiometabolically unhealthy. There was no significant race x BMI interaction, but there was a significant gender x BMI interaction, F(4,64)=3.812, P=0.008. Using BMI categories as the main indicator of health, an estimated 74 936 678 US adults are misclassified as cardiometabolically unhealthy or cardiometabolically healthy. Policymakers should consider the unintended consequences of relying solely on BMI, and researchers should seek to improve diagnostic tools related to weight and cardiometabolic health.International Journal of Obesity accepted article preview online, 04 February 2016. doi:10.1038/ijo.2016.17.
In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes.
Body mass index (BMI) is now the most widely used measure of adiposity on a global scale. Nevertheless, intense discussion centers on the appropriateness of BMI as a phenotypic marker of adiposity across populations differing in race and ethnicity. BMI-adiposity relations appear to vary significantly across race/ethnic groups, but a collective critical analysis of these effects establishing their magnitude and underlying body shape/composition basis is lacking. Accordingly, we systematically review the magnitude of these race-ethnic differences across non-Hispanic (NH) white, NH black and Mexican American adults, their anatomic body composition basis and potential biologically linked mechanisms, using both earlier publications and new analyses from the US National Health and Nutrition Examination Survey. Our collective observations provide a new framework for critically evaluating the quantitative relations between BMI and adiposity across groups differing in race and ethnicity; reveal new insights into BMI as a measure of adiposity across the adult age-span; identify knowledge gaps that can form the basis of future research and create a quantitative foundation for developing BMI-related public health recommendations.
In the context of elevated prevalence of obesity-associated metabolic diseases in the human population wordwide, interest in the autophagy degradation pathway is increasing, due to close links with energy metabolism, nutritional state, and inflammation. Here we highlight recent data focusing on adipose tissue which demonstrate alterations in fat cell autophagic flux in human obesity.
The prevalence of obesity is increasing at an alarming rate in many parts of the world. About 2 billion people are overweight and one third of them obese. The plight of the most affected populations, like those in high-income countries in North America, Australasia and Europe, has been well publicized. However, the more recent increases in population obesity in low- and middle-income countries that are now increasingly being observed have been less recognized. Based on the existing prevalence and trend data and the epidemiological evidence linking obesity with a range of physical and psychosocial health conditions, it is reasonable to describe obesity as a public health crisis that severely impairs the health and quality of life of people and adds considerably to national health-care budgets. Intersectoral action to manage and prevent obesity is urgently required to reverse current trends.
Recent evidence that excessive lipid accumulation can decrease cellular levels of autophagy and that autophagy regulates immune responsiveness suggested that impaired macrophage autophagy may promote the increased innate immune activation that underlies obesity. Primary bone marrow-derived macrophages (BMDM) and peritoneal macrophages from high-fat diet (HFD)-fed mice had decreased levels of autophagic flux indicating a generalized impairment of macrophage autophagy in obese mice. To assess the effects of decreased macrophage autophagy on inflammation, mice with a Lyz2-Cre-mediated knockout of Atg5 in macrophages were fed a HFD and treated with low-dose lipopolysaccharide (LPS). Knockout mice developed systemic and hepatic inflammation with HFD feeding and LPS. This effect was liver specific as knockout mice did not have increased adipose tissue inflammation. The mechanism by which the loss of autophagy promoted inflammation was through the regulation of macrophage polarization. BMDM and Kupffer cells from knockout mice exhibited abnormalities in polarization with both increased proinflammatory M1 and decreased anti-inflammatory M2 polarization as determined by measures of genes and proteins. The heightened hepatic inflammatory response in HFD-fed, LPS-treated knockout mice led to liver injury without affecting steatosis. These findings demonstrate that autophagy has a critical regulatory function in macrophage polarization that downregulates inflammation. Defects in macrophage autophagy may underlie inflammatory disease states such as the decrease in macrophage autophagy with obesity that leads to hepatic inflammation and the progression to liver injury.
It is currently routine practice to require a measurement of a housekeeping reference, including actin, glyceraldehyde-3-phosphate dehydrogenase, β-tubulin, among others, in Western blots, as it is the rule in RNA blots. Reversible Ponceau staining has been applied successfully to check equal loading of gels. Here we test a new technique, with the Stain-Free gels from Bio-Rad, against both Ponceau staining and housekeeping protein immunodetection under different conditions. Our results show that Stain-Free gels outperform Ponceau staining and that both are more consistent than housekeeping proteins as a loading control.
Autophagy is a primarily degradative pathway that takes place in all eukaryotic cells. It is used for recycling cytoplasm to generate macromolecular building blocks and energy under stress conditions, to remove superfluous and damaged organelles to adapt to changing nutrient conditions and to maintain cellular homeostasis. In addition, autophagy plays a critical role in cytoprotection by preventing the accumulation of toxic proteins and through its action in various aspects of immunity including the elimination of invasive microbes and its participation in antigen presentation. The most prevalent form of autophagy is macroautophagy, and during this process, the cell forms a double-membrane sequestering compartment termed the phagophore, which matures into an autophagosome. Following delivery to the vacuole or lysosome, the cargo is degraded and the resulting macromolecules are released back into the cytosol for reuse. The past two decades have resulted in a tremendous increase with regard to the molecular studies of autophagy being carried out in yeast and other eukaryotes. Part of the surge in interest in this topic is due to the connection of autophagy with a wide range of human pathophysiologies including cancer, myopathies, diabetes and neurodegenerative disease. However, there are still many aspects of autophagy that remain unclear, including the process of phagophore formation, the regulatory mechanisms that control its induction and the function of most of the autophagy-related proteins. In this review, we focus on macroautophagy, briefly describing the discovery of this process in mammalian cells, discussing the current views concerning the donor membrane that forms the phagophore, and characterizing the autophagy machinery including the available structural information.Cell Research advance online publication 24 December 2013; doi:10.1038/cr.2013.168.
The adipokine resistin is suggested to be an important link between obesity and insulin resistance. In the present study, we assessed the impact of resistin as inflammatogenic cytokine in the setting of arthritis. In vitro experiments on human PBMC were performed to assess cytokine response and transcription pathways of resistin-induced inflammation. Proinflammatory properties of resistin were evaluated in animal model by intra-articular injection of resistin followed by histological evaluation of the joint. Levels of resistin were assessed by ELISA in 74 paired blood and synovial fluid samples of patients with rheumatoid arthritis. Results were compared with the control group comprised blood samples from 34 healthy individuals and 21 synovial fluids from patients with noninflammatory joint diseases. We now show that resistin displays potent proinflammatory properties by 1) strongly up-regulating IL-6 and TNF-alpha, 2) responding to TNF-alpha challenge, 3) enhancing its own activity by a positive feedback, and finally 4) inducing arthritis when injected into healthy mouse joints. Proinflammatory properties of resistin were abrogated by NF-kappaB inhibitor indicating the importance of NF-kappaB signaling pathway for resistin-induced inflammation. Resistin is also shown to specifically accumulate in the inflamed joints of patients with rheumatoid arthritis and its levels correlate with other markers of inflammation. Our results indicate that resistin is a new and important member of the cytokine family with potent regulatory functions. Importantly, the identified properties of resistin make it a novel and interesting therapeutic target in chronic inflammatory diseases such as rheumatoid arthritis.
The adipose tissue-derived hormone leptin acts via its receptor (LRb) in the brain to regulate energy balance and neuroendocrine function. LRb signaling via STAT3 and a number of other pathways is required for the totality of leptin action. The failure of elevated leptin levels to suppress feeding and mediate weight loss in common forms of obesity defines a state of so-called leptin resistance. A number of mechanisms, including the leptin-stimulated phosphorylation of Tyr(985) on LRb and the suppressor of cytokine signaling 3, attenuate leptin signaling and promote a cellular leptin resistance in obesity. Several unique features of the arcuate nucleus of the hypothalamus may contribute to the severity of cellular leptin resistance in this region. Other mechanisms that govern feeding behavior and food reward may also underlie the inception of obesity.
Adipose tissue acts as a dynamic endocrine organ playing critical roles in many metabolic and immune responses. Endocrine functions by adipose tissue are achieved by secretion of diverse cytokines and hormones, collectively called adipokines. Adiponectin and leptin the most abundantly expressed adipokines within adipose tissue have an impact on various physiological responses. While both adiponectin and leptin are secreted from the same location, their physiological functions are not identical. Adiponectin possesses potent anti-inflammatory properties and anti-tumor activities, whereas leptin acts as a pro-inflammatory hormone and generates tumor-promoting effects. Autophagy, a highly conserved intracellular self-digestive process, is implicated in the maintenance of diverse physiological responses. In particular, autophagy plays dual roles in the regulation of cell death/survival (e.g., inducing cell death and cytoprotection) and is associated with anti-inflammatory actions. Increasing recent evidence has indicated that autophagy is implicated in various biological responses by adipokines. Therefore, autophagy would be a promising target for the management of inflammation and tumor growth by adipokines. In this review, we summarize the effects of adiponectin and leptin on autophagy induction and highlight their implications in modulating inflammatory responses and tumor growth.
Previous works have linked high concentrations of palmitate to cellular toxicity by autophagy modulation. However, the ways in which palmitate regulates inflammation and apoptosis in peripheral blood mononuclear cells (PBMCs), has not been well characterized. In the present study, we therefore aimed to investigate the role autophagy in inflammatory responses and apoptotic death of PBMCs treated with palmitate. 0.5mM palmitate increased the level of LC3-II at 6h, peaked at 12h and then decreased at 24h. The protein level of p62 was significantly increased at 6h and 12h, suggesting an impairment of autophagic flux in palmitate-treated PBMCs. Inhibiting autophagy with chloroquine (CQ) and 3-Methyladenine (3-MA) significantly augmented palmitate-induced PBMCs apoptotic death as demonstrated by increased cleaved PARP level and increased the percentage of apoptotic (YO-PRO-1 positive and PI negative) cells. Furthermore, CQ pretreatment exacerbated palmitate-induced TNF-α and IL-6 mRNA expression in PBMCs. Moreover, induction of autophagy by pretreatment of PBMCs with rapamycin resulted in a distinct increase of palmitate-induced apoptosis. The induction of autophagy also led to a further increase in palmitate-induced expression of TNF-α and IL-6. These results indicate that the excess palmitate could impair autophagy, hence contributing to palmitate-induced-inflammation and apoptosis in PBMCs. Therefore, dysregulated autophagy in PBMCs may provide a novel mechanism that connects diet-induced obesity to low grade inflammation in patients with type 2 diabetes.
The merits of physical activity are numerous and well documented. However, the mechanisms underlying these robust adaptations are less clear and much sought after. Recently, an evolutionary conserved cellular recycling mechanism known as autophagy has been implicated in the adaptations to acute and chronic exercise. Autophagy is ever-ongoing in cells and tissues, ensuring cellular clearance and energy homeostasis. This pathway is further induced, as a survival mechanism, by cellular perturbations such as energetic imbalance and oxidative stress. During exercise, a biphasic autophagy response is mobilized, leading to both an acute induction and a long-term potentiation of the process. Post-translational modifications arising from upstream signaling cascades induce an acute autophagic response during a single bout of exercise by mobilizing core autophagy machinery. A longer-term transcriptional program involving FoxO, TFEB, p53 and PGC-1α transcriptional regulators is also induced to fuel sustained increases in autophagic capacity. Autophagy has also been documented to mediate chronic exercise-induced metabolic benefits, and animal models in which autophagy is perturbed do not adapt to exercise to the same extent. In this review we discuss recent developments in the field of autophagy and exercise. We specifically highlight the molecular mechanisms activated during acute exercise which lead to a prolonged adaptive response.
Background:
Body composition changes with aging lead to increased adiposity and decreased muscle mass, making the diagnosis of obesity challenging. Conventional anthropometry, including body mass index (BMI), while easy to use clinically may misrepresent adiposity. We determined the diagnostic accuracy of BMI using dual energy x-ray absorptiometry (DEXA) in assessing the degree of obesity in older adults.
Methods:
The National Health and Nutrition Examination Surveys 1999-2004 were used to identify adults aged ⩾60years with DEXA measures. They were categorized (yes/no) as having elevated body fat by gender (men⩾25%; females ⩾35%) and by body mass index (BMI) ⩾25 and ⩾30 kg/m(2). The diagnostic performance of BMI was assessed. Metabolic characteristics were compared in discordant cases of BMI/body fat. Weighting and analyses were performed per NHANES guidelines.
Results:
We identified 4984 subjects (men:2453; female:2531). Mean BMI and % body fat was 28.0 kg/m(2) and 30.8% in men, and 28.5 kg/m(2) and 42.1% in females. A BMI ⩾30 kg/m(2) had a low sensitivity and moderately high specificity (men:32.9 and 80.8%, concordance index 0.66; females:38.5 and 78.5%, concordance 0.69) correctly classifying 41.0 and 45.1% of obese subjects. A BMI ⩾25 kg/m(2) had a moderately high sensitivity and specificity (men:80.7 and 99.6%, concordance 0.81;females:76.9 and 98.8%, concordance 0.84) correctly classifying 80.8 and 78.5% of obese subjects. In subjects with BMI<30 kg/m(2) body fat was considered elevated in 67.1 and 61.5% of males and females, respectively.For a BMI⩾30 kg/m(2), sensitivity drops from 40.3 to 14.5% and 44.5 to 23.4%, while specificity remains elevated (>98%),in males and females, respectively in those 60-69.9years to subjects aged ⩾80years. Correct classification of obesity using a cutoff of 30 kg/m(2) drops from 48.1 to 23.9% and 49.0 to 19.6%, in males and females in these two age groups.
Conclusions:
Traditional measures poorly identify obesity in the elderly. In older adults, BMI may be a suboptimal marker for adiposity.International Journal of Obesity accepted article preview online, 01 December 2015. doi:10.1038/ijo.2015.243.
Pathophysiology of obesity is closely associated with enhanced autophagy in adipose tissue (AT). Autophagic process can promote survival or activate cell death. Therefore, we examine the occurrence of autophagy in AT of type 2 diabetes (T2D) patients in comparison to obese and lean individuals without diabetes.
Numerous autophagosomes accumulated within adipocytes were visualized by electron transmission microscopy and by immunofluorescence staining for autophagy marker LC3 in obese and T2D patients. Increased autophagy was demonstrated by higher LC3-II/LC3-I ratio, up-regulated expression of LC3 and Atg5 mRNA, along with decreased p62 and mTOR protein levels. Increased autophagy occurred together with AT inflammation.
Our data suggest fat depot-related differences in autophagy regulation. In subcutaneous AT, increased autophagy is accompanied by increased markers of apoptosis in patients with obesity independently of T2D. In contrast, in visceral AT only in T2D patients increased autophagy was related to higher markers of apoptosis.
Copyright © 2015. Published by Elsevier Ireland Ltd.
To evaluate the expression level of NR2E1 (nuclear receptor subfamily 2,group E,member 1) and its correlation with type 2 diabetes (T2DM).
Plasma and peripheral blood mononuclear cells (PBMCs) were collected from 54 T2DM and 88 healthy individuals. The levels of free fatty acids (FFAs), total cholesterol (TC), triglyceride (TG), high density lipoprotein (HDL-c), low density lipoprotein (LDL-c), fasting insulin (FIN), and fasting blood glucose (FBG) were measured. The insulin resistance index was calculated using the homeostasis model assessment (HOMA). NR2E1 in PBMCs were analyzed using real-time RT-PCR and Western blots. Tumor necrosis factor α (TNF-α) and interleukin-6 (IL-6) in the plasma were measured by enzyme-linked immunosorbent assay (ELISA). PBMCs isolated from healthy volunteers were treated with glucose or palmitate for 24h, followed by analysis for the expression level of NR2E1.The amount of TNF-α and IL-6 secreted into the supernatant were measured by ELISA.
FIN, FBG, HOMA and TNF-α, IL-6 were significantly higher in diabetic patients, compared to the control group. Levels of NR2E1 were significantly higher in the PBMCs isolated from the diabetic group, compared to the control group. NR2E1 expression was positively correlated with FBG, FIN, HOMA, FFAs, TNF-α and IL-6. Glucose and palmitate treatment significantly increased NR2E1 gene expression and inflammatory cytokines production in PBMCs in vitro.
Increased NR2E1 level may be closely associated with inflammation and disorder of lipid and glucose metabolism in diabetic patients.
Copyright © 2014. Published by Elsevier Inc.
Autophagy, an evolutionary conserved process aimed at recycling damaged organelles and protein aggregates in the cell, also modulates proinflammatory cytokine production in peripheral blood mononuclear cells. Because adipose tissue inflammation accompanied by elevated levels of proinflammatory cytokines is characteristic for the development of obesity, we hypothesized that modulation of autophagy alters adipose tissue inflammatory gene expression and secretion. We tested our hypothesis using ex vivo and in vivo studies of human and mouse adipose tissue. Levels of the autophagy marker LC3 were elevated in sc adipose tissue of obese vs. lean human subjects and positively correlated to both systemic insulin resistance and morphological characteristics of adipose tissue inflammation. Similarly, autophagic activity levels were increased in adipose tissue of obese and insulin resistant animals as compared with lean mice. Inhibition of autophagy by 3-methylalanine in human and mouse adipose tissue explants led to a significant increase in IL-1β, IL-6, and IL-8 mRNA expression and protein secretion. Noticeably, the enhancement in IL-1β, IL-6, and keratinocyte-derived chemoattractant (KC) by inhibition of autophagy was more robust in the presence of obesity. Similar results were obtained by blocking autophagy using small interfering RNA targeted to ATG7 in human Simpson-Golabi-Behmel syndrome adipocytes. Our results demonstrate that autophagy activity is up-regulated in the adipose tissue of obese individuals and inhibition of autophagy enhances proinflammatory gene expression both in adipocytes and adipose tissue explants. Autophagy may function to dampen inflammatory gene expression and thereby limit excessive inflammation in adipose tissue during obesity.
Autophagy, a vital catabolic process that degrades cytoplasmic components within the lysosome, is an essential cytoprotective response to pathologic stresses that occur during diseases such as cancer, ischemia, and infection. In addition to its role as a stress-response pathway, autophagy plays an essential quality-control function in the cell by promoting basal turnover of long-lived proteins and organelles, as well as by selectively degrading damaged cellular components. This homeostatic function protects against a wide variety of diseases, including neurodegeneration, myopathy, liver disease, and diabetes. This review discusses our current understanding of these two principal functions of autophagy and describes in detail how alterations in autophagy promote human disease. Expected final online publication date for the Annual Review of Pathology: Mechanisms of Disease Volume 8 is January 24, 2013. Please see http://www.annualreviews.org/catalog/pubdates.aspx for revised estimates.
The prevalence of obesity, metabolic syndrome, and diabetes worldwide is a significant health problem due to serious medical complications that include cardiovascular disease and renal failure. In these diseases, elevated serum triglycerides (TAG) and free fatty acids (FFAs) cause lipid accumulation in nonadipose tissues, including the pancreas, heart, liver, kidney, and blood vessel wall. While FFAs and their metabolites play a key role in membrane structure, intracellular signaling and energy homeostasis, accumulation of excess lipid in these organs causes cell dysfunction and cell death. This process, termed lipotoxicity, has been implicated in β cell loss during the progression of type 2 diabetes—and in the pathogenesis of diabetic complications through loss of cardiomyocytes, hepatocytes, renal parenchymal cells, and endothelial cells.
The steady-state basal plasma glucose and insulin concentrations are determined by their interaction in a feedback loop. A computer-solved model has been used to predict the homeostatic concentrations which arise from varying degrees beta-cell deficiency and insulin resistance. Comparison of a patient's fasting values with the model's predictions allows a quantitative assessment of the contributions of insulin resistance and deficient beta-cell function to the fasting hyperglycaemia (homeostasis model assessment, HOMA). The accuracy and precision of the estimate have been determined by comparison with independent measures of insulin resistance and beta-cell function using hyperglycaemic and euglycaemic clamps and an intravenous glucose tolerance test. The estimate of insulin resistance obtained by homeostasis model assessment correlated with estimates obtained by use of the euglycaemic clamp (Rs = 0.88, p less than 0.0001), the fasting insulin concentration (Rs = 0.81, p less than 0.0001), and the hyperglycaemic clamp, (Rs = 0.69, p less than 0.01). There was no correlation with any aspect of insulin-receptor binding. The estimate of deficient beta-cell function obtained by homeostasis model assessment correlated with that derived using the hyperglycaemic clamp (Rs = 0.61, p less than 0.01) and with the estimate from the intravenous glucose tolerance test (Rs = 0.64, p less than 0.05). The low precision of the estimates from the model (coefficients of variation: 31% for insulin resistance and 32% for beta-cell deficit) limits its use, but the correlation of the model's estimates with patient data accords with the hypothesis that basal glucose and insulin interactions are largely determined by a simple feed back loop.
Autophagy is a highly conserved process in eukaryotes in which the cytoplasm, including excess or aberrant organelles, is sequestered into double-membrane vesicles and delivered to the degradative organelle, the lysosome/vacuole, for breakdown and eventual recycling of the resulting macromolecules. This process has an important role in various biological events such as adaptation to changing environmental conditions, cellular remodeling during development and differentiation, and determination of lifespan. Auto-phagy is also involved in preventing certain types of disease, although it may contribute to some pathologies. Recent studies have identified many components that are required to drive this complicated cellular process. Auto-phagy-related genes were first identified in yeast, but homologs are found in all eukaryotes. Analyses in a range of model systems have provided huge advances toward understanding the molecular basis of autophagy. Here we review our current knowledge on the machinery and molecular mechanism of autophagy.
Microtubule-associated protein light chain 3 (LC3) is now widely used to monitor autophagy. One approach is to detect LC3 conversion (LC3-I to LC3-II) by immunoblot analysis because the amount of LC3-II is clearly correlated with the number of autophagosomes. However, LC3-II itself is degraded by autophagy, making interpretation of the results of LC3 immunoblotting problematic. Furthermore, the amount of LC3 at a certain time point does not indicate autophagic flux, and therefore, it is important to measure the amount of LC3-II delivered to lysosomes by comparing LC3-II levels in the presence and absence of lysosomal protease inhibitors. Another problem with this method is that LC3-II tends to be much more sensitive to be detected by immunoblotting than LC3-I. Accordingly, simple comparison of LC3-I and LC3-II, or summation of LC3-I and LC3-II for ratio determinations, may not be appropriate, and rather, the amount of LC3-II can be compared between samples.
Autophagy as a stress-response and quality-control mechanism: implications for cell injury and human disease. Annual review of pathology
- L Murrow
- J Debnath
Murrow, L. and Debnath, J., 2013. Autophagy as a stress-response and
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- H Unzberg
Myers, M.G., Cowley, M.A., and M€ unzberg, H., 2008. Mechanisms of leptin
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