Autophagy regulates inflammation following oxidative injury in diabetes

T1D (type 1 diabetes) is an autoimmune disease characterized by lymphocytic infiltration, or inflammation in pancreatic islets called ‘insulitis.’ Comparatively speaking, T2D (type 2 diabetes) is traditionally characterized by insulin resistance and islet β cell dysfunction; however, a number of studies have clearly demonstrated that chronic tissue inflammation is a key contributing factor to T2D. The NLR (Nod-like receptor) family of innate immune cell sensors such as the NLRP3 inflammasome are implicated in leading to CASP1 activation and subsequent IL1B (interleukin 1, β) and IL18 secretion in T2D. Recent developments reveal a crucial role for the autophagy pathway under conditions of oxidative stress and inflammation. Increasingly, research on autophagy has begun to focus on its role in interacting with inflammatory processes, and thereby how it potentially affects the outcome of disease progression. In this review, we explore the pathophysiological pathways associated with oxidative stress and inflammation in T2D. We also explore how autophagy influences glucose homeostasis by modulating the inflammatory response. We will provide here a perspective on the current research between autophagy, inflammation and T2D.     

Autophagy gene ATG7 regulates ultraviolet radiation-induced inflammation and skin tumorigenesis

Macroautophagy (hereafter autophagy) is a cellular “self-eating” process that is implicated in many human cancers, where it can act to either promote or suppress tumorigenesis. However, the role of autophagy in regulation of inflammation during tumorigenesis remains unclear. Here we show that autophagy is induced in the epidermis by ultraviolet (UV) irradiation and autophagy gene Atg7 promoted UV-induced inflammation and skin tumorigenesis. Atg7 regulated UV-induced cytokine expression and secretion, and promoted Ptgs2/Cox-2 expression through both a CREB1/CREB-dependent cell autonomous mechanism and an IL1B/IL1β-dependent non-cell autonomous mechanism. Adding PGE₂ increased UV-induced skin inflammation and tumorigenesis, reversing the epidermal phenotype in mice with Atg7 deletion in keratinocytes. Similar to ATG7 knockdown in human keratinocytes, ATG5 knockdown inhibited UVB-induced expression of PTGS2 and cytokines. Furthermore, ATG7 loss increased the activation of the AMPK pathway and the phosphorylation of CRTC1, and led to endoplasmic reticulum (ER) accumulation and reduction of ER stress. Inducing ER stress and inhibiting calcium influx into the ER by thapsigargin reverses the inflammation and tumorigenesis phenotype in mice with epidermal Atg7 deletion. Taken together, these findings demonstrate that deleting autophagy gene Atg7 leads to a suppression of carcinogen-induced protumorigenic inflammatory microenvironment and tumorigenesis of the epithelium.     

The density of extracellular matrix proteins regulates inflammation and insulin signaling in adipocytes

Cells can not only sense the type of extracellular matrix (ECM) protein that is present in the microenvironment, but they can also sense its density. Here, we investigated the effects of ECM protein density on adipokine secretion and insulin signaling in adipocytes. To this end, 3T3-L1 adipocytes were cultured on the surface of polyacrylamide gels that were coated with gradient densities of a collagen type I and fibronectin mixture. We found that high density ECM causes a decrease in insulin signaling and adiponectin secretion, whereas the secretion of monocyte chemoattractant protein-1 (MCP-1) was increased via the activation of nuclear factor-κB (NF-κB). These results indicate that the density of the ECM directly regulates the inflammatory response and insulin sensitivity of adipocytes.

Structured summary

MINT-7992217: Irs1 (uniprotkb:P35569) physically interacts (MI:0915) with phosphatidylinositol 3-kinase 85 kDa regulatory subunit alpha (uniprotkb:P26450) by anti bait coimmunoprecipitation (MI:0006)     

Autophagy and kidney inflammation

Inflammation plays a pivotal role in pathophysiological processes of kidney diseases. Macroautophagy/autophagy plays multiple roles in inflammatory responses, and the regulation of inflammation by autophagy has great potential as a treatment for damaged kidneys. A growing body of evidence suggests autophagy protects kidney from versatile kidney inflammatory insults, including those that are acute, chronic, metabolic, and aging-related. It is noteworthy that, in kidney, mitophagy is active, and damaged lysosomes are removed by autophagy. In this mode, autophagy suppresses inflammation to protect the kidney. Systemic inflammation also affects the kidney via pro-inflammatory cytokines and infiltration of inflammatory cells, and autophagy also has a regulatory role in systemic inflammation. This review focuses on the roles of autophagy in kidney diseases and aging through inflammation, and discusses the potential usage of autophagy as an inflammatory modulator for the treatment of kidney diseases.     

Autophagy balances inflammation in innate immunity

Macroautophagy/autophagy is a homeostatic process with multiple effects on immunity. One of the pivotal contributions of autophagy in immunity is the cell autonomous control of inflammation. This property leads to systemic consequences and thereby influences the development of innate and adaptive immunity, which promotes or suppresses pathology in various disease contexts. In this review we focus on the intersections between autophagy and inflammasome activation, autophagy and interferons, and autophagy and inflammation in association with infection.     

Autophagy regulates sphingolipid levels in the liver

Sphingolipid levels are tightly regulated to maintain cellular homeostasis. During pathologic conditions such as in aging, inflammation, and metabolic and neurodegenerative diseases, levels of some sphingolipids, including the bioactive metabolite ceramide, are elevated. Sphingolipid metabolism has been linked to autophagy, a critical catabolic process in both normal cell function and disease; however, the in vivo relevance of the interaction is not well-understood. Here, we show that blocking autophagy in the liver by deletion of the Atg7 gene, which is essential for autophagosome formation, causes an increase in sphingolipid metabolites including ceramide. We also show that overexpression of serine palmitoyltransferase to elevate de novo sphingolipid biosynthesis induces autophagy in the liver. The results reveal autophagy as a process that limits excessive ceramide levels and that is induced by excessive elevation of de novo sphingolipid synthesis in the liver. Dysfunctional autophagy may be an underlying mechanism causing elevations in ceramide that may contribute to pathogenesis in diseases.     

Autophagy regulates ageing in C. elegans

The role of autophagy in ageing regulation has been suggested based on studies in C. elegans, in which knockdown of the expression of bec-1 (ortholog of the yeast and mammalian autophagy genes ATG6/VPS30 and beclin 1, respectively) shortens lifespan of the daf-2(e1370) mutant C. elegans. However, Beclin1/ATG6 is also known to be involved in other cellular functions in addition to autophagy. In the current study, we knocked down two other autophagy genes, atg-7 and atg-12, in C. elegans using RNAi. We showed that RNAi shortened the lifespan of both wild type and daf-2 mutant C. elegans, providing strong support for a role of autophagy in ageing regulation.     

Autophagy and inflammation in chronic respiratory disease

Persistent inflammation within the respiratory tract underlies the pathogenesis of numerous chronic pulmonary diseases including chronic obstructive pulmonary disease, asthma and pulmonary fibrosis. Chronic inflammation in the lung may arise from a combination of genetic susceptibility and environmental influences, including exposure to microbes, particles from the atmosphere, irritants, pollutants, allergens, and toxic molecules. To this end, an immediate, strong, and highly regulated inflammatory defense mechanism is needed for the successful maintenance of homeostasis within the respiratory system. Macroautophagy/autophagy plays an essential role in the inflammatory response of the lung to infection and stress. At baseline, autophagy may be critical for inhibiting spontaneous pulmonary inflammation and fundamental for the response of pulmonary leukocytes to infection; however, when not regulated, persistent or inefficient autophagy may be detrimental to lung epithelial cells, promoting lung injury. This perspective will discuss the role of autophagy in driving and regulating inflammatory responses of the lung in chronic lung diseases with a focus on potential avenues for therapeutic targeting.

Abbreviations AR allergic rhinitis

AM alveolar macrophage

ATG autophagy-related

CF cystic fibrosis

CFTR cystic fibrosis transmembrane conductance regulator

COPD chronic obstructive pulmonary disease

CS cigarette smoke

CSE cigarette smoke extract

DC dendritic cell

IH intermittent hypoxia

IPF idiopathic pulmonary fibrosis

ILD interstitial lung disease

MAP1LC3B microtubule associated protein 1 light chain 3 beta

MTB Mycobacterium tuberculosis

MTOR mechanistic target of rapamycin kinase

NET neutrophil extracellular traps

OSA obstructive sleep apnea

PAH pulmonary arterial hypertension

PH pulmonary hypertension

ROS reactive oxygen species

TGFB1 transforming growth factor beta 1

TNF tumor necrosis factor

     

Autophagy regulates endoplasmic reticulum stress in ischemic preconditioning

Recent studies have suggested that autophagy plays a prosurvival role in ischemic preconditioning (IPC). This study was taken to assess the linkage between autophagy and endoplasmic reticulum (ER) stress during the process of IPC. The effects of IPC on ER stress and neuronal injury were determined by exposure of primary cultured murine cortical neurons to 30 min of OGD 24 h prior to a subsequent lethal OGD. The effects of IPC on ER stress and ischemic brain damage were evaluated in rats by a brief ischemic insult followed by permanent focal ischemia (PFI) 24 h later using the suture occlusion technique. The results showed that both IPC and lethal OGD increased the LC3-II expression and decreased p62 protein levels, but the extent of autophagy activation was varied. IPC treatment ameliorated OGD-induced cell damage in cultured cortical neurons, whereas 3-MA (5-20 mM) and bafilomycin A 1 (75-150 nM) suppressed the neuroprotection induced by IPC. 3-MA, at the dose blocking autophagy, significantly inhibited IPC-induced HSP70, HSP60 and GRP78 upregulation; meanwhile, it also aggregated the ER stress and increased activated caspase-12, caspase-3 and CHOP protein levels both in vitro and in vivo models. The ER stress inhibitor Sal (75 pmol) recovered IPC-induced neuroprotection in the presence of 3-MA. Rapamycin 50-200 nM in vitro and 35 pmol in vivo 24 h before the onset of lethal ischemia reduced ER stress and ischemia-induced neuronal damage. These results demonstrated that pre-activation of autophagy by ischemic preconditioning can boost endogenous defense mechanisms to upregulate molecular chaperones, and hence reduce excessive ER stress during fatal ischemia.     

Autophagy regulates endoplasmic reticulum stress in ischemic preconditioning

Recent studies have suggested that autophagy plays a prosurvival role in ischemic preconditioning (IPC). This study was taken to assess the linkage between autophagy and endoplasmic reticulum (ER) stress during the process of IPC. The effects of IPC on ER stress and neuronal injury were determined by exposure of primary cultured murine cortical neurons to 30 min of OGD 24 h prior to a subsequent lethal OGD. The effects of IPC on ER stress and ischemic brain damage were evaluated in rats by a brief ischemic insult followed by permanent focal ischemia (PFI) 24 h later using the suture occlusion technique. The results showed that both IPC and lethal OGD increased the LC3-II expression and decreased p62 protein levels, but the extent of autophagy activation was varied. IPC treatment ameliorated OGD-induced cell damage in cultured cortical neurons, whereas 3-MA (5–20 mM) and bafilomycin A₁ (75–150 nM) suppressed the neuroprotection induced by IPC. 3-MA, at the dose blocking autophagy, significantly inhibited IPC-induced HSP70, HSP60 and GRP78 upregulation; meanwhile, it also aggregated the ER stress and increased activated caspase-12, caspase-3 and CHOP protein levels both in vitro and in vivo models. The ER stress inhibitor Sal (75 pmol) recovered IPC-induced neuroprotection in the presence of 3-MA. Rapamycin 50–200 nM in vitro and 35 pmol in vivo 24 h before the onset of lethal ischemia reduced ER stress and ischemia-induced neuronal damage. These results demonstrated that pre-activation of autophagy by ischemic preconditioning can boost endogenous defense mechanisms to upregulate molecular chaperones, and hence reduce excessive ER stress during fatal ischemia.     

Autophagy: cellular defense to excessive inflammation

Autophagy can orchestrate a variety of cellular responses to dangerous stimuli. Our understanding of the physiologic roles of autophagy has recently expanded; in addition to its other roles, autophagy now appears to play an essential role in regulating inflammatory responses. This review describes recent findings concerning the roles and mechanisms of autophagy in controlling excessive inflammation.     

Rosiglitazone regulates IL-6-stimulated lipolysis in porcine adipocytes

Interleukin (IL)-6, a proinflammatory cytokine, stimulates adipocyte lipolysis and induces insulin resistance in obese and diabetic subjects. However, the effects of the anti-diabetic drug rosiglitazone on IL-6-stimulated lipolysis and the underlying molecular mechanism are largely unknown. In this study, we demonstrated that rosiglitazone suppressed IL-6-stimulated lipolysis in differentiated porcine adipocytes by inactivation of extracellular signal-related kinase (ERK). Meanwhile, rosiglitazone enhanced the lipolysis response of adipocytes to isoprenaline. In addition, rosiglitazone significantly reversed IL-6-induced down-regulation of several genes such as perilipin A, peroxisome proliferators activated receptor gamma (PPARγ), and fatty acid synthetase, as well as the up-regulation of IL-6 mRNA. However, mRNA expression of PPARγ coactivator-1 alpha (PCG-1α) was enhanced by rosiglitazone in IL-6-stimulated adipocytes. These results indicate that rosiglitazone suppresses IL-6-stimulated lipolysis in porcine adipocytes through multiple molecular mechanisms.     

Autophagy in the intestinal epithelium regulates Citrobacter rodentium infection

Autophagy, a ubiquitous degradation pathway, is important for the survival and homeostasis of cells. Previous studies have demonstrated the role of autophagy in host defense against bacterial infection, but the importance of autophagy in the intestinal epithelium for the regulation of bacterial infection has not been fully elucidated. In this study, we showed that the essential autophagy protein Atg7 is required for resistance to Citrobacter rodentium infection in the intestinal epithelium. Infected mice in which Atg7 had been conditionally deleted from the intestinal epithelium exhibited greater clinical evidence of disease and higher expression levels of pro-inflammatory cytokine mRNA in the large intestine. Moreover, C. rodentium clearance was reduced in the Atg7 conditional knockout mice. These results demonstrate that autophagy in intestinal epithelial cells plays an important role in host defense against C. rodentium infection and the regulation of C. rodentium infectious colitis.     

Hypoxia regulates macrophage functions in inflammation

The presence of areas of hypoxia is a prominent feature of various inflamed, diseased tissues, including malignant tumors, atherosclerotic plaques, myocardial infarcts, the synovia of joints with rheumatoid arthritis, healing wounds, and sites of bacterial infection. These areas form when the blood supply is occluded and/or unable to keep pace with the growth and/or infiltration of inflammatory cells in a given area. Macrophages are present in all tissues of the body where they normally assist in guarding against invading pathogens and regulate normal cell turnover and tissue remodeling. However, they are also known to accumulate in large numbers in such ischemic/hypoxic sites. Recent studies show that macrophages then respond rapidly to the hypoxia present by altering their expression of a wide array of genes. In the present study, we outline and compare the phenotypic responses of macrophages to hypoxia in different diseased states and the implications of these for their progression and treatment.     

Autophagy triggered by magnolol derivative negatively regulates angiogenesis

Angiogenesis has a key role in the tumor progression and metastasis; targeting endothelial cell proliferation has emerged as a promising therapeutic strategy for the prevention of cancer. Previous studies have revealed a complex association between the process of angiogenesis and autophagy and its outcome on tumorigenesis. Autophagy, also known as type-II cell death, has been identified as an alternative way of cell killing in apoptotic-resistant cancer cells. However, its involvement in chemoresistance and tumor promotion is also well known. In this study, we used a derivate of natural product magnolol (Ery5), a potent autophagy inducer, to study the association between the autophagy and angiogenesis in both in vitro and in vivo model system. We found that the robust autophagy triggered by Ery5, inhibited angiogenesis and caused cell death independent of the apoptosis in human umbilical cord vein endothelial cells and PC-3 cells. Ery5 induced autophagy effectively inhibited cell proliferation, migration, invasion and tube formation. We further demonstrated that Ery5-mediated autophagy and subsequent inhibition of angiogenesis was reversed when autophagy was inhibited through 3-methyl adenine and knocking down of key autophagy proteins ATG7 and microtubule-associated protein light chain 3. While evaluating the negative regulation of autophagy on angiogenesis, it was interesting to find that angiogenic environment produced by the treatment of VEGF and CoCl2 remarkably downregulated the autophagy and autophagic cell death induced by Ery5. These studies, while disclosing the vital role of autophagy in the regulation of angiogenesis, also suggest that the potent modulators of autophagy can lead to the development of effective therapeutics in apoptosis-resistant cancer.     

Autophagy regulates apoptosis by targeting NOXA for degradation

Apoptosis and autophagy mutually regulate various cellular physiological and pathological processes. The crosstalk between autophagy and apoptosis is multifaceted and complicated. Elucidating the molecular mechanism of their crosstalk will advance the therapeutic applications of autophagy for treating cancer and other diseases. NOXA, a BH3-only member of the BCL-2 family, was reported to induce apoptosis and promote autophagy. Here, we report that autophagy regulates apoptosis by targeting NOXA for degradation. Inhibiting autophagy increases NOXA protein levels by extending the protein half-life. NOXA accumulation effectively suppresses tumor cell growth by inducing apoptosis, which is further enhanced when p53 is present. Mechanistically, NOXA is hijacked by p62 as autophagic cargo, and its three lysine residues at the C-terminus are necessary for NOXA degradation in lysosomes. Taken together, our study demonstrates that NOXA serves as a bridge in the crosstalk between autophagy and apoptosis and implies that autophagy inhibitors could be an effective therapy for cancer, especially wild-type p53-containing cancer.