TCF7L1 Accelerates Smooth Muscle Cell Phenotypic Switching and Aggravates Abdominal Aortic Aneurysms

Phenotypic switching of vascular smooth muscle cells is a central process in abdominal aortic aneurysm (AAA) pathology. We found that knockdown TCF7L1 (transcription factor 7-like 1), a member of the TCF/LEF (T cell factor/lymphoid enhancer factor) family of transcription factors, inhibits vascular smooth muscle cell differentiation. This study hints at potential interventions to maintain a normal, differentiated smooth muscle cell state, thereby eliminating the pathogenesis of AAA. In addition, our study provides insights into the potential use of TCF7L1 as a biomarker for AAA.

A Role for Polo-Like Kinase 4 in Vascular Fibroblast Cell-Type Transition

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PLK4, previously known as a centriole-associated factor, regulates the transcription factor activity of serum response factor.

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PLK4 inhibition blocks the profibrogenic cell state transition of vascular fibroblasts.

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PLK4’s activation and gene expression are regulated by PDGF receptor and epigenetic reader BRD4, respectively.

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Periadventitial administration of a PLK4 inhibitor mitigates vascular fibrosis.

Polo-like kinase 4 (PLK4) is canonically known for its cytoplasmic function in centriole duplication. Here we show a noncanonical PLK4 function of regulating the transcription factor SRF’s nuclear activity and associated myofibroblast-like cell-type transition. In this context, we have further found that PLK4’s phosphorylation and transcription are respectively regulated by PDGF receptor and epigenetic factor BRD4. Furthermore, in vivo experiments suggest PLK4 inhibition as a potential approach to mitigating vascular fibrosis.

PERK Inhibition Mitigates Restenosis and Thrombosis: A Potential Low-Thrombogenic Antirestenotic Paradigm

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Drug-eluting stents impede neointimal smooth muscle cell hyperplasia but exacerbate endothelial cell dysfunction and thrombogenicity. It has been a challenge to identify a common target to inhibit both. Findings in this study suggest PERK as such a target.

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A PERK inhibitor administered either via an endovascular (in biomimetic nanocarriers) or perivascular (in hydrogel) route effectively mitigated neointimal hyperplasia in rats.

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Oral gavage of the PERK inhibitor partially preserved the normal blood flow in a mouse model of induced thrombosis.

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Dampening PERK activity inhibited STAT3 while activating SRF in smooth muscle cells, and also reduced prothrombogenic tissue factor and growth impairment of endothelial cells.

Developing endothelial-protective, nonthrombogenic antirestenotic treatments has been a challenge. A major hurdle to this has been the identification of a common molecular target in both smooth muscle cells and endothelial cells, inhibition of which blocks dysfunction of both cell types. The authors’ findings suggest that the PERK kinase could be such a target. Importantly, PERK inhibition mitigated both restenosis and thrombosis in preclinical models, implicating a low-thrombogenic antirestenotic paradigm.

HDAC6 Regulates the MRTF-A/SRF Axis and Vascular Smooth Muscle Cell Plasticity

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Distinct from other histone deacetylases, HDAC6 primarily resides in the cytosol.

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Unexpectedly, HDAC6-selective inhibition (or silencing) enhances the nuclear activity of SRF.

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HDAC6 inhibition elevates acetylation and protein levels of myocardin-related transcription factor A, a cytoplasmic-nuclear shuttling co-activator of SRF. Myocardin-related transcription factor A/SRF are known to critically regulate vascular smooth muscle cell phenotypic stability.

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HDAC6 inhibition prevents smooth muscle cell dedifferentiation in vitro and reduces neointima and restenosis in vivo.

Cellular plasticity is fundamental in biology and disease. Vascular smooth muscle cell (SMC) dedifferentiation (loss of contractile proteins) initiates and perpetrates vascular pathologies such as restenosis. Contractile gene expression is governed by the master transcription factor, serum response factor (SRF). Unlike other histone deacetylases, histone deacetylase 6 (HDAC6) primarily resides in the cytosol. Whether HDAC6 regulates SRF nuclear activity was previously unknown in any cell type. This study found that selective inhibition of HDAC6 with tubastatin A preserved the contractile protein (alpha-smooth muscle actin) that was otherwise diminished by platelet-derived growth factor-BB. Tubastatin A also enhanced SRF transcriptional (luciferase) activity, and this effect was confirmed by HDAC6 knockdown. Interestingly, HDAC6 inhibition increased acetylation and total protein of myocardin-related transcription factor A (MRTF-A), a transcription co-activator known to translocate from the cytosol to the nucleus, thereby activating SRF. Consistently, HDAC6 co-immunoprecipitated with MRTF-A. In vivo studies showed that tubastatin A treatment of injured rat carotid arteries mitigated neointimal lesion, which is known to be formed largely by dedifferentiated SMCs. This report is the first to show HDAC6 regulation of the MRTF-A/SRF axis and SMC plasticity, thus opening a new perspective for interventions of vascular pathologies.

Reduced NGF in Gastric Endothelial Cells Is One of the Main Causes of Impaired Angiogenesis in Aging Gastric Mucosa

BACKGROUND & AIMS

Aging gastric mucosa has increased susceptibility to injury and delayed healing owing to impaired angiogenesis, but the mechanisms are not fully known. We examined whether impairment of angiogenesis in aging gastric mucosa is caused by deficiency of nerve growth factor (NGF) in gastric endothelial cells (ECs), and whether NGF therapy could reverse this impairment.

METHODS

In gastric mucosal ECs (GECs) isolated from young and aging rats we examined the following: (1) in vitro angiogenesis, (2) NGF expression, and (3) the effect of NGF treatment on angiogenesis, GEC proliferation and migration, and dependence on serum response factor. In in vivo studies in young and aging rats, we examined NGF expression in gastric mucosa and the effect of NGF treatment on angiogenesis and gastric ulcer healing. To determine human relevance, we examined NGF expression in gastric mucosal biopsy specimens of aging (≥70 y) and young (≤40 y) individuals.

RESULTS

In cultured aging GECs, NGF expression and angiogenesis were reduced significantly by 3.0-fold and 4.1-fold vs young GECs. NGF therapy reversed impairment of angiogenesis in aging GECs, and serum response factor silencing completely abolished this response. In gastric mucosa of aging rats, NGF expression in GECs was reduced significantly vs young rats. In aging rats, local NGF treatment significantly increased angiogenesis and accelerated gastric ulcer healing. In aging human subjects, NGF expression in ECs of gastric mucosal vessels was 5.5-fold reduced vs young individuals.

CONCLUSIONS

NGF deficiency in ECs is a key mechanism underlying impaired angiogenesis and delayed ulcer healing in aging gastric mucosa. Local NGF therapy can reverse these impairments.

Transcriptional regulation of tenascin genes

Extracellular matrix proteins of the tenascin family resemble each other in their domain structure, and also share functions in modulating cell adhesion and cellular responses to growth factors. Despite these common features, the 4 vertebrate tenascins exhibit vastly different expression patterns. Tenascin-R is specific to the central nervous system. Tenascin-C is an “oncofetal” protein controlled by many stimuli (growth factors, cytokines, mechanical stress), but with restricted occurrence in space and time. In contrast, tenascin-X is a constituitive component of connective tissues, and its level is barely affected by external factors. Finally, the expression of tenascin-W is similar to that of tenascin-C but even more limited. In accordance with their highly regulated expression, the promoters of the tenascin-C and -W genes contain TATA boxes, whereas those of the other 2 tenascins do not. This article summarizes what is currently known about the complex transcriptional regulation of the 4 tenascin genes in development and disease.

G17V RHOA: Genetic evidence of GTP-unbound RHOA playing a role in tumorigenesis in T cells

RHOA is a member of RHO family small GTPases. Over the past 2 decades, numerous biochemical and cell biological studies on RHOA have demonstrated signalings such as activation of RHO-associated coiled-coil forming kinases through guanine nucleotide exchange and GTP hydrolysis, cellular responses such as actin fiber formation and myocin activation, biological consequences such as cell motility and cytokineses, etc. There have also been a plenty of active discussion on the roles of RHOA in tumorigenesis, primarily based on gain- and loss-of-function experiments. However, cell-type-specific functions of RHOA have only recently been delineated by conditional gene targeting strategies. Furthermore, very little information had been available on human cancer genetics until we and others recently reported frequent somatic RHOA mutations in a distinct subtype of T-cell-type malignant lymphoma called angioimmunoblastic T-cell lymphoma (AITL), and other T-cell lymphoma with AITL-like features. The RHOA mutations were very specific to these types of lymphoma among hematologic malignancies, and a single hotspot, glycine at the 17th position, was affected by the replacement with valine (G17V). Remarkably, G17V RHOA did not bind GTP, and moreover, it inhibited the GTP binding to wild-type RHOA. How G17V RHOA contributes to T-cell lymphomagenesis needs to be clarified.

Identification, expression and characterization of rat isoforms of the serum response factor (SRF) coactivator MKL1

Megakaryoblastic leukemia 1 (MKL1) is a member of the MKL family of serum response factor (SRF) coactivators. Here we have identified three rat MKL1 transcripts: two are homologues of mouse MKL1 transcripts, full-length MKL1 (FLMKL1) and basic, SAP, and coiled-coil domains (BSAC), the third is a novel transcript, MKL1-elongated derivative of yield (MELODY). These rat MKL1 transcripts are differentially expressed in a wide variety of tissues with highest levels in testis and brain. During brain development, these transcripts display differential patterns of expression. The FLMKL1 transcript encodes two isoforms that utilize distinct translation start sites. The longer form possesses three actin-binding RPXXXEL (RPEL) motifs and the shorter form, MKL1met only has two RPEL motifs. All four rat MKL1 isoforms, FLMKL1, BSAC, MKL1met and MELODY increased SRF-mediated transcription, but not CREB-mediated transcription. Accordingly, the differential expression of MKL1 isoforms may help fine-tune gene expression during brain development.

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Megakaryoblastic leukemia 1 (MKL1) is a serum response factor (SRF) coactivator.

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We have identified multiple rat MKL1 isoforms, including a novel one named MELODY.

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Rat MKL1 isoforms are enriched in testis and brain.

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Expression of rat MKL1 isoforms is regulated during brain development.

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All rat MKL1 isoforms act as SRF transcriptional coactivators.