STAT4 deficiency reduces the development of atherosclerosis in mice

Effects of STAT4 on myocardial ischemia‑reperfusion injury and the underlying mechanisms

The regulation of cardiac function by the nuclear transcription factor signal transducer and activator of transcription 4 (STAT4) has been recently recognized. Nevertheless, the role and mechanisms of action of STAT4 in myocardial ischemia‑reperfusion (I/R) injury remain unknown. Consequently, the present study constructed a rat model of I/R by ligation of the left anterior descending coronary artery. Following sacrifice, the rat hearts were excised and analyzed to investigated the effects of STAT4 on I/R‑induced myocardial injury. Western blotting demonstrated that expression of STAT4 decreased significantly in the rat model of cardiac I/R and in H9C2 cells that were subjected to hypoxia and reoxygenation (H/R). The overexpression of STAT4 in H9C2 cells reduced cell damage and apoptosis induced by H/R. Furthermore, both in vivo and in vitro, the level of PI3K decreased significantly. Although the AKT protein expression levels were not altered, the AKT phosphorylation levels decreased significantly. STAT4 overexpression enhanced the expression of PI3K and AKT in the H9C2 cells. On the whole, the present study demonstrated that STAT4 alleviated I/R‑induced myocardial injury through the PI3K/AKT signaling pathway.

The association between the single-nucleotide polymorphism of site rs1333040 in region 9p21 and the risk of coronary heart disease in Chinese population

BACKGROUND

Rs1333040 is the single-nucleotide polymorphisms (SNP) related with coronary heart disease (CHD). The aim of the present study is to examine the association between rs1333040 polymorphism genotypes and CHD and to further explore the molecular mechanism in Chinese population.

METHODS

A case-control study was used in this study, including 500 CHD patients and 500 control subjects. CHD patients and controls were distinguished by coronary angiography. Genotypes of rs1333040 were determined on the Agena MassARRAY system. Statistical analysis was conducted by SPSS (Ver 16.0) and plink (Ver. 1.07, Shaun Purcell).

RESULTS

Fisher's exact test by plink indicated a significant difference in the allele distribution between cases and controls, the allele T may be associated with a higher risk of CHD (p = 0.012, odds ratio (OR) = 1.258). The serum levels of low-density lipoprotein cholesterol (LDL-C) (p = 0.029) and Gensini score (p = 0.008) distributed differently in patients with various alleles. In the recessive model, the levels of high-density lipoprotein (HDL) and apolipoprotein A (ApoA) were higher in the TC + CC genotype than in the TT genotype. The TC + TT genotype was found to be risk factors against CHD in a dominant model (OR = 1.278, p = 0.014). The TC + TT genotype along with multiple risk factors significantly positively correlated with the risk of CHD.

CONCLUSIONS

The present study investigates the association between the rs1333040 polymorphism genotypes and CHD. The T allele of rs1333040 is the susceptibility site of CHD. The interaction between SNP and various risk factors plays an important role in the development of CHD.

STAT4 targets KISS1 to inhibit the oxidative damage, inflammation and neuronal apoptosis in experimental PD models by inactivating the MAPK pathway

BACKGROUND

Oxidative stress and neuroinflammation are proven to play critical roles in the pathogenesis of Parkinson's disease (PD). As reported, patients with PD have lower level of STAT4 compared with healthy subjects. However, the biological functions and mechanisms of STAT4 in PD pathogenesis remain uncertain. This study aimed to investigate the roles and related mechanisms of STAT4 in PD development.

METHODS

The intraperitoneal injection of MPTP (20 mg/kg) dissolved in physiological saline was performed to mimic PD-like conditions in vivo. MPP + solution was prepared for cell model of PD. Cell viability was measured by CCK-8. Griess reaction was conducted to measure NO concentrations. The mRNA and protein levels were evaluated by RT-qPCR and western blotting. ROS generation was assessed by DCFH-DA. The levels of inflammatory cytokines were measured by ELISA. Cell apoptosis was examined by flow cytometry and western blotting. Moreover, the SH-SY5Y cells were treated with conditioned medium from LPS-stimulated microglia and subjected to CCK-8 assays and ELISA. Mechanistically, CHIP assays and luciferase reporter assays were performed to verify the binding relationship between KISS1 and STAT4. For in vivo analysis, the histological changes of midbrain tissues of mice were determined by hematoxylin and eosin staining. The expression of tyrosine hydroxylase (TH) was detected by immunohistochemistry staining. Iba-1 positive microglial cells in the striatum were assessed by immunofluorescence staining.

RESULTS

For in vitro analysis, STAT4 level was downregulated after MPP+ treatment, and STAT4 upregulation inhibited the oxidative damage, inflammation and apoptosis in SH-SY5Y cells. STAT4 bound at +215-228 region of KISS1, and KISS1 upregulation counteracted the protection of STAT4 upregulation against cell damage. Moreover, STAT4 upregulation inhibited cell viability loss and inflammation induced by conditioned medium from LPS-treated microglia, whereas KISS1 upregulation had the opposite effect. For in vivo analysis, the protective effects of STAT4 upregulation against inflammatory response, oxidative stress, dopaminergic neuronal loss and microglia activation were attenuated by KISS1 upregulation. Moreover, the inactivation of MAPK pathway caused by STAT4 upregulation was reversed by KISS1 upregulation, and MAPK inhibition attenuated the MPP+-induced inflammation, oxidative stress and apoptosis in SH-SY5Y cells.

CONCLUSION

STAT4 inhibits KISS1 to attenuate the oxidative damage, inflammation and neuronal apoptosis in PD by inactivating the MAPK pathway.

STAT protein family and cardiovascular diseases: overview of pathological mechanisms and therapeutic implications

Globally, cardiovascular diseases (CVD) are one of the significant causes of death and are considered a major concern of human society. One of the most crucial objectives of scientists is to reveal the mechanisms associated with the pathogenesis of CVD, which has attracted the attention of many scientists. Accumulating evidence showed that the signal transducer and activator of transcription (STAT) signaling pathway is involved in various physiological and pathological processes. According to research on the molecular mechanisms of CVDs, the STAT family of proteins is one of the most crucial players in these diseases. Numerous studies have demonstrated the undeniable relevance of STAT family proteins in various CVDs. The aim of this review is to shed light on how STAT signaling pathways are related to CVD and the potential for using these signaling pathways as therapeutic targets.

The Biological Parallels Between Atherosclerosis and Cardiac Allograft Vasculopathy: Implications for Solid Organ Chronic Rejection

Atherosclerosis and solid organ chronic rejection are pervasive chronic disease states that account for significant morbidity and mortality in developed countries. Recently, a series of shared molecular pathways have emerged, revealing biological parallels from early stages of development up to the advanced forms of pathology. These shared mechanistic processes are inflammatory in nature, reflecting the importance of inflammation in both disorders. Vascular inflammation triggers endothelial dysfunction and disease initiation through aberrant vasomotor control and shared patterns of endothelial activation. Endothelial dysfunction leads to the recruitment of immune cells and the perpetuation of the inflammatory response. This drives lesion formation through the release of key cytokines such as IFN-y, TNF-alpha, and IL-2. Continued interplay between the adaptive and innate immune response (represented by T lymphocytes and macrophages, respectively) promotes lesion instability and thrombotic complications; hallmarks of advanced disease in both atherosclerosis and solid organ chronic rejection. The aim of this study is to identify areas of overlap between atherosclerosis and chronic rejection. We then discuss new approaches to improve current understanding of the pathophysiology of both disorders, and eventually design novel therapeutics.

Myeloid cell deficiency of the inflammatory transcription factor Stat4 protects long-term synaptic plasticity from the effects of a high-fat, high-cholesterol diet

Neuroinflammation is associated with neurodegenerative diseases, including Alzheimer's and Parkinson's. The cytokine interleukin-12 activates signal transducer and activator of transcription 4 (Stat4), and consumption of a high-fat, high-cholesterol diet (HFD-C) and Stat4 activity are associated with inflammation, atherosclerosis, and a diabetic metabolic phenotype. In studies of in vitro hippocampal slices from control Stat4fl/flLdlr-/- mice fed a HFD-C diabetogenic diet, we show that Schaffer collateral-CA1 synapses exhibited larger reductions in activity-dependent, long-term potentiation (LTP) of synaptic transmission, compared to mice fed a standard diet. Glucose tolerance and insulin sensitivity shifts produced by HFD-C diet were reduced in Stat4ΔLysMLdlr-/- mice compared to Stat4fl/flLdlr-/- controls. Stat4ΔLysMLdlr-/- mice, which lack Stat4 under control of the LysMCre promoter, were resistant to HFD-C induced impairments in LTP. In contrast, Schaffer collateral-CA1 synapses in Stat4ΔLysMLdlr-/- mice fed the HFD-C diet showed larger LTP than control Stat4fl/flLdlr-/- mice. Expression of a number of neuroinflammatory and synaptic plasticity genes was reduced by HFD-C diet in control mice, and less affected by HFD-C diet in Stat4ΔLysMLdlr-/- mice. These data suggest that suppression of Stat4 activation may protect against effects of Western diet on cognition, type 2 diabetes, and reduce risk of Alzheimer's disease and other neurodegenerative disorders associated with neuroinflammation.

Neutrophil-specific STAT4 deficiency attenuates atherosclerotic burden and improves plaque stability via reduction in neutrophil activation and recruitment into aortas of Ldlr-/- mice

Background and aims

Neutrophils drive atheroprogression and directly contribute to plaque instability. We recently identified signal transducer and activator of transcription 4 (STAT4) as a critical component for bacterial host defense in neutrophils. The STAT4-dependent functions of neutrophils in atherogenesis are unknown. Therefore, we investigated a contributory role of STAT4 in neutrophils during advanced atherosclerosis.

Methods

We generated myeloid-specific Stat4^ΔLysMLdlr^-/-, neutrophil-specific Stat4^ΔS100A8Ldlr^-/-, and control Stat4^fl/flLdlr^-/- mice. All groups were fed a high-fat/cholesterol diet (HFD-C) for 28 weeks to establish advanced atherosclerosis. Aortic root plaque burden and stability were assessed histologically by Movat pentachrome staining. Nanostring gene expression analysis was performed on isolated blood neutrophils. Flow cytometry was utilized to analyze hematopoiesis and blood neutrophil activation. In vivo homing of neutrophils to atherosclerotic plaques was performed by adoptively transferring prelabeled Stat4^ΔLysMLdlr^-/- and Stat4^fl/flLdlr^-/- bone marrow cells into aged atherosclerotic Apoe^-/- mice and detected by flow cytometry.

Results

STAT4 deficiency in both myeloid-specific and neutrophil-specific mice provided similar reductions in aortic root plaque burden and improvements in plaque stability via reduction in necrotic core size, improved fibrous cap area, and increased vascular smooth muscle cell content within the fibrous cap. Myeloid-specific STAT4 deficiency resulted in decreased circulating neutrophils via reduced production of granulocyte-monocyte progenitors in the bone marrow. Neutrophil activation was dampened in HFD-C fed Stat4^ΔLysMLdlr^-/- mice via reduced mitochondrial superoxide production, attenuated surface expression of degranulation marker CD63, and reduced frequency of neutrophil-platelet aggregates. Myeloid-specific STAT4 deficiency diminished expression of chemokine receptors CCR1 and CCR2 and impaired in vivo neutrophil trafficking to atherosclerotic aorta.

Conclusions

Our work indicates a pro-atherogenic role for STAT4-dependent neutrophil activation and how it contributes to multiple factors of plaque instability during advanced atherosclerosis in mice.

Neutrophil-specific STAT4 deficiency attenuates atherosclerotic burden and improves plaque stability via reduction in neutrophil activation and recruitment into aortas of Ldlr -/- mice

Background and Aims

Neutrophils drive atheroprogression and directly contribute to plaque instability. We recently identified signal transducer and activator of transcription 4 (STAT4) as a critical component for bacterial host defense in neutrophils. The STAT4-dependent functions of neutrophils in atherogenesis are unknown. Therefore, we investigated a contributory role of STAT4 in neutrophils during advanced atherosclerosis.

Methods

We generated myeloid-specific Stat4 ^ΔLysM Ldlr ^-/- , neutrophil-specific Stat4 ^ΔS100A8 Ldlr ^-/- , and control Stat4 ^fl/fl Ldlr ^-/- mice. All groups were fed a high-fat/cholesterol diet (HFD-C) for 28 weeks to establish advanced atherosclerosis. Aortic root plaque burden and stability were assessed histologically by Movat Pentachrome staining. Nanostring gene expression analysis was performed on isolated blood neutrophils. Flow cytometry was utilized to analyze hematopoiesis and blood neutrophil activation. In vivo homing of neutrophils to atherosclerotic plaques was performed by adoptively transferring prelabeled Stat4 ^ΔLysM Ldlr ^-/- and Stat4 ^fl/fl Ldlr ^-/- bone marrow cells into aged atherosclerotic Apoe ^-/- mice and detected by flow cytometry.

Results

STAT4 deficiency in both myeloid-specific and neutrophil-specific mice provided similar reductions in aortic root plaque burden and improvements in plaque stability via reduction in necrotic core size, improved fibrous cap area, and increased vascular smooth muscle cell content within the fibrous cap. Myeloid-specific STAT4 deficiency resulted in decreased circulating neutrophils via reduced production of granulocyte-monocyte progenitors in the bone marrow. Neutrophil activation was dampened in Stat4 ^ΔLysM Ldlr ^-/- mice via reduced mitochondrial superoxide production, attenuated surface expression of degranulation marker CD63, and reduced frequency of neutrophil-platelet aggregates. Myeloid-specific STAT4 deficiency diminished expression of chemokine receptors CCR1 and CCR2 and impaired in vivo neutrophil trafficking to atherosclerotic aorta.

Conclusions

Our work indicates a pro-atherogenic role for STAT4-dependent neutrophil activation and how it contributes to multiple factors of plaque instability during advanced atherosclerosis in mice.

Levocarnitine regulates the growth of angiotensin II-induced myocardial fibrosis cells via TIMP-1

This study aimed to explore the effects of tissue inhibitor of metalloproteinases-1 (TIMP-1) on levocarnitine (LC)-mediated regulation of angiotensin II (AngII)-induced myocardial fibrosis (MF) and its underlying mechanisms. H9C2 cells were treated with AngII for 24 h to induce fibrosis. The cells were then treated with LC or transfected with TIMP-1-OE plasmid/si‑TIMP-1. Cell apoptosis, viability, migration, and related gene expression were analyzed. AngII treatment significantly upregulated Axl, α-SMA, and MMP3 expression (P < 0.05) and downregulated STAT4 and TIMP1 expression (P < 0.05) relative to the control levels. After transfection, cells with TIMP-1 overexpression/knockdown were successfully established. Compared with that of the control, AngII significantly inhibited cell viability and cell migration while promoting cell apoptosis (P < 0.05). LC and TIMP-1-OE transfection further suppressed cell viability and migration induced by Ang II and upregulated apoptosis, whereas si-TIMP-1 had the opposite effect. Furthermore, LC and TIMP-1-OE transfection downregulated Axl, AT1R, α-SMA, collagen III, Bcl-2, and MMP3 expression caused by AngII and upregulated caspase 3, p53, and STAT4 expression, whereas si-TIMP-1 had the opposite effect. TIMP-1 is therefore a potential therapeutic target for delaying MF progression.

Novel Computational Approaches to Developing Potential STAT4 Silencing siRNAs for Immunomodulation of Atherosclerosis

BACKGROUND

Small interfering RNAs (siRNAs) are known as commonly used targeting mRNAs tools for suppressing gene expression. Since Signal Transducer and Activator of Transcription 4 (STAT4) is considered as a significant transcription factor for generation and differentiation of Th1 cells during vascular dysfunction and atherosclerosis, suppressing STAT4 could represent novel immunomodulatory therapies against atherosclerosis.

OBJECTIVE

Therefore, the current study was conducted to design efficient siRNAs specific for STAT4 and to evaluate different criteria affecting their functionality.

METHODS

In the present study, all related sequences of STAT4 gene were retrieved from Gen Bank database. Multiple sequence alignment was carried out to recognize Open Reading Frame (ORF) and conserved region. Then, siDirect 2.0 server was applied for the development of candidate siRNA molecules and confirmation of predicted molecules was performed using Dharma siRNA technology and GeneScript siRNA targetfinder. In addition, BLAST tool was used against whole Genebank databases to identify potential off-target genes. DNA/RNA GC content calculator and mfold server were used to calculate GC content and secondary structure prediction of designed siRNA, respectively. Finally, IntaRNA program was used to study the thermodynamics of interaction between predicted siRNA and target gene.

RESULTS

Based on the obtained results, three efficient siRNA molecules were designed and validated for STAT4 gene silencing using computational methods, which may result in suppressing STAT4 gene expression.

CONCLUSION

According to our results, this study shows that siRNA targeting STAT4 can be considered as a therapeutic agent in many Th1-mediated pathologic conditions specially atherosclerosis.

The role of Wnt signaling pathway in atherosclerosis and its relationship with angiogenesis

Expression and function of Wnt signaling pathway in rats with atherosclerosis (AS) were investegated. The AS model of rats was established after 8-week continuous feeding of a high-fat diet, with normal rats as the control. Blood was taken from the carotid artery to detect the level of blood lipid. Aortic slices were made to observe the pathological changes of the aorta after the rats were sacrificed. Enzyme-linked immunosorbent assay kits were used to detect the contents of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α). Western blot analysis and semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) were performed to detect the expression levels of related proteins and mRNA in rat Wnt signaling pathway. Correlation analysis between the protein expression level of vascular endothelial growth factor (VEGF) and that of Wnt1 was conducted. Aortic slices showed that the ratio of intima thickness to media thickness of the rats in the model group was higher than that of in the control group (P<0.01). Blood lipid and the contents of IL-6 and TNF-α of the rats in the model group were higher than those of the rats in the control group (P<0.01). Semi-quantitative RT-PCR indicated that mRNA expression levels of Wnt1, β-catenin and dickkopf1 in the aorta of rats in the model group were increased compared with those of control group (P<0.01). The results of western blot analysis revealed that the protein expression levels of Wnt1, β-catenin, DKK1 and VEGF of the rats in the model group were remarkably higher than those of the control group (P<0.01). The level of VEGF protein was positively correlated with that of Wnt1 (P<0.05, r=0.7810). The activation of Wnt signaling pathway in the aorta of the rats with AS can induce the expression of relevant inflammatory cytokines. It has the effects of promoting the progression of AS and accelerating angiogenesis.

STAT4 Regulates the CD8+ Regulatory T Cell/T Follicular Helper Cell Axis and Promotes Atherogenesis in Insulin-Resistant Ldlr-/- Mice

The metabolic syndrome and diabetic conditions support atherosclerosis, but the exact mechanisms for accelerated atherogenesis remain unclear. Although the proinflammatory role of STAT4 in atherosclerosis and diet-induced insulin resistance (IR) was recently established, the impact of STAT4 on atherogenesis in conditions of IR is not known. In this study, we generated Stat4^-/-Ldlr^-/- mice that were fed a diabetogenic diet with added cholesterol (DDC). DDC-fed Stat4^-/-Ldlr^-/- mice demonstrated improved glucose tolerance, insulin sensitivity, and a 36% reduction in atherosclerosis compared with Ldlr^-/- controls. Interestingly, we detected a reduction in T follicular helper (Tfh) cells and plasma B cells but a sharp elevation in CD8⁺ regulatory T cells (Tregs) in spleens and aortas of Stat4^-/-Ldlr^-/- mice compared with Ldlr^-/- mice. Similarly, STAT4 deficiency supported CD8⁺ Treg differentiation in vitro. STAT4-deficient CD8⁺ Tregs suppressed Tfh cell and germinal center B cell development upon immunization with keyhole limpet hemocyanin, indicating an important role for STAT4 in CD8⁺ Treg functions in vivo. Furthermore, adoptive transfer of Stat4^-/-Ldlr^-/- CD8⁺ Tregs versus Ldlr^-/- CD8⁺ Tregs resulted in a significant reduction in plaque burden and suppression of Tfh cell and germinal center B cells in DDC-fed Ldlr^-/- recipients. STAT4 expression in macrophages (MΦs) also affected the Tfh/CD8⁺ Treg axis, because conditioned media from Stat4^-/-Ldlr^-/- MΦs supported CD8⁺ Treg differentiation, but not Tfh cell differentiation, in a TGF-β-dependent manner. These findings suggest a novel mechanism by which STAT4 supports atherosclerosis in IR Ldlr^-/- mice via STAT4-dependent MΦs, as well as cell-intrinsic suppression of CD8⁺ Treg generation and functions and maintenance of Tfh cell generation and the accompanying humoral immune response.