Clinically confirmed DEL-1 as a myokine attenuates lipid-induced inflammation and insulin resistance in 3T3-L1 adipocytes via AMPK/HO-1- pathway

AMPK pathway: an emerging target to control diabetes mellitus and its related complications

Purpose

In this extensive review work, the important role of AMP-activated protein kinase (AMPK) in causing of diabetes mellitus has been highlighted. Structural feature of AMPK as well its regulations and roles are described nicely, and the association of AMPK with the diabetic complications like nephropathy, neuropathy and retinopathy are also explained along with the connection between AMPK and β-cell function, insulin resistivity, mTOR, protein metabolism, autophagy and mitophagy and effect on protein and lipid metabolism.

Methods

Published journals were searched on the database like PubMed, Medline, Scopus and Web of Science by using keywords such as AMPK, diabetes mellitus, regulation of AMPK, complications of diabetes mellitus, autophagy, apoptosis etc.

Result

After extensive review, it has been found that, kinase enzyme like AMPK is having vital role in management of type II diabetes mellitus. AMPK involve in enhance the concentration of glucose transporter like GLUT 1 and GLUT 4 which result in lowering of blood glucose level in influx of blood glucose into the cells; AMPK increases the insulin sensitivity and decreases the insulin resistance and further AMPK decreases the apoptosis of β-cells which result into secretion of insulin and AMPK is also involve in declining of oxidative stress, lipotoxicity and inflammation, owing to which organ damage due to diabetes mellitus can be lowered by activation of AMPK.

Conclusion

As AMPK activation leads to overall control of diabetes mellitus, designing and developing of small molecules or peptide that can act as AMPK agonist will be highly beneficial for control or manage diabetes mellitus.

Musclin Mitigates the Attachment of HUVECs to THP-1 Monocytes in Hyperlipidemic Conditions through PPARα/HO-1-Mediated Attenuation of Inflammation

Musclin, a myokine, undergoes modulation during exercise and has demonstrated anti-inflammatory effects in cardiomyocytes and glomeruli. However, its role in atherosclerotic responses remains unclear. This study aimed to explore the impact of musclin on inflammatory responses and the interaction between endothelial cells and monocytes under hyperlipidemic conditions. The attachment levels of THP-1 monocytes on cultured HUVECs were examined. Inflammation and the expression of cell adhesion molecules were also evaluated. To explore the molecular mechanisms of musclin, PPARα or heme oxygenase 1 (HO-1) siRNA transfection was performed in HUVECs. The results revealed that treatment with recombinant musclin effectively suppressed the attachment of palmitate-induced HUVECs to THP-1 cells and reduced the expression of cell adhesion proteins (ICAM-1, VCAM-1, and E-selectin) in HUVECs. Furthermore, musclin treatment ameliorated the expression of inflammation markers (phosphorylated NFκB and IκB) in both HUVECs and THP-1 monocytes, as well as the release of TNFα and MCP-1 from HUVECs and THP-1 monocytes. Notably, musclin treatment augmented the expression levels of PPARα and HO-1. However, when PPARα or HO-1 siRNA was employed, the beneficial effects of musclin on inflammation, cell attachment, and adhesion molecule expression were abolished. These findings indicate that musclin exerts anti-inflammatory effects via the PPARα/HO-1 pathway, thereby mitigating the interaction between endothelial cells and monocytes. This study provides evidence supporting the important role of musclin in ameliorating obesity-related arteriosclerosis and highlights its potential as a therapeutic agent for treating arteriosclerosis.

DEL-1: a promising treatment for AMD-associated ER stress in retinal pigment epithelial cells

BACKGROUND

Age-related macular degeneration (AMD) is an irreversible eye disease that can cause blurred vision. Regular exercise has been suggested as a therapeutic strategy for treating AMD, but how exercise improves AMD is not yet understood. This study investigated the protective effects of developmental endothelial locus-1 (DEL-1), a myokine upregulated during exercise, on endoplasmic reticulum (ER) stress-induced injury in retinal pigment epithelial cells.

METHODS

We evaluated the levels of AMPK phosphorylation, autophagy markers, and ER stress markers in DEL-1-treated human retinal pigment epithelial cells (hRPE) using Western blotting. We also performed cell viability, caspase 3 activity assays, and autophagosome staining.

RESULTS

Our findings showed that treatment with recombinant DEL-1 dose-dependently reduced the impairment of cell viability and caspase 3 activity in tunicamycin-treated hRPE cells. DEL-1 treatment also alleviated tunicamycin-induced ER stress markers and VEGF expression. Moreover, AMPK phosphorylation and autophagy markers were increased in hRPE cells in the presence of DEL-1. However, the effects of DEL-1 on ER stress, VEGF expression, and apoptosis in tunicamycin-treated hRPE cells were reduced by AMPK siRNA or 3-methyladenine (3-MA), an autophagy inhibitor.

CONCLUSIONS

Our study suggests that DEL-1, a myokine, may have potential as a treatment strategy for AMD by attenuating ER stress-induced injury in retinal pigment epithelial cells.

Cytokines and exosomal miRNAs in skeletal muscle-adipose crosstalk

Skeletal muscle and adipose tissues (ATs) are secretory organs that release secretory factors including cytokines and exosomes. These factors mediate muscle-adipose crosstalk to regulate systemic metabolism via paracrine and endocrine pathways. Myokines and adipokines are cytokines secreted by skeletal muscle and ATs, respectively. Exosomes loaded with nucleic acids, proteins, lipid droplets, and organelles can fuse with the cytoplasm of target cells to perform regulatory functions. A major regulatory component of exosomes is miRNA. In addition, numerous novel myokines and adipokines have been identified through technological innovations. These discoveries have identified new biomarkers and sparked new insights into the molecular regulation of skeletal muscle growth and adipose deposition. The knowledge may contribute to potential diagnostic and therapeutic targets in metabolic disease.

Del1 Is a Growth Factor for Skeletal Progenitor Cells in the Fracture Callus

Failure to properly form bone or integrate surgical implants can lead to morbidity and additional surgical interventions in a significant proportion of orthopedic surgeries. While the role of skeletal stem cells (SSCs) in bone formation and repair is well-established, very little is known about the factors that regulate the downstream Bone, Cartilage, Stromal, Progenitors (BCSPs). BCSPs, as transit amplifying progenitor cells, undergo multiple mitotic divisions to expand the pool of lineage committed progenitors allowing stem cells to preserve their self-renewal and stemness. Del1 is a protein widely expressed in the skeletal system, but its deletion led to minimal phenotype changes in the uninjured mouse. In this paper, we demonstrate that Del1 is a key regulator of BCSP expansion following injury. In Del1 knockout mice, there is a significant reduction in the number of BCSPs which leads to a smaller callus and decreased bone formation compared with wildtype (WT) littermates. Del1 serves to promote BCSP proliferation and prevent apoptosis in vivo and in vitro. Moreover, exogenous Del1 promotes proliferation of aged human BCSPs. Our results highlight the potential of Del1 as a therapeutic target for improving bone formation and implant success. Del1 injections may improve the success of orthopedic surgeries and fracture healing by enhancing the proliferation and survival of BCSPs, which are crucial for generating new bone tissue during the process of bone formation and repair.

Efferocytosis: An Emerging Therapeutic Strategy for Type 2 Diabetes Mellitus and Diabetes Complications

Increasing evidence indicates that chronic, low-grade inflammation is a significant contributor to the fundamental pathogenesis of type 2 diabetes mellitus (T2DM). Efferocytosis, an effective way to eliminate apoptotic cells (ACs), plays a critical role in inflammation resolution. Massive accumulation of ACs and the proliferation of persistent inflammation caused by defective efferocytosis have been proven to be closely associated with pancreatic islet β cell destruction, adipose tissue inflammation, skeletal muscle dysfunction, and liver metabolism abnormalities, which together are considered the most fundamental pathological mechanism underlying T2DM. Therefore, here we outline the association between the molecular mechanisms of efferocytosis in glucose homeostasis, T2DM, and its complications, and we analyzed the present constraints and potential future prospects for therapeutic targets in T2DM and its complications.

Experimental Approaches to Diabetes Mellitus

One of the most common health problems today, diabetes is a serious, chronic, and complex disease characterized by high blood glucose levels. Nowadays, experimental diabetes models are being developed to study existing diabetes in depth, to improve diabetes medications, or to develop new medications. The protocols developed to date to create an experimental diabetes model are finalized in different time intervals and depending on various factors. With these models, which can be designed in vivo and in vitro, a picture similar to type 1 and type 2 diabetes can be created. In this review, we aimed to present the methodology, advantages, and disadvantages of all currently used experimental diabetes models in the light of current literature.

Developmental endothelial locus-1 attenuates palmitate-induced apoptosis in tenocytes through the AMPK/autophagy-mediated suppression of inflammation and endoplasmic reticulum stress

AIMS

Myokine developmental endothelial locus-1 (DEL-1) has been documented to alleviate inflammation and endoplasmic reticulum (ER) stress in various cell types. However, the effects of DEL-1 on inflammation, ER stress, and apoptosis in tenocytes remain unclear.

METHODS

Human primary tenocytes were cultured in palmitate (400 μM) and palmitate plus DEL-1 (0 to 2 μg/ml) conditions for 24 hours. The expression levels of ER stress markers and cleaved caspase 3, as well as phosphorylated 5' adenosine monophosphate-activated protein kinase (AMPK) and autophagy markers, were assessed by Western blotting. Autophagosome formation was measured by staining with monodansylcadaverine, and apoptosis was determined by cell viability assay and caspase 3 activity assay.

RESULTS

We found that treatment with DEL-1 suppressed palmitate-induced inflammation, ER stress, and apoptosis in human primary tenocytes. DEL-1 treatment augmented LC3 conversion and p62 degradation as well as AMPK phosphorylation. Moreover, small interfering RNA for AMPK or 3-methyladenine (3-MA), an autophagy inhibitor, abolished the suppressive effects of DEL-1 on inflammation, ER stress, and apoptosis in tenocytes. Similar to DEL-1, 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR), an activator of AMPK, also attenuated palmitate-induced inflammation, ER stress, and apoptosis in tenocytes, which 3-MA reversed.

CONCLUSION

These results revealed that DEL-1 suppresses inflammation and ER stress, thereby attenuating tenocyte apoptosis through AMPK/autophagy-mediated signalling. Thus, regular exercise or administration of DEL-1 may directly contribute to improving tendinitis exacerbated by obesity and insulin resistance.Cite this article: Bone Joint Res 2022;11(12):854-861.

Developmental endothelial locus-1 in cardiovascular and metabolic diseases: A promising biomarker and therapeutic target

Cardiovascular and metabolic diseases (CVMDs) are a leading cause of death worldwide and impose a major socioeconomic burden on individuals and healthcare systems, underscoring the urgent need to develop new drug therapies. Developmental endothelial locus-1 (DEL-1) is a secreted multifunctional domain protein that can bind to integrins and play an important role in the occurrence and development of various diseases. Recently, DEL-1 has attracted increased interest for its pharmacological role in the treatment and/or management of CVMDs. In this review, we present the current knowledge on the predictive and therapeutic role of DEL-1 in a variety of CVMDs, such as atherosclerosis, hypertension, cardiac remodeling, ischemic heart disease, obesity, and insulin resistance. Collectively, DEL-1 is a promising biomarker and therapeutic target for CVMDs.

Stachydrine alleviates lipid-induced skeletal muscle insulin resistance via AMPK/HO-1-mediated suppression of inflammation and endoplasmic reticulum stress

OBJECTIVE

Insulin resistance develops due to skeletal muscle inflammation and endoplasmic reticulum (ER) stress. Stachydrine (STA), extracted from Leonurus heterophyllus, has been shown to suppress proliferation and induce apoptosis in breast cancer cells and exert anti-inflammatory properties in the brain, heart, and liver. However, the roles of STA in insulin signaling in skeletal muscle remain unclear. Herein, we examined the impacts of STA on insulin signaling in skeletal muscle under hyperlipidemic conditions and its related molecular mechanisms.

METHODS

Various protein expression levels were determined by Western blotting. Levels of mouse serum cytokines were measured by ELISA.

RESULTS

We found that STA-ameliorated inflammation and ER stress, leading to attenuation of insulin resistance in palmitate-treated C2C12 myocytes. STA dose-dependently enhanced AMPK phosphorylation and HO-1 expression. Administration of STA attenuated not only insulin resistance but also inflammation and ER stress in the skeletal muscle of high-fat diet (HFD)-fed mice. Additionally, STA-ameliorated glucose tolerance and insulin sensitivity, as well as serum TNFα and MCP-1, in mice fed a HFD. Small interfering (si) RNA-associated suppression of AMPK or HO-1 expression abolished the effects of STA in C2C12 myocytes.

CONCLUSIONS

These results suggest that STA activates AMPK/HO-1 signaling, resulting in reduced inflammation and ER stress, thereby improving skeletal muscle insulin resistance. Using STA as a natural ingredient, this research successfully treated insulin resistance and type 2 diabetes.

The regulation of efferocytosis signaling pathways and adipose tissue homeostasis in physiological conditions and obesity: Current understanding and treatment options

Obesity is associated with changes in the resolution of acute inflammation that contribute to the clinical complications. The exact mechanisms underlying unresolved inflammation in obesity are not fully understood. Adipocyte death leads to pro-inflammatory adipose tissue macrophages, stimulating additional adipocyte apoptosis. Thus, a complex and tightly regulated process to inhibit inflammation and maintain homeostasis after adipocyte apoptosis is needed to maintain health. In normal condition, a specialized phagocytic process (efferocytosis) performs this function, clearing necrotic and apoptotic cells (ACs) and controlling inflammation. For efficient and continued efferocytosis, phagocytes must internalize multiple ACs in physiological conditions and handle the excess metabolic burden in adipose tissue. In obesity, this control is lost and can be an important hallmark of the disease. In this regard, the deficiency of efferocytosis leads to delayed resolution of acute inflammation and can result in ongoing inflammation, immune system dysfunction, and insulin resistance in obesity. Hence, efficient clearance of ACs by M2 macrophages could limit long-term inflammation and ensue clinical complications, such as cardiovascular disease and diabetes. This review elaborates upon the molecular mechanisms to identify efferocytosis regulators in obesity, and the mechanisms that can improve efferocytosis and reduce obesity-related complications, such as the use of pharmacological agents and regular exercise.

Effect of diabetes on efferocytosis process

Diabetes is a complex of genetic, metabolic, and autoimmune disorders that are characterized by hyperglycemia. Elevated apoptotic cell count following defective clearance of dead cells that can cause chronic inflammation is a hallmark of the diabetic wound. Effective dead cell clearance is a prerequisite for rapid inflammation resolution and successful recovery. Efferocytosis is a multistep process in which phagocytes engulf the dead cells. Cell body elimination is of great significance in disease and homeostasis. Recent research has clarified that diabetic wounds have an enhanced load of the apoptotic cell, which is partly attributed to the dysfunction of macrophages in apoptotic clearance at the site of the diabetic wounds. In the current work, we highlight the pathways implicated in efferocytosis, from the diagnosis of apoptotic cells to the phagocytic swallowing and the homeostatic resolution, and explain the possible pathophysiological episodes occurring when the proceeding is abrogated. Also, we describe the last development in the management of inflammation in diabetes wound and future directions of surveillance.

AMPK signaling in diabetes mellitus, insulin resistance and diabetic complications: A pre-clinical and clinical investigation

Diabetes mellitus (DM) is considered as a main challenge in both developing and developed countries, as lifestyle has changed and its management seems to be vital. Type I and type II diabetes are the main kinds and they result in hyperglycemia in patients and related complications. The gene expression alteration can lead to development of DM and related complications. The AMP-activated protein kinase (AMPK) is an energy sensor with aberrant expression in various diseases including cancer, cardiovascular diseases and DM. The present review focuses on understanding AMPK role in DM. Inducing AMPK signaling promotes glucose in DM that is of importance for ameliorating hyperglycemia. Further investigation reveals the role of AMPK signaling in enhancing insulin sensitivity for treatment of diabetic patients. Furthermore, AMPK upregulation inhibits stress and cell death in β cells that is of importance for preventing type I diabetes development. The clinical studies on diabetic patients have shown the role of AMPK signaling in improving diabetic complications such as brain disorders. Furthermore, AMPK can improve neuropathy, nephropathy, liver diseases and reproductive alterations occurring during DM. For exerting such protective impacts, AMPK signaling interacts with other molecular pathways such as PGC-1α, PI3K/Akt, NOX4 and NF-κB among others. Therefore, providing therapeutics based on AMPK targeting can be beneficial for amelioration of DM.

Adipokines, Hepatokines and Myokines: Focus on Their Role and Molecular Mechanisms in Adipose Tissue Inflammation

Chronic low-grade inflammation in adipose tissue (AT) is a hallmark of obesity and contributes to various metabolic disorders, such as type 2 diabetes and cardiovascular diseases. Inflammation in ATs is characterized by macrophage infiltration and the activation of inflammatory pathways mediated by NF-κB, JNK, and NLRP3 inflammasomes. Adipokines, hepatokines and myokines - proteins secreted from AT, the liver and skeletal muscle play regulatory roles in AT inflammation via endocrine, paracrine, and autocrine pathways. For example, obesity is associated with elevated levels of pro-inflammatory adipokines (e.g., leptin, resistin, chemerin, progranulin, RBP4, WISP1, FABP4, PAI-1, Follistatin-like1, MCP-1, SPARC, SPARCL1, and SAA) and reduced levels of anti-inflammatory adipokines such as adiponectin, omentin, ZAG, SFRP5, CTRP3, vaspin, and IL-10. Moreover, some hepatokines (Fetuin A, DPP4, FGF21, GDF15, and MANF) and myokines (irisin, IL-6, and DEL-1) also play pro- or anti-inflammatory roles in AT inflammation. This review aims to provide an updated understanding of these organokines and their role in AT inflammation and related metabolic abnormalities. It serves to highlight the molecular mechanisms underlying the effects of these organokines and their clinical significance. Insights into the roles and mechanisms of these organokines could provide novel and potential therapeutic targets for obesity-induced inflammation.

Patchouli alcohol improves wound healing in high fat diet-fed mice through AMPK-mediated suppression of inflammation and TGFb1 signaling

Obesity impairs wound healing with substantial alterations in skin inflammation. Patchouli alcohol (PA), extracted from patchouli, has been reported to ameliorate inflammation in various cell types. However, the effects of PA on inflammation and wound healing have not been reported to date. In the present study, we examined whether PA affects cutaneous wound healing in high fat diet (HFD)-fed mice and explored PA-mediated molecular mechanisms through in vitro experiments. We found that PA administration accelerated wound healing as well as ameliorates inflammation in skin of HFD-fed mice. PA treatment augmented AMP-activated protein kinase (AMPK) phosphorylation and TGFb1 expression. PA enhanced cell migration and suppressed inflammation in LPS-treated HaCaT cells. Further, PA increased dose-dependently AMPK phosphorylation as along with TGFb1 and cell migration markers expression. siRNA for AMPK or TGFb1 abrogated the effects of PA on cell migration and inflammation. TGFb1 siRNA mitigated PA-induced expression of cell migration markers. These results suggest that PA ameliorates wound healing via AMPK and TGFb1-mediated suppression of inflammation. In sum, PA can be used as a novel treatment strategy for wound healing in obesity or insulin resistance.

Role of HO-1 against Saturated Fatty Acid-Induced Oxidative Stress in Hepatocytes

Increased circulating levels of free fatty acids, especially saturated ones, are involved in disease progression in the non-alcoholic fatty liver. Although the mechanism of saturated fatty acid-induced toxicity in the liver is not fully understood, oxidative stress may be deeply involved. We examined the effect of increased palmitic acid, the most common saturated fatty acid in the blood, on the liver of BALB/c mice via tail vein injection with palmitate. After 24 h, among several anti-oxidative stress response genes, only heme oxygenase-1 (HO-1) was significantly upregulated in palmitate-injected mice compared with that in vehicle-injected mice. Elevation of HO-1 mRNA was also observed in the fatty liver of high-fat-diet-fed mice. To further investigate the role of HO-1 on palmitic acid-induced oxidative stress, in vitro experiments were performed to expose palmitate to HepG2 cells. SiRNA-mediated knockdown of HO-1 significantly increased the oxidative stress induced by palmitate, whereas pre-treatment with SnCl₂, a well-known HO-1 inducer, significantly decreased it. Moreover, SB203580, a selective p38 inhibitor, reduced HO-1 mRNA expression and increased palmitate-induced oxidative stress in HepG2 cells. These results suggest that the HO-1-mediated anti-oxidative stress compensatory reaction plays an essential role against saturated fatty acid-induced lipotoxicity in the liver.

Mitochondria at Work: New Insights into Regulation and Dysregulation of Cellular Energy Supply and Metabolism

Mitochondria are of great relevance to health, and their dysregulation is associated with major chronic diseases. Research on mitochondria-156 brand new publications from 2019 and 2020-have contributed to this review. Mitochondria have been fundamental for the evolution of complex organisms. As important and semi-autonomous organelles in cells, they can adapt their function to the needs of the respective organ. They can program their function to energy supply (e.g., to keep heart muscle cells going, life-long) or to metabolism (e.g., to support hepatocytes and liver function). The capacity of mitochondria to re-program between different options is important for all cell types that are capable of changing between a resting state and cell proliferation, such as stem cells and immune cells. Major chronic diseases are characterized by mitochondrial dysregulation. This will be exemplified by cardiovascular diseases, metabolic syndrome, neurodegenerative diseases, immune system disorders, and cancer. New strategies for intervention in chronic diseases will be presented. The tumor microenvironment can be considered a battlefield between cancer and immune defense, competing for energy supply and metabolism. Cancer cachexia is considered as a final stage of cancer progression. Nevertheless, the review will present an example of complete remission of cachexia via immune cell transfer. These findings should encourage studies along the lines of mitochondria, energy supply, and metabolism.