Gene deletion of Interleukin-1α reduces ER stress-induced CHOP expression in macrophages and attenuates the progression of atherosclerosis in apoE-deficient mice

The pathophysiology of atherosclerosis initiation and progression involves many inflammatory cytokines, one of them is interleukin (IL)-1α that has been shown to be secreted by activated macrophages. We have previously shown that IL-1α from bone marrow-derived cells is critical for early atherosclerosis development in mice. It is known that endoplasmic reticulum (ER) stress in macrophages is involved in progression to more advanced atherosclerosis, but it is still unknown whether this effect is mediated through cytokine activation or secretion. We previously demonstrated that IL-1α is required in ER stress-induced activation of inflammatory cytokines in hepatocytes and in the associated induction of steatohepatitis. In the current study, we aimed to examine the potential role of IL-1α in ER stress-induced activation of macrophages, which is relevant to progression of atherosclerosis. First, we demonstrated that IL-1α is required for atherosclerosis development and progression in the apoE knockout (KO) mouse model of atherosclerosis. Next, we showed that ER stress in mouse macrophages results in the protein production and secretion of IL-1α in a dose-dependent manner, and that IL-1α is required in ER stress-induced production of the C/EBP homologous protein (CHOP), a critical step in ER stress-mediated apoptosis. We further demonstrated that IL-1α-dependent CHOP production in macrophages is specifically mediated through the PERK-ATF4 signaling pathway. Altogether, these findings highlight IL-1α as a potential target for prevention and treatment of atherosclerotic cardiovascular disease.

Interleukin-1α deficiency reduces adiposity, glucose intolerance and hepatic de-novo lipogenesis in diet-induced obese mice

OBJECTIVE

While extensive research revealed that interleukin (IL)-1β contributes to insulin resistance (IR) development, the role of IL-1α in obesity and IR was scarcely studied. Using control, whole body IL-1α knockout (KO) or myeloid-cell-specific IL-1α-deficient mice, we tested the hypothesis that IL-1α deficiency would protect against high-fat diet (HFD)-induced obesity and its metabolic consequences.

RESEARCH DESIGN AND METHODS

To induce obesity and IR, control and IL-1α KO mice were given either chow or HFD for 16 weeks. Glucose tolerance test was performed at 10 and 15 weeks, representing early and progressive stages of glucose intolerance, respectively. Liver and epididymal white adipose tissue (eWAT) samples were analyzed for general morphology and adipocyte size. Plasma levels of adiponectin, insulin, total cholesterol and triglyceride (TG), lipoprotein profile as well as hepatic lipids were analyzed. Expression of lipid and inflammation-related genes in liver and eWAT was analyzed. Primary mouse hepatocytes isolated from control mice were treated either with dimethyl sulfoxide (DMSO) (control) or 20 ng/mL recombinant IL-1α for 24 hours and subjected to gene expression analysis.

RESULTS

Although total body weight gain was similar, IL-1α KO mice showed reduced adiposity and were completely protected from HFD-induced glucose intolerance. In addition, plasma total cholesterol and TG levels were lower and HFD-induced accumulation of liver TGs was completely inhibited in IL-1α KO compared with control mice. Expression of stearoyl-CoA desaturase1 (SCD1), fatty acid synthase (FASN), elongation of long-chain fatty acids family member 6 (ELOVL6), acetyl-CoA carboxylase (ACC), key enzymes that promote de-novo lipogenesis, was lower in livers of IL-1α KO mice. Treatment with recombinant IL-1α elevated the expression of ELOVL6 and FASN in mouse primary hepatocytes. Finally, mice with myeloid-cell-specific deletion of IL-1α did not show reduced adiposity and improved glucose tolerance.

CONCLUSIONS

We demonstrate a novel role of IL-1α in promoting adiposity, obesity-induced glucose intolerance and liver TG accumulation and suggest that IL-1α blockade could be used for treatment of obesity and its metabolic consequences.

A-Kinase Anchoring Protein 4 (AKAP4) is an ERK1/2 substrate and a switch molecule between cAMP/PKA and PKC/ERK1/2 in human spermatozoa

Mammalian spermatozoa undergo capacitation and acrosome reaction in order to fertilize the egg. The PKC-ERK1/2 pathway plays an important role in human spermatozoa motility, capacitation and the acrosome reaction. Here we demonstrate that ERK1/2 phosphorylates proAKAP4 on Thr265 in human spermatozoa in vitro and in vivo. Cyclic AMP (cAMP) had no effect on ERK1/2 activity in human spermatozoa, but stimulated the MAPK in mouse pituitary LβT2 gonadotrope cells. cAMP via PKA attenuates PKC-dependent ERK1/2 activation only in the presence of proAKAP4. St-HT31, which disrupts PKA-regulatory subunit II (PKA-RII) binding to AKAP abrogates the inhibitory effect of cAMP in human spermatozoa and in HEK293T cells expressing proAKAP4. In transfected HEK293T cells, PMA relocated proAKAP4, but not proAKAP4-T265A to the Golgi in an ERK1/2-dependnet manner. Similarly, AKAP4 is localized to the spermatozoa principal piece and is relocated to the mid-piece and the postacrosomal region by PMA. Furthermore, using capacitated sperm we found that cAMP reduced PMA-induced ERK1/2 activation and acrosome reaction. Thus, the physiological role of the negative crosstalk between the cAMP/PKA/AKAP4 and the PKC/ERK1/2 pathways is to regulate capacitation and acrosome reaction.

The Effect of Klotho Treatment on Atherogenesis, Blood Pressure, and Metabolic Parameters in Experimental Rodent Models

Klotho is a transmembrane protein, expressed mainly in the kidneys and the choroid plexus. The extracellular domain of klotho is composed of 2 internal repeats, KL1 and KL2, which can be cleaved and act as hormones. Klotho-deficient mice develop a phenotype resembling human aging. Laboratory and clinical data suggest a favorable effect of klotho on atherosclerosis, high blood pressure, and metabolic syndrome. Therefore, we aimed to study the effect of klotho treatment on atherogenesis, blood pressure, and metabolic parameters in experimental rodent models. Fructose-fed Sprague-Dawley rats (metabolic syndrome model) and apolipoprotein E (apoE -/-) knock-out mice (atherosclerosis model) were treated with either klotho or its active domain KL1. In apoE -/- mice, klotho unexpectedly elevated plasma cholesterol and triglyceride levels compared to the control group. Yet, it did not increase the aortic sinus atherosclerotic lesion area. In fructose-fed Sprague-Dawley rats, klotho treatment did not lower blood pressure or plasma triglyceride levels. Although KL1 treatment did not lower blood pressure or plasma insulin levels, it significantly reduced the elevation of total plasma triglyceride levels (from 2.3-fold to 1.6-fold, p<0.05) due to lower triglyceride-rich VLDL levels. Klotho did not show any beneficial effects on atherosclerosis and components of the metabolic syndrome and was associated with increased plasma cholesterol levels. On the other hand, treatment with KL1 may lower plasma triglyceride levels independent of insulin. Additional studies are required in order to decipher the complex role of klotho and its active domains in the regulation of plasma lipid levels.

Interleukin-1α deficiency attenuates endoplasmic reticulum stress-induced liver damage and CHOP expression in mice

BACKGROUND & AIMS

ER stress promotes liver fat accumulation and induction of inflammatory cytokines, which contribute to the development of steatohepatitis. Unresolved ER stress upregulates the pro-apoptotic CHOP. IL-1α is localized to the nucleus in apoptotic cells, but is released when these cells become necrotic and induce sterile inflammation. We investigated whether IL-1α is involved in ER stress-induced apoptosis and steatohepatitis.

METHODS

We employed WT and IL-1α-deficient mice to study the role of IL-1α in ER stress-induced steatohepatitis.

RESULTS

Liver CHOP mRNA was induced in a time dependent fashion in the atherogenic diet-induced steatohepatitis model, and was twofold lower in IL-1α deficient compared to WT mice. In the ER stress-driven steatohepatitis model, IL-1α deficiency decreased the elevation in serum ALT levels, the number of apoptotic cells (measured as caspase-3-positive hepatocytes), and the expression of IL-1β, IL-6, TNFα, and CHOP, with no effect on the degree of fatty liver formation. IL-1α was upregulated in ER-stressed-macrophages and the protein was localized to the nucleus. IL-1β mRNA and CHOP mRNA and protein levels were lower in ER-stressed-macrophages from IL-1α deficient compared to WT mice. ER stress induced the expression of IL-1α and IL-1β also in mouse primary hepatocytes. Recombinant IL-1α treatment in hepatocytes did not affect CHOP expression but upregulated both IL-1α and IL-1β mRNA levels.

CONCLUSION

We show that IL-1α is upregulated in response to ER stress and IL-1α deficiency reduces ER stress-induced CHOP expression, apoptosis and steatohepatitis. As a dual function cytokine, IL-1α may contribute to the induction of CHOP intracellularly, while IL-1α released from necrotic cells accelerates steatohepatitis via induction of inflammatory cytokines by neighboring cells.

Lack of interleukin-1α in Kupffer cells attenuates liver inflammation and expression of inflammatory cytokines in hypercholesterolaemic mice

BACKGROUND

The role of Kupffer cell interleukin (IL)-1 in non-alcoholic steatohepatitis development remains unclear.

AIMS

To evaluate the role of Kupffer cell IL-1α, IL-1β or IL-1 receptor type-1 (IL-1R1) in steatohepatitis.

METHODS

C57BL/6 mice were irradiated and transplanted with bone marrow-derived cells from WT, IL-1α-/-, IL-1β-/- or IL-1R1-/- mice combined with Kupffer cell ablation with Gadolinium Chloride, and fed atherogenic diet. Plasma and liver triglycerides and cholesterol, serum alanine aminotransferase (ALT), liver histology and expression levels of inflammatory genes were assessed.

RESULTS

The ablation and replacement of Kupffer cells with bone marrow-derived cells was confirmed. The atherogenic diet elevated plasma and liver cholesterol, reduced plasma and liver triglycerides and increased serum ALT levels in all groups. Steatosis and steatohepatitis were induced, but without liver fibrosis. A reduction in the severity of portal inflammation was observed only in mice with Kupffer cell deficiency of IL-1α. Accordingly, liver mRNA levels of inflammatory genes encoding for IL-1α, IL-1β, TNFα, SAA1 and IL-6 were significantly lower in mice with Kupffer cell deficiency of IL-1α compared to WT mice.

CONCLUSION

Selective deficiency of IL-1α in Kupffer cells reduces liver inflammation and expression of inflammatory cytokines, which may implicate Kupffer cell-derived IL-1α in steatohepatitis development.

The role of Mitogen activated protein kinase (MAPK) in sperm functions

The generation of mature spermatozoa in the epididymis includes the activation of the MAPK cascade in a complex manner. MAPKs are thought to be involved in the regulation of transcription and ectoplasmic specialization (ES) in the testis. MAPKs also regulate mature spermatozoa flagellar motility, hyperactivation and the acrosome reaction. Here we review the current data regarding the functions of MAPKs in spermatogenesis and in mature spermatozoa.

A preformed signaling complex mediates GnRH-activated ERK phosphorylation of paxillin and FAK at focal adhesions in L beta T2 gonadotrope cells

Most receptor tyrosine kinases and G protein-coupled receptors (GPCRs) operate via a limited number of MAPK cascades but still exert diverse functions, and therefore signal specificity remains an enigma. Also, most GPCR ligands utilize families of receptors for mediation of diverse biological actions; however, the mammalian type I GnRH receptor (GnRHR) seems to be the sole receptor mediating GnRH-induced gonadotropin synthesis and release. Signaling complexes associated with GPCRs may thus provide the means for signal specificity. Here we describe a signaling complex associated with the GnRHR, which is a unique GPCR lacking a C-terminal tail. Unlike other GPCRs, this signaling complex is preformed, and exposure of L beta T2 gonadotropes to GnRH induces its dynamic rearrangement. The signaling complex includes c-Src, protein kinase C delta, -epsilon, and -alpha, Ras, MAPK kinase 1/2, ERK1/2, tubulin, focal adhesion kinase (FAK), paxillin, vinculin, caveolin-1, kinase suppressor of Ras-1, and the GnRHR. Exposure to GnRH (5 min) causes MAPK kinase 1/2, ERK1/2, tubulin, vinculin, and the GnRHR to detach from c-Src, but they reassociate within 30 min. On the other hand, FAK, paxillin, the protein kinase Cs, and caveolin-1 stay bound to c-Src, whereas kinase suppressor of Ras-1 appears in the complex only 30 min after GnRH stimulation. GnRH was found to activate ERK1/2 in the complex in a c-Src-dependent manner, and the activated ERK1/2 subsequently phosphorylates FAK and paxillin. In parallel, caveolin-1, FAK, vinculin, and paxillin are phosphorylated on Tyr residues apparently by GnRH-activated c-Src. Receptor tyrosine kinases and GPCRs translocate ERK1/2 to the nucleus to phosphorylate and activate transcription factors. We therefore propose that the role of the multiprotein signaling complex is to sequester a cytosolic pool of activated ERK1/2 to phosphorylate FAK and paxillin at focal adhesions.

Identification of extracellular signal-regulated kinase 1/2 and p38 MAPK as regulators of human sperm motility and acrosome reaction and as predictors of poor spermatozoan quality

Mature spermatozoa acquire progressive motility only after ejaculation. Their journey in the female reproductive tract also includes suppression of progressive motility, reactivation, capacitation, and hyperactivation of motility (whiplash), the mechanisms of which are obscure. MAPKs are key regulatory enzymes in cell signaling, participating in diverse cellular functions such as growth, differentiation, stress, and apoptosis. Here we report that ERK1/2 and p38 MAPK are primarily localized to the tail of mature human spermatozoa. Surprisingly, c-Jun N-terminal kinase 1/2, which is thought to be ubiquitously expressed, could not be detected in mature human spermatozoa. ERK1/2 stimulation is downstream to protein kinase C (PKC) activation, which is also present in the human sperm tail (PKCbetaI and PKCepsilon). ERK1/2 stimulates and p38 inhibits forward and hyperactivated motility, respectively. Both ERK1/2 and p38 MAPK are involved in the acrosome reaction. Using a proteomic approach, we identified ARHGAP6, a RhoGAP, as an ERK substrate in PMA-stimulated human spermatozoa. Inverse correlation was obtained between the relative expression level of ERK1 or the relative activation level of p38 and sperm motility, forward progression motility, sperm morphology, and viability. Therefore, increased expression of ERK1 and activated p38 can predict poor human sperm quality.

Mitogen activated protein kinases (MAPKs) as regulators of spermatogenesis and spermatozoa functions

Spermatogenesis, culminating in the generation of mature motile spermatozoa, is a complex biological process that is regulated by cytokines and hormones of the male reproductive system. Spermatozoa must first undergo a series of biochemical processes termed capacitation, which is followed by acrosome reaction and egg fertilization. Here we review the role of mitogen-activated protein kinases (MAPK) cascades in spermatogenesis and spermatozoa functions.