MAPK-activated protein kinase-5 (MK5) is a protein serine/threonine kinase that is activated by p38 MAPK and the atypical MAPKs ERK3 and ERK4. The physiological function(s) of MK5 remains unknown. Here, we examined the effect of MK5 haplodeficiency on cardiac function and myocardial remodeling. At 12 wk of age, MK5 haplodeficient mice (MK5) were smaller than age-matched wild-type littermates (MK5), with similar diastolic function but reduced systolic function. Transverse aortic constriction (TAC) was used to induce chronic pressure overload in 12-wk-old male MK5 and MK5 mice. Two weeks post-TAC, heart weight-to-tibia length ratios were similarly increased in MK5 and MK5 hearts, as was the abundance of B-type natriuretic peptide and β-myosin heavy chain mRNA. Left ventricular ejection fraction was reduced in both MK5 and MK5 mice, whereas regional peak systolic tissue velocities were reduced and isovolumetric relaxation time was prolonged in MK5 hearts but not in MK5 hearts. The TAC-induced increase in collagen type 1-α mRNA observed in MK5 hearts was markedly attenuated in MK5 hearts. Eight weeks post-TAC, systolic function was equally impaired in MK5 and MK5 mice. In contrast, the increase in E wave deceleration rate and progression of hypertrophy observed in TAC MK5 mice were attenuated in TAC MK5 mice. MK5 immunoreactivity was detected in adult fibroblasts but not in myocytes. MK5, MK5, and MK5 fibroblasts all expressed α-smooth muscle actin in culture. Hence, reduced MK5 expression in cardiac fibroblasts was associated with the attenuation of both hypertrophy and development of a restrictive filling pattern during myocardial remodeling in response to chronic pressure overload. MAPK-activated protein kinase-5 (MK5)/p38-regulated/activated protein kinase is a protein serine/threonine kinase activated by p38 MAPK and/or the atypical MAPKs ERK3 and ERK4. MK5 immunoreactivity was detected in adult ventricular fibroblasts but not in myocytes. MK5 haplodeficiency attenuated the progression of hypertrophy, reduced collagen type 1 mRNA, and protected diastolic function in response to chronic pressure overload.

The G 1 /S transition is a critical control point for cell proliferation and involves essential transcription complexes termed SBF and MBF in Saccharomyces cerevisiae or MBF in Schizosaccharomyces pombe. In the fungal pathogen Candida albicans, G 1 /S regulation is not clear. To gain more insight into the G 1 /S circuitry, we characterized Swi6p, Swi4p and Mbp1p, the closest orthologues of SBF (Swi6p and Swi4p) and MBF (Swi6p and Mbp1p) components in S. cerevisiae. The mbp1⌬/⌬ cells showed minor growth defects, whereas swi4⌬/⌬ and swi6⌬/⌬ yeast cells dramatically increased in size, suggesting a G 1 phase delay. Gene set enrichment analysis (GSEA) of transcription profiles revealed that genes associated with G 1 /S phase were significantly enriched in cells lacking Swi4p and Swi6p. These expression patterns suggested that Swi4p and Swi6p have repressing as well as activating activity. Intriguingly, swi4⌬/⌬ swi6⌬/⌬ and swi4⌬/⌬ mbp1⌬/⌬ strains were viable, in contrast to the situation in S. cerevisiae, and showed pleiotropic phenotypes that included multibudded yeast, pseudohyphae, and intriguingly, true hyphae. Consistently, GSEA identified strong enrichment of genes that are normally modulated during C. albicans-host cell interactions. Since Swi4p and Swi6p influence G 1 phase progression and SBF binding sites are lacking in the C. albicans genome, these factors may contribute to MBF activity. Overall, the data suggest that the putative G 1 /S regulatory machinery of C. albicans contains novel features and underscore the existence of a relationship between G 1 phase and morphogenetic switching, including hyphal development, in the pathogen.

Objective— Lipoprotein lipase (LPL)–mediated triglyceride hydrolysis is the major source of fatty acid for cardiac energy. LPL, synthesized in cardiomyocytes, is translocated across endothelial cells (EC) by its transporter glycosylphosphatidylinositol-anchored high-density lipoprotein–binding protein 1 (GPIHBP1). Previously, we have reported an augmentation in coronary LPL, which was linked to an increased expression of GPIHBP1 following moderate diabetes mellitus. We examined the potential mechanism by which hyperglycemia amplifies GPIHBP1. Approach and Results— Exposure of rat aortic EC to high glucose induced GPIHBP1 expression and amplified LPL shuttling across these cells. This effect coincided with an elevated secretion of heparanase. Incubation of EC with high glucose or latent heparanase resulted in secretion of vascular endothelial growth factor (VEGF). Primary cardiomyocytes, being a rich source of VEGF, when cocultured with EC, restored EC GPIHBP1 that is lost because of cell passaging. Furthermore, recombinant VEGF induced EC GPIHBP1 mRNA and protein expression within 24 hours, an effect that could be prevented by a VEGF neutralizing antibody. This VEGF-induced increase in GPIHBP1 was through Notch signaling that encompassed Delta-like ligand 4 augmentation and nuclear translocation of the Notch intracellular domain. Finally, cardiomyocytes from severely diabetic animals exhibiting attenuation of VEGF were unable to increase EC GPIHBP1 expression and had lower LPL activity at the vascular lumen in perfused hearts. Conclusion— EC, as the first responders to hyperglycemia, can release heparanase to liberate myocyte VEGF. This growth factor, by activating EC Notch signaling, is responsible for facilitating GPIHBP1-mediated translocation of LPL across EC and regulating LPL-derived fatty acid delivery to the cardiomyocytes.

Vascular endothelial growth factor B (VEGFB) is highly expressed in metabolically active tissues, such as the heart and skeletal muscle, suggesting a function in maintaining oxidative metabolic and contractile function in these tissues. Multiple models of heart failure have indicated a significant drop in VEGFB. However, whether there is a role for decreased VEGFB in diabetic cardiomyopathy is currently unknown. Of the VEGFB located in cardiomyocytes, there is a substantial and readily releasable pool localized on the cell surface. The immediate response to high glucose and the secretion of endothelial heparanase is the release of this surface-bound VEGFB, which triggers signaling pathways and gene expression to influence endothelial cell (autocrine action) and cardiomyocyte (paracrine effects) survival. Under conditions of hyperglycemia, when VEGFB production is impaired, a robust increase in vascular endothelial growth factor receptor (VEGFR)-1 expression ensues as a possible mechanism to enhance or maintain VEGFB signaling. However, even with an increase in VEGFR1 after diabetes, cardiomyocytes are unable to respond to VEGFB. In addition to the loss of VEGFB production and signaling, evaluation of latent heparanase, the protein responsible for VEGFB release, also showed a significant decline in expression in whole hearts from animals with chronic or acute diabetes. Defects in these numerous VEGFB pathways were associated with an increased cell death signature in our models of diabetes. Through this bidirectional interaction between endothelial cells (which secrete heparanase) and cardiomyocytes (which release VEGFB), this growth factor could provide the diabetic heart protection against cell death and may be a critical tool to delay or prevent cardiomyopathy. We discovered a bidirectional interaction between endothelial cells (which secrete heparanase) and cardiomyocytes [which release vascular endothelial growth factor B (VEGFB)]. VEGFB promoted cell survival through ERK and cell death gene expression. Loss of VEGFB and its downstream signaling is an early event following hyperglycemia, is sustained with disease progression, and could explain diabetic cardiomyopathy.

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