Regulation of the Activity of the Dual Leucine Zipper Kinase by Distinct Mechanisms

The dual leucine zipper kinase (DLK) alias mitogen-activated protein 3 kinase 12 (MAP3K12) has gained much attention in recent years. DLK belongs to the mixed lineage kinases, characterized by homology to serine/threonine and tyrosine kinase, but exerts serine/threonine kinase activity. DLK has been implicated in many diseases, including several neurodegenerative diseases, glaucoma, and diabetes mellitus. As a MAP3K, it is generally assumed that DLK becomes phosphorylated and activated by upstream signals and phosphorylates and activates itself, the downstream serine/threonine MAP2K, and, ultimately, MAPK. In addition, other mechanisms such as protein-protein interactions, proteasomal degradation, dephosphorylation by various phosphatases, palmitoylation, and subcellular localization have been shown to be involved in the regulation of DLK activity or its fine-tuning. In the present review, the diverse mechanisms regulating DLK activity will be summarized to provide better insights into DLK action and, possibly, new targets to modulate DLK function.

VEGF beta is a candidate biomarker for cardiovascular risk stratification

Background

The blood-based transcriptome changes in relation to body weight but longitudinal data on specific transcripts are rare. Monocytes play a crucial role in the development of atherosclerosis and coronary artery disease. Monitoring monocytic gene expression patterns could aid to identify biomarkers for improved cardiovascular risk stratification. BMI and diabetes mellitus (T2DM) are associated with coronary artery disease (CAD). There are mRNAs associated with the development of atherosclerosis and CAD, which can be detected in circulating cells. The exact pathways and direct targets have not been explored.

Objective

To apply transcriptome screening and validation analysis to identify novel biomarker candidates associated with longitudinal changes of BMI as cardiovascular risk factors and test association with clinical endpoints.

Methods

Transcriptome-wide monocytic gene expression changes were screened in relation to changes in BMI over a time period of 5 years in 1,092 participants of the Gutenberg Health Study with available transcriptomics data at baseline investigation and at 5-years follow-up. Functional enrichment of BMI-related genes (FDR <0.01) was tested based on pathway databases and selected gene sets. Serum VEGFB levels were quantified and validated in serum from n=1,895 individuals from an independent cohort study (FinRisk). In-vitro, THP1 cells were stimulated with recombinant VEGFB.

Results

143 transcripts showed a significant association with change in BMI over 5 years. Decreased VEGFB mRNA levels strongly associated with increased BMI (p=2.8x10–9). Lower levels of VEGFB mRNA were associated with increased mortality (HRperSD=0.757, 95% CI: 0.647–0.885, p=0.0005) following adjustment for age and sex and incident diabetes (p=0.01). Circulating VEGFB levels inversely correlated with VEGFB mRNA (r=−0.2, p=0.0024) and positively correlated with an increase in BMI (beta=0.226, p=8.4x10–6), type 2 diabetes mellitus risk (HRperSD=1.279, 95% CI: 1.148–1.425, p=7.8x10–6) and all-cause mortality (HRperSD=1.184, 95% CI: 1.045–1.342, p=0.008). Further exploration in n=1,895 individuals from FinRisk revealed an association of increased VEGFB levels with increased risk for heart failure (HRperSD=1.373, 95% CI: 1.210–1.560, p=1.0x10–6) and coronary artery disease (HR=1.018, 95% CI: 1.003–1.034, p=0.019), even after adjustment for BMI. In THP-1 culture, stimulation with VEGFB resulted in downregulation of VEGFB mRNA levels.

Conclusion

Decreased monocytic gene expression of VEGFB is related to increased BMI, increased risk of T2DM and all-cause mortality. Vice versa,circulating VEGFB levels associates positively with BMI, diabetes, mortality as well as heart failure and coronary heart disease. We hypothesize that monocytes regulate VEGFB expression by a negative feed-back mechanism based. Circulating VEGFB is a potential novel biomarker candidate for weight-related diabetes risk and cardiovascular risk evaluation.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): DZHK

Arginine:Glycine Amidinotransferase Is Essential for Creatine Supply in Mice During Chronic Hypoxia

Objective: Chronic hypoxia induces pulmonary and cardiovascular pathologies, including pulmonary hypertension (PH). L-arginine:glycine amidinotransferase (AGAT) is essential for homoarginine (hArg) and guanidinoacetate synthesis, the latter being converted to creatine by guanidinoacetate methyltransferase. Low hArg concentrations are associated with cardiovascular morbidity and predict mortality in patients with PH. We therefore aimed to investigate the survival and cardiac outcome of AGAT knockout (Agat^−/−) mice under hypoxia and a possible rescue of the phenotype.

Methods:Agat^−/− mice and wild-type (WT) littermates were subjected to normoxia or normobaric hypoxia (10% oxygen) for 4 weeks. A subgroup of Agat^−/− mice was supplemented with 1% creatine from weaning. Survival, hematocrit, blood lactate and glucose, heart weight-to-tibia length (HW/TL) ratio, hArg plasma concentration, and Agat and Gamt expression in lung, liver, and kidneys were evaluated.

Results: After 6 h of hypoxia, blood lactate was lower in Agat^−/−-mice as compared to normoxia (p < 0.001). Agat^−/− mice died within 2 days of hypoxia, whereas Agat^−/− mice supplemented with creatine and WT mice survived until the end of the study. In WT mice, hematocrit (74 ± 4 vs. 55 ± 2%, mean ± SD, p < 0.001) and HW/TL (9.9 ± 1.3 vs. 7.3 ± 0.7 mg/mm, p < 0.01) were higher in hypoxia, while hArg plasma concentration (0.25 ± 0.06 vs. 0.38 ± 0.12 μmol/L, p < 0.01) was lower. Agat and Gamt expressions were differentially downregulated by hypoxia in lung, liver, and kidneys.

Conclusion:Agat and Gamt are downregulated in hypoxia. Agat^−/− mice are nonviable in hypoxia. Creatine rescues the lethal phenotype, but it does not reduce right ventricular hypertrophy of Agat^−/− mice in hypoxia.

Bicuspid aortopathy - molecular involvement of microRNAs and MMP-TIMP

OBJECTIVES

We aimed to elucidate the correlation between expression patterns of aortic tissue microRNAs and the aortopathy formation in bicuspid aortic valve (BAV) disease.

METHODS

All 65 patients who underwent elective aortic valve repair/replacement +/- proximal aortic replacement due to BAV disease with or without concomitant aortic aneurysm were identified from our BAV registry. Aortic tissue was collected intraoperatively from the ascending aorta at the greater and lesser curvature. Aortic tissue microRNAs analysis included 11 microRNAs (miR-1, miR-17, miR-18a, miR-19a, miR-20a, miR-21, miR-29b, miR-106a, miR-133a, miR-143 and miR-145). Furthermore, analysis of MMP2, TIMP1/2 mRNA and the protein expression was subsequently performed. The primary study endpoint was the correlation between microRNAs and MMP2, TIMP1/2 mRNA/protein expression.

RESULTS

We found a significant association between miR-133a and TIMP1 mRNA (r = 0.870, p < 0.001), an inverse correlation between miR-143a and MMP2 protein expression (r= -0.614, p = 0.044) and a positive correlation between miR-133a and TIMP-2 protein expression (r = 0.583, p = 0.036) at the greater curvature.

CONCLUSION

Our findings indicate that aortic tissue microRNAs may reflect remodelling processes of the proximal aorta in BAV aortopathy. Specific aortic tissue microRNAs may exert their regulatory effects on the aortopathy through their impact on MMPs/TIMPs homeostasis at the level of the greater curvature.

Distinct functions of the dual leucine zipper kinase depending on its subcellular localization

The dual leucine zipper kinase DLK induces β-cell apoptosis by inhibiting the transcriptional activity conferred by the β-cell protective transcription factor cAMP response element binding protein CREB. This action might contribute to β-cell loss and ultimately diabetes. Within its kinase domain DLK shares high homology with the mixed lineage kinase (MLK) 3, which is activated by tumor necrosis factor (TNF) α and interleukin (IL)-1β, known prediabetic signals. In the present study, the regulation of DLK in β-cells by these cytokines was investigated. Both, TNFα and IL-1β induced the nuclear translocation of DLK. Mutations within a putative nuclear localization signal (NLS) prevented basal and cytokine-induced nuclear localization of DLK and binding to the importin receptor importin α, thereby demonstrating a functional NLS within DLK. DLK NLS mutants were catalytically active as they phosphorylated their down-stream kinase c-Jun N-terminal kinase to the same extent as DLK wild-type but did neither inhibit CREB-dependent gene transcription nor transcription conferred by the promoter of the anti-apoptotic protein BCL-xL. In addition, the β-cell apoptosis-inducing effect of DLK was severely diminished by mutation of its NLS. In a murine model of prediabetes, enhanced nuclear DLK was found. These data demonstrate that DLK exerts distinct functions, depending on its subcellular localization and thus provide a novel level of regulating DLK action. Furthermore, the prevention of the nuclear localization of DLK as induced by prediabetic signals with consecutive suppression of β-cell apoptosis might constitute a novel target in the therapy of diabetes mellitus.

Neighborhood environment and risk of ischemic stroke: the brain attack surveillance in Corpus Christi (BASIC) Project

The authors explored whether neighborhood-level characteristics are associated with ischemic stroke and whether the association differs by ethnicity, age, and gender. Using data from the Brain Attack Surveillance in Corpus Christi Project (January 2000-June 2003), they identified cases of ischemic stroke (n = 1,247) from both hospital and out-of-hospital sources. Census tracts served as proxies for neighborhoods, and neighborhood socioeconomic status scores were constructed from census variables (higher scores represented less disadvantage). In Poisson regression analyses comparing the 90th percentile of neighborhood score with the 10th, the relative risk of stroke was 0.49 (95% confidence interval (CI): 0.41, 0.58). After adjustment for age, gender, and ethnicity, this association was attenuated (relative risk (RR) = 0.79, 95% CI: 0.63, 1.00). There was no ethnic difference in the association of score with stroke (p for interaction = 0.79). Significant effect modification was found for age (p for interaction < 0.001) and gender (p for interaction = 0.04), with increasing scores being protective against stroke in men and younger persons. Associations were attenuated after adjustment for education (men: RR = 0.77, 95% CI: 0.55, 1.07; persons aged <65 years: RR = 0.65, 95% CI: 0.41, 1.02). Neighborhood characteristics may influence stroke risk in certain gender and age groups. Mechanisms for these associations should be examined.