Geranylgeranyl isoprenoids and hepatic Rap1a regulate basal and statin-induced expression of PCSK9

LDL-C lowering is the main goal of atherosclerotic cardiovascular disease prevention, and proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibition is now a validated therapeutic strategy that lowers serum LDL-C and reduces coronary events. Ironically, the most widely used medicine to lower cholesterol, statins, has been shown to increase circulating PCSK9 levels, which limits their efficacy. Here, we show that geranylgeranyl isoprenoids and hepatic Rap1a regulate both basal and statin-induced expression of PCSK9 and contribute to LDL-C homeostasis. Rap1a prenylation and activity is inhibited upon statin treatment, and statin-mediated PCSK9 induction is dependent on geranylgeranyl synthesis and hepatic Rap1a. Accordingly, treatment of mice with a small-molecule activator of Rap1a lowered PCSK9 protein and plasma cholesterol and inhibited statin-mediated PCSK9 induction in hepatocytes. The mechanism involves inhibition of the downstream RhoA-ROCK pathway and regulation of PCSK9 at the post-transcriptional level. These data further identify Rap1a as a novel regulator of PCSK9 protein and show that blocking Rap1a prenylation through lowering geranylgeranyl levels contributes to statin-mediated induction of PCSK9.

Rap1 in the Context of PCSK9, Atherosclerosis, and Diabetes

PURPOSE OF REVIEW

The focus of this article is to highlight the importance of the small GTPase, Ras-associated protein 1 (Rap1), in proprotein convertase subtilisin/kexin type 9 (PCSK9) regulation and atherosclerosis and type 2 diabetes etiology and discuss the potential therapeutic implications of targeting Rap1 in these disease areas.

REVIEW FINDINGS

Cardiometabolic disease characterized by obesity, glucose intolerance, dyslipidemia, and atherosclerotic cardiovascular disease remain an important cause of mortality. Evidence using mouse models of obesity and insulin resistance indicates that Rap1 deficiency increases proatherogenic PCSK9 and low-density lipoprotein cholesterol levels and predisposes these mice to develop obesity- and statin-induced hyperglycemia, which highlights Rap1's role in cardiometabolic dysfunction. Rap1 may also contribute to cardiovascular disease through its effects on vascular wall cells involved in the atherosclerosis progression. Rap1 activation, specifically in the liver, could be beneficial in the prevention of cardiometabolic perturbations, including type 2 diabetes, hypercholesterolemia, and atherosclerosis.

Rap1 Activation Protects Against Fatty Liver and Non-Alcoholic Steatohepatitis Development

We previously demonstrated that hepatic activation of a small G protein of the Ras family, Rap1a, is suppressed in obesity, which results in increased hepatic glucose production and glucose intolerance in obese mice. Here, we show that Rap1a inhibition in obese mice liver also results in fatty liver formation, which is characteristic of the diabetic liver. Specifically, we report that Rap1a activity is decreased in the livers of patients with non-alcoholic steatohepatitis (NASH) and mouse models of non-alcoholic fatty liver disease (NAFLD) and NASH. Restoring hepatic Rap1a activity by overexpressing a constitutively active mutant form of Rap1a lowered the mature, processed form of lipogenic transcription factor, Srebp1, without an effect on the unprocessed Srebp1 and suppressed hepatic TG accumulation, whereas liver Rap1a deficiency increased Srebp1 processing and exacerbated steatosis. Mechanistically, we show that mTORC1, which promotes Srebp1 cleavage, is hyperactivated upon Rap1a deficiency despite disturbed insulin signaling. In proof-of-principle studies, we found that treatment of obese mice with a small molecule activator of Rap1a (8-pCPT) or inhibiting Rap1a's endogenous inhibitor, Rap1Gap, recapitulated our hepatic gain-of-function model and resulted in improved hepatic steatosis and lowered lipogenic genes. Thus, hepatic Rap1a serves as a signaling molecule that suppresses both hepatic gluconeogenesis and steatosis, and inhibition of its activity in the liver contributes to the pathogenesis of glucose intolerance and NAFLD/NASH development.

Geranylgeranyl Isoprenoids and Hepatic Rap1a Regulate Basal and Statin-Induced Expression of PCSK9

Low-density lipoprotein cholesterol (LDL-C) lowering is the main goal of atherosclerotic cardiovascular disease prevention, and proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibition is now a validated therapeutic strategy that lowers serum LDL-C and reduces coronary events. Ironically, the most widely used medicine to lower cholesterol, statins, has been shown to increase circulating PCSK9 levels, which limits their efficacy. Here, we show that geranylgeranyl isoprenoids and hepatic Rap1a regulate both basal and statin induced expression of PCSK9 and contribute to LDL-C homeostasis. Rap1a prenylation and activity is inhibited upon statin treatment, and statin mediated PCSK9 induction is dependent on geranylgeranyl synthesis and hepatic Rap1a. Accordingly, treatment of mice with a small molecule activator of Rap1a lowered PCSK9 protein and plasma cholesterol and inhibited statin mediated PCSK9 induction in hepatocytes. The mechanism involves inhibition of the downstream RhoA-ROCK pathway and regulation of PCSK9 at the post transcriptional level. These data further identify Rap1a as a novel regulator of PCSK9 protein and show that blocking Rap1a prenylation through lowering geranylgeranyl levels contributes to statin-mediated induction of PCSK9.

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.

Effect of Oltipraz on urethral healing: An experimental study

BACKGROUND

We aimed to examine the oral and topical effect of Oltipraz (OPZ) on fibrosis and healing after urethra injury in a rat model.

METHODS

In all, 33 adult Sprague-Dawley rats were divided randomly into 5 different groups: sham, urethral injury group (UI), oral Oltipraz treatment group for 14 days after urethral injury (UI+oOPZ), intraurethral Oltipraz treatment group for 14 days after urethral injury (UI+iOPZ) and only intraurethral Oltipraz treatment for 14 days without urethral injury (sham+iOPZ). Pediatric urethrotome blade was used to create the urethral injury model for the injury groups (UI, UI+oOPZ and UI+iOPZ). After 14 days of treatment, all rats were sacrificed after penectomy under general anesthesia. Urethral tissue was evaluated histopathologically for congestion, inflammatory cell infiltration and spongiofibrosis, and immunohistochemically for transforming growth factor Beta-1 (TBF) and vascular endothelial growth factor receptor2 (VEGFR2).

RESULTS

The congestion score was not statistically significantly different between the groups. Spongiofibrosis was distinctive in UI group and OPZ given groups. Inflammation and spongiofibrosis score were statistically significantly higher in the sham+iOPZ group compared to the sham group (P<0.05). VEGFR2 and TGF Beta-1 scores were statistically significantly higher in the sham+iOPZ group compared to the sham group (P<0.05). We did not find beneficial effect of OPZ on urethral healing. We found the harmful effect of intraurethral administration of OPZ in the group without urethral injury in compared to sham.

CONCLUSIONS

According to our results, we cannot suggest OPZ in the treatment of urethral injury. Future studies in this area are needed.

Effect of Nintedanib on healing and fibrosis in rats with experimentally induced urethral injury

AIM

We aimed to determine the effectiveness of Nintedanib treatment, which has known antifibrotic effect, in preventing fibrosis after urethral trauma.

MATERIAL AND METHODS

Twenty-three adult Sprague-Dawley rats were divided randomly into 3 different groups: Sham, Urethral injury group (UI) and Urethral injury+ Nintedanib (UI+N). The urethral injury model was made with a pediatric urethrotome knife. Nintedanib was administered at a dose of 50mg/kg by oral gavage for 14 days at the same time every day. After 14 days of treatment, all rats were performed penectomy under general anesthesia. Urethral tissue was evaluated histopathologically (congestion, inflammatory cell infiltration and spongiofibrosis) and immunohistochemically (transforming growth factor (TBF) Beta-1 and vascular endothelial growth factor receptor 2 (VEBFR2)).

RESULTS

Histopathological findings: Group UI had higher scores in all categories (congestion, inflammatory cell infiltration, and spongiofibrosis), followed by Group UI+N and Group Sham, respectively. A statistically significant difference was found between Group UI and Group UI+N in terms of the scores of histopathological parameters (p<0.05). Immunohistochemical findings: Group UI had higher scores in both categories, followed by Group UI+N and Group Sham, respectively. A statistically significant difference was found between Group UI and Group UI+N in TGF Beta-1 and VEGF scores (p<0.05).

CONCLUSION

We found that Nintedanib administration after urethral trauma reduced inflammation and fibrosis histologically and immunohistochemically. The positive effect of Nintedanib on inflammation and fibrosis after urethral trauma reported in this animal study is encouraging for a potential clinical human application.

Evaluation of Telemedicine awareness, knowledge, attitude, skill levels of physicians and students

Background

The increase in the use of information and communication technologies around the world brings about developments and changes in the provision of health services. It is accepted that telemedicine applications will facilitate health services for patients and health personnel. This study aimed to evaluate the telemedicine awareness, knowledge, attitude and skill levels of physicians and medical school students.

Methods

This cross-sectional study was conducted between July and August 2021. A questionnaire form was prepared using the relevant literature then filled online by the participants. Telemedicine Awareness, Knowledge, Attitudes and Skills Questionnaire was used in the research. The universe of the research consisted of medical faculty students and physicians across Turkey. In the study, 933 people were reached by using the purposeful snowball sampling method, one of the non-probability sampling methods. Mann Whitney-U test, Kruskal Wallis test, Spearman correlation analysis and Multiple Linear Regression analysis were used.

Results

Of the participants, 442 (47.4%) were female, 497 (53.3%) were medical students, and 436 (46.7%) were physicians. Their ages ranged from 18 to 59, with a mean of 28.0±8.8 years. The median (min-max) scores obtained from the Telemedicine Awareness (TA) sub-section were 18(0-24), 51.3% of them had scores above the median score. TA sub-section had a moderate positive correlation (r = 0.559, p &lt; 0.001) with knowledge sub-section and a weak positive correlation (r = 0.208, p &lt; 0.001) with skill level sub-section. TA scores were higher among men, physicians and those who want to participate in a telemedicine training program. TA increased as the level of computer and internet knowledge increased (F = 29.171, R2=0.197, p &lt; 0.001).

Conclusions

It can be said that TA is at a moderate level among medical students and physicians in Turkey. TA increased as the level of computer and internet knowledge, telemedicine knowledge and skills increased.

Key messages

Hepatocyte Rap1a contributes to obesity- and statin-associated hyperglycemia

Excessive hepatic glucose production contributes to the development of hyperglycemia and is a key feature of type 2 diabetes. Here, we report that activation of hepatocyte Rap1a suppresses gluconeogenic gene expression and glucose production, whereas Rap1a silencing stimulates them. Rap1a activation is suppressed in obese mouse liver, and restoring its activity improves glucose intolerance. As Rap1a′s membrane localization and activation depends on its geranylgeranylation, which is inhibited by statins, we show that statin-treated hepatocytes and the human liver have lower active-Rap1a levels. Similar to Rap1a inhibition, statins stimulate hepatic gluconeogenesis and increase fasting blood glucose in obese mice. Geranylgeraniol treatment, which acts as the precursor for geranylgeranyl isoprenoids, restores Rap1a activity and improves statin-mediated glucose intolerance. Mechanistically, Rap1a activation induces actin polymerization, which suppresses gluconeogenesis by Akt-mediated FoxO1 inhibition. Thus, Rap1a regulates hepatic glucose homeostasis, and blocking its activity, via lowering geranylgeranyl isoprenoids, contributes to statin-induced glucose intolerance.

Wang et al. show that activation of hepatic Rap1a suppresses gluconeogenic gene expression and improves glucose intolerance via Akt-mediated FoxO1 inhibition. Statins lower intracellular isoprenoid levels and inhibit Rap1a activation, which contributes to their hyperglycemic effect. These findings identify a role of hepatic Rap1a in obesity- and statin-associated glucose homeostasis.

Adipocyte CAMK2 deficiency improves obesity-associated glucose intolerance

OBJECTIVE

Obesity-related adipose tissue dysfunction has been linked to the development of insulin resistance, type 2 diabetes, and cardiovascular disease. Impaired calcium homeostasis is associated with altered adipose tissue metabolism; however, the molecular mechanisms that link disrupted calcium signaling to metabolic regulation are largely unknown. Here, we investigated the contribution of a calcium-sensing enzyme, calcium/calmodulin-dependent protein kinase II (CAMK2), to adipocyte function, obesity-associated insulin resistance, and glucose intolerance.

METHODS

To determine the impact of adipocyte CAMK2 deficiency on metabolic regulation, we generated a conditional knockout mouse model and acutely deleted CAMK2 in mature adipocytes. We further used in vitro differentiated adipocytes to dissect the mechanisms by which CAMK2 regulates adipocyte function.

RESULTS

CAMK2 activity was increased in obese adipose tissue, and depletion of adipocyte CAMK2 in adult mice improved glucose intolerance and insulin resistance without an effect on body weight. Mechanistically, we found that activation of CAMK2 disrupted adipocyte insulin signaling and lowered the amount of insulin receptor. Further, our results revealed that CAMK2 contributed to adipocyte lipolysis, tumor necrosis factor alpha (TNFα)-induced inflammation, and insulin resistance.

CONCLUSIONS

These results identify a new link between adipocyte CAMK2 activity, metabolic regulation, and whole-body glucose homeostasis.

Parental Beliefs on the Harmfull Effects of Third Hand Smoke: Systematic Review and Meta-analysis

Background

Third-hand smoke (THS); occurs as a result of the reaction of tobacco smoke residues left on furnitures or on smokers with the chemical substances in the environment. Children are a risky group in terms of THS exposure because they spend a lot of time at home and touch surfaces frequently. The aim is to systematically compile and meta-analyze studies in which parents' beliefs that THS are harmful are evaluated.

Methods

Pubmed, Scpous and Web of Science databases were scanned until April 6, 2021. Selective keywords were ‘third-hand smoke', ‘third hand smoke', ‘thirdhand smoke' and ‘belief'. Articles that were found to be suitable for the purpose of the study were also included by manually searching the references of the included articles. The PRISMA checklist was followed in the study. Studies that could not be clearly differentiated from THS from second-hand tobacco smoke and were not performed in parents were excluded. Duplicates were eliminated and the remaining article abstracts were read double-blind. Study data were entered into the OpenMeta [Analyst] program. Fixed effects model in the presence of homogeneous groups and random effects model in the presence of heterogeneous groups were used.

Results

As a result of the first literature search, 302 articles were reached. A total of 7 studies were included in the meta-analysis. As a result of the analysis, 4274 (57.3%, 95% CI 51.5-63.2) of 7632 parents were smoking and 5864 (76.3%, 95 CI 64.3-88.4) believed THS harms the health of children. In 4 studies, 2037 of 3581 parents (45.2%, 95% CI 24.2-66.1) were implementing a smoking ban at home. In 3 studies, the belief that THS is harmful to child health was higher in the presence of smoking ban at home (OR: 2.03, 95% GA 1.45-2.85, p &lt; 0.001).

Conclusions

The frequency of smoking and smoking at home is high in parents. One in four parents does not believe THS is harmful to children's health.

Key messages

In order to protect children from THS harms, it is not enough just to not smoke in the house, and smoking should be evoided everywhere. Educational interventions should be planned to convince parents about the harmful effects of THS on child health.

Double daily doses of cetrorelix may raise follicular phase progesterone more compared to single doses in poor ovarian response patients

PURPOSE

There is evidence that follicular phase progesterone rise [FPPR] adversely affects fresh in vitro fertilization [IVF] cycles. A single daily dose of cetrorelix has been used to prevent early luteinizing Hormone (LH) surge. We speculated that doubling the daily dose might have a positive effect in patients who have early LH surges despite receiving the single daily dose treatment. However, a double daily dose of cetrorelix seems to cause FPPR in poor ovarian response (POR) patients.

MATERIALS AND METHODS

On human chorionic gonadotropin [hCG] injection days, the progesterone levels of POR patients who received a single daily dose of cetrorelix (group 1, n = 59) were compared with progesterone levels of the patients who received a double daily dose of cetrorelix (group 2, n = 75). The two groups had statistically similar demographic data. The patients who had FPPR were detected, and a comparison of progesterone levels, using 0.8, 1.0, and 1.2 [ng/mL] of progesterone as cut-off levels, was made between patients of both groups.

RESULTS

FPPR patients in group 2 had significantly higher progesterone levels during hCG day, contrary to expectations. When progesterone cut-off levels of 0.8, 1.0, and 1.2 [ng/mL] were used for group 1 patients, 15.3%, 13.6%, and 6.8% of the patients developed FPPR, respectively When the progesterone cut-off levels of 0.8, 1.0, and 1.2 [ng/mL] were used for group 2, the results detected were 45.3%, 30.7%, and 21.3%, respectively. A significant statistical difference in progesterone levels was observed between the groups.

CONCLUSION

While the double daily dose of cetrorelix was initially thought to more effectively suppress early LH rise by some authors, we have seen that it increases the FPPR more when compared to a single daily dose regime. We suggest using frozen cycles instead of fresh cycles in order to have better endometrial receptivity in patients who seem to benefit from higher daily doses of cetrorelix.

Allosteric MAPKAPK2 inhibitors improve plaque stability in advanced atherosclerosis

Atherosclerotic vascular disease resulting from unstable plaques is the leading cause of morbidity and mortality in subjects with type 2 diabetes (T2D), and thus a major therapeutic goal is to discover T2D drugs that can also promote atherosclerotic plaque stability. Genetic or pharmacologic inhibition of mitogen-activated protein kinase-activated protein kinase-2 (MAPKAPK2 or MK2) in obese mice improves glucose homeostasis and enhances insulin sensitivity. We developed two novel orally active small-molecule inhibitors of MK2, TBX-1 and TBX-2, and tested their effects on metabolism and atherosclerosis in high-fat Western diet (WD)-fed Ldlr-/- mice. Ldlr-/- mice were first fed the WD to allow atherosclerotic lesions to become established, and the mice were then treated with TBX-1 or TBX-2. Both compounds improved glucose metabolism and lowered plasma cholesterol and triglyceride, without an effect on body weight. Most importantly, the compounds decreased lesion area, lessened plaque necrosis, and increased fibrous cap thickness in the aortic root lesions of the mice. Thus, in a preclinical model of high-fat feeding and established atherosclerosis, MK2 inhibitors improved metabolism and also enhanced atherosclerotic plaque stability, suggesting potential for further clinical development to address the epidemic of T2D associated with atherosclerotic vascular disease.

Interacting hepatic PAI-1/tPA gene regulatory pathways influence impaired fibrinolysis severity in obesity

Fibrinolysis is initiated by tissue-type plasminogen activator (tPA) and inhibited by plasminogen activator inhibitor 1 (PAI-1). In obese humans, plasma PAI-1 and tPA proteins are increased, but PAI-1 dominates, leading to reduced fibrinolysis and thrombosis. To understand tPA–PAI-1 regulation in obesity, we focused on hepatocytes, a functionally important source of tPA and PAI-1 that sense obesity-induced metabolic stress. We showed that obese mice, like humans, had reduced fibrinolysis and increased plasma PAI-1 and tPA, due largely to their increased hepatocyte expression. A decrease in the PAI-1 (SERPINE1) gene corepressor Rev-Erbα increased PAI-1, which then increased the tPA gene PLAT via a PAI-1/LRP1/PKA/p-CREB1 pathway. This pathway was partially counterbalanced by increased DACH1, a PLAT-negative regulator. We focused on the PAI-1/PLAT pathway, which mitigates the reduction in fibrinolysis in obesity. Thus, silencing hepatocyte PAI-1, CREB1, or tPA in obese mice lowered plasma tPA and further impaired fibrinolysis. The PAI-1/PLAT pathway was present in primary human hepatocytes, and associations among PAI-1, tPA, and PLAT in livers from obese and lean humans were consistent with these findings. Knowledge of PAI-1 and tPA regulation in hepatocytes in obesity may suggest therapeutic strategies for improving fibrinolysis and lowering the risk of thrombosis in this setting.

Targeting NASH with OxPL neutralization

Accumulation of oxidized phospholipids (OxPLs) contribute to NASH development.

Biliopancreatic diversion is beyond just weight loss

Biliopancreatic diversion slows glucose absorption and increases insulin sensitivity, which results in better glycemic control than other gastric bypass procedures.

Hepatic Glucagon Signaling Regulates PCSK9 and Low-Density Lipoprotein Cholesterol

RATIONALE

Glucagon is a key hormone that regulates the adaptive metabolic responses to fasting. In addition to maintaining glucose homeostasis, glucagon participates in the regulation of cholesterol metabolism; however, the molecular pathways underlying this effect are incompletely understood.

OBJECTIVE

We sought to determine the role of hepatic Gcgr (glucagon receptor) signaling in plasma cholesterol regulation and identify its underlying molecular mechanisms.

METHODS AND RESULTS

We show that Gcgr signaling plays an essential role in LDL-C (low-density lipoprotein cholesterol) homeostasis through regulating the PCSK9 (proprotein convertase subtilisin/kexin type 9) levels. Silencing of hepatic Gcgr or inhibition of glucagon action increased hepatic and plasma PCSK9 and resulted in lower LDLR (LDL receptor) protein and increased plasma LDL-C. Conversely, treatment of wild-type (WT) mice with glucagon lowered LDL-C levels, whereas this response was abrogated in Pcsk9^-/- and Ldlr^-/- mice. Our gain- and loss-of-function studies identified Epac2 (exchange protein activated by cAMP-2) and Rap1 (Ras-related protein-1) as the downstream mediators of glucagon's action on PCSK9 homeostasis. Moreover, mechanistic studies revealed that glucagon affected the half-life of PCSK9 protein without changing the level of its mRNA, indicating that Gcgr signaling regulates PCSK9 degradation.

CONCLUSIONS

These findings provide novel insights into the molecular interplay between hepatic glucagon signaling and lipid metabolism and describe a new posttranscriptional mechanism of PCSK9 regulation.

More than a gut feeling

Intestinal IgA contributes to high-fat diet feeding–induced glucose intolerance.

A new player in hunger games

Hypoleptinemia-mediated food intake requires the activation of the hypothalamic-pituitary-adrenal axis.

Proprotein convertase subtilisin/kexin type 9 and lipid metabolism

PURPOSE OF REVIEW

The purpose of this review is to highlight the recent findings of one of the most promising therapeutic targets in LDL cholesterol (LDL-C) management, proprotein convertase subtilisin/kexin type 9 (PCSK9).

RECENT FINDINGS

Endoplasmic reticulum cargo receptor, surfeit locus protein 4 interacts with PCSK9 and regulates its exit from endoplasmic reticulum and its secretion. Once secreted, PCSK9 binds to heparin sulfate proteoglycans on the hepatocyte surface and this binding is required for PCSK9-LDL receptor (LDLR) complex formation and LDLR degradation. Posttranscriptionally, recent work has shown that PCSK9 gets degraded in lysosomes by activation of the glucagon receptor signaling, providing more data on the hormonal regulation of PCSK9. Finally, human studies with PCSK9 inhibitors offered more evidence on their benefits and safe use.

SUMMARY

Recent work on the regulation of PCSK9 has enhanced our understanding of its biology, which may provide important information for future PCSK9-based therapies.

And the MVP award goes to: Major vault protein

MVP functions as an endogenous suppressor of NF-κB and regulates obesity-associated metabolic disease.

When fat is beneficial

In response to exercise, adipose tissue secretes TGF-β2 that improves metabolic health.

A Hepatocyte FOXN3-α Cell Glucagon Axis Regulates Fasting Glucose

The common genetic variation at rs8004664 in the FOXN3 gene is independently and significantly associated with fasting blood glucose, but not insulin, in non-diabetic humans. Recently, we reported that primary hepatocytes from rs8004664 hyperglycemia risk allele carriers have increased FOXN3 transcript and protein levels and liver-limited overexpression of human FOXN3, a transcriptional repressor that had not been implicated in metabolic regulation previously, increases fasting blood glucose in zebrafish. Here, we find that injection of glucagon into mice and adult zebrafish decreases liver Foxn3 protein and transcript levels. Zebrafish foxn3 loss-of-function mutants have decreased fasting blood glucose, blood glucagon, liver gluconeogenic gene expression, and α cell mass. Conversely, liver-limited overexpression of foxn3 increases α cell mass. Supporting these genetic findings in model organisms, non-diabetic rs8004664 risk allele carriers have decreased suppression of glucagon during oral glucose tolerance testing. By reciprocally regulating each other, liver FOXN3 and glucagon control fasting glucose.

Abstract 177: Glucagon Receptor Signaling-Mediated Regulation of PCSK9 and Cholesterol Metabolism

Glucagon is one of the key hormones important in hepatic glucose homeostasis, and the pathophysiological role of hyperglucagonemia and unopposed hepatic glucagon action in type 2 diabetes (T2D) is now well-established. Accordingly, there has been great interest in developing glucagon receptor antagonists (GRAs) as a treatment for T2D. Although phase 2 clinical trials have shown that GRAs effectively lower blood glucose in T2D subjects, they increase plasma low density lipoprotein cholesterol (LDL-C), which has presented a significant block to their development. Consistent with a role of glucagon in cholesterol metabolism, recent studies suggested that proprotein convertase subtilisin/kexin type 9 (PCSK9), which increases plasma LDL-C through targeting LDL receptor (LDLR) for degradation, can be regulated by fasting, however, in-depth mechanistic information is lacking. In order to test the functional importance of hepatic glucagon action on cholesterol metabolism, we silenced hepatic glucagon receptor (GcgR) in obese mice using AAV8-mediated shRNA treatment. Consistent with previous reports, this treatment effectively lowered blood glucose in obese mice without a change in body weight. Moreover, GcgR silencing, like GRAs in humans, significantly increased plasma LDL-C. In search for the mechanism, we found that inhibition of GcgR significantly lowered hepatic LDLR protein levels and increased both hepatic and circulating PCSK9, without an effect on cholesterol synthesis. To determine causation, we silenced hepatic GcgR together with PCSK9 using AAV8 and found that this intervention restored hepatic LDLR and prevented the increase in plasma LDL-C. Further mechanistic studies showed that GcgR silencing in hepatocytes did not increase Pcsk9 mRNA. Rather, blocking GcgR increased the half-life of PCSK9 protein by suppressing signalling through exchange protein activated by cAMP-2 (Epac2). In particular, the ability of GcgR silencing to increase PCSK9 and suppress LDLR protein levels was mimicked by hepatocytes lacking Epac2. Thus, GcgR signalling through Epac2 appears to have critical effects on processes that regulate cholesterol metabolism through PCSK9.

Degradation of PHLPP2 by KCTD17, via a Glucagon-Dependent Pathway, Promotes Hepatic Steatosis

BACKGROUND & AIMS

Obesity-induced nonalcoholic fatty liver disease (NAFLD) develops, in part, via excess insulin-stimulated hepatic de novo lipogenesis, which increases, paradoxically, in patients with obesity-induced insulin resistance. Pleckstrin homology domain leucine-rich repeat protein phosphatase 2 (PHLPP2) terminates insulin signaling by dephosphorylating Akt; levels of PHLPP2 are reduced in livers from obese mice. We investigated whether loss of hepatic PHLPP2 is sufficient to induce fatty liver in mice, mechanisms of PHLPP2 degradation in fatty liver, and expression of genes that regulate PHLPP2 in livers of patients with NAFLD.

METHODS

C57BL/6J mice (controls), obese db/db mice, and mice with liver-specific deletion of PHLPP2 (L-PHLPP2) fed either normal chow or high-fat diet (HFD) were analyzed for metabolic phenotypes, including glucose tolerance and hepatic steatosis. PHLPP2-deficient primary hepatocytes or CRISPR/Cas9-mediated PHLPP2-knockout hepatoma cells were analyzed for insulin signaling and gene expression. We performed mass spectrometry analyses of liver tissues from C57BL/6J mice transduced with Ad-HA-Flag-PHLPP2 to identify posttranslational modifications to PHLPP2 and proteins that interact with PHLPP2. We measured levels of mRNAs by quantitative reverse transcription polymerase chain reaction in liver biopsies from patients with varying degrees of hepatic steatosis.

RESULTS

PHLPP2-knockout hepatoma cells and hepatocytes from L-PHLPP2 mice showed normal initiation of insulin signaling, but prolonged insulin action. Chow-fed L-PHLPP2 mice had normal glucose tolerance but hepatic steatosis. In HFD-fed C57BL/6J or db/db obese mice, endogenous PHLPP2 was degraded by glucagon and PKA-dependent phosphorylation of PHLPP2 (at Ser1119 and Ser1210), which led to PHLPP2 binding to potassium channel tetramerization domain containing 17 (KCTD17), a substrate-adaptor for Cul3-RING ubiquitin ligases. Levels of KCTD17 mRNA were increased in livers of HFD-fed C57BL/6J or db/db obese mice and in liver biopsies patients with NAFLD, compared with liver tissues from healthy control mice or patients without steatosis. Knockdown of KCTD17 with small hairpin RNA in primary hepatocytes increased PHLPP2 protein but not Phlpp2 mRNA, indicating that KCTD17 mediates PHLPP2 degradation. KCTD17 knockdown in obese mice prevented PHLPP2 degradation and decreased expression of lipogenic genes.

CONCLUSIONS

In mouse models of obesity, we found that PHLPP2 degradation induced lipogenesis without affecting gluconeogenesis. KCTD17, which is up-regulated in liver tissues of obese mice and patients with NAFLD, binds to phosphorylated PHLPP2 to target it for ubiquitin-mediated degradation; this increases expression of genes that regulate lipogenesis to promote hepatic steatosis. Inhibitors of this pathway might be developed for treatment of patients with NAFLD.

CAMKIIγ suppresses an efferocytosis pathway in macrophages and promotes atherosclerotic plaque necrosis

Atherosclerosis is the underlying etiology of cardiovascular disease, the leading cause of death worldwide. Atherosclerosis is a heterogeneous disease in which only a small fraction of lesions lead to heart attack, stroke, or sudden cardiac death. A distinct type of plaque containing large necrotic cores with thin fibrous caps often precipitates these acute events. Here, we show that Ca2+/calmodulin-dependent protein kinase γ (CaMKIIγ) in macrophages plays a major role in the development of necrotic, thin-capped plaques. Macrophages in necrotic and symptomatic atherosclerotic plaques in humans as well as advanced atherosclerotic lesions in mice demonstrated activation of CaMKII. Western diet-fed LDL receptor-deficient (Ldlr-/-) mice with myeloid-specific deletion of CaMKII had smaller necrotic cores with concomitantly thicker collagen caps. These lesions demonstrated evidence of enhanced efferocytosis, which was associated with increased expression of the macrophage efferocytosis receptor MerTK. Mechanistic studies revealed that CaMKIIγ-deficient macrophages and atherosclerotic lesions lacking myeloid CaMKIIγ had increased expression of the transcription factor ATF6. We determined that ATF6 induces liver X receptor-α (LXRα), an Mertk-inducing transcription factor, and that increased MerTK expression and efferocytosis in CaMKIIγ-deficient macrophages is dependent on LXRα. These findings identify a macrophage CaMKIIγ/ATF6/LXRα/MerTK pathway as a key factor in the development of necrotic atherosclerotic plaques.

Abstract 203: Role of Glucagon Receptor Signalling in PCSK9 Regulation

Excessive glucagon receptor action in hepatocytes is a major contributing factor to type 2 diabetes (T2D). Accordingly, there has been great interest in developing glucagon receptor antagonists (GRAs) as a treatment for T2D. Although phase 2 clinical trials have shown that GRAs effectively lower blood glucose in T2D subjects, they increase plasma low density lipoprotein (LDL) cholesterol levels, which has presented a significant block to their development. In this context, recent studies have suggested that cholesterol and proprotein convertase subtilisin/kexin type 9 (PCSK9) levels can be regulated by fasting and perhaps glucagon, but in-depth mechanistic insight is lacking. In order to test the functional importance of hepatic glucagon action on lipid metabolism, we silenced glucagon receptor (GcgR) in obese mice using AAV8-H1-shGcgr to silence the receptor in hepatocytes. Consistent with previous reports, this treatment effectively lowered blood glucose in obese mice without a change in body weight. Moreover, GcgR silencing, like GRAs in humans, significantly increased plasma LDL cholesterol. In search for the mechanism, we found that inhibition of GcgR significantly lowered hepatic LDL-receptor protein levels and increased both hepatic PCSK9 and circulating PCSK9. To determine causation, we treated GcgR-silenced mice with a neutralizing monoclonal antibody against PCSK9 and found that this intervention restored hepatic LDL-receptor protein levels and prevented the increase in LDL cholesterol. Further mechanistic work revealed that GcgR silencing in hepatocytes did not increase Pcsk9 mRNA. Rather, blocking GcgR increased the half-life of PCSK9 protein by suppressing signalling through exchange protein activated by cAMP 1 (Epac1). In particular, the ability of GcgR silencing to increase PCSK9 and suppress LDL receptor protein levels was mimicked by hepatocytes lacking Epac1. Thus, GcgR signalling through Epac1 appears to have critical effects on processes that regulate cholesterol metabolism through PCSK9. These new findings have important implications for the lipid metabolism effects of hepatic glucagon signalling in both normal physiology and metabolic disease, and for the development of safer GRA-like drugs to treat T2D.

Effects of taking tadalafil 5 mg once daily on erectile function and total testosterone levels in patients with metabolic syndrome

We aimed to evaluate the efficacy of tadalafil 5 mg once-daily treatment on testosterone levels in patients with erectile dysfunction (ED) accompanied by the metabolic syndrome. A total of 40 men with metabolic syndrome were evaluated for ED in this study. All the patients received 5 mg tadalafil once a day for 3 months. Erectile function was assessed using the five-item version of the International Index of Erectile Function (IIEF) questionnaire. Serum testosterone, follicle-stimulating hormone and luteinising hormone levels were also evaluated, and blood samples were taken between 08.00 and 10.00 in the fasting state. All participants have three or more criteria of metabolic syndrome. At the end of 3 months, mean testosterone values and IIEF scores showed an improvement from baseline values (from 3.6 ± 0.5 to 5.2 ± 0.3, from 11.3 ± 1.9 to 19 ± 0.8 respectively). After the treatment, serum LH levels were decreased (from 5.6 ± 0.6 to 4.6 ± 0.5). There was significantly difference in terms of baseline testosterone and luteinising hormone values and IIEF scores (p < .05). Based on our findings, we recommend tadalafil 5 mg once daily in those men with erectile dysfunction especially low testosterone levels accompanied by metabolic syndrome.

Calcium signalling and ER stress in insulin resistance and atherosclerosis

The burden of type 2 diabetes and its major complication cardiovascular disease is rapidly increasing worldwide. Understanding the underlying pathogenic mechanisms of these diseases is crucial to develop novel therapeutics. Recent work using genetic and biochemical methods in mouse models and human samples have identified disturbed calcium signalling and endoplasmic reticulum stress as emerging factors involved in the pathogenesis of many metabolic diseases. In this review, we will highlight the specific roles of calcium signalling and endoplasmic reticulum stress response in the development of insulin resistance and atherosclerosis.

Hepatocyte DACH1 Is Increased in Obesity via Nuclear Exclusion of HDAC4 and Promotes Hepatic Insulin Resistance

Defective insulin signaling in hepatocytes is a key factor in type 2 diabetes. In obesity, activation of calcium/calmodulin-dependent protein kinase II (CaMKII) in hepatocytes suppresses ATF6, which triggers a PERK-ATF4-TRB3 pathway that disrupts insulin signaling. Elucidating how CaMKII suppresses ATF6 is therefore essential to understanding this insulin resistance pathway. We show that CaMKII phosphorylates and blocks nuclear translocation of histone deacetylase 4 (HDAC4). As a result, HDAC4-mediated SUMOylation of the corepressor DACH1 is decreased, which protects DACH1 from proteasomal degradation. DACH1, together with nuclear receptor corepressor (NCOR), represses Atf6 transcription, leading to activation of the PERK-TRB3 pathway and defective insulin signaling. DACH1 is increased in the livers of obese mice and humans, and treatment of obese mice with liver-targeted constitutively nuclear HDAC4 or DACH1 small hairpin RNA (shRNA) increases ATF6, improves hepatocyte insulin signaling, and protects against hyperglycemia and hyperinsulinemia. Thus, DACH1-mediated corepression in hepatocytes emerges as an important link between obesity and insulin resistance.

Treatment of Obese Insulin-Resistant Mice With an Allosteric MAPKAPK2/3 Inhibitor Lowers Blood Glucose and Improves Insulin Sensitivity

The prevalence of obesity-induced type 2 diabetes (T2D) is increasing worldwide, and new treatment strategies are needed. We recently discovered that obesity activates a previously unknown pathway that promotes both excessive hepatic glucose production (HGP) and defective insulin signaling in hepatocytes, leading to exacerbation of hyperglycemia and insulin resistance in obesity. At the hub of this new pathway is a kinase cascade involving calcium/calmodulin-dependent protein kinase II (CaMKII), p38α mitogen-activated protein kinase (MAPK), and MAPKAPK2/3 (MK2/3). Genetic-based inhibition of these kinases improves metabolism in obese mice. Here, we report that treatment of obese insulin-resistant mice with an allosteric MK2/3 inhibitor, compound (cmpd) 28, ameliorates glucose homeostasis by suppressing excessive HGP and enhancing insulin signaling. The metabolic improvement seen with cmpd 28 is additive with the leading T2D drug, metformin, but it is not additive with dominant-negative MK2, suggesting an on-target mechanism of action. Allosteric MK2/3 inhibitors represent a potentially new approach to T2D that is highly mechanism based, has links to human T2D, and is predicted to avoid certain adverse effects seen with current T2D drugs.

Combination therapy with selective serotonin reuptake inhibitors and phosphodiesterase-5 inhibitors in the treatment of premature ejaculation

We aimed to evaluate the effectiveness of paroxetine and tadalafil combination in the treatment of premature ejaculation (PE). A total of 150 primary (lifelong)PE patients were randomly distributed into three groups of 50 patients each. Group 1 received 20 mg paroxetine every day for 1 month, Group 2 received 20 mg tadalafil on demand 2 h before intercourse, and Group 3 received paroxetine and tadalafil on demand 2 h before intercourse. Intravaginal ejaculatory latency times (IELT) scores were evaluated at baseline, at the end of the first month of therapy and 1 month after discontinuation of the treatment, while International Index of Erectile Function (IIEF) questionnaire scores were evaluated both prior to and after the treatment. At the end of the first month of therapy, IELT scores were compared with the basal values and statistically significant changes were detected (60.6 ± 30.2-117.3 ± 67.3, 68.5 ± 21.4-110.2 ± 37.3, 71.56 ± 40.23-175.2 ± 60.2)(P < 0.01). IELT scores after discontinuation of treatment were found to be close to the baseline IELT scores (P > 0.05). IIEF scores were evaluated both prior to and after the treatment, and no statistically significant difference was detected (P > 0.05). It is concluded that utilisation of selective serotonin reuptake inhibitors (SSRI) and phosphodiesterase-5 inhibitors (PDE5i) combination before intercourse seems to provide significantly longer ejaculatory latency times as compared with SSRI alone for a long time in patients with PE.

Common therapeutic targets in cardiometabolic disease

The interactions between cardiovascular disease (CVD) and insulin resistance syndromes suggest the possibility of joint targets for cardiometabolic research. The best drugs would go beyond minimizing adverse effects and have protective actions against both metabolic disease and CVD. In this perspective, we will outline a few examples in which a deep mechanistic understanding of the many cellular pathways that contribute to type 2 diabetes and CVD, regardless of cell type, have resulted in common upstream pathogenic pathways that can be therapeutically targeted.

Activation of calcium/calmodulin-dependent protein kinase II in obesity mediates suppression of hepatic insulin signaling

A hallmark of obesity is selective suppression of hepatic insulin signaling ("insulin resistance"), but critical gaps remain in our understanding of the molecular mechanisms. We now report a major role for hepatic CaMKII, a calcium-responsive kinase that is activated in obesity. Genetic targeting of hepatic CaMKII, its downstream mediator p38, or the p38 substrate and stabilizer MK2 enhances insulin-induced p-Akt in palmitate-treated hepatocytes and obese mouse liver, leading to metabolic improvement. The mechanism of improvement begins with induction of ATF6 and the ATF6 target p58(IPK), a chaperone that suppresses the PERK-p-eIF2α-ATF4 branch of the UPR. The result is a decrease in the ATF4 target TRB3, an inhibitor of insulin-induced p-Akt, leading to enhanced activation of Akt and its downstream metabolic mediators. These findings increase our understanding of the molecular mechanisms linking obesity to selective insulin resistance and suggest new therapeutic targets for type 2 diabetes and metabolic syndrome.

Role of endoplasmic reticulum stress in metabolic disease and other disorders

Perturbations in the normal functions of the endoplasmic reticulum (ER) trigger a signaling network that coordinates adaptive and apoptotic responses. There is accumulating evidence implicating prolonged ER stress in the development and progression of many diseases, including neurodegeneration, atherosclerosis, type 2 diabetes, liver disease, and cancer. With the improved understanding of the underlying molecular mechanisms, therapeutic interventions that target the ER stress response would be potential strategies to treat various diseases driven by prolonged ER stress.

Calcium signaling through CaMKII regulates hepatic glucose production in fasting and obesity

Hepatic glucose production (HGP) is crucial for glucose homeostasis, but the underlying mechanisms have not been fully elucidated. Here, we show that a calcium-sensing enzyme, CaMKII, is activated in a calcium- and IP3R-dependent manner by cAMP and glucagon in primary hepatocytes and by glucagon and fasting in vivo. Genetic deficiency or inhibition of CaMKII blocks nuclear translocation of FoxO1 by affecting its phosphorylation, impairs fasting- and glucagon/cAMP-induced glycogenolysis and gluconeogenesis, and lowers blood glucose levels, while constitutively active CaMKII has the opposite effects. Importantly, the suppressive effect of CaMKII deficiency on glucose metabolism is abrogated by transduction with constitutively nuclear FoxO1, indicating that the effect of CaMKII deficiency requires nuclear exclusion of FoxO1. This same pathway is also involved in excessive HGP in the setting of obesity. These results reveal a calcium-mediated signaling pathway involved in FoxO1 nuclear localization and hepatic glucose homeostasis.

NADPH oxidase links endoplasmic reticulum stress, oxidative stress, and PKR activation to induce apoptosis

The endoplasmic reticulum (ER) is a cellular membrane organelle that plays important roles in virus replication and maturation. Accumulating evidence indicates that virus infection often disturbs ER homeostasis and leads to ER stress, which is associated with a variety of prevalent diseases. To cope with the deleterious effects of virus-induced ER stress, cells activate critical signaling pathways including the unfolded protein response (UPR) and intrinsic mitochondrial apoptosis, which have complex effects on virus replication and pathogenesis. In this review, we present a comprehensive summary of recent research in this field, which revealed that about 36 viruses trigger ER stress and differentially activate ER stress-related signaling pathways. We also highlight the strategies evolved by viruses to modulate ER stress-related signaling networks including immune responses in order to ensure their survival and pathogenesis. Together, the knowledge gained from this field will shed light on unveiling the mechanisms of virus replication and pathogenesis and provide insight for future research as well as antiviral development.

NADPH oxidase links endoplasmic reticulum stress, oxidative stress, and PKR activation to induce apoptosis

ER stress signaling involving calcium and CaMKII induces NADPH oxidase and oxidative stress, which amplify CHOP-mediated apoptosis via PKR activation.

Endoplasmic reticulum (ER)–induced apoptosis and oxidative stress contribute to several chronic disease processes, yet molecular and cellular mechanisms linking ER stress and oxidative stress in the setting of apoptosis are poorly understood and infrequently explored in vivo. In this paper, we focus on a previously elucidated ER stress–apoptosis pathway whose molecular components have been identified and documented to cause apoptosis in vivo. We now show that nicotinamide adenine dinucleotide phosphate reduced oxidase (NOX) and NOX-mediated oxidative stress are induced by this pathway and that apoptosis is blocked by both genetic deletion of the NOX subunit NOX2 and by the antioxidant N-acetylcysteine. Unexpectedly, NOX and oxidative stress further amplify CCAAT/enhancer binding protein homologous protein (CHOP) induction through activation of the double-stranded RNA–dependent protein kinase (PKR). In vivo, NOX2 deficiency protects ER-stressed mice from renal cell CHOP induction and apoptosis and prevents renal dysfunction. These data provide new insight into how ER stress, oxidative stress, and PKR activation can be integrated to induce apoptosis in a pathophysiologically relevant manner.

Calcium/calmodulin-dependent protein kinase II links ER stress with Fas and mitochondrial apoptosis pathways

ER stress-induced apoptosis is implicated in various pathological conditions, but the mechanisms linking ER stress-mediated signaling to downstream apoptotic pathways remain unclear. Using human and mouse cell culture and in vivo mouse models of ER stress-induced apoptosis, we have shown that cytosolic calcium resulting from ER stress induces expression of the Fas death receptor through a pathway involving calcium/calmodulin-dependent protein kinase IIgamma (CaMKIIgamma) and JNK. Remarkably, CaMKIIgamma was also responsible for processes involved in mitochondrial-dependent apoptosis, including release of mitochondrial cytochrome c and loss of mitochondrial membrane potential. CaMKII-dependent apoptosis was also observed in a number of cultured human and mouse cells relevant to ER stress-induced pathology, including cultured macrophages, endothelial cells, and neuronal cells subjected to proapoptotic ER stress. Moreover, WT mice subjected to systemic ER stress showed evidence of macrophage mitochondrial dysfunction and apoptosis, renal epithelial cell apoptosis, and renal dysfunction, and these effects were markedly reduced in CaMKIIgamma-deficient mice. These data support an integrated model in which CaMKII serves as a unifying link between ER stress and the Fas and mitochondrial apoptotic pathways. Our study also revealed what we believe to be a novel proapoptotic function for CaMKII, namely, promotion of mitochondrial calcium uptake. These findings raise the possibility that CaMKII inhibitors could be useful in preventing apoptosis in pathological settings involving ER stress-induced apoptosis.

Loss of the tuberous sclerosis complex tumor suppressors triggers the unfolded protein response to regulate insulin signaling and apoptosis

Mammalian target of rapamycin, mTOR, is a major sensor of nutrient and energy availability in the cell and regulates a variety of cellular processes, including growth, proliferation, and metabolism. Loss of the tuberous sclerosis complex genes (TSC1 or TSC2) leads to constitutive activation of mTOR and downstream signaling elements, resulting in the development of tumors, neurological disorders, and at the cellular level, severe insulin/IGF-1 resistance. Here, we show that loss of TSC1 or TSC2 in cell lines and mouse or human tumors causes endoplasmic reticulum (ER) stress and activates the unfolded protein response (UPR). The resulting ER stress plays a significant role in the mTOR-mediated negative-feedback inhibition of insulin action and increases the vulnerability to apoptosis. These results demonstrate ER stress as a critical component of the pathologies associated with dysregulated mTOR activity and offer the possibility to exploit this mechanism for new therapeutic opportunities.