FoxO1 integrates direct and indirect effects of insulin on hepatic glucose production and glucose utilization

Ribosomal modification protein rimK-like family member A activates betaine-homocysteine S-methyltransferase 1 to ameliorate hepatic steatosis

Nonalcoholic fatty liver disease (NAFLD) is a serious threat to public health, but its underlying mechanism remains poorly understood. In screening important genes using Gene Importance Calculator (GIC) we developed previously, ribosomal modification protein rimK-like family member A (RIMKLA) was predicted as one essential gene but its functions remained largely unknown. The current study determined the roles of RIMKLA in regulating glucose and lipid metabolism. RIMKLA expression was reduced in livers of human and mouse with NAFLD. Hepatic RIMKLA overexpression ameliorated steatosis and hyperglycemia in obese mice. Hepatocyte-specific RIMKLA knockout aggravated high-fat diet (HFD)-induced dysregulated glucose/lipid metabolism in mice. Mechanistically, RIMKLA is a new protein kinase that phosphorylates betaine-homocysteine S-methyltransferase 1 (BHMT1) at threonine 45 (Thr45) site. Upon phosphorylation at Thr45 and activation, BHMT1 eliminated homocysteine (Hcy) to inhibit the activity of transcription factor activator protein 1 (AP1) and its induction on fatty acid synthase (FASn) and cluster of differentiation 36 (CD36) gene transcriptions, concurrently repressing lipid synthesis and uptake in hepatocytes. Thr45 to alanine (T45A) mutation inactivated BHMT1 to abolish RIMKLA's repression on Hcy level, AP1 activity, FASn/CD36 expressions, and lipid deposition. BHMT1 overexpression rescued the dysregulated lipid metabolism in RIMKLA-deficient hepatocytes. In summary, RIMKLA is a novel protein kinase that phosphorylates BHMT1 at Thr45 to repress lipid synthesis and uptake. Under obese condition, inhibition of RIMKLA impairs BHMT1 activity to promote hepatic lipid deposition.

Forkhead box protein FOXK1 disrupts the circadian rhythm to promote breast tumorigenesis in response to insulin resistance

The dysregulation of circadian rhythm oscillation is a prominent feature of various solid tumors. Thus, clarifying the molecular mechanisms that maintain the circadian clock is important. In the present study, we revealed that the transcription factor forkhead box FOXK1 functions as an oncogene in breast cancer. We showed that FOXK1 recruits multiple transcription corepressor complexes, including NCoR/SMRT, SIN3A, NuRD, and REST/CoREST. Among them, the FOXK1/NCoR/SIN3A complex transcriptionally regulates a cohort of genes, including CLOCK, PER2, and CRY2, that are critically involved in the circadian rhythm. The complex promoted the proliferation of breast cancer cells by disturbing the circadian rhythm oscillation. Notably, the nuclear expression of FOXK1 was positively correlated with tumor grade. Insulin resistance gradually became more severe with tumor progression and was accompanied by the increased expression of OGT, which caused the nuclear translocation and increased expression of FOXK1. Additionally, we found that metformin downregulates FOXK1 and exports it from the nucleus, while HDAC inhibitors (HDACi) inhibit the FOXK1-related enzymatic activity. Combined treatment enhanced the expression of circadian clock genes through the regulation of FOXK1, thereby exerting an antitumor effect, indicating that highly nuclear FOXK1-expressing breast cancers are potential candidates for the combined application of metformin and HDACi.

Deficiency of ASGR1 Alleviates Diet-Induced Systemic Insulin Resistance via Improved Hepatic Insulin Sensitivity

BACKGRUOUND

Insulin resistance (IR) is the key pathological basis of many metabolic disorders. Lack of asialoglycoprotein receptor 1 (ASGR1) decreased the serum lipid levels and reduced the risk of coronary artery disease. However, whether ASGR1 also participates in the regulatory network of insulin sensitivity and glucose metabolism remains unknown.

METHODS

The constructed ASGR1 knockout mice and ASGR1-/- HepG2 cell lines were used to establish the animal model of metabolic syndrome and the IR cell model by high-fat diet (HFD) or drug induction, respectively. Then we evaluated the glucose metabolism and insulin signaling in vivo and in vitro.

RESULTS

ASGR1 deficiency ameliorated systemic IR in mice fed with HFD, evidenced by improved insulin intolerance, serum insulin, and homeostasis model assessment of IR index, mainly contributed from increased insulin signaling in the liver, but not in muscle or adipose tissues. Meanwhile, the insulin signal transduction was significantly enhanced in ASGR1-/- HepG2 cells. By transcriptome analyses and comparison, those differentially expressed genes between ASGR1 null and wild type were enriched in the insulin signal pathway, particularly in phosphoinositide 3-kinase-AKT signaling. Notably, ASGR1 deficiency significantly reduced hepatic gluconeogenesis and glycogenolysis.

CONCLUSION

The ASGR1 deficiency was consequentially linked with improved hepatic insulin sensitivity under metabolic stress, hepatic IR was the core factor of systemic IR, and overcoming hepatic IR significantly relieved the systemic IR. It suggests that ASGR1 is a potential intervention target for improving systemic IR in metabolic disorders.

Punicalagin Ameliorates Diabetic Liver Injury by Inhibiting Pyroptosis and Promoting Autophagy via Modulation of the FoxO1/TXNIP Signaling Pathway

Diabetic liver injury (DLI) is one of the complications of diabetes mellitus, which seriously jeopardizes human health. Punicalagin (PU), a polyphenolic compound mainly found in pomegranate peel, has been shown to ameliorate metabolic diseases such as DLI, and the mechanism needs to be further explored. In this study, a HFD/STZ-induced diabetic mouse model is established to investigate the effect and mechanism of PU on DLI. The results show that PU intervention significantly improves liver histology and serum biochemical abnormalities in diabetic mice, significantly inhibits the expression of pyroptosis-related proteins such as NLRP3, Caspase1, IL-1β, and GSDMD in the liver of diabetic mice, and up-regulated the expression of autophagy-related proteins. Meanwhile, PU treatment significantly increases FoxO1 protein expression and inhibits TXNIP protein expression in the liver of diabetic mice. The above results are further verified in the HepG2 cell injury model induced by high glucose. AS1842856 is a FoxO1 specific inhibitor. The intervention of AS1842856 combined with PU reverses the regulatory effects of PU on pyroptosis and autophagy in HepG2 cells. In conclusion, this study demonstrates that PU may inhibit pyroptosis and upregulate autophagy by regulating FoxO1/TXNIP signaling, thereby alleviating DLI.

Hepatic selective insulin resistance at the intersection of insulin signaling and metabolic dysfunction-associated steatotic liver disease

Insulin resistance (IR) is a major pathogenic factor in the progression of MASLD. In the liver, insulin suppresses gluconeogenesis and enhances de novo lipogenesis (DNL). During IR, there is a defect in insulin-mediated suppression of gluconeogenesis, but an unrestrained increase in hepatic lipogenesis persists. The mechanism of increased hepatic steatosis in IR is unclear and remains controversial. The key discrepancy is whether insulin retains its ability to directly regulate hepatic lipogenesis. Blocking insulin/IRS/AKT signaling reduces liver lipid deposition in IR, suggesting insulin can still regulate lipid metabolism; hepatic glucose metabolism that bypasses insulin's action may contribute to lipogenesis; and due to peripheral IR, other tissues are likely to impact liver lipid deposition. We here review the current understanding of insulin's action in governing different aspects of hepatic lipid metabolism under normal and IR states, with the purpose of highlighting the essential issues that remain unsettled.

Hepatic glucose metabolism in the steatotic liver

The liver is central in regulating glucose homeostasis, being the major contributor to endogenous glucose production and the greatest reserve of glucose as glycogen. It is both a target and regulator of the action of glucoregulatory hormones. Hepatic metabolic functions are altered in and contribute to the highly prevalent steatotic liver disease (SLD), including metabolic dysfunction-associated SLD (MASLD) and metabolic dysfunction-associated steatohepatitis (MASH). In this Review, we describe the dysregulation of hepatic glucose metabolism in MASLD and MASH and associated metabolic comorbidities, and how advances in techniques and models for the assessment of hepatic glucose fluxes in vivo have led to the identification of the mechanisms related to the alterations in glucose metabolism in MASLD and comorbidities. These fluxes can ultimately increase hepatic glucose production concomitantly with fat accumulation and alterations in the secretion and action of glucoregulatory hormones. No pharmacological treatment has yet been approved for MASLD or MASH, but some antihyperglycaemic drugs approved for treating type 2 diabetes have shown positive effects on hepatic glucose metabolism and hepatosteatosis. A deep understanding of how MASLD affects glucose metabolic fluxes and glucoregulatory hormones might assist in the early identification of at-risk individuals and the use or development of targeted therapies.

Loss of FoxO1 activates an alternate mechanism of mitochondrial quality control for healthy adipose browning

Browning of white adipose tissue is hallmarked by increased mitochondrial density and metabolic improvements. However, it remains largely unknown how mitochondrial turnover and quality control are regulated during adipose browning. In the present study, we found that mice lacking adipocyte FoxO1, a transcription factor that regulates autophagy, adopted an alternate mechanism of mitophagy to maintain mitochondrial turnover and quality control during adipose browning. Post-developmental deletion of adipocyte FoxO1 (adO1KO) suppressed Bnip3 but activated Fundc1/Drp1/OPA1 cascade, concurrent with up-regulation of Atg7 and CTSL. In addition, mitochondrial biogenesis was stimulated via the Pgc1α/Tfam pathway in adO1KO mice. These changes were associated with enhanced mitochondrial homeostasis and metabolic health (e.g., improved glucose tolerance and insulin sensitivity). By contrast, silencing Fundc1 or Pgc1α reversed the changes induced by silencing FoxO1, which impaired mitochondrial quality control and function. Ablation of Atg7 suppressed mitochondrial turnover and function, causing metabolic disorder (e.g., impaired glucose tolerance and insulin sensitivity), regardless of elevated markers of adipose browning. Consistently, suppression of autophagy via CTSL by high-fat diet was associated with a reversal of adO1KO-induced benefits. Our data reveal a unique role of FoxO1 in coordinating mitophagy receptors (Bnip3 and Fundc1) for a fine-tuned mitochondrial turnover and quality control, underscoring autophagic clearance of mitochondria as a prerequisite for healthy browning of adipose tissue.

Network pharmacological analysis on the mechanism of Linggui Zhugan decoction for nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD), represents a chronic progressive disease that imposes a significant burden on patients and the healthcare system. Linggui Zhugan decoction (LGZGD) plays a substantial role in treating NAFLD, but its exact molecular mechanism is unknown. Using network pharmacology, this study aimed to investigate the mechanism of action of LGZGD in treating NAFLD. Active ingredients and targets were identified through the integration of data from the TCMSP, GEO, GeneCards, and OMIM databases. Cytoscape 3.9.1 software, in conjunction with the STRING platform, was employed to construct network diagrams and screen core targets. The enrichment analysis of gene ontology and the Kyoto Encyclopedia of Genes and Genomes pathways were conducted by using the R. Molecular docking of the active ingredients and core targets was performed with AutoDock Vina software. We obtained 93 and 112 active ingredients and potential targets using the bioinformatic analysis of LGZGD in treating NAFLD. The primary ingredients of LGZGD included quercetin, kaempferol, and naringenin. The core targets were identified AKT1, MYC, HSP90AA1, HIF1A, ESR1, TP53, and STAT3. Gene ontology function enrichment analysis revealed associations with responses to nutrient and oxygen levels, nuclear receptor activity, and ligand-activated transcription factor activity. Kyoto Encyclopedia of Genes and Genomes signaling pathway analysis implicated the involvement of the PI3K-Akt, IL-17, TNF, Th17 cell differentiation, HIF-1, and TLR signaling pathways. Molecular docking studies indicated strong binding affinities between active ingredients and targets. LGZGD intervenes in NAFLD through a multi-ingredient, multi-target, and multi-pathway approach. Treatment with LGZGD can improve insulin resistance, oxidative stress, inflammation, and lipid metabolism associated with NAFLD.

Effects of Alterations in Acid-Base Effects on Insulin Signaling

Insulin tightly regulates glucose levels within a narrow range through its action on muscle, adipose tissue and the liver. The activation of insulin receptors activates multiple intracellular pathways with different functions. Another tightly regulated complex system in the body is acid-base balance. Metabolic acidosis, defined as a blood pH < 7.35 and serum bicarbonate < 22 mmol/L, has clear pathophysiologic consequences including an effect on insulin action. With the ongoing intake of typical acid-producing Western diets and the age-related decline in renal function, there is an increase in acid levels within the range considered to be normal. This modest increase in acidosis is referred to as "acid stress" and it may have some pathophysiological consequences. In this article, we discuss the effects of acid stress on insulin actions in different tissues.

Regulation of protein O-GlcNAcylation by circadian, metabolic, and cellular signals

O-linked β-N-acetylglucosamine (O-GlcNAcylation) is a dynamic post-translational modification that regulates thousands of proteins and almost all cellular processes. Aberrant O-GlcNAcylation has been associated with numerous diseases, including cancer, neurodegenerative diseases, cardiovascular diseases, and type 2 diabetes. O-GlcNAcylation is highly nutrient-sensitive since it is dependent on UDP-GlcNAc, the end product of the hexosamine biosynthetic pathway (HBP). We previously observed daily rhythmicity of protein O-GlcNAcylation in a Drosophila model that is sensitive to the timing of food consumption. We showed that the circadian clock is pivotal in regulating daily O-GlcNAcylation rhythms given its control of the feeding-fasting cycle and hence nutrient availability. Interestingly, we reported that the circadian clock also modulates daily O-GlcNAcylation rhythm by regulating molecular mechanisms beyond the regulation of food consumption time. A large body of work now indicates that O-GlcNAcylation is likely a generalized cellular status effector as it responds to various cellular signals and conditions, such as ER stress, apoptosis, and infection. In this review, we summarize the metabolic regulation of protein O-GlcNAcylation through nutrient availability, HBP enzymes, and O-GlcNAc processing enzymes. We discuss the emerging roles of circadian clocks in regulating daily O-GlcNAcylation rhythm. Finally, we provide an overview of other cellular signals or conditions that impact O-GlcNAcylation. Many of these cellular pathways are themselves regulated by the clock and/or metabolism. Our review highlights the importance of maintaining optimal O-GlcNAc rhythm by restricting eating activity to the active period under physiological conditions and provides insights into potential therapeutic targets of O-GlcNAc homeostasis under pathological conditions.

Targeting the Metabolic Paradigms in Cancer and Diabetes

Dysregulated metabolic dynamics are evident in both cancer and diabetes, with metabolic alterations representing a facet of the myriad changes observed in these conditions. This review delves into the commonalities in metabolism between cancer and type 2 diabetes (T2D), focusing specifically on the contrasting roles of oxidative phosphorylation (OXPHOS) and glycolysis as primary energy-generating pathways within cells. Building on earlier research, we explore how a shift towards one pathway over the other serves as a foundational aspect in the development of cancer and T2D. Unlike previous reviews, we posit that this shift may occur in seemingly opposing yet complementary directions, akin to the Yin and Yang concept. These metabolic fluctuations reveal an intricate network of underlying defective signaling pathways, orchestrating the pathogenesis and progression of each disease. The Warburg phenomenon, characterized by the prevalence of aerobic glycolysis over minimal to no OXPHOS, emerges as the predominant metabolic phenotype in cancer. Conversely, in T2D, the prevailing metabolic paradigm has traditionally been perceived in terms of discrete irregularities rather than an OXPHOS-to-glycolysis shift. Throughout T2D pathogenesis, OXPHOS remains consistently heightened due to chronic hyperglycemia or hyperinsulinemia. In advanced insulin resistance and T2D, the metabolic landscape becomes more complex, featuring differential tissue-specific alterations that affect OXPHOS. Recent findings suggest that addressing the metabolic imbalance in both cancer and diabetes could offer an effective treatment strategy. Numerous pharmaceutical and nutritional modalities exhibiting therapeutic effects in both conditions ultimately modulate the OXPHOS-glycolysis axis. Noteworthy nutritional adjuncts, such as alpha-lipoic acid, flavonoids, and glutamine, demonstrate the ability to reprogram metabolism, exerting anti-tumor and anti-diabetic effects. Similarly, pharmacological agents like metformin exhibit therapeutic efficacy in both T2D and cancer. This review discusses the molecular mechanisms underlying these metabolic shifts and explores promising therapeutic strategies aimed at reversing the metabolic imbalance in both disease scenarios.

Adipose Tissue Plasticity and Insulin Signaling in the Pathogenesis of Type 2 Diabetes

Obesity is a major cause of various metabolic disorders, including type 2 diabetes, nonalcoholic fatty liver disease (NAFLD) and cardiovascular diseases, in modern times. Fat tissue originally evolved as an organ to prepare for food shortages. However, when individuals consume excessive calories and engage in insufficient physical activity, it can lead to the excessive accumulation of lipids in white adipose tissue, potentially causing problems. In response to this excessive lipid accumulation extending to other tissues, insulin resistance is triggered in the body as a physiological response to prevent harmful effects. Additionally, in mammals, brown adipose tissue has evolved to generate energy and maintain body temperature. These inconspicuous defense mechanisms function coordinately to protect against systemic metabolic abnormalities affecting multiple organs. Understanding the dynamic nature of adipose tissues is now crucial for elucidating the details of the molecular abnormalities in obesity-associated metabolic diseases. This review outlines adipocyte plasticity and function with a focus on the physiological relevance and new pathways of insulin signaling.

Leptin Decreases Gluconeogenesis and Gluconeogenic Substrate Availability in Patients With Lipodystrophy

CONTEXT

The effects of leptin, an adipocyte-derived hormone that signals overall energy sufficiency, can only be studied in leptin-deficient conditions. In patients with lipodystrophy, a rare disease and unique model of leptin deficiency, treatment with recombinant leptin (metreleptin) improves glycemia and decreases energy expenditure. We hypothesized that these improvements might be mediated by reduced gluconeogenesis (GNG), an energy-requiring process.

OBJECTIVE

To determine the effects of metreleptin on GNG and GNG substrates.

METHODS

This was a single-arm prospective study of metreleptin administration in 15 patients with lipodystrophy, 9 of whom had data on GNG (NIH, 2013-2018). We analyzed total GNG, insulin-mediated suppression of GNG, glycerol, palmitate, alanine, lactate, peripheral and hepatic insulin sensitivity, and markers of glycemia (eg, HbA1c, glucose, fasting insulin).

RESULTS

Metreleptin administration decreased basal GNG, increased insulin-mediated suppression of GNG, and improved insulin sensitivity and markers of glycemic control. Metreleptin reduced carbon sources for GNG, including plasma alanine and lactate, and rate of appearance (Ra) of glycerol, and decreased Ra of palmitate, a driver of GNG. Glycerol and palmitate Ra correlated with GNG prior to but not during metreleptin administration. Alanine strongly correlated with GNG both before and during metreleptin administration.

CONCLUSIONS

Metreleptin treatment in patients with lipodystrophy reduced GNG likely through decreased availability of carbon sources for gluconeogenesis, such as alanine, lactate, and glycerol. Associations between alanine and GNG persisted after metreleptin treatment while correlations with glycerol and palmitate Ra did not persist, suggesting reduced importance of lipolysis as a driver of GNG in the leptin-replete state.

Preventive Effects of Apple Polyphenol Extract on High-Fat-Diet-Induced Hepatic Steatosis Are Related to the Regulation of Hepatic Lipid Metabolism, Autophagy, and Gut Microbiota in Aged Mice

Our previous study confirmed that the ameliorated effects of an intervention with an apple polyphenol extract (APE) on hepatic steatosis induced by a high-fat diet (HFD) are dependent on SIRT1. Since SIRT1 expression decreases with age, it remains unclear whether APE intervention is effective against hepatic steatosis in aged mice. Thus, 12-month-old C57BL/6 male mice were fed with an HFD to establish an aging model of hepatic steatosis and treated with 500 mg/(kg·bw·d) APE for 12 weeks. Young mice (two months old) and baseline mice were used as controls to examine the effects of natural aging on hepatic steatosis. Compared with baseline mice, no obvious difference in hepatic histopathological assessment was observed for both young and aged mice on normal diets. Meanwhile, HFD induced much higher nonalcoholic fatty liver disease (NAFLD) activity scores in aged mice than in young mice. APE intervention ameliorated lipid and glucose metabolic disorders and liver injury in HFD-fed aged mice, improved hepatic steatosis, and reduced NAFLD activity scores. The upregulated expressions of SIRT1, HSL, ATG5, Ulk1, and Becn1 and downregulated expressions of HMGCR and FOXO1 suggested improved lipid metabolism and activated autophagy. APE intervention decreased the ratio of Firmicutes/Bacteroidetes and elevated the Akkermansia probiotics abundance. In summary, HFD showed a more significant effect on hepatic steatosis compared to the natural aging process in aged mice, and APE might be a promising dietary ingredient for alleviating hepatic steatosis.

Nutrigenomics and redox regulation: Concepts relating to the Special Issue on nutrigenomics

During our whole lifespan, from conception to death, the epigenomes of all tissues and cell types of our body integrate signals from the environment. This includes signals derived from our diet and the uptake of macro- and micronutrients. In most cases, this leads only to transient changes, but some effects of this epigenome programming process are persistent and can even be transferred to the next generation. Both epigenetic programming and redox processes are affected by the individual choice of diet and other lifestyle decisions like physical activity. The nutrient-gene communication pathways have adapted during human evolution and are essential for maintaining health. However, when they are maladaptive, such as in long-term obesity, they significantly contribute to diseases like type 2 diabetes and cancer. The field of nutrigenomics investigates nutrition-related signal transduction pathways and their effect on gene expression involving interactions both with the genome and the epigenomes. Several of these diet-(epi)genome interactions and the involved signal transduction cascades are redox-regulated. Examples include the effects of the NAD+/NADH ratio, vitamin C levels and secondary metabolites of dietary molecules from plants on the acetylation and methylation state of the epigenome as well as on gene expression through redox-sensitive pathways via the transcription factors NFE2L2 and FOXO. In this review, we summarize and extend on these topics as well as those discussed in the articles of this Special Issue and take them into the context of redox biology.

FoxK1 associated gene regulatory network in hepatic insulin action and its relationship to FoxO1 and insulin receptor mediated transcriptional regulation

OBJECTIVE

Insulin acts on the liver via changes in gene expression to maintain glucose and lipid homeostasis. This study aimed to the Forkhead box protein K1 (FOXK1) associated gene regulatory network as a transcriptional regulator of hepatic insulin action and to determine its role versus FoxO1 and possible actions of the insulin receptor at the DNA level.

METHODS

Genome-wide analysis of FoxK1 binding were studied by chromatin immunoprecipitation sequencing and compared to those for IR and FoxO1. These were validated by knockdown experiments and gene expression analysis.

RESULTS

Chromatin immunoprecipitation (ChIP) sequencing shows that FoxK1 binds to the proximal promoters and enhancers of over 4000 genes, and insulin enhances this interaction for about 75% of them. These include genes involved in cell cycle, senescence, steroid biosynthesis, autophagy, and metabolic regulation, including glucose metabolism and mitochondrial function and are enriched in a TGTTTAC consensus motif. Some of these genes are also bound by FoxO1. Comparing this FoxK1 ChIP-seq data to that of the insulin receptor (IR) reveals that FoxK1 may act as the transcription factor partner for some of the previously reported roles of IR in gene regulation, including for LARS1 and TIMM22, which are involved in rRNA processing and cell cycle.

CONCLUSION

These data demonstrate that FoxK1 is an important regulator of gene expression in response to insulin in liver and may act in concert with FoxO1 and IR in regulation of genes in metabolism and other important biological pathways.

Hepatocyte TIPE2 is a fasting-induced Raf-1 inactivator that drives hepatic gluconeogenesis to maintain glucose homeostasis

BACKGROUND

The liver regulates metabolic balance during fasting-feeding cycle. Hepatic adaptation to fasting is precisely modulated on multiple levels. Tumor necrosis factor-α-induced protein 8-like 2 (TIPE2) is a negative regulator of immunity that reduces several liver pathologies, but its physiological roles in hepatic metabolism are largely unknown.

METHODS

TIPE2 expression was examined in mouse liver during fasting-feeding cycle. TIPE2-knockout mice, liver-specific TIPE2-knockout mice, liver-specific TIPE2-overexpressed mice were examined for fasting blood glucose and pyruvate tolerance test. Primary hepatocytes or liver tissues from these mice were evaluated for glucose production, lipid accumulation, gene expression and regulatory pathways. TIPE2 interaction with Raf-1 and TIPE2 transcription regulated by PPAR-α were examined using gene overexpression or knockdown, co-immunoprecipitation, western blot, luciferase reporter assay and DNA-protein binding assay.

RESULTS

TIPE2 expression was upregulated in fasted mouse liver and starved hepatocytes, which was positively correlated with gluconeogenic genes. Liver-specific TIPE2 deficiency impaired blood glucose homeostasis and gluconeogenic capacity in mice upon fasting, while liver-specific TIPE2 overexpression elevated fasting blood glucose and hepatic gluconeogenesis in mice. In primary hepatocytes upon starvation, TIPE2 interacted with Raf-1 to accelerate its ubiquitination and degradation, resulting in ERK deactivation and FOXO1 maintenance to sustain gluconeogenesis. During prolonged fasting, hepatic TIPE2 deficiency caused aberrant activation of ERK-mTORC1 axis that increased hepatic lipid accumulation via lipogenesis. In hepatocytes upon starvation, PPAR-α bound with TIPE2 promoter and triggered its transcriptional expression.

CONCLUSIONS

Hepatocyte TIPE2 is a PPAR-α-induced Raf-1 inactivator that sustains hepatic gluconeogenesis and prevents excessive hepatic lipid accumulation, playing beneficial roles in hepatocyte adaptation to fasting.

FoxO1 as a tissue-specific therapeutic target for type 2 diabetes

Forkhead box O (FoxO) proteins are transcription factors that mediate many aspects of physiology and thus have been targeted as therapeutics for several diseases including metabolic disorders such as type 2 diabetes mellitus (T2D). The role of FoxO1 in metabolism has been well studied, but recently FoxO1's potential for diabetes prevention and therapy has been debated. For example, studies have shown that increased FoxO1 activity in certain tissue types contributes to T2D pathology, symptoms, and comorbidities, yet in other tissue types elevated FoxO1 has been reported to alleviate symptoms associated with diabetes. Furthermore, studies have reported opposite effects of active FoxO1 in the same tissue type. For example, in the liver, FoxO1 contributes to T2D by increasing hepatic glucose production. However, FoxO1 has been shown to either increase or decrease hepatic lipogenesis as well as adipogenesis in white adipose tissue. In skeletal muscle, FoxO1 reduces glucose uptake and oxidation, promotes lipid uptake and oxidation, and increases muscle atrophy. While many studies show that FoxO1 lowers pancreatic insulin production and secretion, others show the opposite, especially in response to oxidative stress and inflammation. Elevated FoxO1 in the hypothalamus increases the risk of developing T2D. However, increased FoxO1 may mitigate Alzheimer's disease, a neurodegenerative disease strongly associated with T2D. Conversely, accumulating evidence implicates increased FoxO1 with Parkinson's disease pathogenesis. Here we review FoxO1's actions in T2D conditions in metabolic tissues that abundantly express FoxO1 and highlight some of the current studies targeting FoxO1 for T2D treatment.

Insulin sensitization by hepatic FoxO deletion is insufficient to lower atherosclerosis in mice

Background–

Type 2 diabetes is associated with an increased risk of atherosclerotic cardiovascular disease. It has been suggested that insulin resistance underlies this link, possibly by altering the functions of cells in the artery wall. We aimed to test whether improving systemic insulin sensitivity reduces atherosclerosis.

Methods–

We used mice that are established to have improved systemic insulin sensitivity: those lacking FoxO transcription factors in hepatocytes. Three hepatic FoxO isoforms (FoxO1, FoxO3, and FoxO4) function together to promote hepatic glucose output, and ablating them lowers glucose production, lowers circulating glucose and insulin, and improves systemic insulin sensitivity. We made these mice susceptible to atherosclerosis in two different ways, by injecting them with gain-of-function AAV8.mPcsk9D377Y and by crossing with Ldlr-/- mice.

Results–

We verified that hepatic FoxO ablation improves systemic insulin sensitivity in these atherosclerotic settings. We observed that FoxO deficiency caused no reductions in atherosclerosis, and in some cases increased atherosclerosis. These phenotypes coincided with large increases in circulating triglycerides in FoxO-ablated mice.

Conclusions–

These findings suggest that systemic insulin sensitization is insufficient to reduce atherosclerosis.

Microbiota dysbiosis associated with type 2 diabetes-like effects caused by chronic exposure to a mixture of chlorinated persistent organic pollutants in zebrafish

Mixtures of chlorinated persistent organic pollutants (C-POPs-Mix) are chemically related risk factors for type 2 diabetes mellitus (T2DM); however, the effects of chronic exposure to C-POPs-Mix on microbial dysbiosis remain poorly understood. Herein, male and female zebrafish were exposed to C-POPs-Mix at a 1:1 ratio of five organochlorine pesticides and Aroclor 1254 at concentrations of 0.02, 0.1, and 0.5 μg/L for 12 weeks. We measured T2DM indicators in blood and profiled microbial abundance and richness in the gut as well as transcriptomic and metabolomic alterations in the liver. Exposure to C-POPs-Mix significantly increased blood glucose levels while decreasing the abundance and alpha diversity of microbial communities only in females at concentrations of 0.02 and 0.1 μg/L. The majorly identified microbial contributors to microbial dysbiosis were Bosea minatitlanensis, Rhizobium tibeticum, Bifidobacterium catenulatum, Bifidobacterium adolescentis, and Collinsella aerofaciens. PICRUSt results suggested that altered pathways were associated with glucose and lipid production and inflammation, which are linked to changes in the transcriptome and metabolome of the zebrafish liver. Metagenomics outcomes revealed close relationships between intestinal and liver disruptions to T2DM-related molecular pathways. Thus, microbial dysbiosis in T2DM-triggered zebrafish occurred as a result of chronic exposure to C-POPs-Mix, indicating strong host-microbiome interactions.

BRD7 improves glucose homeostasis independent of IRS proteins

Bromodomain-containing protein 7 (BRD7) has emerged as a player in the regulation of glucose homeostasis. Hepatic BRD7 levels are decreased in obese mice, and the reinstatement of hepatic BRD7 in obese mice has been shown to establish euglycemia and improve glucose homeostasis. Of note, the upregulation of hepatic BRD7 levels activates the AKT cascade in response to insulin without enhancing the sensitivity of the insulin receptor (InsR)-insulin receptor substrate (IRS) axis. In this report, we provide evidence for the existence of an alternative insulin signaling pathway that operates independently of IRS proteins and demonstrate the involvement of BRD7 in this pathway. To investigate the involvement of BRD7 as a downstream component of InsR, we utilized liver-specific InsR knockout mice. Additionally, we employed liver-specific IRS1/2 knockout mice to examine the requirement of IRS1/2 for the action of BRD7. Our investigation of glucose metabolism parameters and insulin signaling unveiled the significance of InsR activation in mediating BRD7's effect on glucose homeostasis in the liver. Moreover, we identified an interaction between BRD7 and InsR. Notably, our findings indicate that IRS1/2 is not necessary for BRD7's regulation of glucose metabolism, particularly in the context of obesity. The upregulation of hepatic BRD7 significantly reduces blood glucose levels and restores glucose homeostasis in high-fat diet-challenged liver-specific IRS1/2 knockout mice. These findings highlight the presence of an alternative insulin signaling pathway that operates independently of IRS1/2 and offer novel insights into the mechanisms of a previously unknown insulin signaling in obesity.

FoxO1 regulates adipose transdifferentiation and iron influx by mediating Tgfβ1 signaling pathway

Adipose plasticity is critical for metabolic homeostasis. Adipocyte transdifferentiation plays an important role in adipose plasticity, but the molecular mechanism of transdifferentiation remains incompletely understood. Here we show that the transcription factor FoxO1 regulates adipose transdifferentiation by mediating Tgfβ1 signaling pathway. Tgfβ1 treatment induced whitening phenotype in beige adipocytes, reducing UCP1 and mitochondrial capacity and enlarging lipid droplets. Deletion of adipose FoxO1 (adO1KO) dampened Tgfβ1 signaling by downregulating Tgfbr2 and Smad3 and induced browning of adipose tissue in mice, increasing UCP1 and mitochondrial content and activating metabolic pathways. Silencing FoxO1 also abolished the whitening effect of Tgfβ1 on beige adipocytes. The adO1KO mice exhibited a significantly higher energy expenditure, lower fat mass, and smaller adipocytes than the control mice. The browning phenotype in adO1KO mice was associated with an increased iron content in adipose tissue, concurrent with upregulation of proteins that facilitate iron uptake (DMT1 and TfR1) and iron import into mitochondria (Mfrn1). Analysis of hepatic and serum iron along with hepatic iron-regulatory proteins (ferritin and ferroportin) in the adO1KO mice revealed an adipose tissue-liver crosstalk that meets the increased iron requirement for adipose browning. The FoxO1-Tgfβ1 signaling cascade also underlay adipose browning induced by β3-AR agonist CL316243. Our study provides the first evidence of a FoxO1-Tgfβ1 axis in the regulation of adipose browning-whitening transdifferentiation and iron influx, which sheds light on the compromised adipose plasticity in conditions of dysregulated FoxO1 and Tgfβ1 signaling.

FOXO transcription factors as therapeutic targets in human diseases

Forkhead box (FOX)O proteins are transcription factors (TFs) with four members in mammals designated FOXO1, FOXO3, FOXO4, and FOXO6. FOXO TFs play a pivotal role in the cellular adaptation to diverse stress conditions. FOXO proteins act as context-dependent tumor suppressors and their dysregulation has been implicated in several age-related diseases. FOXO3 has been established as a major gene for human longevity. Accordingly, FOXO proteins have emerged as potential targets for the therapeutic development of drugs and geroprotectors. In this review, we provide an overview of the most recent advances in our understanding of FOXO regulation and function in various pathological conditions. We discuss strategies targeting FOXOs directly or by the modulation of upstream regulators, shedding light on the most promising intervention points. We also reveal the most relevant clinical indications and discuss the potential, trends, and challenges of modulating FOXO activity for therapeutic purposes.

Phosphatase protector alpha4 (α4) is involved in adipocyte maintenance and mitochondrial homeostasis through regulation of insulin signaling

Insulin signaling is mediated via a network of protein phosphorylation. Dysregulation of this network is central to obesity, type 2 diabetes and metabolic syndrome. Here we investigate the role of phosphatase binding protein Alpha4 (α4) that is essential for the serine/threonine protein phosphatase 2A (PP2A) in insulin action/resistance in adipocytes. Unexpectedly, adipocyte-specific inactivation of α4 impairs insulin-induced Akt-mediated serine/threonine phosphorylation despite a decrease in the protein phosphatase 2A (PP2A) levels. Interestingly, loss of α4 also reduces insulin-induced insulin receptor tyrosine phosphorylation. This occurs through decreased association of α4 with Y-box protein 1, resulting in the enhancement of the tyrosine phosphatase protein tyrosine phosphatase 1B (PTP1B) expression. Moreover, adipocyte-specific knockout of α4 in male mice results in impaired adipogenesis and altered mitochondrial oxidation leading to increased inflammation, systemic insulin resistance, hepatosteatosis, islet hyperplasia, and impaired thermogenesis. Thus, the α4 /Y-box protein 1(YBX1)-mediated pathway of insulin receptor signaling is involved in maintaining insulin sensitivity, normal adipose tissue homeostasis and systemic metabolism.

Short-Clustered Maltodextrin Activates Ileal Glucose-Sensing and Induces Glucagon-like Peptide 1 Secretion to Ameliorate Glucose Homeostasis in Type 2 Diabetic Mice

Reconstructing molecular structure is an effective approach to attenuating glycemic response to starch. Previously, we rearranged α-1,4 and α-1,6-glycosidic bonds in starch molecules to produce short-clustered maltodextrin (SCMD). The present study revealed that SCMD slowly released glucose until the distal ileum. The activated ileal glucose-sensing enabled SCMD to be a potent inducer for glucagon-like peptide-1 (GLP-1). Furthermore, SCMD was found feasible to serve as the dominant dietary carbohydrate to rescue mice from diabetes. Interestingly, a mixture of normal maltodextrin and resistant dextrin (MD+RD), although it caused an attenuated glycemic response similar to that of SCMD, failed to ameliorate glucose homeostasis because it hardly induced GLP-1 secretion. The serum GLP-1 levels seen in MD+RD-fed mice (5.25 ± 1.51 pmol/L) were significantly lower than those seen in SCMD-fed mice (8.25 ± 2.01 pmol/L, p < 0.05). Further investigation revealed that the beneficial effects of SCMD could be abolished by a GLP-1 receptor (GLP-1R) antagonist. These results identify GLP-1R signaling as a critical contributor to SCMD-exerted health benefits and highlight the role of ileal glucose-sensing in designing dietary carbohydrates.

Heterozygous Loss of KRIT1 in Mice Affects Metabolic Functions of the Liver, Promoting Hepatic Oxidative and Glycative Stress

KRIT1 loss-of-function mutations underlie the pathogenesis of Cerebral Cavernous Malformation (CCM), a major vascular disease affecting the central nervous system (CNS). However, KRIT1 is also expressed outside the CNS and modulates key regulators of metabolic and oxy-inflammatory pathways, including the master transcription factor FoxO1, suggesting a widespread functional significance. Herein, we show that the KRIT1/FoxO1 axis is implicated in liver metabolic functions and antioxidative/antiglycative defenses. Indeed, by performing comparative studies in KRIT1 heterozygous (KRIT1^+/−) and wild-type mice, we found that KRIT1 haploinsufficiency resulted in FoxO1 expression/activity downregulation in the liver, and affected hepatic FoxO1-dependent signaling pathways, which are markers of major metabolic processes, including gluconeogenesis, glycolysis, mitochondrial respiration, and glycogen synthesis. Moreover, it caused sustained activation of the master antioxidant transcription factor Nrf2, hepatic accumulation of advanced glycation end-products (AGEs), and abnormal expression/activity of AGE receptors and detoxifying systems. Furthermore, it was associated with an impairment of food intake, systemic glucose disposal, and plasma levels of insulin. Specific molecular alterations detected in the liver of KRIT1^+/− mice were also confirmed in KRIT1 knockout cells. Overall, our findings demonstrated, for the first time, that KRIT1 haploinsufficiency affects glucose homeostasis and liver metabolic and antioxidative/antiglycative functions, thus inspiring future basic and translational studies.

Integrating pharmacological evaluation and computational identification for deciphering the action mechanism of Yunpi-Huoxue-Sanjie formula alleviates diabetic cardiomyopathy

Background: Yunpi-Huoxue-Sanjie (YP-SJ) formula is a Chinese herbal formula with unique advantages for the treatment of diabetic cardiovascular complications, such as Diabetic cardiomyopathy (DCM). However, potential targets and molecular mechanisms remain unclear. Therefore, our research was designed to evaluate rat myocardial morphology, fat metabolism and oxidative stress to verify myocardial protective effect of YP-SJ formula in vivo. And then to explore and validate its probable mechanism through network pharmacology and experiments in vitro and in vivo.

Methods: In this study, DCM rats were randomly divided into five groups: control group, model group, and three YP-SJ formula groups (low-dose, middle-dose, and high-dose groups). Experimental rats were treated with 6 g/kg/d, 12 g/kg/d and 24 g/kg/d YP-SJ formula by gavage for 10 weeks, respectively. Cardiac function of rats was measured by high-resolution small-animal imaging system. The cells were divided into control group, high glucose group, high glucose + control serum group, high glucose + dosed serum group, high glucose + NC-siRNA group, high glucose + siRNA-FoxO1 group. The extent of autophagy was measured by flow cytometry, immunofluorescence, and western blotting.

Results: It was found that YP-SJ formula could effectively improve cardiac systolic function in DCM rats. We identified 46 major candidate YP-SJ formula targets that are closely related to the progression of DCM. Enrichment analysis revealed key targets of YP-SJ formula related to environmental information processing, organic systems, and the metabolic occurrence of reactive oxygen species. Meanwhile, we verified that YP-SJ formula can increase the expression of forkhead box protein O1 (FoxO1), autophagy-related protein 7 (Atg7), Beclin 1, and light chain 3 (LC3), and decrease the expression of phosphorylated FoxO1 in vitro and in vivo. The results showed that YP-SJ formula could activate the FoxO1 signaling pathway associated with DCM rats. Further experiments showed that YP-SJ formula could improve cardiac function by regulating autophagy.

Conclusion: YP-SJ formula treats DCM by modulating targets that play a key role in autophagy, improving myocardial function through a multi-component, multi-level, multi-target, multi-pathway, and multi-mechanism approach.

Peroxisomal regulation of energy homeostasis: Effect on obesity and related metabolic disorders

BACKGROUND

Peroxisomes are single membrane-bound organelles named for their role in hydrogen peroxide production and catabolism. However, their cellular functions extend well beyond reactive oxygen species (ROS) metabolism and include fatty acid oxidation of unique substrates that cannot be catabolized in mitochondria, and synthesis of ether lipids and bile acids. Metabolic functions of peroxisomes involve crosstalk with other organelles, including mitochondria, endoplasmic reticulum, lipid droplets and lysosomes. Emerging studies suggest that peroxisomes are important regulators of energy homeostasis and that disruption of peroxisomal functions influences the risk for obesity and the associated metabolic disorders, including type 2 diabetes and hepatic steatosis.

SCOPE OF REVIEW

Here, we focus on the role of peroxisomes in ether lipid synthesis, β-oxidation and ROS metabolism, given that these functions have been most widely studied and have physiologically relevant implications in systemic metabolism and obesity. Efforts are made to mechanistically link these cellular and systemic processes.

MAJOR CONCLUSIONS

Circulating plasmalogens, a form of ether lipids, have been identified as inversely correlated biomarkers of obesity. Ether lipids influence metabolic homeostasis through multiple mechanisms, including regulation of mitochondrial morphology and respiration affecting brown fat-mediated thermogenesis, and through regulation of adipose tissue development. Peroxisomal β-oxidation also affects metabolic homeostasis through generation of signaling molecules, such as acetyl-CoA and ROS that inhibit hydrolysis of stored lipids, contributing to development of hepatic steatosis. Oxidative stress resulting from increased peroxisomal β-oxidation-generated ROS in the context of obesity mediates β-cell lipotoxicity. A better understanding of the roles peroxisomes play in regulating and responding to obesity and its complications will provide new opportunities for their treatment.

Adipose methylome integrative-omic analyses reveal genetic and dietary metabolic health drivers and insulin resistance classifiers

BACKGROUND

There is considerable evidence for the importance of the DNA methylome in metabolic health, for example, a robust methylation signature has been associated with body mass index (BMI). However, visceral fat (VF) mass accumulation is a greater risk factor for metabolic disease than BMI alone. In this study, we dissect the subcutaneous adipose tissue (SAT) methylome signature relevant to metabolic health by focusing on VF as the major risk factor of metabolic disease. We integrate results with genetic, blood methylation, SAT gene expression, blood metabolomic, dietary intake and metabolic phenotype data to assess and quantify genetic and environmental drivers of the identified signals, as well as their potential functional roles.

METHODS

Epigenome-wide association analyses were carried out to determine visceral fat mass-associated differentially methylated positions (VF-DMPs) in SAT samples from 538 TwinsUK participants. Validation and replication were performed in 333 individuals from 3 independent cohorts. To assess functional impacts of the VF-DMPs, the association between VF and gene expression was determined at the genes annotated to the VF-DMPs and an association analysis was carried out to determine whether methylation at the VF-DMPs is associated with gene expression. Further epigenetic analyses were carried out to compare methylation levels at the VF-DMPs as the response variables and a range of different metabolic health phenotypes including android:gynoid fat ratio (AGR), lipids, blood metabolomic profiles, insulin resistance, T2D and dietary intake variables. The results from all analyses were integrated to identify signals that exhibit altered SAT function and have strong relevance to metabolic health.

RESULTS

We identified 1181 CpG positions in 788 genes to be differentially methylated with VF (VF-DMPs) with significant enrichment in the insulin signalling pathway. Follow-up cross-omic analysis of VF-DMPs integrating genetics, gene expression, metabolomics, diet, and metabolic traits highlighted VF-DMPs located in 9 genes with strong relevance to metabolic disease mechanisms, with replication of signals in FASN, SREBF1, TAGLN2, PC and CFAP410. PC methylation showed evidence for mediating effects of diet on VF. FASN DNA methylation exhibited putative causal effects on VF that were also strongly associated with insulin resistance and methylation levels in FASN better classified insulin resistance (AUC=0.91) than BMI or VF alone.

CONCLUSIONS

Our findings help characterise the adiposity-associated methylation signature of SAT, with insights for metabolic disease risk.

Global-run on sequencing identifies Gm11967 as an Akt-dependent long noncoding RNA involved in insulin sensitivity

The insulin responsive Akt and FoxO1 signaling axis is a key regulator of the hepatic transcriptional response to nutrient intake. Here, we used global run-on sequencing (GRO-seq) to measure the nascent transcriptional response to fasting and refeeding as well as define the specific role of hepatic Akt and FoxO1 signaling in mediating this response. We identified 599 feeding-regulated transcripts, as well as over 6,000 eRNAs, and mapped their dependency on Akt and FoxO1 signaling. Further, we identified several feeding-regulated lncRNAs, including the lncRNA Gm11967, whose expression was dependent upon the liver Akt-FoxO1 axis. Restoring Gm11967 expression in mice lacking liver Akt improved insulin sensitivity and induced glucokinase protein expression, indicating that Akt-dependent control of Gm11967 contributes to the translational control of glucokinase. More broadly, we have generated a unique genome-wide dataset that defines the feeding and Akt/FoxO1-dependent transcriptional changes in response to nutrient availability.

The hepatocyte insulin receptor is required to program the liver clock and rhythmic gene expression

Liver physiology is circadian and sensitive to feeding and insulin. Food intake regulates insulin secretion and is a dominant signal for the liver clock. However, how much insulin contributes to the effect of feeding on the liver clock and rhythmic gene expression remains to be investigated. Insulin action partly depends on changes in insulin receptor (IR)-dependent gene expression. Here, we use hepatocyte-restricted gene deletion of IR to evaluate its role in the regulation and oscillation of gene expression as well as in the programming of the circadian clock in the adult mouse liver. We find that, in the absence of IR, the rhythmicity of core-clock gene expression is altered in response to day-restricted feeding. This change in core-clock gene expression is associated with defective reprogramming of liver gene expression. Our data show that an intact hepatocyte insulin receptor is required to program the liver clock and associated rhythmic gene expression.

Menin regulates lipid deposition in mouse hepatocytes via interacting with transcription factor FoxO1

Non-alcoholic fatty liver disease (NAFLD) is rapidly being recognized as the leading cause of chronic liver disease worldwide. Men1, encoding protein of menin, is a key causative gene of multiple endocrine neoplasia type 1 syndrome including pancreatic tumor. It is known that insulin that secretes by endocrine tissue pancreatic islets plays a critical role in hepatic metabolism. Mouse model of hemizygous deletion of Men1 was shown to have severe hepatic metabolism disorders. However, the molecular function of menin on lipid deposition in hepatocytes needs to be further studied. Transcriptome sequencing does show that expression suppression of Men1 in mouse hepatocytes widely affect signaling pathways involved in hepatic metabolism, such as fatty acid metabolism, insulin response, glucose metabolism and inflammation. Further molecular studies indicates that menin overexpression inhibits expressions of the fat synthesis genes Srebp-1c, Fas, and Acc1, the fat differentiation genes Pparγ1 and Pparγ2, and the fat transport gene Cd36, thereby inhibiting the fat accumulation in hepatocytes. The biological process of menin regulating hepatic lipid metabolism was accomplished by interacting with the transcription factor FoxO1, which is also found to be critical for lipid metabolism. Moreover, menin responds to insulin in hepatocytes and mediates its regulatory effect on hepatic metabolism. Our findings suggest that menin is a crucial mediation factor in regulating the hepatic fat deposition, suggesting it could be a potential important therapeutic target for NAFLD.

FoxO transcription factors in mitochondrial homeostasis

Mitochondria play essential roles in cellular energetics, biosynthesis, and signaling transduction. Dysfunctional mitochondria have been implicated in different diseases such as obesity, diabetes, cardiovascular disease, nonalcoholic fatty liver disease, neurodegenerative disease, and cancer. Mitochondrial homeostasis is controlled by a triad of mitochondrial biogenesis, dynamics (fusion and fission), and autophagy (mitophagy). Studies have underscored FoxO transcription factors as key mitochondrial regulators. Specifically, FoxOs regulate mitochondrial biogenesis by dampening NRF1-Tfam and c-Myc-Tfam cascades directly, and inhibiting NAD-Sirt1-Pgc1α cascade indirectly by inducing Hmox1 or repressing Fxn and Urod. In addition, FoxOs mediate mitochondrial fusion (via Mfn1 and Mfn2) and fission (via Drp1, Fis1, and MIEF2), during which FoxOs elicit regulatory mechanisms at transcriptional, posttranscriptional (e.g. via miR-484/Fis1), and posttranslational (e.g. via Bnip3-calcineurin mediated Drp1 dephosphorylation) levels. Furthermore, FoxOs control mitochondrial autophagy in the stages of autophagosome formation and maturation (e.g. initiation, nucleation, and elongation), mitochondria connected to and engulfed by autophagosome (e.g. via PINK1 and Bnip3 pathways), and autophagosome-lysosome fusion to form autolysosome for cargo degradation (e.g. via Tfeb and cathepsin proteins). This article provides an up-to-date view of FoxOs regulating mitochondrial homeostasis and discusses the potential of targeting FoxOs for therapeutics.

Central Nervous System Control of Glucose Homeostasis: A Therapeutic Target for Type 2 Diabetes?

Historically, pancreatic islet beta cells have been viewed as principal regulators of glycemia, with type 2 diabetes (T2D) resulting when insulin secretion fails to compensate for peripheral tissue insulin resistance. However, glycemia is also regulated by insulin-independent mechanisms that are dysregulated in T2D. Based on evidence supporting its role both in adaptive coupling of insulin secretion to changes in insulin sensitivity and in the regulation of insulin-independent glucose disposal, the central nervous system (CNS) has emerged as a fundamental player in glucose homeostasis. Here, we review and expand upon an integrative model wherein the CNS, together with the islet, establishes and maintains the defended level of glycemia. We discuss the implications of this model for understanding both normal glucose homeostasis and T2D pathogenesis and highlight centrally targeted therapeutic approaches with the potential to restore normoglycemia to patients with T2D.

TOX4, an insulin receptor-independent regulator of hepatic glucose production, is activated in diabetic liver

Increased hepatic glucose production (HGP) contributes to hyperglycemia in type 2 diabetes. Hormonal regulation of this process is primarily, but not exclusively, mediated by the AKT-FoxO1 pathway. Here, we show that cAMP and dexamethasone regulate the high-mobility group superfamily member TOX4 to mediate HGP, independent of the insulin receptor/FoxO1 pathway. TOX4 inhibition decreases glucose production in primary hepatocytes and liver and increases glucose tolerance. Combined genetic ablation of TOX4 and FoxO1 in liver has additive effects on glucose tolerance and gluconeogenesis. Moreover, TOX4 ablation fails to reverse the metabolic derangement brought by insulin receptor knockout. TOX4 expression is increased in livers of patients with steatosis and diabetes and in diet-induced obese and db/db mice. In the latter two murine models, knockdown Tox4 decreases glycemia and improves glucose tolerance. We conclude that TOX4 is an insulin receptor-independent regulator of HGP and a candidate contributor to the pathophysiology of diabetes.

The Role of Notch Signaling Pathway in Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease worldwide, and progressive NAFLD can develop into non-alcoholic steatohepatitis (NASH), liver cirrhosis, or hepatocellular carcinoma (HCC). NAFLD is a kind of metabolic disordered disease, which is commonly associated with lipid metabolism, insulin resistance, oxidative stress, inflammation, and fibrogenesis, as well as autophagy. Growing studies have shown Notch signaling pathway plays a pivotal role in the regulation of NAFLD progression. Here, we review the profile of the Notch signaling pathway, new evidence of Notch signaling involvement in NAFLD, and describe the potential of Notch as a biomarker and therapeutic target for NAFLD treatment.

Role of FoxO transcription factors in aging and age-related metabolic and neurodegenerative diseases

Aging happens to all of us as we live. Thanks to the improved living standard and discovery of life-saving medicines, our life expectancy has increased substantially across the world in the past century. However, the rise in lifespan leads to unprecedented increases in both the number and the percentage of individuals 65 years and older, accompanied by the increased incidences of age-related diseases such as type 2 diabetes mellitus and Alzheimer’s disease. FoxO transcription factors are evolutionarily conserved molecules that play critical roles in diverse biological processes, in particular aging and metabolism. Their dysfunction is often found in the pathogenesis of many age-related diseases. Here, we summarize the signaling pathways and cellular functions of FoxO proteins. We also review the complex role of FoxO in aging and age-related diseases, with focus on type 2 diabetes and Alzheimer’s disease and discuss the possibility of FoxO as a molecular link between aging and disease risks.

Signaling defects associated with insulin resistance in nondiabetic and diabetic individuals and modification by sex

Insulin resistance is present in one-quarter of the general population, predisposing these people to a wide range of diseases. Our aim was to identify cell-intrinsic determinants of insulin resistance in this population using induced pluripotent stem cell-derived (iPSC-derived) myoblasts (iMyos). We found that these cells exhibited a large network of altered protein phosphorylation in vitro. Integrating these data with data from type 2 diabetic iMyos revealed critical sites of conserved altered phosphorylation in IRS-1, AKT, mTOR, and TBC1D1 in addition to changes in protein phosphorylation involved in Rho/Rac signaling, chromatin organization, and RNA processing. There were also striking differences in the phosphoproteome in cells from men versus women. These sex-specific and insulin-resistance defects were linked to functional differences in downstream actions. Thus, there are cell-autonomous signaling alterations associated with insulin resistance within the general population and important differences between men and women, many of which also occur in diabetes, that contribute to differences in physiology and disease.

Functionalized Gadofullerene Ameliorates Impaired Glycolipid Metabolism in Type 2 Diabetic Mice

The soaring global prevalence of diabetes makes it urgent to explore new drugs with high efficacy and safety. Nanomaterial-derived bioactive agents are emerging as one of the most promising candidates for biomedical application. In the present study, we investigated the anti-diabetic effects of a functionalized gadofullerene (GF) using obese db/db and non-obese MKR mouse T2DM models. In both mouse models, the diabetic phenotypes including hyperglycemia, impaired glucose tolerance and insulin sensitivity were ameliorated following 2 or 4 weeks of i.p. administration of GF. GF lowered blood glucose levels in a dose-dependent manner. Importantly, the restored blood glucose levels could persist 10 days after withdrawal of GF treatment. The hepatic AKT/GSK3β/FoxO1 pathway is shown to be the main target of GF for re-balancing gluconeogenesis and glycogen synthesis in vivo and in vitro. In addition, GF treatment significantly reduced weight gain of db/db mice with reduced hepatic fat storage by the inhibition of de novo lipogenesis through mTOR/S6K/SREBP1 pathway. Our data provide compelling evidence to support the promising application of GF for the treatment of T2DM.

Role of hepatic PKCβ in nutritional regulation of hepatic glycogen synthesis

The signaling mechanisms by which dietary fat and cholesterol signals regulate central pathways of glucose homeostasis are not completely understood. By using a hepatocyte-specific PKCβ-deficient (PKCβHep-/-) mouse model, we demonstrated the role of hepatic PKCβ in slowing disposal of glucose overload by suppressing glycogenesis and increasing hepatic glucose output. PKCβHep-/- mice exhibited lower plasma glucose under the fed condition, modestly improved systemic glucose tolerance and mildly suppressed gluconeogenesis, increased hepatic glycogen accumulation and synthesis due to elevated glucokinase expression and activated glycogen synthase (GS), and suppressed glucose-6-phosphatase expression compared with controls. These events were independent of hepatic AKT/GSK-3α/β signaling and were accompanied by increased HNF-4α transactivation, reduced FoxO1 protein abundance, and elevated expression of GS targeting protein phosphatase 1 regulatory subunit 3C in the PKCβHep-/- liver compared with controls. The above data strongly imply that hepatic PKCβ deficiency causes hypoglycemia postprandially by promoting glucose phosphorylation via upregulating glucokinase and subsequently redirecting more glucose-6-phosphate to glycogen via activating GS. In summary, hepatic PKCβ has a unique and essential ability to induce a coordinated response that negatively affects glycogenesis at multiple levels under physiological postprandial conditions, thereby integrating nutritional fat intake with dysregulation of glucose homeostasis.

Differential roles of FOXO transcription factors on insulin action in brown and white adipose tissue

Insulin and IGF-1 are essential for adipocyte differentiation and function. Mice lacking insulin and IGF-1 receptors in fat (FIGIR-KO, fat-specific IGF-1 receptor and insulin receptor-KO) exhibit complete loss of white and brown adipose tissue (WAT and BAT), glucose intolerance, insulin resistance, hepatosteatosis, and cold intolerance. To determine the role of FOXO transcription factors in the altered adipose phenotype, we generated FIGIR-KO mice with fat-specific KO of fat-expressed Foxos [Foxo1, Foxo3, Foxo4] (F-Quint-KO). Unlike FIGIR-KO mice, F-Quint-KO mice had normal BAT, glucose tolerance, insulin-regulated hepatic glucose production, and cold tolerance. However, loss of FOXOs only partially rescued subcutaneous WAT and hepatosteatosis, did not rescue perigonadal WAT or systemic insulin resistance, and led to even more marked hyperinsulinemia. Thus, FOXOs play different roles in insulin/IGF-1 action in different adipose depots, being most important in BAT, followed by subcutaneous WAT and then by visceral WAT. Disruption of FOXOs in fat also led to a reversal of insulin resistance in liver, but not in skeletal muscle, and an exacerbation of hyperinsulinemia. Thus, adipose FOXOs play a unique role in regulating crosstalk between adipose depots, liver, and β cells.

Mibefradil reduces hepatic glucose output in HepG2 cells via Ca2+/calmodulin-dependent protein kinase II-dependent Akt/forkhead box O1signaling

The effects and underlying mechanisms of mibefradil on gluconeogenesis and glycogenesis were investigated using insulin-resistant HepG2 human hepatocellular carcinoma cells and a mouse model of type 2 diabetes mellitus (T2DM). HepG2 cells were divided into one of four groups: control, palmitate (PA)-induced insulin-resistance (0.25 mM), low-concentration mibefradil (0.025 μM), or high-concentration mibefradil (0.05 μM). Glycogen synthesis and glucose consumption were evaluated in these HepG2 cells, and quantitative polymerase chain reaction (qPCR) and western blotting techniques were used to detect expression of forkhead box O1 (FoxO1), phosphoenolpyruvate carboxykinase (PEPCK), and glucose 6-phosphatase (G6Pase). Intracellular calcium concentrations were determined using Fluo-4 AM, and phosphorylation levels of calmodulin-dependent protein kinase II (CaMKII), protein kinase B (Akt) and FoxO1were detected by western blotting. Immunofluorescence was used for the localization and quantification of FoxO1.In vitro results were verified using a mouse model of T2DM. In HepG2 cells and mouse liver tissues, mibefradil decreased PA-induced cytoplasmic calcium levels and CaMKII phosphorylation, but increased the phosphorylation of Akt and FoxO1, thereby contributing to the cytoplasmic localization of FoxO1. Additionally, mibefradil alleviated PA-induced glucose output and insulin resistance through increased glucose consumption and glycogen synthesis, while decreasing the expression of key gluconeogenesis enzymes, including PEPCK and G6Pase. Mibefradil may help to control blood sugar levels by reducing glucose output and insulin resistance, and the mechanism of action may involve the Ca2+-CaMKII-dependent Akt/FoxO1 signaling pathway.

Effects of High Dietary Carbohydrate and Lipid Intake on the Lifespan of C. elegans

Health and lifespan are influenced by dietary nutrients, whose balance is dependent on the supply or demand of each organism. Many studies have shown that an increased carbohydrate–lipid intake plays a critical role in metabolic dysregulation, which impacts longevity. Caenorhabditis elegans has been successfully used as an in vivo model to study the effects of several factors, such as genetic, environmental, diet, and lifestyle factors, on the molecular mechanisms that have been linked to healthspan, lifespan, and the aging process. There is evidence showing the causative effects of high glucose on lifespan in different diabetic models; however, the precise biological mechanisms affected by dietary nutrients, specifically carbohydrates and lipids, as well as their links with lifespan and longevity, remain unknown. Here, we provide an overview of the deleterious effects caused by high-carbohydrate and high-lipid diets, as well as the molecular signals that affect the lifespan of C. elegans; thus, understanding the detailed molecular mechanisms of high-glucose- and lipid-induced changes in whole organisms would allow the targeting of key regulatory factors to ameliorate metabolic disorders and age-related diseases.

Insulin signaling in health and disease

The molecular mechanisms of cellular insulin action have been the focus of much investigation since the discovery of the hormone 100 years ago. Insulin action is impaired in metabolic syndrome, a condition known as insulin resistance. The actions of the hormone are initiated by binding to its receptor on the surface of target cells. The receptor is an α2β2 heterodimer that binds to insulin with high affinity, resulting in the activation of its tyrosine kinase activity. Once activated, the receptor can phosphorylate a number of intracellular substrates that initiate discrete signaling pathways. The tyrosine phosphorylation of some substrates activates phosphatidylinositol-3-kinase (PI3K), which produces polyphosphoinositides that interact with protein kinases, leading to activation of the kinase Akt. Phosphorylation of Shc leads to activation of the Ras/MAP kinase pathway. Phosphorylation of SH2B2 and of Cbl initiates activation of G proteins such as TC10. Activation of Akt and other protein kinases produces phosphorylation of a variety of substrates, including transcription factors, GTPase-activating proteins, and other kinases that control key metabolic events. Among the cellular processes controlled by insulin are vesicle trafficking, activities of metabolic enzymes, transcriptional factors, and degradation of insulin itself. Together these complex processes are coordinated to ensure glucose homeostasis.