Suppression of CD36 attenuates adipogenesis with a reduction of P2X7 expression in 3T3-L1 cells

Targeting Metabolic Syndrome Pathways: Carrot microRNAs As Potential Modulators

Metabolic syndrome is a condition characterized by metabolic alterations that culminate in chronic noncommunicable diseases of high morbidity and mortality, such as cardiovascular diseases, type 2 diabetes, nonalcoholic fatty liver disease, and colon cancer. Developing new therapeutic strategies with a multifactorial approach is important since current therapies focus on only one or two components of the metabolic syndrome. In this sense, plant-based gene regulation represents an innovative strategy to prevent or modulate human metabolic pathologies, including metabolic syndrome. Here, using a computational and systems biology approach, it was found that carrot microRNAs can modulate key BMPs/SMAD signaling members, C/EBPs, and KLFs involved in several aspects associated with metabolic syndrome, including the hsa04350:TGF-beta signaling pathway, hsa04931:insulin resistance, hsa04152:AMPK signaling pathway, hsa04933:AGE-RAGE signaling pathway in diabetic complications, hsa04010:MAPK signaling pathway, hsa04350:TGF-beta signaling pathway, hsa01522:endocrine resistance, and hsa04910:insulin signaling pathway. These data demonstrated the potential applications of carrot microRNAs as effective food-based therapeutics for obesity and associated metabolic diseases.

Kindlin-2 maintains liver homeostasis by regulating GSTP1-OPN-mediated oxidative stress and inflammation in mice

Hepatocyte plays a principal role in preserving integrity of the liver homeostasis. Our recent study demonstrated that Kindlin-2, a focal adhesion protein that activates integrins and regulates cell-extracellular matrix interactions, plays an important role in regulation of liver homeostasis by inhibiting inflammation pathway; however, the molecular mechanism of how Kindlin-2 KO activates inflammation is unknown. Here, we show that Kindlin-2 loss largely downregulates the antioxidant glutathione-S-transferase P1 in hepatocytes by promoting its ubiquitination and degradation via a mechanism involving protein-protein interaction. This causes overproduction of intracellular reactive oxygen species and excessive oxidative stress in hepatocytes. Kindlin-2 loss upregulates osteopontin in hepatocytes partially because of upregulation of reactive oxygen species and consequently stimulates overproduction of inflammatory cytokines and infiltration in liver. The molecular and histological deteriorations caused by Kindlin-2 deficiency are markedly reversed by systemic administration of an antioxidant N-acetylcysteine in mice. Taken together, Kindlin-2 plays a pivotal role in preserving integrity of liver function.

Extract of Isatidis Radix Inhibits Lipid Accumulation in In Vitro and In Vivo by Regulating Oxidative Stress

Isatidis Radix (IR), the root of Isatis tinctoria L. belonging to Brassicaceae, has been traditionally used as a fever reducer. Although some pharmacological effects, such as anti-diabetes, anti-virus, and anti-inflammatory, have been reported, there is no study on the anti-obesity effect of IR. This study used 3T3-L1 cells, human mesenchymal adipose stem cells (hAMSCs), and a high-fat diet (HFD)-induced obese mouse model to confirm the anti-adipogenic effect of IR. Intracellular lipid accumulation in 3T3-L1 cells and hAMSCs was decreased by IR treatment.IR extract especially suppressed reactive oxygen species (ROS) production through a cluster of differentiation 36 (CD36)-AMP-activated protein kinase (AMPK) pathway. Consequently, the expressions of peroxisome proliferator-activated receptor gamma (PPARγ), CCAAT-enhancer-binding proteins alpha (C/EBPα), and fatty acid synthesis (FAS) were inhibited by IR extract. In addition, β-oxidation-related genes were also decreased by treatment of IR extract. IR inhibited weight gain through this cascade in the HFD-induced obese mouse model. IR significantly suppressed lipid accumulation in epididymal white adipose tissue (eWAT). Furthermore, the administration of IR extract decreased serum free fatty acid (FFA), total cholesterol (TC), and LDL cholesterol, suggesting that it could be a potential drug for obesity by inhibiting lipid accumulation.

Kindlin-2 inhibits TNF/NF-κB-Caspase 8 pathway in hepatocytes to maintain liver development and function

Inflammatory liver diseases are a major cause of morbidity and mortality worldwide; however, underlying mechanisms are incompletely understood. Here we show that deleting the focal adhesion protein Kindlin-2 expression in hepatocytes using the Alb-Cre transgenic mice causes a severe inflammation, resulting in premature death. Kindlin-2 loss accelerates hepatocyte apoptosis with subsequent compensatory cell proliferation and accumulation of the collagenous extracellular matrix, leading to massive liver fibrosis and dysfunction. Mechanistically, Kindlin-2 loss abnormally activates the tumor necrosis factor (TNF) pathway. Blocking activation of the TNF signaling pathway by deleting TNF receptor or deletion of Caspase 8 expression in hepatocytes essentially restores liver function and prevents premature death caused by Kindlin-2 loss. Finally, of translational significance, adeno-associated virus mediated overexpression of Kindlin-2 in hepatocytes attenuates the D-galactosamine and lipopolysaccharide-induced liver injury and death in mice. Collectively, we establish that Kindlin-2 acts as a novel intrinsic inhibitor of the TNF pathway to maintain liver homeostasis and may define a useful therapeutic target for liver diseases.

The purinergic signalling and inflammation in the pathogenesis and progression of diabetes: key factors and therapeutic targets

Type 2 diabetes mellitus (T2DM) is an important chronic disease around the world, and according to the World Health Organization, it is the 9th principal cause of global death. This pathology is characterized by high levels of circulating glucose as a result of insulin resistance, and it is well stated that inflammation related to obesity is directly associated with the development of the disease. The purinergic signalling is involved in both pancreatic destruction, which impairs insulin secretion, and the cytokine production that favors insulin resistance in T2DM. In this review, the purinergic signalling aspects will be discussed, showing the impact of the enzymes, nucleotides, nucleosides, and receptors of this system and the cytokines that result in inflammation, in the development and progression of T2DM, besides, pointing the purinergic receptors as a possible therapeutic approach.

P2X7 Activation Enhances Lipid Accumulation During Adipocytes Differentiation Through Suppressing the Expression of Sirtuin-3, Sirtuin-5, and Browning Genes

P2X7 signaling has been explored in adipose tissue because of its potential to promote ATP-activated inflammatory cascades during obesogenic environments. However, limited literature has investigated the role of the P2X7 receptor in lipid metabolism during adipocyte differentiation. This study sought to explore the regulatory roles of P2X7 in adipocytes. This study utilized the in vitro 3T3-L1 differentiation model. Lipid accumulation, intracellular triglyceride, and extracellular glycerol were determined. The selective P2X7 agonist BzATP and antagonist A438079 were administered to investigate the functions of P2X7. We found that the expression of P2X7 and the lipid accumulation increased during adipocyte differentiation from D0 to D4. When administered at D0/D2, A438079 attenuated, while BzATP enhanced the degree of lipid accumulation during adipocyte differentiation. Neither did BzATP and A438079 administration affect the expression of PPARγ and C/EBPα genes that increased at D4. In addition, both intracellular triglyceride and extracellular glycerol levels at D4 were reduced by A438079 treatment and enhanced by BzATP administration. When administered at stage 2 of adipocyte differentiation, BzATP consistently enhanced lipid accumulation and intracellular triglyceride and extracellular glycerol levels without affecting mRNA and protein levels of PPARγ and C/EBPα that increased at D4. However, treating A438079 or BzATP at D4 did not affect intracellular triglyceride formation and extracellular glycerol release in differentiated adipocytes at D7. Notably, BzATP administration at stage 2 exerted a concentration-dependent inhibition on the enhanced expression of PRDM16, PGC-1α, and UCP-1 at D4. Furthermore, BzATP administration at D0/D2 inhibited the protein and mRNA levels of sirtuin-3/5 at D4. BzATP treatment at stage 2 also suppressed the mRNA levels of sirtuin-3/5 genes upregulated by insulin. In conclusion, this study demonstrated P2X7 enhances lipid accumulation during adipogenesis by suppressing the expression of sirtuin-3/5 and the browning genes.

Kindlin-2 haploinsufficiency protects against fatty liver by targeting Foxo1 in mice

Nonalcoholic fatty liver disease (NAFLD) affects a large population with incompletely defined mechanism(s). Here we report that Kindlin-2 is dramatically up-regulated in livers in obese mice and patients with NAFLD. Kindlin-2 haploinsufficiency in hepatocytes ameliorates high-fat diet (HFD)-induced NAFLD and glucose intolerance without affecting energy metabolism in mice. In contrast, Kindlin-2 overexpression in liver exacerbates NAFLD and promotes lipid metabolism disorder and inflammation in hepatocytes. A C-terminal region (aa 570-680) of Kindlin-2 binds to and stabilizes Foxo1 by inhibiting its ubiquitination and degradation through the Skp2 E3 ligase. Kindlin-2 deficiency increases Foxo1 phosphorylation at Ser256, which favors its ubiquitination by Skp2. Thus, Kindllin-2 loss down-regulates Foxo1 protein in hepatocytes. Foxo1 overexpression in liver abrogates the ameliorating effect of Kindlin-2 haploinsufficiency on NAFLD in mice. Finally, AAV8-mediated shRNA knockdown of Kindlin-2 in liver alleviates NAFLD in obese mice. Collectively, we demonstrate that Kindlin-2 insufficiency protects against fatty liver by promoting Foxo1 degradation.

Here, the authors show that expression of kindlin-2 is increased in patients with nonalcoholic fatty liver disease (NAFLD). In mouse models, specific deletion of kindlin-2 in liver ameliorates, while its overexpression exacerbates, NAFLD by modulating Foxo1 in hepatocytes.

Adipocyte-specific deletion of PIP5K1c reduces diet-induced obesity and insulin resistance by increasing energy expenditure

Background

Phosphatidylinositol 4-phosphate 5-kinase type I c (PIP5K1c) catalyses the synthesis of phospholipid phosphatidylinositol 4,5-bisphosphate (PIP2) by phosphorylating phosphatidylinositol 4 phosphate, which plays multiple roles in regulating focal adhesion formation, invasion, and cell migration signal transduction cascades. Here, a new physiological mechanism of PIP5K1c in adipocytes and systemic metabolism is reported.

Methods

Adipose-specific conditional knockout mice were generated to delete the PIP5K1c gene in adipocytes. In addition, in vitro research investigated the effect of PIP5K1c deletion on adipogenesis.

Results

Deletion of PIP5K1c in adipocytes significantly alleviated high fat diet (HFD)-induced obesity, hyperlipidaemia, hepatic steatosis, and insulin resistance. PIP5K1c deficiency in adipocytes also decreased adipocyte volume in HFD-induced obese mice, whereas no significant differences were observed in body weight and adipose tissue weight under normal chow diet conditions. PIP5K1c knockout in adipocytes significantly enhanced energy expenditure, which protected mice from HFD-induced weight gain. In addition, adipogenesis was markedly impaired in mouse stromal vascular fraction (SVF) from PIP5K1c-deleted mice.

Conclusion

Under HFD conditions, PIP5K1c regulates adipogenesis and adipose tissue homeostasis. Together, these data indicate that PIP5K1c could be a novel potential target for regulating fat accumulation, which could provide novel insight into the treatment of obesity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12944-021-01616-4.

Purinergic 2X7 receptor is involved in adipogenesis and lipid degradation

Obesity and dyslipidemia are two metabolic syndrome disorders that have serious effects on the health of patients. Purinergic 2X receptor ligand-gated ion channel 7 (P2X7R) has been reported to play a role in regulating lipid storage and metabolism. However, the role and potential mechanism of P2X7R in adipogenesis and lipid degradation remain unknown. In the present study, a mouse model of obesity was established by feeding mice a high-fat diet, and the 3T3-L1 cell line was used to analyze the function of P2X7R in vitro. Reverse transcription-quantitative PCR and western blot analyses were performed to detect the expression levels of P2X7R, sterol regulatory element-binding protein 1 (SREBP1) and other associated transcription factors. Bioinformatics analysis was used to predict the potential target gene of P2X7R and a dual luciferase reporter assay was used to confirm this prediction. Oil Red O staining was used to evaluate the adipogenic capacity of preadipocytes. AdipoRed assay, cholesterol assay and a free glycerol reagent were used to measure the expression levels of triglyceride (TGs), total cholesterol (TC) and glycerin, respectively. The results indicated that P2X7R was highly expressed in obese mice and that it was involved in adipogenic differentiation in vitro. SREBP1 enhanced the transcription activities of P2X7R to promote its expression. Inhibition of P2X7R significantly reduced the adipogenic capacity of preadipocytes, decreased the expression levels of adipogenesis-associated transcription factors (peroxisome proliferator-activated receptor γ, CCAAT-enhancer-binding protein α and fatty-acid-binding protein 4), enhanced the expression levels of lipolytic enzymes (adipose triglyceride lipase, phosphorylated hormone-sensitive lipase and monoacylglycerol lipase) and regulated the expression of TG, TC and glycerin in mature 3T3-L1 cells. These effects were reversed by a small interfering RNA targeting Wnt3a. Therefore, the results suggested that P2X7R, the transcription activities of which were regulated by SREBP1, regulated adipogenesis and lipid degradation by targeting SREBP1, indicating its potential effects on obesity-associated metabolism.

Temporal correlation of morphological and biochemical changes with the recruitment of different mechanisms of reactive oxygen species formation during human SW872 cell adipogenic differentiation

Human SW872 preadipocyte conversion to mature adipocytes is associated with time-dependent changes in differentiation markers' expression and with morphological changes accompanied by the accumulation of lipid droplets (LDs) as well as by increased mitochondriogenesis and mitochondrial membrane potential. Under identical conditions, the formation of reactive oxygen species (ROS) revealed with a general probe was significant at days 3 and 10 of differentiation and bearly detectable at day 6. NADPH oxidase (NOX)-2 activity determined with an immunocytochemical approach followed a very similar pattern. There was no evidence of mitochondrial ROS (mROS), as detected with a selective fluorescence probe, at days 3 and 6, possibly due to the triggering of the Nrf-2 antioxidant response. mROS were instead clearly detected at day 10, concomitantly with the accumulation of very large LDs, oxidation of both cardiolipin and thioredoxin 2, and decreased mitochondrial glutathione. In conclusion, the morphological and biochemical changes of differentiating SW872 cells are accompanied by the discontinuous formation of ROS derived from NOX-2, increasingly implicated in adipogenesis and adipose tissue dysfunction. In addition, mROS formation was significant only in the late phase of differentiation and was associated with mitochondrial dysfunction.

Involvement of calcium channels in the regulation of adipogenesis

As an important second messenger in adipocytes, calcium ions (Ca²⁺) are essential in regulating various intracellular signalling pathways that control critical cellular functions. Calcium channels show selective permeability to Ca²⁺ and facilitate Ca²⁺ entry into the cytoplasm, which are normally located in the plasmatic and intracellular membranes. The increase of cytosolic Ca²⁺ modulates a variety of signalling pathways and results in the transcription of target genes that contribute to adipogenesis, a key cellular event includes proliferation and differentiation of adipocyte. In the past decades, the involvement of some Ca²⁺-permeable ion channels, such as Ca²⁺ release-activated Ca²⁺ channels, transient receptor potential channels, voltage-gated calcium channels and others, in adipogenesis has been extensively explored. In the present review, we provided a summary of the expression and contributions of these Ca²⁺-permeable channels in mediating Ca²⁺ influxes that drive adipogenesis. Moreover, we discussed their potentials as future therapeutic targets.

Fibroblast Heterogeneity in and Its Implications for Plastic and Reconstructive Surgery: A Basic Science Review

Fibroblasts’ integral role in tissue development, maintenance, and disease represents a fast-growing field of basic science research. Although fibroblasts were long thought to be a homogeneous cell population, recent research has illuminated the unforeseen complexity of these cells, giving rise to the rapidly expanding research field of “fibroblast heterogeneity.” Fibroblasts play a critical role in states of tissue fibrosis such as skin scarring, which affects hundreds of millions of patients annually and causes severe aesthetic, developmental, and functional morbidity. Beyond scarring, major organ fibrosis is an enormous public health concern responsible for nearly half of all deaths in the United States. Because fibrosis is a conserved response to tissue damage in all organs, the study of fibroblasts throughout the body may help us to understand their role in the conditions most relevant to plastic and reconstructive surgery—for instance, skin scarring (eg, from burns, traumatic lacerations, or surgical incisions), “pathological” scarring (hypertrophic scars, keloids), and capsular contracture. Here, we present a basic science review of fibroblast heterogeneity in wound healing, cancer, organ fibrosis, and human dermal architecture. The field of fibroblast heterogeneity is young, and many of the insights discussed have yet to be translated clinically. However, plastic surgeons stand in a unique position to bridge these discoveries into clinical realities. We hope this information can spur readers to consider both what questions in plastic surgery can be studied from the lens of fibroblast heterogeneity, and how these preclinical insights can be translated to improving care of our patients.

Obesity induces preadipocyte CD36 expression promoting inflammation via the disruption of lysosomal calcium homeostasis and lysosome function

Background

Preadipocyte is closely related to obesity-induced inflammation. The impairment of autophagic flux by defective lysosomal function has been observed in adipose tissue from obese mice. While the fatty acid translocase CD36 is an important immuno-metabolic receptor, it remains unclear whether preadipocyte CD36 is involved in adipose tissue inflammation and whether CD36 regulates lysosomal function.

Methods

Using visceral adipose tissue from obese patients, a high-fat diet (HFD)-induced obese mice model, primary mouse preadipocytes and 3T3L1 cells we analyzed whether and how preadipocyte CD36 modulates lysosomal function and adipose tissue inflammation.

Findings

CD36 expression in preadipocytes is induced in obese patients and HFD-fed mice, accompanied with the disruption of lysosome function. CD36 knockout protects primary preadipocytes of HFD-fed mice from lysosomal impairment. In vitro, CD36 interacts with Fyn to phosphorylate and activate Inositol (1,4,5)-trisphosphate receptor 1 (IP3R1), causing excess calcium transport from endoplasmic reticulum (ER) to lysosome, which results in lysosomal impairment and inflammation. Moreover, IP3R inhibitor 2-aminoethoxydiphenyl borate (2APB) attenuates lysosomal impairment, inflammation and lipid accumulation in CD36-overexpressing preadipocytes.

Interpretation

Our data support that the abnormal upregulation of CD36 in preadipocytes may contribute to the development of adipose tissue inflammation. CD36/Fyn/IP3R1-mediated lysosomal calcium overload leads to lysosomal impairment and inflammation in preadipocyte. Thus targeting improving lysosomal calcium homeostasis may represent a novel strategy for treating obesity-induced inflammation.

The Effect of Early Rounds of ex vivo Expansion and Cryopreservation on the Adipogenic Differentiation Capacity of Adipose-Derived Stromal/Stem Cells

Multipotent adipose-derived stromal/stem cells (ASCs) are candidates for use in cellular therapies for the treatment of a variety of conditions/diseases. Ex vivo expansion of freshly isolated ASCs may be necessary prior to clinical application to ensure that clinically relevant cell numbers are administered during treatment. In addition, cryopreserving cells at early passages allows for storage of freshly isolated cells for extended periods of time before expanding these cells for clinical usage. There are however several concerns that these laboratory-based procedures may alter the characteristics of the cells and in so doing decrease their regenerative potential. In this study we report on the impact of early rounds of cryopreservation (P0) and ex vivo expansion (P0 to P5) on the phenotypic characteristics and adipogenic differentiation potential of ASCs. Our results show that ASCs that upregulate CD36 expression during adipogenic differentiation gradually decrease with increasing expansion rounds. The consequent decrease in adipogenic differentiation capacity was evident in both gene expression and flow cytometry-based phenotypic studies. Successive rounds of expansion did not however alter cell surface marker expression of the cells. We also show that early cryopreservation of ASCs (at P0) does not affect the adipogenic differentiation potential of the cells.

Stimulation of P2X7 Enhances Whole Body Energy Metabolism in Mice

The P2X7 receptor, a member of the ionotropic purinergic P2X family of extracellular ATP-gated receptors, exerts strong trophic effects when tonically activated in cells, in addition to cytotoxic effects after a sustained activation. Because of its widespread distribution, P2X7 regulates several cell- and tissue-specific physiological functions, and is involved in a number of disease conditions. A novel role has recently emerged for P2X7 in the regulation of glucose and energy metabolism. In previous work, we have demonstrated that genetic depletion, and to a lesser extent also pharmacological inhibition of P2X7, elicits a significant decrease of the whole body energy expenditure and an increase of the respiratory exchange ratio. In the present work, we have investigated the effects of P2X7 stimulation in vivo on the whole body energy metabolism. Adult mice were daily injected with the specific P2X7 agonist 2′(3′)-O-(4-Benzoylbenzoyl)adenosine 5′-triphosphate for 1 week and subjected to indirect calorimetric analysis for 48 h. We report that 2′(3′)-O-(4-Benzoylbenzoyl)adenosine 5′-triphosphate increases metabolic rate and O₂ consumption, concomitantly decreasing respiratory rate and upregulating NADPH oxidase 2 in gastrocnemius and tibialis anterior muscles. Our results indicate a major impact on energy homeostasis and muscle metabolism by activation of P2X7.

Lipoatrophy and metabolic disturbance in mice with adipose-specific deletion of kindlin-2

Kindlin-2 regulates integrin-mediated cell adhesion to and migration on the extracellular matrix. Our recent studies demonstrate important roles of kindlin-2 in regulation of mesenchymal stem cell differentiation and skeletal development. In this study, we generated adipose tissue-specific conditional knockout of kindlin-2 in mice by using Adipoq-Cre BAC-transgenic mice. The results showed that deleting kindlin-2 expression in adipocytes in mice caused a severe lipodystrophy with drastically reduced adipose tissue mass. Kindlin-2 ablation elevated the blood levels of nonesterified fatty acids and triglycerides, resulting in massive fatty livers in the mutant mice fed with high-fat diet (HFD). Furthermore, HFD-fed mutant mice displayed type II diabetes-like phenotypes, including elevated levels of fasting blood glucose, glucose intolerance, and peripheral insulin resistance. Kindlin-2 loss dramatically reduced the expression levels of multiple key factors, including PPARγ, mTOR, AKT, and β-catenin proteins, and suppressed adipocyte gene expression and differentiation. Finally, kindlin-2 loss drastically reduced leptin production and caused a high bone mass phenotype. Collectively, these studies establish a critical role of kindlin-2 in control of adipogenesis and lipid metabolism as well as bone homeostasis.

Lineage Identity and Location within the Dermis Determine the Function of Papillary and Reticular Fibroblasts in Human Skin

Human skin dermis is composed of the superficial papillary dermis and the reticular dermis in the lower layers, which can easily be distinguished histologically. In vitro analyses of fibroblasts from explant cultures from superficial and lower dermal layers suggest that human skin comprises at least two fibroblast lineages with distinct morphology, expression profiles, and functions. However, while for mouse skin cell surface markers have been identified, allowing the isolation of pure populations of one lineage or the other via FACS, this has not been achieved for human skin fibroblasts. We have now discovered two cell surface markers that discriminate between papillary and reticular fibroblasts. While FAP⁺CD90^- cells display increased proliferative potential, express PDPN and NTN1, and cannot be differentiated into adipocytes, FAP^-CD90⁺ fibroblasts express high levels of ACTA2, MGP, PPARγ, and CD36 and readily undergo adipogenic differentiation, a hallmark of reticular fibroblasts. Flow cytometric analysis of fibroblasts isolated from superficial and lower layers of human dermis showed that FAP⁺CD90^- cells are enriched in the papillary dermis. Altogether, functional analysis and expression profiling confirms that FAP⁺CD90^- cells represent papillary fibroblasts, whereas FAP^-CD90⁺ fibroblasts derive from the reticular lineage. Although papillary and reticular fibroblasts are enriched in the upper or lower dermis, respectively, they are not spatially restricted, and the microenvironment seems to affect their function.