Overstimulation can create health problems due to increases in PI3K/Akt/GSK3 insensitivity and GSK3 activity

The Effects of Artificial Diets on the Expression of Molecular Marker Genes Related to Honey Bee Health

Honey bees are commonly used to study metabolic processes, yet the molecular mechanisms underlying nutrient transformation, particularly proteins and their effects on development, health, and diseases, still evoke varying opinions among researchers. To address this gap, we investigated the digestibility and transformation of water-soluble proteins from four artificial diets in long-lived honey bee populations (Apis mellifera ligustica), alongside their impact on metabolism and DWV relative expression ratio, using transcriptomic and protein quantification methods. Diet 2, characterized by its high protein content and digestibility, was selected for further analysis from the other studied diets. Subsequently, machine learning was employed to identify six diet-related molecular markers: SOD1, Trxr1, defensin2, JHAMT, TOR1, and vg. The expression levels of these markers were found to resemble those of honey bees who were fed with Diet 2 and bee bread, renowned as the best natural food. Notably, honey bees exhibiting chalkbrood symptoms (Control-N) responded differently to the diet, underscoring the unique nutritional effects on health-deficient bees. Additionally, we proposed a molecular model to elucidate the transition of long-lived honey bees from diapause to development, induced by nutrition. These findings carry implications for nutritional research and beekeeping, underscoring the vital role of honey bees in agriculture.

Alzheimer's Disease and Cancer: Common Targets

There is growing epidemiologic evidence of an inverse association between cancer and AD. In addition, both cell survival and death are regulated by the same signaling pathways, and their abnormal regulation may be implicated in the occurrence and development of cancer and AD. Research shows that there may be a common molecular mechanism between cancer and AD. This review will discuss the role of GSK3, DAPK1, PP2A, P53 and CB2R in the pathogenesis of cancer and AD and describe the current research status of drug development based on these targets.

Anti-Gene IGF-I Vaccines in Cancer Gene Therapy: A Review of a Case of Glioblastoma

OBJECTIVE

Vaccines for the deadliest brain tumor - glioblastoma (GBM) - are generally based on targeting growth factors or their receptors, often using antibodies. The vaccines described in the review were prepared to suppress the principal cancer growth factor - IGF-I, using anti-gene approaches either of antisense (AS) or of triple helix (TH) type. Our objective was to increase the median survival of patients treated with AS and TH cell vaccines.

METHODOLOGY

The cells were transfected in vitro by both constructed IGF-I AS and IGF-I TH expression episomal vectors; part of these cells was co-cultured with plant phytochemicals, modulating IGF-I expression. Both AS and TH approaches completely suppressed IGF-I expression and induced MHC-1 / B7 immunogenicity related to the IGF-I receptor signal.

RESULTS

This immunogenicity proved to be stronger in IGF-I TH than in IGF-I AS-prepared cell vaccines, especially in TH / phytochemical cells. The AS and TH vaccines generated an important TCD8+ and TCD8+CD11b- immune response in treated GBM patients and increased the median survival of patients up to 17-18 months, particularly using TH vaccines; in some cases, 2- and 3-year survival was reported. These clinical results were compared with those obtained in therapies targeting other growth factors.

CONCLUSION

The anti-gene IGF-I vaccines continue to be applied in current GBM personalized medicine. Technical improvements in the preparation of AS and TH vaccines to increase MHC-1 and B7 immunogenicity have, in parallel, allowed to increase in the median survival of patients.

A randomized controlled trial of Vitamin D supplementation in Iranian patients with schizophrenia: Effects on serum levels of glycogen synthase kinase-3β and symptom severity

BACKGROUND

Growing evidence has shown that hypovitaminosis D is a risk factor for developing schizophrenia and comorbid conditions. Therefore, this study aimed to examine the effect of vitamin D supplementation on serum levels of vitamin D, metabolic factors related to insulin resistance (IR) and the severity of the disorder in patients with schizophrenia.

METHODS

Forty-eight chronic male patients with schizophrenia with vitamin D deficiency (≤20 ng/mL= (≤50 nmol/l) were selected and randomly assigned to vitamin D treatment and placebo groups. Subjects were supplemented for 8 weeks with vitamin D (2000 IU/day) or placebo.

RESULTS

Within-group comparison revealed that the vitamin D group had a significant reduction in waist circumference, Positive and Negative Syndrome Scale - total score (PANSS-TS), and glycogen synthase kinase 3 beta (GSK-3β) levels (P = .022, P = <.001 and P = .013, respectively). On the other hand, the placebo group showed a significant increase in the level of fasting serum insulin and Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) (P = .003 and P = .003). The between-group comparison showed a significant difference in terms of PANSS-TS, GSK-3β, fasting serum insulin (FSI), and HOMA-IR (P = .022, P = .048, P = .013 and P = .014 respectively).

CONCLUSIONS

Among vitamin D deficient patients with schizophrenia, vitamin D supplementation may affect GSK-3 β, an important biomarker in schizophrenia and insulin resistance. In addition, vitamin D supplementation in such patients may reduce the disorder's symptom severity.

Association between Age-Related Macular Degeneration and the Risk of Diabetes Mellitus: A Nationwide Cohort Study

Age-related macular degeneration (AMD) is a degenerative and progressive disease of the macula, the part of the retina that is responsible for central vision. AMD shares some risk factors with diabetes mellitus (DM), but little is known about the risk of DM in individuals with AMD. With the goal of establishing novel perspectives, this study aimed to investigate the association between AMD and the risk of DM using the Korean Nationwide Health Insurance Database. Individuals aged ≥ 50 years who underwent a national health screening program in 2009 were enrolled. Participants were categorized by the presence of AMD and visual disability (VD). The Cox hazard regression model was used to examine hazard ratios (HRs) of DM with adjustment for potential confounders. Stratified analyses by age, sex, and comorbidities (hypertension or dyslipidemia) were also performed. During a mean follow-up of 8.61 years, there were 403,367 (11.76%) DM incidences among the final 3,430,532 participants. The crude HR (95% confidence interval (CI)) was 1.16 (1.13–1.20) for AMD. After adjusting for potential confounders, AMD was associated with a 3% decreased risk of DM (aHR 0.97, 95% CI 0.95–1.00), but no significant association with the risk of DM was found in AMD with VD (aHR 1.03, 95% CI 0.93–1.14). In summary, we did not find an increased risk of DM in individuals with AMD. A 3% decreased risk of DM in patients with AMD is not clinically meaningful. Our study suggests that the association between AMD and the risk of DM is weak, considering the potential confounders. Further studies examining this association are needed to extend our knowledge.

Curcumin and Wnt/β‑catenin signaling in exudative age‑related macular degeneration (Review)

Curcumin is a natural product widely used due to its pharmacological effects. Nevertheless, only a limited number of studies concerning the effects of curcumin on exudative age‑related macular degeneration (AMD) is currently available. Since ophthalmic diseases, including exudative AMD, have a marked impact on public health, the prevention and therapy of ophthalmic disorders remain of increasing concern. Exudative AMD is characterized by choroidal neovascularization (CNV) invading the subretinal space, ultimately enhancing exudation and hemorrhaging. The exudative AMD subtype corresponds to 10 to 15% of cases of macular degeneration; however, the occurrence of this subtype has been reported as the major cause of vision loss and blindness, with the occurrence of CNV being responsible for 80% of the cases with vision loss. In CNV increased expression of VEGF has been observed, stimulated by the overactivation of Wnt/β‑catenin signaling pathway. The stimulation of the Wnt/β‑catenin signaling pathway is responsible for the activation of several cellular mechanisms, simultaneously enhancing inflammation, oxidative stress and angiogenesis in numerous diseases, including ophthalmic disorders. Some studies have previously demonstrated the possible advantage of the use of curcumin for the inhibition of Wnt/β‑catenin signaling. In the present review article, the different mechanisms of curcumin are described concerning its effects on oxidative stress, inflammation and angiogenesis in exudative AMD, by interacting with Wnt/β‑catenin signaling.

Insight into glycogen synthase kinase-3β inhibitory activity of phyto-constituents from Melissa officinalis: in silico studies

Over activity of Glycogen synthase kinase-3β (GSK-3β), a serine/threonine-protein kinase has been implicated in a number of diseases including stroke, type II diabetes and Alzheimer disease (AD). This study aimed to find novel inhibitors of GSK-3β from phyto-constituents of Melissa officinalis with the aid of computational analysis. Molecular docking, induced-fit docking (IFD), calculation of binding free energy via the MM-GBSA approach and Lipinski's rule of five (RO5) were employed to filter the compounds and determine their druggability. Most importantly, the compounds pIC50 were predicted by machine learning-based model generated by AutoQSAR algorithm. The generated model was validated to affirm its predictive model. The best model obtained was Model kpls_desc_38 (R2 = 0.8467 and Q2 = 0.8069), and this external validated model was utilized to predict the bioactivities of the lead compounds. While a number of characterized compounds from Melissa officinalis showed better docking score, binding free energy alongside adherence to RO5 than co-cystallized ligand, only three compounds (salvianolic acid C, ellagic acid and naringenin) showed more satisfactory pIC50. The results obtained in this study can be useful to design potent inhibitors of GSK-3β.

Mechanisms of the Regulation and Dysregulation of Glucagon Secretion

Glucagon, a hormone secreted by pancreatic alpha cells, contributes to the maintenance of normal blood glucose concentration by inducing hepatic glucose production in response to declining blood glucose. However, glucagon hypersecretion contributes to the pathogenesis of type 2 diabetes. Moreover, diabetes is associated with relative glucagon undersecretion at low blood glucose and oversecretion at normal and high blood glucose. The mechanisms of such alpha cell dysfunctions are not well understood. This article reviews the genesis of alpha cell dysfunctions during the pathogenesis of type 2 diabetes and after the onset of type 1 and type 2 diabetes. It unravels a signaling pathway that contributes to glucose- or hydrogen peroxide-induced glucagon secretion, whose overstimulation contributes to glucagon dysregulation, partly through oxidative stress and reduced ATP synthesis. The signaling pathway involves phosphatidylinositol-3-kinase, protein kinase B, protein kinase C delta, non-receptor tyrosine kinase Src, and phospholipase C gamma-1. This knowledge will be useful in the design of new antidiabetic agents or regimens.

Genetic determinants of obesity heterogeneity in type II diabetes

Background

Although obesity is considered as the main cause of Type II diabetes (T2DM), non-obese individuals may still develop T2DM and obese individuals may not.

Method

The mRNA expression of PI3K/AKT axis from 100 non-obese and obese participants with insulin sensitivity and insulin resistance states were compared in this study toward the understanding of obesity heterogeneity molecular mechanism.

Result

In present study, there was no statistically significant difference in gene expression levels of IRS1 and PTEN between groups, whereas PI3K, AKT2 and GLUT4 genes were expressed at a lower level in obese diabetic group compared to other groups and were statistically significant. PDK1 gene was expressed at a higher level in non-obese diabetic group compared to obese diabetic and non-obese non-diabetics groups. No statistically significant difference was identified in gene expression pattern of PI3K/AKT pathway between obese non-diabetics and non-obese non-diabetics.

Conclusion

The components of PI3K/AKT pathway which is related to the fasting state, showed reduced expression in obese diabetic group due to the chronic over-nutrition which may induced insensitivity and reduced gene expression. The pathogenesis of insulin resistance in the absence of obesity in non-obese diabetic group could be due to disturbance in another pathway related to the non-fasting state like gluconeogenesis. Therefore, the molecular mechanism of insulin signalling in non-obese diabetic individuals is different from obese diabetics which more investigations are required to study insulin signalling pathways in greater depth, in order to assess nutritional factors, contribute to insulin resistance in obese diabetic and non-obese diabetic individuals.

Circadian Rhythms in Exudative Age-Related Macular Degeneration: The Key Role of the Canonical WNT/β-Catenin Pathway

Age-related macular degeneration (AMD) is considered as the main worldwide cause of blindness in elderly adults. Exudative AMD type represents 10 to 15% of macular degeneration cases, but is the main cause of vision loss and blindness. Circadian rhythm changes are associated with aging and could further accelerate it. However, the link between circadian rhythms and exudative AMD is not fully understood. Some evidence suggests that dysregulation of circadian functions could be manifestations of diseases or could be risk factors for the development of disease in elderly adults. Biological rhythms are complex systems interacting with the environment and control several physiological pathways. Recent findings have shown that the dysregulation of circadian rhythms is correlated with exudative AMD. One of the main pathways involved in exudative AMD is the canonical WNT/β-catenin pathway. Circadian clocks have a main role in some tissues by driving the circadian expression of genes involved in physiological and metabolic functions. In exudative AMD, the increase of the canonical WNT/β-catenin pathway is enhanced by the dysregulation of circadian rhythms. Exudative AMD progression is associated with major metabolic reprogramming, initiated by aberrant WNT/β-catenin pathway, of aerobic glycolysis. This review focuses on the interest of circadian rhythm dysregulation in exudative AMD through the aberrant upregulation of the canonical WNT/β-catenin pathway.

The PI3K subunits, P110α and P110β are potential targets for overcoming P-gp and BCRP-mediated MDR in cancer

BACKGROUND

PI3K/AKT is a vital signaling pathway in humans. Recently, several PI3K/AKT inhibitors were reported to have the ability to reverse cancer multidrug resistance (MDR); however, specific targets in the PI3K/AKT pathways and the mechanisms associated with MDR have not been found because many of the inhibitors have multiple targets within a large candidate protein pool. AKT activation is one presumed mechanism by which MDR develops during cancer treatment.

METHODS

The effects of inhibiting PI3K 110α and 110β by BAY-1082439 treatment and CRISPR/Cas9 knockout were examined to determine the possible functions of BAY-1082439 and the roles of PI3K 110α and 110β in the reversal of MDR that is mediated by the downregulation of P-gp and BCRP. Inhibition of AKT with GSK-2110183 showed that the downregulation of P-gp and BCRP is independent of generalized AKT inactivation. Immunofluorescence, immunoprecipitation, MTT, flow cytometry and JC-1 staining analyses were conducted to study the reversal of MDR that is mediated by P-gp and BCRP in cancer cells. An ATPase assay and a structural analysis were also used to analyze the potential mechanisms by which BAY-1082439 specifically targets PI3K 110α and 110β and nonspecifically influences P-gp and BCRP.

RESULTS

By inhibiting the activation of the PI3K 110α and 110β catalytic subunits through both the administration of BAY-1082439 and the CRISPR/Cas9 deletion of Pik3ca and Pik3cb, the ATP-binding cassette transporters P-gp/ABCB1 and BCRP/ABCG2 were downregulated, thereby reestablishing the drug sensitivity of human epidermoid carcinoma and non-small cell lung cancer (NSCLC) MDR cells. Inhibition of AKT did not reverse the MDR mediated by P-gp or BCRP. The ABC family proteins and AKT may play MDR-enhancing roles independently.

CONCLUSIONS

The reversal of the dual functions of ABC-transporter-mediated and AKT-activation-enhanced MDR through the inhibition or knockout of PI3K 110α or 110β promises to improve current strategies based on combined drug treatments to overcome MDR challenges.

Targeting IL-17 attenuates hypoxia-induced pulmonary hypertension through downregulation of β-catenin

BACKGROUND

The role of interleukin 17 (IL-17) in hypoxic pulmonary hypertension (HPH) remains unclear. This study is designed to explore whether IL-17 is a potential target for HPH treatment.

METHODS

Clinic samples from the lung tissue and serum were obtained from qualified patients. Western blotting, immunohistochemistry and/or ELISA were used to measure the expression of relevant proteins. HPH models were established in C57BL/6 wild-type (WT) and IL-17 ^-/- mice and were treated with exogenous recombinant mouse IL-17 (rmIL-17) or an IL-17 neutralising antibody. Assays for cell proliferation, angiogenesis and adhesion were employed to analyse the behaviours of human pulmonary arterial endothelial cells (HPAECs). A non-contact Transwell coculture model was used to evaluate intercellular interactions.

RESULTS

Expression of IL-17 was increased in lung tissue of both patients with bronchiectasis/COPD-associated PH and HPH mouse model. Compared with WT mice, IL-17 ^-/- mice had attenuated HPH, whereas administration of rmIL-17 aggravated HPH. In vitro, recombinant human IL-17 (rhIL-17) promoted proliferation, angiogenesis and adhesion in HPAECs through upregulation of Wnt3a/β-catenin/CyclinD1 pathway, and siRNA-mediated knockdown of β-catenin almost completely reversed this IL-17-mediated phenomena. IL-17 promoted the proliferation but not the migration of human pulmonary arterial smooth muscle cells (HPASMCs) cocultured with HPAECs under both normoxia and hypoxia, but IL-17 had no direct effect on proliferation and migration of HPASMCs. Blockade of IL-17 with a neutralising antibody attenuated HPH in WT mice.

CONCLUSIONS

IL-17 contributes to the pathogenesis of HPH through upregulation of β-catenin expression. Targeting IL-17 might provide potential benefits for alternative therapeutic strategies for HPH.

PPARγ agonists: Potential treatments for exudative age-related macular degeneration

Choroidal neovascularization (CNV) characterizes the progression of exudative age-related macular degeneration (AMD) with the deterioration in the central vision. Vascular inflammation, and overproduction of inflammatory cytokines, growth factors and aberrant endothelial cell migration, initiate defective blood vessel proliferation in exudative AMD. CNV formation is initiated by the interplay between inflammation, the hallmark of exudative AMD, and the activation of WNT/β-catenin pathway. Upregulation of WNT/β-catenin pathway involves activation of PI3K/Akt pathway and then the Warburg effect to produce lactate. Lactate production generates VEGF expression and then participates to the initiation of CNV in exudative AMD. WNT/β-catenin pathway and PPARγ act in an opposite manner in several diseases. We focus this review on the interplay between PPARγ and canonical WNT/β-catenin pathway and the anti-inflammatory role of PPARγ in exudative AMD. In exudative AMD, PPARγ agonists downregulate inflammation and the WNT/β-catenin pathway. PPARγ agonists can appear as promising treatment against the initiation and the progression of CNV in exudative AMD.

Aerobic Glycolysis Hypothesis Through WNT/Beta-Catenin Pathway in Exudative Age-Related Macular Degeneration

Exudative age-related macular degeneration (AMD) is characterized by molecular mechanisms responsible for the initiation of choroidal neovascularization (CNV). Inflammatory processes are associated with upregulation of the canonical WNT/beta-catenin pathway in exudative AMD. We focus this review on the link between WNT/beta-catenin pathway activation and neovascular progression in exudative AMD through activation of aerobic glycolysis for production of angiogenic factors. Increased WNT/beta-catenin pathway involves hexokinase 2 (HK2) and pyruvate kinase M2 (PKM2). WNT/beta-catenin pathway stimulates PI3K/Akt pathway and then HIF-1alpha which activates glycolytic enzymes: glucose transporter (Glut), pyruvate dehydrogenase kinase 1 (PDK1), lactate dehydrogenase A (LDH-A), and monocarboxylate lactate transporter (MCT-1). This phenomenon is called aerobic glycolysis or the Warburg effect. Consequently, phosphorylation of PDK-1 inhibits the pyruvate dehydrogenase complex (PDH). Thus, a large part of pyruvate cannot be converted into acetyl-CoA in mitochondria and only a part of acetyl-CoA can enter the tricarboxylic acid cycle. Cytosolic pyruvate is converted into lactate through the action of LDH-A. In exudative AMD, high level of cytosolic lactate is correlated with increase of VEGF expression, the angiogenic factor of CNV. Photoreceptors in retina cells can metabolize glucose through aerobic glycolysis to protect them against oxidative damage, as cancer cells do.

Insensitivity of PI3K/Akt/GSK3 signaling in peripheral blood mononuclear cells of age-related macular degeneration patients

Our recent studies with cultured retinal pigment epithelium cells suggested that overexpression of interleukin 17 receptor C (IL-17RC), a phenomenon observed in peripheral blood and chorioretinal tissues with age-related macular degeneration (AMD), was associated with altered activation of phosphatidylinositide 3-kinase (PI3K), Akt, and glycogen synthase kinase 3 (GSK3). We wondered whether or not altered PI3K, Akt, and GSK3 activities could be detected in peripheral blood mononuclear cells (PBMC) obtained from AMD patients. In the patients' PBMC, absent or reduced serine-phosphorylation of GSK3α or GSK3β was observed, which was accompanied with increased phosphorylation of GSK3 substrates (e.g. CCAAT enhancer binding protein α, insulin receptor substrate 1, and TAU), indicative of enhanced GSK3 activation. In addition, decreased protein mass of PI3K85α and tyrosine-phosphorylation of PI3K50α was present in PBMC of the AMD patients, suggesting impaired PI3K activation. Moreover, abnormally lowered molecular weight forms of Akt and GSK3 were detected in PBMC of the AMD patients. These data demonstrate that despite the presence of high levels of IL-17RC, Wnt-3a and vascular endothelial growth factor, the PI3K/Akt/GSK3 signaling pathway is insensitive to these stimuli in PBMC of the AMD patients. Thus, measurement of PI3K/Akt/GSK3 expression and activity in PBMC may serve as a surrogate biomarker for AMD.

Chronic over-nutrition and dysregulation of GSK3 in diseases

Loss of cellular response to hormonal regulation in maintaining metabolic homeostasis is common in the process of aging. Chronic over-nutrition may render cells insensitive to such a hormonal regulation owing to overstimulation of certain signaling pathways, thus accelerating aging and causing diseases. The glycogen synthase kinase 3 (GSK3) plays a pivotal role in relaying various extracellular and intracellular regulatory signals critical to cell growth, survival, regeneration, or death. The main signaling pathway regulating GSK3 activity through serine-phosphorylation is the phosphoinositide 3-kinase (PI3K)/phosphoinositide-dependent kinase-1 (PDK1)/Akt relay that catalyzes serine-phosphorylation and thus inactivation of GSK3. In addition, perilipin 2 (PLIN2) has recently been shown to regulate GSK3 activation through direct association with GSK3. This review summarizes current understanding on environmental and nutritional factors contributing to GSK3 regulation (or dysregulation) through the PI3K/PDK1/Akt/GSK3 axis, and highlights the newly discovered role that PLIN2 plays in regulating GSK3 activity and GSK3 downstream pathways.

Fluorescence-based gene reporter plasmid to track canonical Wnt signaling in ENS inflammation

In several gut inflammatory or cancer diseases, cell-cell interactions are compromised, and an increased cytoplasmic expression of β-catenin is observed. Over the last decade, numerous studies provided compelling experimental evidence that the loss of cadherin-mediated cell adhesion can promote β-catenin release and signaling without any specific activation of the canonical Wnt pathway. In the present work, we took advantage of the ability of lipofectamine-like reagent to cause a synchronous dissociation of adherent junctions in cells isolated from the rat enteric nervous system (ENS) for obtaining an in vitro model of deregulated β-catenin signaling. Under these experimental conditions, a green fluorescent protein Wnt reporter plasmid called ΔTop_EGFP3a was successfully tested to screen β-catenin stabilization at resting and primed conditions with exogenous Wnt3a or lipopolysaccharide (LPS). ΔTop_EGFP3a provided a reliable and strong fluorescent signal that was easily measurable and at the same time highly sensitive to modulations of Wnt signaling following Wnt3a and LPS stimulation. The reporter gene was useful to demonstrate that Wnt3a exerts a protective activity in the ENS from overstimulated Wnt signaling by promoting a downregulation of the total β-catenin level. Based on this evidence, the use of ΔTop_EGFP3a reporter plasmid could represent a more reliable tool for the investigation of Wnt and cross-talking pathways in ENS inflammation.

The Succinate Receptor GPR91 Is Involved in Pressure Overload-Induced Ventricular Hypertrophy

Background

Pulmonary arterial hypertension is characterized by increased pressure overload that leads to right ventricular hypertrophy (RVH). GPR91 is a formerly orphan G-protein-coupled receptor (GPCR) that has been characterized as a receptor for succinate; however, its role in RVH remains unknown.

Methods and Results

We investigated the role of succinate-GPR91 signaling in a pulmonary arterial banding (PAB) model of RVH induced by pressure overload in SD rats. GPR91 was shown to be located in cardiomyocytes. In the sham and PAB rats, succinate treatment further aggravated RVH, up-regulated RVH-associated genes and increased p-Akt/t-Akt levels in vivo. In vitro, succinate treatment up-regulated the levels of the hypertrophic gene marker anp and p-Akt/t-Akt in cardiomyocytes. All these effects were inhibited by the PI3K antagonist wortmannin both in vivo and in vitro. Finally, we noted that the GPR91-PI3K/Akt axis was also up-regulated compared to that in human RVH.

Conclusions

Our findings indicate that succinate-GPR91 signaling may be involved in RVH via PI3K/Akt signaling in vivo and in vitro. Therefore, GPR91 may be a novel therapeutic target for treating pressure overload-induced RVH.

Natural Functions of PLIN2 Mediating Wnt/LiCl Signaling and Glycogen Synthase Kinase 3 (GSK3)/GSK3 Substrate-Related Effects Are Modulated by Lipid

Belonging to the PLIN family, PLIN2 associates with lipid storage droplets (LSDs), but other functions of PLIN2 remain unclear. Here, we suggest that PLIN2 mediates Wnt signaling because PLIN2 small interfering RNA (siRNA) suppresses activation of Wnt/coreceptor pathways. The mediation in the Wnt/Frizzled pathway seems to occur from Dishevelleds to axin/glycogen synthase kinase 3(GSK3)/β-catenin complexes (AGβC) as Wnt decreases Dishevelled/PLIN2 but increases AGβC/PLIN2 associations. Augmenting cellular LSDs that affect PLIN2 associations with these proteins, oleic acid (OA) treatment inhibits Wnt-increased AGβC/PLIN2 associations and β-catenin T-cell factor signaling (β-CTS). Revealing that PLIN2 is a GSK3-associated protein, the study explored PLIN2-mediated effects on GSK3/GSK3 substrates. PLIN2 siRNA reduces inhibitory GSK3 levels and lithium chloride (LiCl)-upregulated β-catenin or CCAAT/enhancer binding protein α (c/EBPα) expression. OA treatment decreases LiCl-increased c/EBPα via PLIN2-c/EBPα dissociation. In addition to PLIN2 overexpression increasing β-CTS, PLIN2 depletion or overexpression drops or adds expression of GSK3 substrates, such as β-catenin, c/EBPα,c-Myc, cyclin D1, and insulin receptor substrate 1, and cell growth/survival. PLIN2 N or C terminus overexpression that is associated with higher levels of the substrates suggests that those substrates bind to specific regions of PLIN2. Mimicking the possible high lipid concentrations in cells in the human body under conditions of hyperlipidemia/obesity, OA-treated cells gain or reduce GSK3 substrate expression in parallel with a decrease (a Wnt-like effect) or increase in GSK3 activity, likely regulated by GSK3/PLIN2/GSK3 substrate associations.