GPR21 Inhibition Increases Glucose-Uptake in HepG2 Cells

Mitochondria targeted esculetin administration improves insulin resistance and hyperglycemia-induced atherosclerosis in db/db mice

The development and progression of hyperglycemia (HG) and HG-associated atherosclerosis are exacerbated by mitochondrial dysfunction due to dysregulated mitochondria-derived ROS generation. We recently synthesized a novel mitochondria-targeted esculetin (Mito-Esc) and tested its dose-response therapeutic efficacy in mitigating HG-induced atherosclerosis in db/db mice. In comparison to simvastatin and pioglitazone, Mito-Esc administration resulted in a considerable reduction in body weights and improved glucose homeostasis, possibly by reducing hepatic gluconeogenesis, as indicated by a reduction in glycogen content, non-esterified free fatty acids (NEFA) levels, and fructose 1,6-bisphosphatase (FBPase) activity. Interestingly, Mito-Esc treatment, by regulating phospho-IRS and phospho-AKT levels, greatly improved palmitate-induced insulin resistance, resulting in enhanced glucose uptake in adipocytes and HepG2 cells. Also, and importantly, Mito-Esc administration prevented HG-induced atheromatous plaque formation and lipid accumulation in the descending aorta. In addition, Mito-Esc administration inhibited the HG-mediated increase in VACM, ICAM, and MAC3 levels in the aortic tissue, as well as reduced the serum pro-inflammatory cytokines and markers of senescence. In line with this, Mito-Esc significantly inhibited monocyte adherence to human aortic endothelial cells (HAECs) treated with high glucose and reduced high glucose-induced premature senescence in HAECs by activating the AMPK-SIRT1 pathway. In contrast, Mito-Esc failed to regulate high glucose-induced endothelial cell senescence under AMPK/SIRT1-depleted conditions. Together, the therapeutic efficacy of Mito-Esc in the mitigation of hyperglycemia-induced insulin resistance and the associated atherosclerosis is in part mediated by potentiating the AMPK-SIRT1 axis. KEY MESSAGES: Mito-Esc administration significantly mitigates diabetes-induced atherosclerosis. Mito-Esc improves hyperglycemia (HG)-associated insulin resistance. Mito-Esc inhibits HG-induced vascular senescence and inflammation in the aorta. Mito-Esc-mediated activation of the AMPK-SIRT1 axis regulates HG-induced endothelial cell senescence.

MicroRNA-721 regulates gluconeogenesis via KDM2A-mediated epigenetic modulation in diet-induced insulin resistance in C57BL/6J mice

BACKGROUND

Aberrant gluconeogenesis is considered among primary drivers of hyperglycemia under insulin resistant conditions, with multiple studies pointing towards epigenetic dysregulation. Here we examine the role of miR-721 and effect of epigenetic modulator laccaic acid on the regulation of gluconeogenesis under high fat diet induced insulin resistance.

RESULTS

Reanalysis of miRNA profiling data of high-fat diet-induced insulin-resistant mice model, GEO dataset (GSE94799) revealed a significant upregulation of miR-721, which was further validated in invivo insulin resistance in mice and invitro insulin resistance in Hepa 1-6 cells. Interestingly, miR-721 mimic increased glucose production in Hepa 1-6 cells via activation of FOXO1 regulated gluconeogenic program. Concomitantly, inhibition of miR-721 reduced glucose production in palmitate induced insulin resistant Hepa 1-6 cells by blunting the FOXO1 induced gluconeogenesis. Intriguingly, at epigenetic level, enrichment of the transcriptional activation mark H3K36me2 got decreased around the FOXO1 promoter. Additionally, identifying targets of miR-721 using miRDB.org showed H3K36me2 demethylase KDM2A as a potential target. Notably, miR-721 inhibitor enhanced KDM2A expression which correlated with H3K36me2 enrichment around FOXO1 promoter and the downstream activation of the gluconeogenic pathway. Furthermore, inhibition of miR-721 in high-fat diet-induced insulin-resistant mice resulted in restoration of KDM2A levels, concomitantly reducing FOXO1, PCK1, and G6PC expression, attenuating gluconeogenesis, hyperglycemia, and improving glucose tolerance. Interestingly, the epigenetic modulator laccaic acid also reduced the hepatic miR-721 expression and improved KDM2A expression, supporting our earlier report that laccaic acid attenuates insulin resistance by reducing gluconeogenesis.

CONCLUSION

Our study unveils the role of miR-721 in regulating gluconeogenesis through KDM2A and FOXO1 under insulin resistance, pointing towards significant clinical and therapeutic implications for metabolic disorders. Moreover, the promising impact of laccaic acid highlights its potential as a valuable intervention in managing insulin resistance-associated metabolic diseases.

Thapsigargin and Tunicamycin Block SARS-CoV-2 Entry into Host Cells via Differential Modulation of Unfolded Protein Response (UPR), AKT Signaling, and Apoptosis

BACKGROUND

SARS-Co-V2 infection can induce ER stress-associated activation of unfolded protein response (UPR) in host cells, which may contribute to the pathogenesis of COVID-19. To understand the complex interplay between SARS-Co-V2 infection and UPR signaling, we examined the effects of acute pre-existing ER stress on SARS-Co-V2 infectivity.

METHODS

Huh-7 cells were treated with Tunicamycin (TUN) and Thapsigargin (THA) prior to SARS-CoV-2pp transduction (48 h p.i.) to induce ER stress. Pseudo-typed particles (SARS-CoV-2pp) entry into host cells was measured by Bright GloTM luciferase assay. Cell viability was assessed by cell titer Glo® luminescent assay. The mRNA and protein expression was evaluated by RT-qPCR and Western Blot.

RESULTS

TUN (5 µg/mL) and THA (1 µM) efficiently inhibited the entry of SARS-CoV-2pp into host cells without any cytotoxic effect. TUN and THA's attenuation of virus entry was associated with differential modulation of ACE2 expression. Both TUN and THA significantly reduced the expression of stress-inducible ER chaperone GRP78/BiP in transduced cells. In contrast, the IRE1-XBP1s and PERK-eIF2α-ATF4-CHOP signaling pathways were downregulated with THA treatment, but not TUN in transduced cells. Insulin-mediated glucose uptake and phosphorylation of Ser307 IRS-1 and downstream p-AKT were enhanced with THA in transduced cells. Furthermore, TUN and THA differentially affected lipid metabolism and apoptotic signaling pathways.

CONCLUSIONS

These findings suggest that short-term pre-existing ER stress prior to virus infection induces a specific UPR response in host cells capable of counteracting stress-inducible elements signaling, thereby depriving SARS-Co-V2 of essential components for entry and replication. Pharmacological manipulation of ER stress in host cells might provide new therapeutic strategies to alleviate SARS-CoV-2 infection.

HM-chromanone isolated from Portulaca oleracea L. alleviates insulin resistance and inhibits gluconeogenesis by regulating palmitate-induced activation of ROS/JNK in HepG2 cells

Oxidative stress is a major cause of hepatic insulin resistance. This study investigated whether (E)-5-hydroxy-7-methoxy-3-(2-hydroxybenzyl)-4-chromanone (HM-chromanone), a homoisoflavonoid compound isolated from Portulaca oleracea L., alleviates insulin resistance and inhibits gluconeogenesis by reducing palmitate (PA)-induced reactive oxygen species (ROS)/c-Jun NH2-terminal kinase (JNK) activation in HepG2 cells. PA treatment (0.5 mM) for 16 h resulted in the highest production of ROS and induced insulin resistance in HepG2 cells. HM-chromanone, like N-acetyl-1-cysteine, significantly decreased PA-induced ROS production in the cells. HM-chromanone also significantly inhibited PA-induced JNK activation, showing a significant reduction in tumor necrosis factor and interleukin expression levels. Thus, HM-chromanone decreased the phosphorylation of Ser307 in insulin receptor substrate 1, while increasing phosphorylation of serine-threonine kinase (AKT), thereby restoring the insulin signaling pathway impaired by PA. HM-chromanone also significantly increased the phosphorylation of forkhead box protein O, thereby inhibiting the expression of gluconeogenic enzymes and reducing glucose production in PA-treated HepG2 cells. HM-chromanone also increased glycogen synthesis by phosphorylating glycogen synthase kinase-3β. Therefore, HM-chromanone may alleviate insulin resistance and inhibit gluconeogenesis by regulating PA-induced ROS/JNK activation in HepG2 cells.