Reversal of Aging-Induced Increases in Aortic Stiffness by Targeting Cytoskeletal Protein-Protein Interfaces

Background

The proximal aorta normally functions as a critical shock absorber that protects small downstream vessels from damage by pressure and flow pulsatility generated by the heart during systole. This shock absorber function is impaired with age because of aortic stiffening.

Methods and Results

We examined the contribution of common genetic variation to aortic stiffness in humans by interrogating results from the AortaGen Consortium genome‐wide association study of carotid‐femoral pulse wave velocity. Common genetic variation in the N‐WASP (WASL) locus is associated with carotid‐femoral pulse wave velocity (rs600420, P=0.0051). Thus, we tested the hypothesis that decoy proteins designed to disrupt the interaction of cytoskeletal proteins such as N‐WASP with its binding partners in the vascular smooth muscle cytoskeleton could decrease ex vivo stiffness of aortas from a mouse model of aging. A synthetic decoy peptide construct of N‐WASP significantly reduced activated stiffness in ex vivo aortas of aged mice. Two other cytoskeletal constructs targeted to VASP and talin‐vinculin interfaces similarly decreased aging‐induced ex vivo active stiffness by on‐target specific actions. Furthermore, packaging these decoy peptides into microbubbles enables the peptides to be ultrasound‐targeted to the wall of the proximal aorta to attenuate ex vivo active stiffness.

Conclusions

We conclude that decoy peptides targeted to vascular smooth muscle cytoskeletal protein‐protein interfaces and microbubble packaged can decrease aortic stiffness ex vivo. Our results provide proof of concept at the ex vivo level that decoy peptides targeted to cytoskeletal protein‐protein interfaces may lead to substantive dynamic modulation of aortic stiffness.

Role of Matrix Metalloproteinases 2 and 9 in Lacrimal Gland Disease in Animal Models of Sjögren's Syndrome

PURPOSE

Chronic inflammation of the lacrimal gland results in changes in the composition of the extracellular matrix (ECM), which is believed to compromise tissue repair. We hypothesized that increased production/activity of matrix metalloproteinases (MMPs), especially MMP-2 and -9, in inflamed lacrimal glands modifies the ECM environment, therefore disrupting tissue repair.

METHODS

The lacrimal glands from female MRL/lpr and male NOD mice along with their respective control strains were harvested and divided into three pieces and processed for histology, immunohistochemistry, zymography, Western blotting, and RNA analyses. In another study, MRL/lpr mice were treated for 5 weeks with a selective MMP2/9 inhibitor peptide or a control peptide. At the end of treatment, the lacrimal glands were excised and the tissue was processed as described above.

RESULTS

There was a 2.5- and 2.7-fold increase in MMP2 gene expression levels in MRL/lpr and NOD mice, respectively. Matrix metalloproteinase 2 and 9 enzymatic activities and protein expression levels were significantly upregulated in the lacrimal glands of MRL/lpr and NOD mice compared to controls. Treatment with the MMP2/9 inhibitor resulted in decreased activity of MMP-2 and -9 both in vitro and in vivo. Importantly, MMP2/9 inhibitor treatment of MRL/lpr mice improved aqueous tear production and resulted in reduced number and size of lymphocytic foci in diseased lacrimal glands.

CONCLUSIONS

We conclude that MMP2/9 expression and activity are elevated in lacrimal glands of two murine models of Sjögren's syndrome, suggesting that manipulation of MMP2/9 activity might be a potential therapeutic target in chronically inflamed lacrimal glands.

Arginyltransferase ATE1 catalyzes midchain arginylation of proteins at side chain carboxylates in vivo

Arginylation is an emerging posttranslational modification mediated by Arg-tRNA-protein-transferase (ATE1). It is believed that ATE1 links Arg solely to the N terminus of proteins, requiring prior proteolysis or action by Met-aminopeptidases to expose the arginylated site. Here, we tested the possibility of Arg linkage to midchain sites within intact protein targets and found that many proteins in vivo are modified on the side chains of Asp and Glu by unconventional chemistry that targets the carboxy rather than the amino groups at the target sites. Such arginylation appears to be functionally regulated, and it can be directly mediated by ATE1, in addition to the more conventional ATE1-mediated linkage of Arg to the N-terminal alpha amino group. This midchain arginylation implies an unconventional mechanism of ATE1 action that likely facilitates its major biological role.

Tropomyosin variants describe distinct functional subcellular domains in differentiated vascular smooth muscle cells

Tropomyosin (Tm) is known to be an important gatekeeper of actin function. Tm isoforms are encoded by four genes, and each gene produces several variants by alternative splicing, which have been proposed to play roles in motility, proliferation, and apoptosis. Smooth muscle studies have focused on gizzard smooth muscle, where a heterodimer of Tm from the α-gene (Tmsm-α) and from the β-gene (Tmsm-β) is associated with contractile filaments. In this study we examined Tm in differentiated mammalian vascular smooth muscle (dVSM). Liquid chromatography-tandem mass spectrometry (LC MS/MS) analysis and Western blot screening with variant-specific antibodies revealed that at least five different Tm proteins are expressed in this tissue: Tm6 (Tmsm-α) and Tm2 from the α-gene, Tm1 (Tmsm-β) from the β-gene, Tm5NM1 from the γ-gene, and Tm4 from the δ-gene. Tm6 is by far most abundant in dVSM followed by Tm1, Tm2, Tm5NM1, and Tm4. Coimmunoprecipitation and coimmunofluorescence studies demonstrate that Tm1 and Tm6 coassociate with different actin isoforms and display different intracellular localizations. Using an antibody specific for cytoplasmic γ-actin, we report here the presence of a γ-actin cortical cytoskeleton in dVSM cells. Tm1 colocalizes with cortical cytoplasmic γ-actin and coprecipitates with γ-actin. Tm6, on the other hand, is located on contractile bundles. These data indicate that Tm1 and Tm6 do not form a classical heterodimer in dVSM but rather describe different functional cellular compartments.

Smooth muscle archvillin is an ERK scaffolding protein

ERK influences a number of pathways in all cells, but how ERK activities are segregated between different pathways has not been entirely clear. Using immunoprecipitation and pulldown experiments with domain-specific recombinant fragments, we show that smooth muscle archvillin (SmAV) binds ERK and members of the ERK signaling cascade in a domain-specific, stimulus-dependent, and pathway-specific manner. MEK binds specifically to the first 445 residues of SmAV. B-Raf, an upstream regulator of MEK, constitutively interacts with residues 1-445 and 446-1250. Both ERK and 14-3-3 bind to both fragments, but in a stimulus-specific manner. Phosphorylated ERK is associated only with residues 1-445. An ERK phosphorylation site was determined by mass spectrometry to reside at Ser132. A phospho-antibody raised to this site shows that the site is phosphorylated during alpha-agonist-mediated ERK activation in smooth muscle tissue. Phosphorylation of SmAV by ERK decreases the association of phospho-ERK with SmAV. These results, combined with previous observations, indicate that SmAV serves as a new ERK scaffolding protein and provide a mechanism for regulation of ERK binding, activation, and release from the signaling complex.

Zinc inhibits nuclear factor-kappa B activation and sensitizes prostate cancer cells to cytotoxic agents

Prostate carcinogenesis involves transformation of zinc-accumulating normal epithelial cells to malignant cells, which do not accumulate zinc. In this study, we demonstrate by immunoblotting and immunohistochemistry that physiological levels of zinc inhibit activation of nuclear factor (NF)-kappa B transcription factor in PC-3 and DU-145 human prostate cancer cells, reduce expression of NF-kappa B-controlled antiapoptotic protein c-IAP2, and activate c-Jun NH(2)-terminal kinases. Preincubation of PC-3 cells with physiological concentrations of zinc sensitized tumor cells to tumor necrosis factor (TNF)-alpha, and paclitaxel mediated cell death as defined by terminal deoxynucleotidyl transferase-mediated nick end labeling assay. These results suggest one possible mechanism for the inhibitory effect of zinc on the development and progression of prostate malignancy and might have important consequences for the prevention and treatment of prostate cancer.

Leptin upregulates beta3-integrin expression and interleukin-1beta, upregulates leptin and leptin receptor expression in human endometrial epithelial cell cultures

Human endometrium and endometrial epithelial cells (EECs) either cultured alone or cocultured with human embryos express leptin and leptin receptor. This study compares the effect of leptin with that of interleukin-1beta (IL-1beta) on the expression of beta3-EEC integrin, a marker of endometrial receptivity. Both cytokines increased the expression of beta3-EEC at concentrations in the range of 0.06-3 nM; however, leptin exhibited a significantly greater effect than IL-1beta. We also determined the regulatory effects of IL-1beta on leptin secretion and on the expression of leptin and leptin receptor at the protein level in both EEC and endometrial stromal cell (ESC) cultures. In EEC cultures, IL-1beta upregulated secretion of leptin and expression of both leptin and leptin receptors. No effect of IL-1beta was found in the ESC cultures. However, leptin exhibited marginal upregulation of leptin receptor. The upregulation of beta3-integrin and leptin/leptin receptor expression by IL-1beta in EEC cultures indicates that both cytokines may be implicated in embryonic-maternal cross-talk during the early phase of human implantation. Our present data also raise the possibility that leptin is an endometrial molecular effector of IL-1beta action on beta3-integrin upregulation. Thus, a new role for leptin in human reproduction as an autocrine/paracrine regulator of endometrial receptivity is proposed.

Inhibition of PKCalpha and rhoA translocation in differentiated smooth muscle by a caveolin scaffolding domain peptide

Receptor-coupled contraction of smooth muscle involves recruitment to the plasma membrane of downstream effector molecules PKCalpha and rhoA but the mechanism of this signal integration is unclear. Caveolins, the principal structural proteins of caveolar plasma membrane invaginations, have been implicated in the organization and regulation of many signal transducing molecules. Thus, using laser scanning confocal immunofluorescent microscopy, we tested the hypothesis that caveolin is involved in smooth muscle signaling by investigating caveolin isoform expression and localization, together with the effect of a peptide inhibitor of caveolin function, in intact differentiated smooth muscle cells. All three main caveolin isoforms were identified in uterine, stomach, and ileal smooth muscles and assumed a predominantly plasma membranous localization in myometrial cells. Cytoplasmic introduction of a peptide corresponding to the caveolin-1 scaffolding domain-an essential region for caveolin interaction with signaling molecules--significantly inhibited agonist-induced translocation of both PKCalpha and rhoA. Translocation was unimpaired by a scrambled peptide and was unaltered in sham-treated cells. The membranous localization of caveolins, and direct inhibition of receptor-coupled PKCalpha and rhoA translocation by the caveolin-1 scaffolding domain, supports the concept that caveolins can regulate the integration of extracellular contractile stimuli and downstream intracellular effectors in smooth muscle.

In vitro activation of a 60-70 kDa histone H4 protein kinase from neutrophils by limited proteolysis

Neutrophils stimulated with the chemotactic peptide fMet-Leu-Phe (fMLP) are known to exhibit a rapid and transient activation of a histone H4 kinase that may function in a stimulatory pathway downstream of phosphatidylinositol 3-kinase. The activity of this histone kinase in unstimulated neutrophils and cells treated with 1.0 microM fMLP for 10 sec was 8.8 +/- 5 and 43 +/- 2 pmol P/min per 10(7) cells, respectively. In this paper, we report that unstimulated neutrophils contain a latent H4 kinase in the 100,000 x g soluble fraction that can be markedly activated by treatment with trypsin. The values for the untreated and trypsin treated enzyme were 5.5 +/- 1.0 and 63.6 +/- 18 pmol P/min per 10(7) cell-equivalents, respectively. This kinase was insensitive to a selective antagonist of protein kinase C (i.e., 50 microM 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7)) but completely blocked by 100 nM staurosporine. Only a single peak of activity was observed for this enzyme when the 100,000 x g supernatant fraction was fractionated on either an exclusion (KW-803) or an anion exchange column (DEAE), or during isoelectric focusing. The molecular weight of the latent kinase was 64 +/- 6 kDa and the isoelectric point was 7.6 +/- 0.1. During all fractionation procedures, the H4 kinase co-chromatographed with a trypsin-activated kinase that catalyzed the phosphorylation of a peptide which corresponds to residues 297-331 of the 47 kDa subunit of the NADPH-oxidase complex (p47-phox). The properties of the trypsin-activated H4 kinase from unstimulated neutrophils are very similar to those reported for this enzyme from fMLP-stimulated cells.

Effect of Ca2+ binding on troponin C. Changes in spin label mobility, extrinsic fluorescence, and sulfhydryl reactivity

The Ca2+ binding component (TnC) of troponin has been selectively labeled with either a spin label, N-(1-oxyl-2,2,6,6-tetramethyl-4-piperidinyl) iodoacetamide, or with a fluorescent probe, S-mercuric-N-dansyl cysteine, presumably at its single cysteine residue (Cys-98) in order to probe the interactions of TnC with divalent metals and with other subunits of troponin. The modified protein has the same Ca2+ binding properties as native TnC (Potter, J. D., and Gergely, J. (1975) J. Biol. Chem. 250, 4628), viz. two Ca2+ binding sites at which Mg2+ appears to compete (Ca2+-Mg2+ sites, KCa = 2 X 10(7) M-1) and two sites at which Mg2+ does not compete (Ca2+-specific sites, KCa = 2 X 10(5) M-1). Either Ca2+ or Mg2+ alters the ESR spectrum of spin-labeled TnC in a manner that indicates a decrease in the mobility of the label, Ca2+ having a slightly greater effect. In systems containing both Ca2+ and Mg2+ the mobility of the spin label is identical with that in systems containing Ca2+ alone. The binding constants for Ca2+ and Mg2+ deduced from ESR spectral changes are 10(7) and 10(3) M-1, respectively, and the apparent affinity for Ca2+ decreases by about an order of magnitude on adding 2 mM Mg2+. Thus, the ESR spectral change is associated with binding of Ca2+ to one or both of the Ca2+-Mg2+ sites. Addition of Ca2+ to the binary complexes of spin-labeled TnC with either troponin T (TnT) or troponin I (TnI) produces greater reduction in the mobility of the spin label than in the case of spin-labeled TnC alone, and in the case of the complex with TnI the affinity for Ca2+ is increased by an order of magnitude. The fluorescence of dansyl (5-dimethylaminonaphthalene-1-sulfonyl)-labeled TnC is enhanced by Ca2+ binding to both high and low affinity sites with apparent binding constants of 2.6 X 10(7) M-1 and 2.9 X 10(5) M-1, respectively, calculated from the transition midpoints. The presence of 2 mM Mg2+, which produces no effect on dansyl fluorescence itself, in contrast to its effect on the spin label, shifts the high affinity constant to 2 X 10(6) M-1. Spectral changes produced by Ca2+ binding to the TnC-TnI complex furnish evidence that the affinity of TnC for Ca2+ is increased in the complex. The reactivity of Cys-98 to the labels and to 5,5'-dithiobis(2-nitrobenzoic acid) (Nbs2) is decreased by Ca2+ or Mg2+ both with native TnC and in 6 M urea. The reaction rate between Cys-98 and Nbs2 decreases to one-half the maximal value at a Ca2+ concentration that suggests binding to the Ca2+-Mg2+ sites. Formation of a binary complex between TnI and TnC reduces the rate of reaction, and there is a further reduction by Ca2+. The effect of Ca2+ takes place at concentrations that are 1 order of magnitude lower than in the case of TnC alone. These results suggest that the Ca2+ binding site adjacent to Cys-98 is one of the Ca2+-Mg2+ binding sites.