Targeted deletion of autophagy-related 5 (atg5) impairs adipogenesis in a cellular model and in mice

Morin inhibits the activity of pancreatic lipase and adipogenesis

Obesity is a major health issue that contributes significantly to increased mortality and morbidity worldwide. Obesity is caused by uncontrolled adipogenesis and lipogenesis, leading to several metabolism-associated problems. Pancreatic lipase, an enzyme that breaks down dietary lipids, is a prominent target for obesity. Orlistat, a known inhibitor of pancreatic lipase, is commonly employed for the management of obesity. However, its side effects, such as diarrhoea, nausea and bladder pain, urge to look out for safer alternatives. Morin is a pentahydroxyflavone, exerts a broad spectrum of pharmacological effects including antioxidant, anti-inflammatory, lipid lowering, anti-diabetic, anti-fibrotic, anti-cancer, etc. This study investigated the effect of morin on pancreatic lipase activity, in vitro and in vivo adipogenesis. Molecular docking and simulation studies showed morin to have a higher binding affinity towards pancreatic lipase compared with orlistat, which also inhibited its activity in vitro. Morin also reduced lipid droplet accretion and downregulated the expression of adipogenic and lipogenic genes. The acute oral toxicity of morin was determined in C57BL/6 mice, where morin did not show toxicity up to 2000 mg/kg body weight dose. Oral administration of morin to high fat diet fed mice reduced body weight, glucose and insulin levels. Also, the histopathological examination revealed reduction in adipocyte size and decreased mRNA expression of adipogenesis markers in white adipose tissue of morin administered group compared to high fat diet group. Overall, the results suggested morin inhibited pancreatic lipase activity, adipogenesis and further studies are warranted to explore its therapeutic potential for obesity.

Role of diacylglycerol O-acyltransferase 1 (DGAT1) in lipolysis and autophagy of adipose tissue from ketotic dairy cows

High-yielding dairy cows in early lactation often encounter difficulties in meeting the energy requirements essential for maintaining milk production. This is primarily attributed to insufficient dry matter intake, which consequently leads to sustained lipolysis of adipose tissue. Fatty acids released by lipolysis can disrupt metabolic homeostasis. Autophagy, an adaptive response to intracellular environmental changes, is considered a crucial mechanism for regulating lipid metabolism and maintaining a proper cellular energy status. Despite its close relationship with aberrant lipid metabolism and cytolipotoxicity in animal models of metabolic disorders, the precise function of diacylglycerol o-acyltransferase 1 (DGAT1) in bovine adipose tissue during periods of negative energy balance is not fully understood, particularly regarding its involvement in lipolysis and autophagy. The objective of the present study was to assess the effect of DGAT1 on both lipolysis and autophagy in bovine adipose tissue and isolated adipocytes. Adipose tissue and blood samples were collected from cows diagnosed as clinically ketotic (n = 15) or healthy (n = 15) following a veterinary evaluation based on clinical symptoms and serum concentrations of BHB, which were 3.19 mM (interquartile range = 0.20) and 0.50 mM (interquartile range = 0.06), respectively. Protein abundance of DGAT1 and phosphorylation levels of unc-51-like kinase 1 (ULK1), were greater in adipose tissue from cows with ketosis, whereas phosphorylation levels of phosphoinositide 3-kinase (PI3K), protein kinase B (AKT), and mammalian target of rapamycin (mTOR) were lower. Furthermore, when adipocytes isolated from the harvested adipose tissue of 15 healthy cows were transfected with DGAT1 overexpression adenovirus or DGAT1 small interfering RNA followed by exposure to epinephrine (EPI), it led to greater ratios and protein abundance of phosphorylated hormone-sensitive triglyceride lipase (LIPE) to total LIPE and adipose triglyceride lipase (ATGL), while inhibiting the protein phosphorylation levels of ULK1, PI3K, AKT, and mTOR. Overexpression of DGAT1 in EPI-treated adipocytes reduced lipolysis and autophagy, whereas silencing DGAT1 further exacerbated EPI-induced lipolysis and autophagy. Taken together, these findings indicate that upregulation of DGAT1 may function as an adaptive response to suppress adipocytes lipolysis, highlighting the significance of maintaining metabolic homeostasis in dairy cows during periods of negative energy balance.

Novel perspectives on autophagy-oxidative stress-inflammation axis in the orchestration of adipogenesis

Adipose tissue, an indispensable organ, fulfils the pivotal role of energy storage and metabolism and is instrumental in maintaining the dynamic equilibrium of energy and health of the organism. Adipocyte hypertrophy and adipocyte hyperplasia (adipogenesis) are the two primary mechanisms of fat deposition. Mature adipocytes are obtained by differentiating mesenchymal stem cells into preadipocytes and redifferentiation. However, the mechanisms orchestrating adipogenesis remain unclear. Autophagy, an alternative cell death pathway that sustains intracellular energy homeostasis through the degradation of cellular components, is implicated in regulating adipogenesis. Furthermore, adipose tissue functions as an endocrine organ, producing various cytokines, and certain inflammatory factors, in turn, modulate autophagy and adipogenesis. Additionally, autophagy influences intracellular redox homeostasis by regulating reactive oxygen species, which play pivotal roles in adipogenesis. There is a growing interest in exploring the involvement of autophagy, inflammation, and oxidative stress in adipogenesis. The present manuscript reviews the impact of autophagy, oxidative stress, and inflammation on the regulation of adipogenesis and, for the first time, discusses their interactions during adipogenesis. An integrated analysis of the role of autophagy, inflammation and oxidative stress will contribute to elucidating the mechanisms of adipogenesis and expediting the exploration of molecular targets for treating obesity-related metabolic disorders.

Atg7 autophagy-independent role on governing neural stem cell fate could be potentially applied for regenerative medicine

A literature review showed that Atg7 biological role was associated with the development and pathogenesis of nervous system, but very few reports focused on Atg7 role on neurogenesis at the region of spinal cord, so that we are committed to explore the subject. Atg7 expression in neural tube is incrementally increased during neurogenesis. Atg7 neural-specific knockout mice demonstrated the impaired motor function and imbalance of neuronal and glial cell differentiation during neurogenesis, which was similarly confirmed in primary neurosphere culture and reversely verified by Atg7 overexpression in unilateral neural tubes of gastrula chicken embryos. Furthermore, activating autophagy in neural stem cells (NSCs) of neurospheres did not rescue Atg7 deficiency-suppressed neuronal differentiation, but Atg7 overexpression on the basis of autophagy inhibition could reverse Atg7 deficiency-suppressed neuronal differentiation, which provides evidence for the existence of Atg7 role of autophagy-independent function. The underlying mechanism is that Atg7 deficiency directly caused the alteration of cell cycle length of NSCs, which is controlled by Atg7 through specifically binding Mdm2, thereby affecting neuronal differentiation during neurogenesis. Eventually, the effect of overexpressing Atg7-promoting neuronal differentiation was proved in spinal cord injury model as well. Taken together, this study revealed that Atg7 was involved in regulating neurogenesis by a non-autophagic signaling process, and this finding also shed light on the potential application in regenerative medicine.

The autophagic regulation of rosiglitazone-promoted adipocyte browning

Objective: Browning of white adipocytes is considered an efficient approach to combat obesity. Rosiglitazone induces the thermogenetic program of white adipocytes, but the underlying mechanisms remain elusive. Methods: Expression levels of browning and autophagy flux markers were detected by real-time PCR and immunoblotting. H&E and Oil Red O staining were performed to evaluate the lipid droplets area. Nuclear protein extraction and immunoprecipitation were used to detect the proteins interaction. Results: In this study, we reported that rosiglitazone promoted adipocyte browning and inhibited autophagy. Rapamycin, an autophagy inducer, reversed adipocyte browning induced by rosiglitazone. Autophagy inhibition by rosiglitazone does not prevent mitochondrial clearance, which was considered to promote adipose whitening. Instead, autophagy inhibition increased p62 nuclear translocation and stabilized the PPARγ-RXRα heterodimer, which is an essential transcription factor for adipocyte browning. We found that rosiglitazone activated NRF2 in mature adipocytes. Inhibition of NRF2 by ML385 reversed autophagy inhibition and the pro-browning effect of rosiglitazone. Conclusion: Our study linked autophagy inhibition with rosiglitazone-promoted browning of adipocytes and provided a mechanistic insight into the pharmacological effects of rosiglitazone.

Autophagic Regulation of Adipogenesis Through TP53INP2: Insights from In Silico and In Vitro Analysis

Obesity is an epidemic disease associated with multimorbidity resulting in higher mortality risk. The imbalance between energy storage and expenditure is the prime factor in the prognosis of the disease. Specifically, excessive lipid storage through adipogenesis leads to obesity. Adipogenesis is the process that converts preadipocytes into mature adipocytes by regulating major transcription factors like PPARγ and C/EBPα, contributes to lipid storage in adipose tissue. On the contrary, autophagy is a self-degradative process that maintains homeostasis in adipose tissue by regulating adipogenesis and lipolysis. TP53INP2 is a key player that regulates the autophagy process, and it negatively regulates adipogenesis and lipid storage. The gene expression profile GSE93637 was retrieved from the GEO database and analyzed using an integrated bioinformatics approach. The differentially expressed genes (DEGs) were analyzed using R-Bioconductor for TP53INP2 knockdown microarray dataset of 3T3L1 cells, and the DEGs were analyzed for the functional enrichment analysis. Further, the genes involved in the potential biological and molecular functions were evaluated for pathway enrichment analysis by KEGG (Kyoto Encyclopedia of Genes and Genomes). A total of 726 DEGs were found including 391 upregulated and 335 downregulated genes. Further, the functional and pathway enrichment analysis was employed to identify the highly interacting genes, and we identified a total of 56 genes that are highly interacting through a protein-protein interaction network. The DEGs mainly regulate the Peroxisome proliferator-activated receptor (PPAR) signaling pathway, lipolysis, and autophagy. Further, we investigated the associated Hub genes for enriched pathway genes and found the involvement of two autophagic genes ATG7 and sequestosome 1 (p62). In addition, in vitro studies of qRT-PCR (Quantitative real-time polymerase chain reaction) and Western blot analysis revealed that increased autophagy resulted in reduced lipid storage through down-regulation of the adipogenic gene. Moreover, increased expression of autophagic gene TP53INP2 and ATG7 facilitates the down-regulation of p62 and PPARγ gene resulting in lipolysis in mature adipocytes through autophagy. There is no specific treatment to reduce obesity other than a caloric diet and exercise. Hence, this study provides sufficient evidence to conclude that TP53INP2 negatively regulates adipogenesis and increases the degradation of lipids in mature adipocytes which is crucial for reducing obesity. Therefore, it is plausible to consider TP53INP2 as a promising therapeutic target for managing adipogenesis and obesity. However, further studies are necessary to validate their functional and molecular pathway analysis in the regulation of adipogenesis and obesity.

White adipose tissue in metabolic associated fatty liver disease

BACKGROUND

Metabolic associated fatty liver disease (MAFLD) is a prevalent chronic liver condition globally, currently lacking universally recognized therapeutic drugs, thereby increasing the risk of cirrhosis and hepatocellular carcinoma. Research has reported an association between white adipose tissue and MAFLD.

SCOPE OF REVIEW

White adipose tissue (WAT) is involved in lipid metabolism and can contribute to the progression of MAFLD by mediating insulin resistance, inflammation, exosomes, autophagy, and other processes. This review aims to elucidate the mechanisms through which WAT plays a role in the development of MAFLD.

MAJOR CONCLUSIONS

WAT participates in the occurrence and progression of MAFLD by mediating insulin resistance, inflammation, autophagy, and exosome secretion. Fibrosis and restricted expansion of adipose tissue can lead to the release of more free fatty acids (FFA), exacerbating the progression of MAFLD. WAT-secreted TNF-α and IL-1β, through the promotion of JNK/JKK/p38MAPK expression, interfere with insulin receptor serine and tyrosine phosphorylation, worsening insulin resistance. Adiponectin, by inhibiting the TLR-4-NF-κB pathway and suppressing M2 to M1 transformation, further inhibits the secretion of IL-6, IL-1β, and TNF-α, improving insulin resistance in MAFLD patients. Various gene expressions within WAT, such as MBPAT7, Nrf2, and Ube4A, can ameliorate insulin resistance in MAFLD patients. Autophagy-related gene Atg7 promotes the expression of fibrosis-related genes, worsening MAFLD. Non-pharmacological treatments, including diabetes-related medications and exercise, can improve MAFLD.

Caspase-1 Deficiency Modulates Adipogenesis through Atg7-Mediated Autophagy: An Inflammatory-Independent Mechanism

Obesity stands as a significant risk factor for type 2 diabetes, hyperlipidemia, and cardiovascular diseases, intertwining increased inflammation and decreased adipogenesis with metabolic disorders. Studies have highlighted the correlation between Caspase-1 and inflammation in obesity, elucidating its essential role in the biological functions of adipose tissue. However, the impact of Caspase-1 on adipogenesis and the underlying mechanisms remain largely elusive. In our study, we observed a positive correlation between Caspase-1 expression and obesity and its association with adipogenesis. In vivo experiments revealed that, under normal diet conditions, Caspase-1 deficiency improved glucose homeostasis, stimulated subcutaneous adipose tissue expansion, and enhanced adipogenesis. Furthermore, our findings indicate that Caspase-1 deficiency promotes the expression of autophagy-related proteins and inhibits autophagy with 3-MA or CQ blocked Caspase-1 deficiency-induced adipogenesis in vitro. Notably, Caspase-1 deficiency promotes adipogenesis via Atg7-mediated autophagy activation. In addition, Caspase-1 deficiency resisted against high-fat diet-induced obesity and glucose intolerance. Our study proposes the downregulation of Caspase-1 as a promising strategy for mitigating obesity and its associated metabolic disorders.

Knockdown of ANGPTL4 inhibits adipogenesis of preadipocyte via autophagy

It has been demonstrated that angiopoietin-like protein 4 (ANGPTL4) plays an important regulatory role in lipid metabolism and backfat deposition appears to vary in different pig breeds. However, the correlation between ANGPTL4 and backfat deposition have not been well characterized and the role of ANGPTL4 in regulating adipogenesis remains unclear. Therefore, this study aimed to investigate correlation between ANGPTL4 and backfat deposition and to explore the effects of ANGPTL4 on preadipocyte differentiation and the underlying mechanism. Our results showed that the backfat thickness and the ANGPTL4 gene expression of Laiwu pigs were significantly higher than those in DLY pigs and the ANGPTL4 gene expression was positively correlated with backfat thickness both in DLY pigs and Laiwu pigs. Moreover, an increase in ANGPTL4 expression and activation of autophagy were observed during the differentiation of stromal vascular fraction cells. In addition, knockdown of ANGPTL4 inhibited the differentiation of 3T3-L1 cells with decreased expression of LC3-II and ATG5 and increased expression of SQSTM1, suggesting the involvement of autophagy in ANGPTL4-mediated adipogenesis. In conclusion, these results suggested that ANGPTL4 is positively correlated with backfat deposition in pigs and knockdown of ANGPTL4 inhibits adipogenesis of preadipocyte via autophagy, providing new insights into the regulation of fat deposition and to improve the carcass quality and meat quality of porcine.

Enhancer-mediated FOXO3 expression promotes MSC adipogenic differentiation by activating autophagy

BACKGROUND

Mesenchymal stem cells (MSCs) are pluripotent stem cells capable of differentiating into osteocytes, adipocytes and chondrocytes. However, in osteoporosis, the balance of differentiation is tipped toward adipogenesis and the key mechanism is controversial. Researches have shown that, as upstream regulatory elements of gene expression, enhancers ar involved in the expression of identity genes. In this study, we identified enhancers-mediated gene FOXO3 promoting MSC adipogenic differentiation by activating autophagy.

METHODS

We integrated data of RNA sequencing (RNA-seq), chromatin immunoprecipitation sequencing (ChIP-seq) and ATAC-sequencing (ATAC-seq) to find the identity gene FOXO3. The expression of FOXO3 protein, adipogenic transcription factors and the substrate of autophagy were measured by western blotting. The Oil Red O (ORO) staining was used to visualize the adipogenesis of MSCs. Immunohistochemistry was used to visualize the FOXO3 expression in adipocytes in bone marrow. Immunofluorescence was used to detect the expression of PPARγ and LC3B.

RESULTS

During adipogenesis, enhancers redistribute to genes associated with adipogenic differentiation, among which we identified the pivotal identity gene FOXO3. FOXO3 could promote the expression of the adipogenic transcription factors PPARγ, CEBPα, and CEBPβ during adipogenic differentiation, while PPARγ, CEBPα, and CEBPβ could in turn bind to FOXO3 and continue to promote FOXO3 expression to form a positive feedback loop. Consistently elevated FOXO3 expression promotes autophagy by activating the PI3K-AKT pathway which mediates adipogenic differentiation.

CONCLUSIONS

Pivotal identity gene FOXO3 promotes autophagy by activating PI3K-AKT pathway, which provokes adipogenic differentiation of MSCs. Enhancer-regulated adipogenic identity gene FOXO3 could be an attractive treatment for osteoporosis.

Lipid droplets, autophagy, and ageing: A cell-specific tale

Lipid droplets are the essential organelle for storing lipids in a cell. Within the variety of the human body, different cells store, utilize and release lipids in different ways, depending on their intrinsic function. However, these differences are not well characterized and, especially in the context of ageing, represent a key factor for cardiometabolic diseases. Whole body lipid homeostasis is a central interest in the field of cardiometabolic diseases. In this review we characterize lipid droplets and their utilization via autophagy and describe their diverse fate in three cells types central in cardiometabolic dysfunctions: adipocytes, hepatocytes, and macrophages.

CTCF modulates adipocyte lipolysis via directly regulating the expression of Beclin 1 with the cooperation of PPARγ

Dysregulated lipolysis is a risk factor contributing to metabolic diseases and autophagy is known to be important in lipolysis. CTCF is involved in diverse cellular processes including adipogenesis, yet its role in lipolysis or autophagy remains unknown. We identified lipolytic genes were downregulated in CTCF knockdown adipocytes based on the RNA-seq data. Further validation showed that CTCF knockdown restrained adipocyte lipolysis while overexpression of CTCF had opposite effects. Similarly, overexpression and knockdown studies demonstrated that CTCF was a positive regulator of autophagy. Treatment with autophagy inducer relieved the suppression of lipolysis caused by CTCF knockdown, while autophagy inhibitor treatment alleviated lipolysis stimulated by CTCF overexpression, indicating that CTCF regulates adipocyte lipolysis through autophagy. Mechanistically, CTCF interacted with PPARγ to coordinately enhanced lipolytic capacity. Data of chip-seq, chip-qPCR and further experiments confirmed that CTCF and PPARγ separately stimulated transactivation of autophagy regulatory protein Beclin 1, while co-expression of the two displayed synergistic effects to regulate autophagy flux. Expectedly, overexpression of Beclin 1 abolished the blockage of lipolysis and autophagy caused by CTCF knockdown. Collectively, CTCF cooperates with PPARγ to regulate autophagy via directly modulating BECLIN 1 transcription, thereby leading to increased adipocyte lipolysis.

Current Advances in the Regulatory Effects of Bioactive Compounds from Dietary Resources on Nonalcoholic Fatty Liver Disease: Role of Autophagy

Nonalcoholic fatty liver disease (NAFLD) is the most prevalent chronic liver disease characterized by lipid metabolic disorder primarily due to sedentary lifestyles and excessive food consumption. However, there are currently no approved and effective drugs available to treat NAFLD. In recent years, research has shown that dietary bioactive compounds, such as polysaccharides, polyphenols, flavones, and alkaloids, have the potential to improve NAFLD by regulating autophagy. However, there is no up-to-date review of research progress in this field. This review aims to systematically summarize and discuss the regulatory effects and molecular mechanisms of dietary bioactive compounds on NAFLD through the modulation of autophagy. The existing research has demonstrated that some dietary bioactive compounds can effectively improve various aspects of NAFLD progression, such as lipid metabolism, insulin resistance (IR), endoplasmic reticulum (ER) stress, oxidative stress, mitochondrial homeostasis, and inflammation. Molecular mechanism studies have revealed that they exert their beneficial effects on NAFLD through autophagy-mediated signaling pathways, predominantly involving transcription factor EB (TFEB), mammalian target of rapamycin (mTOR), adenosine monophosphate-activated protein kinase (AMPK), peroxisome proliferator-activated receptors (PPARs), SIRT, and PTEN-induced kinase 1 (PINK1)/parkin. Furthermore, the challenges and prospects of current research in this field are highlighted. Overall, this review provides valuable insights into the potential treatment of NAFLD using dietary bioactive compounds that can modulate autophagy.

Crosstalk between autophagy and insulin resistance: evidence from different tissues

Insulin is a critical hormone that promotes energy storage in various tissues, as well as anabolic functions. Insulin resistance significantly reduces these responses, resulting in pathological conditions, such as obesity and type 2 diabetes mellitus (T2DM). The management of insulin resistance requires better knowledge of its pathophysiological mechanisms to prevent secondary complications, such as cardiovascular diseases (CVDs). Recent evidence regarding the etiological mechanisms behind insulin resistance emphasizes the role of energy imbalance and neurohormonal dysregulation, both of which are closely regulated by autophagy. Autophagy is a conserved process that maintains homeostasis in cells. Accordingly, autophagy abnormalities have been linked to a variety of metabolic disorders, including insulin resistance, T2DM, obesity, and CVDs. Thus, there may be a link between autophagy and insulin resistance. Therefore, the interaction between autophagy and insulin function will be examined in this review, particularly in insulin-responsive tissues, such as adipose tissue, liver, and skeletal muscle.

Crucial role of iron in epigenetic rewriting during adipocyte differentiation mediated by JMJD1A and TET2 activity

Iron metabolism is closely associated with the pathogenesis of obesity. However, the mechanism of the iron-dependent regulation of adipocyte differentiation remains unclear. Here, we show that iron is essential for rewriting of epigenetic marks during adipocyte differentiation. Iron supply through lysosome-mediated ferritinophagy was found to be crucial during the early stage of adipocyte differentiation, and iron deficiency during this period suppressed subsequent terminal differentiation. This was associated with demethylation of both repressive histone marks and DNA in the genomic regions of adipocyte differentiation-associated genes, 　including Pparg, which encodes PPARγ, the master regulator of adipocyte differentiation. In addition, we identified several epigenetic demethylases to be responsible for iron-dependent adipocyte differentiation, with the histone demethylase jumonji domain-containing 1A and the DNA demethylase ten-eleven translocation 2 as the major enzymes. The interrelationship between repressive histone marks and DNA methylation was indicated by an integrated genome-wide association analysis, and was also supported by the findings that both histone and DNA demethylation were suppressed by either the inhibition of lysosomal ferritin flux or the knockdown of iron chaperone poly(rC)-binding protein 2. In summary, epigenetic regulations through iron-dependent control of epigenetic enzyme activities play an important role in the organized gene expression mechanisms of adipogenesis.

Genetically prolonged beige fat in male mice confers long-lasting metabolic health

A potential therapeutic target to curb obesity and diabetes is thermogenic beige adipocytes. However, beige adipocytes quickly transition into white adipocytes upon removing stimuli. Here, we define the critical role of cyclin dependent kinase inhibitor 2A (Cdkn2a) as a molecular pedal for the beige-to-white transition. Beige adipocytes lacking Cdkn2a exhibit prolonged lifespan, and male mice confer long-term metabolic protection from diet-induced obesity, along with enhanced energy expenditure and improved glucose tolerance. Mechanistically, Cdkn2a promotes the expression and activity of beclin 1 (BECN1) by directly binding to its mRNA and its negative regulator BCL2 like 1 (BCL2L1), activating autophagy and accelerating the beige-to-white transition. Reactivating autophagy by pharmacological or genetic methods abolishes beige adipocyte maintenance induced by Cdkn2a ablation. Furthermore, hyperactive BECN1 alone accelerates the beige-to-white transition in mice and human. Notably, both Cdkn2a and Becn1 exhibit striking positive correlations with adiposity. Hence, blocking Cdkn2a-mediated BECN1 activity holds therapeutic potential to sustain beige adipocytes in treating obesity and related metabolic diseases.

Hyperoside prevents high-fat diet-induced obesity by increasing white fat browning and lipophagy via CDK6-TFEB pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Hypericum perforatum L. (genus Hypericum, family Hypericaceae) is a flowering plant native to Europe, North Africa and Asia, which can be used in the treatment of psychiatric disorder, cardiothoracic depression and diabetes. Crataegus pinnatifida Bunge (genus Crataegus pinnatifida Bunge, family Rosaceae) was another traditional Chinese medicine for treating hyperlipidemia. Hyperoside (Hype), a major flavonoid glycoside component of Hypericum perforatum L. and Crataegus pinnatifida Bunge, possesses multiple physiological activities, such as anti-inflammatory and antioxidant effects. However, the role of Hype on obesity and related metabolic diseases still needs to be further investigated.

AIM OF THE STUDY

We explored the effect of Hype on high-fat diet (HFD)-induced obesity and its metabolic regulation on white fat tissues.

MATERIALS AND METHODS

In vivo four-week-old male C57BL/6J mice were randomly assigned to vehicle (0.5% methycellulose) and Hype (80 mg/kg/day by gavage) group under a normal chow diet (NCD) or HFD for 8 weeks. In vitro, 3T3-L1 preadipocyte cell line and primary stromal vascular fraction (SVF) cells from inguinal white adipose tissue (iWAT) of mice were used to investigate the molecular mechanisms of Hype regulation on adipocyte energy metabolism.

RESULTS

Hype treatment in vivo promotes UCP1-dependent white to beige fat transition, increases glucose and lipid metabolism, and resists HFD-induced obesity. Meanwhile, Hype induces lipophagy, a specific autophagy that facilitates the breakdown of lipid droplets, and blocking autophagy partially reduces UCP1 expression. Mechanistically, Hype inhibited CDK6, leading to the increased nuclear translocation of TFEB, while overexpression of CDK6 partially reversed the enhancement of UCP1 by Hype.

CONCLUSIONS

Hype protects mice from HFD-induced obesity by increasing energy expenditure of white fat tissue via CDK6-TFEB pathway.

Bub1 and Bub3 regulate metabolic adaptation via macrolipophagy in Drosophila

Lipophagy, the process of selective catabolism of lipid droplets (LDs) by autophagy, maintains lipid homeostasis and provides cellular energy under metabolic adaptation, yet its underlying mechanism remains largely ambiguous. Here, we show that the Bub1-Bub3 complex, the crucial regulator involved in the whole process of chromosome alignment and separation during mitosis, controls the fasting-induced lipid catabolism in the fat body (FB) of Drosophila. Bidirectional deviations of the Bub1 or Bub3 level affect the consumption of triacylglycerol (TAG) of fat bodies and the survival rate of adult flies under starving. Moreover, Bub1 and Bub3 work together to attenuate lipid degradation via macrolipophagy upon fasting. Thus, we uncover physiological roles of the Bub1-Bub3 complex on metabolic adaptation and lipid metabolism beyond their canonical mitotic functions, providing insights into the in vivo functions and molecular mechanisms of macrolipophagy during nutrient deprivation.

Dysregulated autophagy: A key player in the pathophysiology of type 2 diabetes and its complications

Autophagy is essential in regulating the turnover of macromolecules via removing damaged organelles, misfolded proteins in various tissues, including liver, skeletal muscles, and adipose tissue to maintain the cellular homeostasis. In these tissues, a specific type of autophagy maintains the accumulation of lipid droplets which is directly related to obesity and the development of insulin resistance. It appears to play a protective role in a normal physiological environment by eliminating the invading pathogens, protein aggregates, and damaged organelles and generating energy and new building blocks by recycling the cellular components. Ageing is also a crucial modulator of autophagy process. During stress conditions involving nutrient deficiency, lipids excess, hypoxia etc., autophagy serves as a pro-survival mechanism by recycling the free amino acids to maintain the synthesis of proteins. The dysregulated autophagy has been found in several ageing associated diseases including type 2 diabetes (T2DM), cancer, and neurodegenerative disorders. So, targeting autophagy can be a promising therapeutic strategy against the progression to diabetes related complications. Our article provides a comprehensive outline of understanding of the autophagy process, including its types, mechanisms, regulation, and role in the pathophysiology of T2DM and related complications. We also explored the significance of autophagy in the homeostasis of β-cells, insulin resistance (IR), clearance of protein aggregates such as islet amyloid polypeptide, and various insulin-sensitive tissues. This will further pave the way for developing novel therapeutic strategies for diabetes-related complications.

PDZK1-Interacting Protein 1(PDZKIP1) Inhibits Goat Subcutaneous Preadipocyte Differentiation through Promoting Autophagy

PDZK1IP1 is highly expressed in tumor tissue and has been identified as a tumor biomarker. However, the role of PDZK1IP1 in goat subcutaneous preadipocyte differentiation remains largely unknown. The molecular mechanism of autophagy in regulating the differentiation of goat subcutaneous preadipocytes has not been clarified yet. In our study, PDZK1IP1 gain of function and loss of function were performed to reveal its functions in preadipocyte differentiation and autophagy. Our results showed that the overexpression of PDZK1IP1 inhibited the differentiation of goat subcutaneous preadipocytes, whereas it promoted autophagy. Consistently, the knockdown of PDZK1IP1 demonstrated the opposite tendency. Next, we investigated whether PDZK1IP1 inhibited the differentiation of goat preadipocytes by regulating autophagy. We found that inhibiting autophagy can rescue the PDZK1IP1-induced differentiation restraint in goat subcutaneous preadipocytes. In conclusion, PDZK1IP1 acts as a regulator of adipogenesis, and inhibits goat subcutaneous preadipocyte differentiation through promoting autophagy. Our results will contribute to further understanding the role and mechanism of PDZK1IP1 in controlling adipogenesis.

Methylmercury drives lipid droplet formation and adipokine expression during the late stages of adipocyte differentiation in 3T3-L1 cells

Chronic exposure to methylmercury (MeHg) is positively associated with obesity and metabolic syndromes. However, the effect of MeHg on adipogenesis has not been thoroughly investigated. This study investigated the effects of continuous exposure to 0.5 µM MeHg on adipocyte differentiation in 3T3-L1 cells. Oil Red O staining and triglycerides (TG) assays demonstrated that MeHg enhanced the TG content in 3T3-L1 cells. MeHg enhanced the mRNA and protein expression of adipocyte differentiation markers including peroxisome proliferator-activated receptor γ, adiponectin, and fatty acid-binding protein, and their expression levels were prominent during the late stages (days 6-8) after the induction of differentiation. In addition, 0.5 µM MeHg promoted the expression of autophagy-related genes, including light chain 3 B-II and p62, after induction of differentiation. Treatment of 3T3-L1 cells with chloroquine (CQ), an autophagy inhibitor, during the early stages (days 0-2) after induction of differentiation inhibited cellular lipid accumulation in the presence of 0.5 µM MeHg. However, treatment with CQ during the late stages (days 6-8) had little effect on the MeHg-induced increase in TG content and the expression of adipocyte differentiation markers. Although the underlying mechanisms in the late stages remain to be completely elucidated, but the present data suggest that autophagy and other mechanisms play critical roles in adipogenesis during MeHg-induced differentiation. Collectively, our results suggest that continuous exposure to MeHg induces TG accumulation and expression of genes related to adipogenesis, especially during the late stages of 3T3-L1 differentiation, which may contribute to an improved understanding of MeHg-induced adipogenesis.

Fatty Acids as Potent Modulators of Autophagy Activity in White Adipose Tissue

A high-fat diet is one of the causative factors of obesity. The dietary profile of fatty acids is also an important variable in developing obesity, as saturated fatty acids are more obesogenic than monounsaturated and polyunsaturated fatty acids. Overweight and obesity are inseparably connected with the excess of adipose tissue in the body, characterized by hypertrophy and hyperplasia of fat cells, which increases the risk of developing metabolic syndrome. Changes observed within hypertrophic adipocytes result in elevated oxidative stress, unfolded protein accumulation, and increased endoplasmic reticulum (ER) stress. One of the processes involved in preservation of cellular homeostasis is autophagy, which is defined as an intracellular lysosome-dependent degradation system that serves to recycle available macromolecules and eliminate damaged organelles. In obesity, activation of autophagy is increased and the process appears to be regulated by different types of dietary fatty acids. This review describes the role of autophagy in adipose tissue and summarizes the current understanding of the effects of saturated and unsaturated fatty acids in autophagy modulation in adipocytes.

Transcriptional and post-transcriptional control of autophagy and adipogenesis by YBX1

Obesity is strongly associated with metabolic diseases, which have become a global health problem. Exploring the underlying mechanism of adipogenesis is crucial for the treatment of excess white fat. Oncogene YBX1 is a multifunctional DNA- and RNA-binding protein that regulates brown adipogenesis. However, the role of YBX1 in white adipogenesis and adipose tissue expansion remains unknown. Here, we showed that YBX1 deficiency inhibited murine and porcine adipocyte differentiation. YBX1 positively regulated adipogenesis through promoting ULK1- and ULK2-mediated autophagy. Mechanistically, we identified YBX1 serves as a 5-methylcytosine (m⁵C)-binding protein directly targeting m⁵C-containing Ulk1 mRNA by using RNA immunoprecipitation. RNA decay assay further proved that YBX1 upregulated ULK1 expression though stabilizing its mRNA. Meanwhile, YBX1 promoted Ulk2 transcription and expression as a transcription factor, thereby enhancing autophagy and adipogenesis. Importantly, YBX1 overexpression in white fat enhanced ULK1/ULK2-mediated autophagy and promoted adipose tissue expansion in mice. Collectively, these findings unveil the post-transcriptional and transcriptional mechanism and functional importance of YBX1 in autophagy and adipogenesis regulation, providing an attractive molecular target for therapies of obesity and metabolic diseases.

Autophagy and Its Lineage-Specific Roles in the Hematopoietic System

Autophagy is a dynamic process that regulates the selective and nonselective degradation of cytoplasmic components, such as damaged organelles and protein aggregates inside lysosomes to maintain tissue homeostasis. Different types of autophagy including macroautophagy, microautophagy, and chaperon-mediated autophagy (CMA) have been implicated in a variety of pathological conditions, such as cancer, aging, neurodegeneration, and developmental disorders. Furthermore, the molecular mechanism and biological functions of autophagy have been extensively studied in vertebrate hematopoiesis and human blood malignancies. In recent years, the hematopoietic lineage-specific roles of different autophagy-related (ATG) genes have gained more attention. The evolution of gene-editing technology and the easy access nature of hematopoietic stem cells (HSCs), hematopoietic progenitors, and precursor cells have facilitated the autophagy research to better understand how ATG genes function in the hematopoietic system. Taking advantage of the gene-editing platform, this review has summarized the roles of different ATGs at the hematopoietic cell level, their dysregulation, and pathological consequences throughout hematopoiesis.

Celastrol directly binds with VAMP7 and RAB7 to inhibit autophagy and induce apoptosis in preadipocytes

Obesity is one of the most prevalent chronic metabolic diseases, and induction of apoptosis in preadipocytes and adipocytes is a potential strategy to treat obesity. Celastrol represents one of the most robust anti-obesity phytochemicals so far, yet its direct binding target remains elusive. Here, we determined that celastrol could induce apoptosis in preadipocytes via mitochondrial mediated pathway. Further study clarified that celastrol inhibited the fusion of autophagosome and lysosome to prohibit autophagy, leading to cell apoptosis. By conducting virtual screening and genetic manipulation, we verified that overexpression of VAMP7 and RAB7 could block the effects of celastrol on inhibiting autophagy and inducing apoptosis. The Surface Plasmon Resonance study confirmed the direct binding of celastrol with VAMP7 and RAB7. The functional study illustrated the inhibition of RAB7 GTPase activity after celastrol treatment. Moreover, celastrol induced comparable apoptosis in murine epididymal adipose tissue, human preadipocytes and adipocytes, but not in human hepatocytes. An inhibitory effect on differentiation of human primary visceral preadipocytes was also observed. In conclusion, celastrol exhibited inhibitory effect of autophagy via direct binding with VAMP7 and RAB7, leading to an increase in preadipocytes apoptosis. These results advance our understanding in the potential application of celastrol in treating obesity.

Role of autophagy in aging: The good, the bad, and the ugly

Autophagy (self-eating) is a conserved catabolic homeostatic process required for cellular metabolic demands by removal of the damaged molecules and organelles and for alleviation of stress initiated by pathology and infection. By such actions, autophagy is essential for the prevention of aging, disease, and cancer. Genetic defects of autophagy genes lead to a host of developmental, metabolic, and pathological aberrations. Similarly, the age-induced decline in autophagy leads to the loss of cellular homeostatic control. Paradoxically, such a valuable mechanism is hijacked by diseases, during tumor progression and by senescence, presumably due to high levels of metabolic demand. Here, we review both the role of autophagy in preventing cellular decline in aging by fulfillment of cellular bioenergetic demands and its contribution to the maintenance of the senescent state and SASP by acting on energy and nutritional sensors and diverse signaling pathways.

Inhibition of autophagy with chloroquine dysregulates mitochondrial quality control and energetics in adipocytes

Autophagy is a complex degradation pathway through which damaged or dysfunctional proteins and organelles are removed. Its pharmacological modulators have been extensively used in a wide range of basic research and preclinical studies. However, the effects of these inhibitors on metabolism, in addition to autophagy inhibition, are not fully elucidated. Chloroquine is a clinically relevant compound that inhibits autophagy by preventing the fusion of autophagosomes with lysosomes. In this study, we aimed to examine the effect of chloroquine on mitochondrial quality control and respiratory function by utilizing 3T3-L1 mouse adipocytes treated with chloroquine at various time points. We found that chloroquine could disturb genes related to mitochondrial fission, biogenesis, and mitophagy, leading to mitochondrial DNA damage. Although the inhibition of autophagy by chloroquine resulted in an increased prohibitin expression, respiratory function was downregulated in a time-dependent manner. Moreover, chloroquine treatment induced oxidative stress, apoptosis, and metabolic dysregulation. These data demonstrated that chloroquine significantly affected mitochondrial respiratory function and metabolism, which was consistent with impaired mitochondrial quality associated with autophagy inhibition.

AFF4 regulates cellular adipogenic differentiation via targeting autophagy

Transcriptional elongation is a universal and critical step during gene expression. The super elongation complex (SEC) regulates the rapid transcriptional induction by mobilizing paused RNA polymerase II (Pol II). Dysregulation of SEC is closely associated with human diseases. However, the physiological role of SEC during development and homeostasis remains largely unexplored. Here we studied the function of SEC in adipogenesis by manipulating an essential scaffold protein AF4/FMR2 family member 4 (AFF4), which assembles and stabilizes SEC. Knockdown of AFF4 in human mesenchymal stem cells (hMSCs) and mouse 3T3-L1 preadipocytes inhibits cellular adipogenic differentiation. Overexpression of AFF4 enhances adipogenesis and ectopic adipose tissue formation. We further generate Fabp4-cre driven adipose-specific Aff4 knockout mice and find that AFF4 deficiency impedes adipocyte development and white fat depot formation. Mechanistically, we discover AFF4 regulates autophagy during adipogenesis. AFF4 directly binds to autophagy-related protein ATG5 and ATG16L1, and promotes their transcription. Depleting ATG5 or ATG16L1 abrogates adipogenesis in AFF4-overepressing cells, while overexpression of ATG5 and ATG16L1 rescues the impaired adipogenesis in Aff4-knockout cells. Collectively, our results unveil the functional importance of AFF4 in regulating autophagy and adipogenic differentiation, which broaden our understanding of the transcriptional regulation of adipogenesis.

Obesity is a major health problem jeopardizing millions of individuals worldwide. From a pathological perspective, obesity occurs in the process of white adipose tissue expanding its mass through the enlargement of adipocyte size or advanced differentiation of adipocyte precursors to mature adipocytes. Studies have documented the dysregulated adipocyte metabolism of adipose tissue and associated disorders. However, our understanding of adipocyte development in which mesenchymal stem cells (MSCs) commit their fate and preadipocytes undergo differentiation and maturation is scarce. Here, we identify the super elongation complex (SEC) scaffold protein AFF4 as an essential regulator of adipogenesis. We reveal that AFF4 promotes adipocyte formation by regulating the cellular autophagic process. AFF4 directly regulates the transcription of the autophagy-related protein ATG5 and ATG16L1, which are essential for autophagosome formation. This finding further elucidates the physiological role of SEC during tissue development, besides its recognized role in cancer occurrence.

Autophagy in adipogenesis: Molecular mechanisms and regulation by bioactive compounds

White adipose tissue expands rapidly due to increased adipocyte number (hyperplasia) and size (hypertrophy), which results in obesity. Adipogenesis is a process of the formation of mature adipocytes from precursor cells. Additionally, obesity-related metabolic complications, such as fatty liver and insulin resistance, are linked to adipogenesis. On the contrary, autophagy is a catabolic process; essential to maintain cellular homeostasis via the degradation or recycling of unnecessary or damaged components. Importantly, autophagy dictates obesity and adipogenesis. Hence, a clear understanding of how autophagy regulates adipogenesis is crucial for drug development and the prevention and treatment of obesity and its associated disorders, such as type 2 diabetes, cardiovascular disease, and cancer. In this review, we highlighted recent findings regarding the crosstalk between adipogenesis and autophagy, as well as the molecules involved. Furthermore, the review discussed how bioactive compounds regulate adipogenesis by manipulating autophagy and underlying molecular mechanisms. Based on in vitro and animal studies, we summarized the effects of bioactive compounds on adipogenesis and autophagy. Hence, human studies are necessary to validate the effectiveness and optimal dosage of these bioactive compounds.

Emerging Roles of Lipophagy in Cancer Metastasis

Simple Summary

Metastasis is the main cause of death in patients with malignant tumors worldwide. Mounting evidence suggests lipid droplet metabolism is involved in the process of metastasis. As a mechanism to selectively degrade lipid droplets, the current research on lipophagy and tumor metastasis is quite limited. This review summarizes the crosstalk among lipophagy, tumor lipid metabolism and cancer metastasis, which will provide a new reference for the development of effective targeted drugs.

Abstract

Obesity is a prominent risk factor for certain types of tumor progression. Adipocytes within tumor stroma contribute to reshaping tumor microenvironment (TME) and the metabolism and metastasis of tumors through the production of cytokines and adipokines. However, the crosstalk between adipocytes and tumor cells remains a major gap in this field. Known as a subtype of selective autophagy, lipophagy is thought to contribute to lipid metabolism by breaking down intracellular lipid droplets (LDs) and generating free fatty acids (FAs). The metastatic potential of cancer cells closely correlates with the lipid degradation mechanisms, which are required for energy generation, signal transduction, and biosynthesis of membranes. Here, we discuss the recent advance in the understanding of lipophagy with tumor lipid metabolism and review current studies on the roles of lipoghagy in the metastasis of certain human malignancies. Additionally, the novel candidate drugs targeting lipophagy are integrated for effective treatment strategies.

ATG5: A central autophagy regulator implicated in various human diseases

Autophagy, an intracellular conserved degradative process, plays a central role in the renewal/recycling of a cell to maintain the homeostasis of nutrients and energy within the cell. ATG5, a key component of autophagy, regulates the formation of the autophagosome, a hallmark of autophagy. ATG5 binds with ATG12 and ATG16L1 resulting in E3 like ligase complex, which is necessary for autophagosome expansion. Available data suggest that ATG5 is indispensable for autophagy and has an imperative role in several essential biological processes. Moreover, ATG5 has also been demonstrated to possess autophagy-independent functions that magnify its significance and therapeutic potential. ATG5 interacts with various molecules for the execution of different processes implicated during physiological and pathological conditions. Furthermore, ATG5 genetic variants are associated with various ailments. This review discusses various autophagy-dependent and autophagy-independent roles of ATG5, highlights its various deleterious genetic variants reported until now, and various studies supporting it as a potential drug target.

Balancing nutrient and energy demand and supply via autophagy

Maintaining nutrient and energy homeostasis is crucial for the survival and function of cells and organisms in response to environmental stress. Cells have evolved a stress-induced catabolic pathway, termed autophagy, to adapt to stress conditions such as starvation. During autophagy, damaged or non-essential cellular structures are broken down in lysosomes, and the resulting metabolites are reused for core biosynthetic processes or energy production. Recent studies have revealed that autophagy can target and degrade different types of nutrient stores and produce a variety of metabolites and fuels, including amino acids, nucleotides, lipids and carbohydrates. Here, we will focus on how autophagy functions to balance cellular nutrient and energy demand and supply - specifically, how energy deprivation switches on autophagic catabolism, how autophagy halts anabolism by degrading the protein synthesis machinery, and how bulk and selective autophagy-derived metabolites recycle and feed into a variety of bioenergetic and anabolic pathways during stress conditions. Recent new insights and progress in these areas provide a better understanding of how resource mobilization and reallocation sustain essential metabolic and anabolic activities under unfavorable conditions.

Integrating the effects of sucrose intake on the brain and white adipose tissue: Could autophagy be a possible link?

Excess dietary sucrose is associated with obesity and metabolic diseases. This relationship is driven by the malfunction of several cell types and tissues critical for the regulation of energy balance, including hypothalamic neurons and white adipose tissue (WAT). However, the mechanisms behind these effects of dietary sucrose are still unclear and might be independent of increased adiposity. Accumulating evidence has indicated that dysregulation of autophagy, a fundamental process for maintenance of cellular homeostasis, alters energy metabolism in hypothalamic neurons and WAT, but whether autophagy could mediate the detrimental effects of dietary sucrose on hypothalamic neurons and WAT that contribute to weight gain is a matter of debate. In this review, we examine the hypothesis that dysregulated autophagy in hypothalamic neurons and WAT is an adiposity-independent effect of sucrose that contributes to increased body weight gain. We propose that excess dietary sucrose leads to autophagy unbalance in hypothalamic neurons and WAT, which increases caloric intake and body weight, favoring the emergence of obesity and metabolic diseases.

Autophagy at the interface of endothelial cell homeostasis and vascular disease

Autophagy is an essential intracellular process for cellular quality control. It enables cell homeostasis through the selective degradation of harmful protein aggregates and damaged organelles. Autophagy is essential for recycling nutrients, generating energy to maintain cell viability in most tissues and during adverse conditions such as hypoxia/ischaemia. The progressive understanding of the mechanisms modulating autophagy in the vasculature has recently led numerous studies to link intact autophagic responses with endothelial cell (EC) homeostasis and function. Preserved autophagic flux within the ECs has an essential role in maintaining their physiological characteristics, whereas defective autophagy can promote endothelial pro-inflammatory and atherogenic phenotype. However, we still lack a good knowledge of the complete molecular repertoire controlling various aspects of endothelial autophagy and how this is associated with vascular diseases. Here, we provide an overview of the current state of the art of autophagy in ECs. We review the discoveries that have so far defined autophagy as an essential mechanism in vascular biology and analyse how autophagy influences ECs behaviour in vascular disease. Finally, we emphasise opportunities for compounds to regulate autophagy in ECs and discuss the challenges of exploiting them to resolve vascular disease.

Degradative and Non-Degradative Roles of Autophagy Proteins in Metabolism and Metabolic Diseases

Autophagy is a stress-induced lysosomal degradation pathway regulated by evolutionarily conserved autophagy-related (ATG) genes. Recent research has revealed that autophagy plays an important role in the regulation of energy metabolism, development of metabolic tissues, and pathogenesis of metabolic disorders. Bulk and selective degradation by autophagy helps maintain protein homeostasis and physiological function of cells. Aside from classical degradative roles, ATG proteins also carry out non-classical secretory functions of metabolic tissues. In this review, we summarize recent progresses and unanswered questions on the mechanisms of autophagy and ATG proteins in metabolic regulation, with a focus on organelle and nutrient storage degradation, as well as vesicular and hormonal secretion. Such knowledge broadens our understanding on the cause, pathophysiology, and prevention of metabolic diseases including obesity and diabetes.

Arsenic Toxicity on Metabolism and Autophagy in Adipose and Muscle Tissues

Arsenic, a naturally occurring metalloid derived from the environment, has been studied worldwide for its causative effects in various cancers. However, the effects of arsenic toxicity on the development and progression of metabolic syndrome, including obesity and diabetes, has received less attention. Many studies suggest that metabolic dysfunction and autophagy dysregulation of adipose and muscle tissues are closely related to the development of metabolic disease. In the USA, arsenic contamination has been reported in some ground water, soil and grain samples in major agricultural regions, but the effects on adipose and muscle tissue metabolism and autophagy have not been investigated much. Here, we highlight arsenic toxicity according to the species, dose and exposure time and the effects on adipose and muscle tissue metabolism and autophagy. Historically, arsenic was used as both a poison and medicine, depending on the dose and treatment time. In the modern era, arsenic intoxication has significantly increased due to exposure from water, soil and food, which could be a contributing factor in the development and progression of metabolic disease. From this review, a better understanding of the pathogenic mechanisms by which arsenic alters metabolism and autophagy regulation could become a cornerstone leading to the development of therapeutic strategies against arsenic-induced toxicity and metabolic disease.

Liquiritigenin Inhibits Lipid Accumulation in 3T3-L1 Cells via mTOR-Mediated Regulation of the Autophagy Mechanism

Liquiritigenin (LQG) is a natural flavonoid from the herb Glycyrrhiza uralensis Fisch that exhibits multiple biological activities. However, its specific role in antiobesity and its related underlying molecular mechanisms remain unknown. The primary purpose of this study is to explore the effects and regulatory mechanisms of LQG on lipid accumulation in 3T3-L1 adipocytes. The results show that LQG significantly reduced triglyceride levels and downregulated the expression of transcription factors such as CCAAT/enhancer-binding protein α (C/EBPα) and peroxisome proliferator-activated receptor γ (PPARγ) in 3T3-L1 adipocytes. Additionally, the expression of sterol-regulatory element-binding protein 1c (SREBP1c), acetyl-CoA carboxylase 1 (ACC1), and fatty acid synthase (FASN) involved in lipogenesis was reduced by treatment with LQG. The protein expression levels of light chain 3B (LC3B), autophagy-related protein 7 (ATG7) and p62 were also modulated by LQG, leading to the suppression of autophagy. Further, LQG activated the phosphorylation of the mammalian target of rapamycin (mTOR), the inhibition of which was followed by the restored expression of autophagy-related proteins. Pretreatment with an mTOR inhibitor also reverted the expression of several genes or proteins involved in lipid synthesis. These results suggest that LQG inhibited lipid accumulation via mTOR-mediated autophagy in 3T3-L1 white adipocytes, indicating the role of LQG as a potential natural bioactive component for use in dietary supplements for preventing obesity.

Autophagy impairment in liver CD11c+ cells promotes non-alcoholic fatty liver disease through production of IL-23

There has been a global increase in rates of obesity with a parallel epidemic of non-alcoholic fatty liver disease (NAFLD). Autophagy is an essential mechanism involved in the degradation of cellular material and has an important function in the maintenance of liver homeostasis. Here, we explore the effect of Autophagy-related 5 (Atg5) deficiency in liver CD11c⁺ cells in mice fed HFD. When compared to control mice, Atg5-deficient CD11c⁺ mice exhibit increased glucose intolerance and decreased insulin sensitivity when fed HFD. This phenotype is associated with the development of NAFLD. We observe that IL-23 secretion is induced in hepatic CD11c⁺ myeloid cells following HFD feeding. We demonstrate that both therapeutic and preventative IL-23 blockade alleviates glucose intolerance, insulin resistance and protects against NAFLD development. This study provides insights into the function of autophagy and IL-23 production by hepatic CD11c⁺ cells in NAFLD pathogenesis and suggests potential therapeutic targets.

The function of autophagy and how this affects non-alcoholic fatty liver disease is not fully known. Here the authors show that in mice with a targeted disruption of the autophagy pathway in CD11c⁺ cells, development of NAFLD is accelerated involving IL-23 and blocking of IL-23 reduces disease.

Pharmacological agents targeting autophagy and their effects on lipolysis in human adipocytes

Adipose tissue of metabolically compromised humans with obesity is often characterized by impaired regulation of autophagy pathway. However, data on the role of autophagy in human adipocyte lipid catabolism is scarce. Therefore, we investigated the effect of pharmacological agents (including 3-methyladenine (3MA), bafilomycin A1 (BAF), chloroquine (CQ) and lalistat-2 (L-stat), that target different stages of the autophagy pathway on lipid hydrolysis in differentiated human multipotent adipose-derived stem cells (hMADs). Glycerol and fatty acid release were measured as marker of lipid hydrolysis following starvation and β-adrenergic stimulation. Microtubule-associated protein light chain 3 ratio (LC3II/LC3I) and HSL phosphorylation (pHSL) were analyzed by Western blot. Our data indicate that pharmacological inhibition of the autophagy pathway reduced lipid hydrolysis in human adipocytes, although to a limited extent (10-15%). However, further research is needed to reveal the exact mechanism of action of these pharmacological agents and their interplay with cytosolic lipid breakdown in human adipocytes.

Hierarchical regulation of autophagy during adipocyte differentiation

We previously showed that some adipogenic transcription factors such as CEBPB and PPARG directly and indirectly regulate autophagy gene expression in adipogenesis. The order and effect of these events are undetermined. In this study, we modeled the gene expression, DNA-binding of transcriptional regulators, and histone modifications during adipocyte differentiation and evaluated the effect of the regulators on gene expression in terms of direction and magnitude. Then, we identified the overlap of the transcription factors and co-factors binding sites and targets. Finally, we built a chromatin state model based on the histone marks and studied their relation to the factors’ binding. Adipogenic factors differentially regulated autophagy genes as part of the differentiation program. Co-regulators associated with specific transcription factors and preceded them to the regulatory regions. Transcription factors differed in the binding time and location, and their effect on expression was either localized or long-lasting. Adipogenic factors disproportionately targeted genes coding for autophagy-specific transcription factors. In sum, a hierarchical arrangement between adipogenic transcription factors and co-factors drives the regulation of autophagy during adipocyte differentiation.

Autophagy: a molecular switch to regulate adipogenesis and lipolysis

Obesity is a complex epidemic disease caused by an imbalance of adipose tissue function that results in hyperglycemia, hyperlipidemia and insulin resistance which further develop into type 2 diabetes, cardiovascular disease and nonalcoholic fatty liver disease/nonalcoholic steatohepatitis. Adipose tissue is responsible for fat storage; white adipose tissue stores excess energy as fat for availability during starvation, whereas brown adipose tissue regulates thermogenesis through fat oxidation using uncoupling protein 1. However, hypertrophic fat storage results in inflammation and increase the chances for obesity which triggers autophagy genes and lipolytic enzymes to regulate lipid metabolism. Autophagy degrades cargo molecule with the help of lysosome and redistributes the energy back to the cell. Autophagy regulates adipocyte differentiation by modulating master regulators of adipogenesis. Adipogenesis is the process which stores excessive energy in the form of lipid droplets. Lipid droplets (LD) are dynamic cellular organelles that store toxic free-fatty acids into neutral triglycerides in adipose tissue. LD activates both lipolysis and lipophagy to degrade excess triglycerides. In obese tissue, autophagy is activated via pro-inflammatory cytokines produced by surplus fat stored in the adipose tissue. This review focused on the process of autophagy and adipogenesis and the transcription factors that regulate lipogenesis and lipolysis in the adipose tissue. We have also discussed about the importance of autophagic regulation within adipose tissue which controls the onset of obesity and its associated diseases.

New Insights Into the Interplay Among Autophagy, the NLRP3 Inflammasome and Inflammation in Adipose Tissue

Obesity is a feature of metabolic syndrome with chronic inflammation in obese subjects, characterized by adipose tissue (AT) expansion, proinflammatory factor overexpression, and macrophage infiltration. Autophagy modulates inflammation in the enlargement of AT as an essential step for maintaining the balance in energy metabolism and waste elimination. Signaling originating from dysfunctional AT, such as AT containing hypertrophic adipocytes and surrounding macrophages, activates NOD-like receptor family 3 (NLRP3) inflammasome. There are interactions about altered autophagy and NLRP3 inflammasome activation during the progress in obesity. We summarize the current studies and potential mechanisms associated with autophagy and NLRP3 inflammasome in AT inflammation and aim to provide further evidence for research on obesity and obesity-related complications.

KRAS Affects Adipogenic Differentiation by Regulating Autophagy and MAPK Activation in 3T3-L1 and C2C12 Cells

Kirsten rat sarcoma 2 viral oncogene homolog (Kras) is a proto-oncogene that encodes the small GTPase transductor protein KRAS, which has previously been found to promote cytokine secretion, cell survival, and chemotaxis. However, its effects on preadipocyte differentiation and lipid accumulation are unclear. In this study, the effects of KRAS inhibition on proliferation, autophagy, and adipogenic differentiation as well as its potential mechanisms were analyzed in the 3T3-L1 and C2C12 cell lines. The results showed that KRAS was localized mainly in the nuclei of 3T3-L1 and C2C12 cells. Inhibition of KRAS altered mammalian target of rapamycin (Mtor), proliferating cell nuclear antigen (Pcna), Myc, peroxisome proliferator-activated receptor γ (PPARγ), CCAAT/enhancer binding protein beta (C/ebp-β), diacylglycerol O-acyltransferase 1 (Dgat1), and stearoyl-coenzyme A desaturase 1 (Scd1) expression, thereby reducing cell proliferation capacity while inducing autophagy, enhancing differentiation of 3T3-L1 and C2C12 cells into mature adipocytes, and increasing adipogenesis and the capacity to store lipids. Moreover, during differentiation, KRAS inhibition reduced the levels of extracellular regulated protein kinases (ERK), c-Jun N-terminal kinase (JNK), p38, and phosphatidylinositol 3 kinase (PI3K) activation. These results show that KRAS has unique regulatory effects on cell proliferation, autophagy, adipogenic differentiation, and lipid accumulation.

Honokiol attenuates lipotoxicity in hepatocytes via activating SIRT3-AMPK mediated lipophagy

Background

Non-alcoholic fatty liver disease (NAFLD) is characterized by ectopic accumulation of triglycerides in the liver. Emerging evidence has demonstrated that lipophagy regulates lipid mobilization and energy homeostasis in the liver. Sirtuin 3 (SIRT3), a mitochondrial NAD⁺-dependent deacetylase, modulates the activities of several substrates involving in autophagy and energy metabolism. Honokiol (HK) is a natural lignan from the plants of Magnolia genus that exhibits potent liver protective property.

Methods

AML12 was challenged with 500 μM palmitic acid and 250 μM oleic acid mixture solution to induce lipotoxicity. C57BL/6J mice were fed with a choline-deficient high fat diet (CDHFD) to generate liver steatosis. The expression of autophagy-related and AMP-activated protein kinase (AMPK) pathway proteins was evaluated by Western blotting and immunofluorescence staining. Intracellular lipid accumulation was validated by Nile red staining. Molecular docking analysis was performed on AutoDock 4.2.

Results

HK (5 and 10 μM) was found to attenuate lipid accumulation through promoting SIRT3-AMPK-mediated autophagy, mainly on lipid droplets. HK had hydrophobic interaction with amino acid residues (PHE294, GLU323 and VAL324) and NAD⁺. Moreover, HK improved mitochondrial function to enhance lipolysis, through decreasing the acetylated long-chain acyl-CoA dehydrogenase level. In CDHFD-fed mice, HK (2.5 and 10 mg/Kg) treatment obviously prevented lipid accumulation in the liver. And co-treatment of the AMPK inhibitor, Compound C, almost abolished the above changes.

Conclusions

These results suggest that HK could ameliorate lipotoxicity in hepatocytes by activating SIRT3-AMPK-lipophagy axis, which might be a potential therapeutic agent against NAFLD.

The Emerging Roles of Autophagy in Human Diseases

Autophagy, a process of cellular self-digestion, delivers intracellular components including superfluous and dysfunctional proteins and organelles to the lysosome for degradation and recycling and is important to maintain cellular homeostasis. In recent decades, autophagy has been found to help fight against a variety of human diseases, but, at the same time, autophagy can also promote the procession of certain pathologies, which makes the connection between autophagy and diseases complex but interesting. In this review, we summarize the advances in understanding the roles of autophagy in human diseases and the therapeutic methods targeting autophagy and discuss some of the remaining questions in this field, focusing on cancer, neurodegenerative diseases, infectious diseases and metabolic disorders.

Autophagy in major human diseases

Autophagy is a core molecular pathway for the preservation of cellular and organismal homeostasis. Pharmacological and genetic interventions impairing autophagy responses promote or aggravate disease in a plethora of experimental models. Consistently, mutations in autophagy-related processes cause severe human pathologies. Here, we review and discuss preclinical data linking autophagy dysfunction to the pathogenesis of major human disorders including cancer as well as cardiovascular, neurodegenerative, metabolic, pulmonary, renal, infectious, musculoskeletal, and ocular disorders.

Nonsteroidal mineralcorticoid receptor antagonists: Novel therapeutic implication in the management of patients with type 2 diabetes

Growing evidencehas described a correlation between aldosterone, obesity, and insulin resistance, suggesting that adipocyte-related factors and mineralocorticoid receptor (MR) overactivation may alter aldosterone secretion, potentially leading to obesity and glucose intolerance. Preclinical studies showed that pharmacological antagonism of MR prevents white adipose tissue dysfunction(s) and expansion, activates brown adipose tissue, and improves glucose tolerance. The clinical use of nonsteroidal MR antagonists has been shown to reduce the risk of diabetic kidney disease progression and cardiovascular events in patients with diabetes. This review aims to summarize the effects of pharmacological MR blockade on obesity and its associated metabolic comorbidities, with a particular focus on the therapeutic implications of nonsteroidal MR antagonists in the management of patients with diabetes.

Activation of autophagy in early neonatal mice increases primordial follicle number and improves lifelong fertility†

The number of stockpiled primordial follicles is thought to be responsible for the fate of female fertility and reproductive lifetime. We previously reported that starvation in nonsuckling early neonatal mice increases the number of primordial follicles with concomitant autophagy activation, suggesting that autophagy may accelerate the formation of primordial follicles. In this study, we attempted to upregulate the numbers of primordial follicles by administering an autophagy inducer and evaluated the progress of primordial follicle formation and their fertility during the life of the mice. To induce autophagy, mice were intraperitoneally injected with the Tat-beclin1 D-11 peptide (0.02 mg/g body weight) at 6-54 h or 60-84 h after birth. In animals that received Tat-beclin 1 D-11 by 54 h after birth, the primordial follicle numbers were significantly increased compared with the control group at 60 h. The ratio of expressed LC3-II/LC3-I proteins was also significantly greater. The numbers of littermates from pregnant females that had been treated with Tat-beclin 1 D-11 were maintained at remarkably greater levels until 10 months old. These results were supported by an abundance of primordial follicles at even 13-15 months old.