BubR1 Insufficiency Inhibits Neointimal Hyperplasia Through Impaired Vascular Smooth Muscle Cell Proliferation in Mice

Arterial Stiffness: From Basic Primers to Integrative Physiology

The elastic properties of conductance arteries are one of the most important hemodynamic functions in the body, and data continue to emerge regarding the importance of their dysfunction in vascular aging and a range of cardiovascular diseases. Here, we provide new insight into the integrative physiology of arterial stiffening and its clinical consequence. We also comprehensively review progress made on pathways/molecules that appear today as important basic determinants of arterial stiffness, particularly those mediating the vascular smooth muscle cell (VSMC) contractility, plasticity and stiffness. We focus on membrane and nuclear mechanotransduction, clearance function of the vascular wall, phenotypic switching of VSMCs, immunoinflammatory stimuli and epigenetic mechanisms. Finally, we discuss the most important advances of the latest clinical studies that revisit the classical therapeutic concepts of arterial stiffness and lead to a patient-by-patient strategy according to cardiovascular risk exposure and underlying disease.

BubR1 controls starvation-induced lipolysis via IMD signaling pathway in Drosophila

Lipolysis, the key process releasing fat acids to generate energy in adipose tissues, correlates with starvation resistance. Nevertheless, its detail mechanisms remain elusive. BubR1, an essential mitotic regulator, ensures proper chromosome alignment and segregation during mitosis, but its physiological functions are largely unknown. Here, we use Drosophila adult fat body, the major lipid storage organ, to study the functions of BubR1 in lipolysis. We show that both whole body- and fat body-specific BubR1 depletions increase lipid degradation and shorten the lifespan under fasting but not feeding. Relish, the conserved regulator of IMD signaling pathway, acts as the downstream target of BubR1 to control the expression level of Bmm and modulate the lipolysis upon fasting. Thus, our study reveals new functions of BubR1 in starvation-induced lipolysis and provides new insights into the molecular mechanisms of lipolysis mediated by IMD signaling pathway.

Translation of Cellular Senescence to Novel Therapeutics: Insights From Alternative Tools and Models

Increasing chronological age is the greatest risk factor for human diseases. Cellular senescence (CS), which is characterized by permanent cell-cycle arrest, has recently emerged as a fundamental mechanism in developing aging-related pathologies. During the aging process, senescent cell accumulation results in senescence-associated secretory phenotype (SASP) which plays an essential role in tissue dysfunction. Although discovered very recently, senotherapeutic drugs have been already involved in clinical studies. This review gives a summary of the molecular mechanisms of CS and its role particularly in the development of cardiovascular diseases (CVD) as the leading cause of death. In addition, it addresses alternative research tools including the nonhuman and human models as well as computational techniques for the discovery of novel therapies. Finally, senotherapeutic approaches that are mainly classified as senolytics and senomorphics are discussed.

Mechanosensitive channel Piezo1 is required for pulmonary artery smooth muscle cell proliferation

Concentric pulmonary vascular wall thickening due partially to increased pulmonary artery (PA) smooth muscle cell (PASMC) proliferation contributes to elevating pulmonary vascular resistance (PVR) in patients with pulmonary hypertension (PH). Although pulmonary vasoconstriction may be an early contributor to increasing PVR, the transition of contractile PASMCs to proliferative PASMCs may play an important role in the development and progression of pulmonary vascular remodeling in PH. A rise in cytosolic Ca2+ concentration ([Ca2+]cyt) is a trigger for PASMC contraction and proliferation. Here, we report that upregulation of Piezo1, a mechanosensitive cation channel, is involved in the contractile-to-proliferative phenotypic transition of PASMCs and potential development of pulmonary vascular remodeling. By comparing freshly isolated PA (contractile PASMCs) and primary cultured PASMCs (from the same rat) in a growth medium (proliferative PASMCs), we found that Piezo1, Notch2/3, and CaSR protein levels were significantly higher in proliferative PASMCs than in contractile PASMCs. Upregulated Piezo1 was associated with an increase in expression of PCNA, a marker for cell proliferation, whereas downregulation (with siRNA) or inhibition (with GsMTx4) of Piezo1 attenuated PASMC proliferation. Furthermore, Piezo1 in the remodeled PA from rats with experimental PH was upregulated compared with PA from control rats. These data indicate that PASMC contractile-to-proliferative phenotypic transition is associated with the transition or adaptation of membrane channels and receptors. Upregulated Piezo1 may play a critical role in PASMC phenotypic transition and PASMC proliferation. Upregulation of Piezo1 in proliferative PASMCs may likely be required to provide sufficient Ca2+ to assure nuclear/cell division and PASMC proliferation, contributing to the development and progression of pulmonary vascular remodeling in PH.

Cell senescence: basic mechanisms and the need for computational networks in vascular ageing

This review seeks to provide an update of the mechanisms of vascular cell senescence, from newly identified molecules to arterial ageing phenotypes, and finally to present a computational approach to connect these selected proteins in biological networks. We will discuss current key signalling and gene expression pathways by which these focus proteins and networks drive normal and accelerated vascular ageing. We also review the possibility that senolytic drugs, designed to restore normal cell differentiation and function, could effectively treat multiple age-related vascular diseases. Finally, we discuss how cell senescence is both a cause and a consequence of vascular ageing because of the possible feedback controls between identified networks.

BubR1 allelic effects drive phenotypic heterogeneity in mosaic-variegated aneuploidy progeria syndrome

Mosaic-variegated aneuploidy (MVA) syndrome is a rare childhood disorder characterized by biallelic BUBR1, CEP57, or TRIP13 aberrations; increased chromosome missegregation; and a broad spectrum of clinical features, including various cancers, congenital defects, and progeroid pathologies. To investigate the mechanisms underlying this disorder and its phenotypic heterogeneity, we mimicked the BUBR1L1012P mutation in mice (BubR1L1002P) and combined it with 2 other MVA variants, BUBR1X753 and BUBR1H, generating a truncated protein and low amounts of wild-type protein, respectively. Whereas BubR1X753/L1002P and BubR1H/X753 mice died prematurely, BubR1H/L1002P mice were viable and exhibited many MVA features, including cancer predisposition and various progeroid phenotypes, such as short lifespan, dwarfism, lipodystrophy, sarcopenia, and low cardiac stress tolerance. Strikingly, although these mice had a reduction in total BUBR1 and spectrum of MVA phenotypes similar to that of BubR1H/H mice, several progeroid pathologies were attenuated in severity, which in skeletal muscle coincided with reduced senescence-associated secretory phenotype complexity. Additionally, mice carrying monoallelic BubR1 mutations were prone to select MVA-related pathologies later in life, with predisposition to sarcopenia correlating with mTORC1 hyperactivity. Together, these data demonstrate that BUBR1 allelic effects beyond protein level and aneuploidy contribute to disease heterogeneity in both MVA patients and heterozygous carriers of MVA mutations.

Attenuation of Angiotensin II-Induced Hypertension in BubR1 Low-Expression Mice Via Repression of Angiotensin II Receptor 1 Overexpression

Background Angiotensin II (Ang II) can cause hypertension and tissue impairment via AGTR1 (Ang II receptor type 1), particularly in renal proximal tubule cells, and can cause DNA damage in renal cells via nicotinamide adenine dinucleotide phosphate oxidase. BubR1 (budding uninhibited by benzimidazole-related 1) is a multifaceted kinase that functions as a mitotic checkpoint. BubR1 expression can be induced by Ang II in smooth muscle cells in vitro, but the relationship between systemic BubR1 expression and the Ang II response is unclear. Methods and Results Twenty 24-week-old male BubR1 low-expression mice (BubR1^L/L mice) and age-matched BubR1^+/+ mice were used in this study. We investigated how Ang II stimulation affects BubR1^L/L mice. The elevated systolic blood pressure caused by Ang II stimulation in BubR1^+/+ mice was significantly attenuated in BubR1^L/L mice. Additionally, an attenuated level of Ang II-induced perivascular fibrosis was observed in the kidneys of BubR1^L/L mice. Immunohistochemistry revealed that the overexpression of AGTR1 induced by Ang II stimulation was repressed in BubR1^L/L mice. We evaluated AGTR1 and Nox-4 (nicotinamide adenine dinucleotide phosphate oxidase-4) levels to determine the role of BubR1 in the Ang II response. Results from in vitro assays of renal proximal tubule cells suggest that treatment with small interfering RNA targeting BubR1 suppressed Ang II-induced overexpression of AGTR1. Similarly, the upregulation in Nox4 and Jun N-terminal kinase induced by Ang II administration was repressed by treatment with small interfering RNA targeting BubR1. Conclusions Ang II-induced hypertension is caused by AGTR1 overexpression in the kidneys via the upregulation of BubR1 and Nox4.

Liver regeneration in aged mice: new insights

The regenerative capacity of the liver after resection is reduced with aging. Recent studies on rodents revealed that both intracellular and extracellular factors are involved in the impairment of liver mass recovery during aging. Among the intracellular factors, age-dependent decrease of BubR1 (budding uninhibited by benzimidazole-related 1), YAP (Yes-associated protein) and SIRT1 (Sirtuin-1) have been associated to dampening of tissue reconstitution and inhibition of cell cycle genes following partial hepatectomy. Extra-cellular factors, such as age-dependent changes in hepatic stellate cells affect liver regeneration through inhibition of progenitor cells and reduction of liver perfusion. Furthermore, chronic release of pro-inflammatory proteins by senescent cells (SASP) affects cell proliferation suggesting that senescent cell clearance might improve tissue regeneration. Accordingly, young plasma restores liver regeneration in aged animals through autophagy re-establishment. This review will discuss how intracellular and extracellular factors cooperate to guarantee a proper liver regeneration and the possible causes of its impairment during aging. The possibility that an improvement of the liver regenerative capacity in elderly might be achieved through elimination of senescent cells via autophagy or by administration of direct mitogenic agents devoid of cytotoxicity will also be entertained.

BubR1 Insufficiency Results in Decreased Macrophage Proliferation and Attenuated Atherogenesis in Apolipoprotein E-Deficient Mice

Background

Budding uninhibited by benzimidazole‐related 1 (BubR1), a cell cycle–related protein, is an essential component of the spindle checkpoint that regulates cell division. BubR1 insufficiency causes early aging‐associated vascular phenotypes. We generated low‐BubR1‐expressing mutant (BubR1^L/L) and apolipoprotein E‐deficient (ApoE^−/−) mice (BubR1^L/L‐ApoE^−/− mice) to investigate the effects of BubR1 on atherosclerosis.

Methods and Results

Eight‐week‐old male BubR1^L/L‐ApoE^−/− mice and age‐matched ApoE^−/− mice were used in this study. Atherosclerotic lesion development after being fed a high‐cholesterol diet for 12 weeks was inhibited in BubR1^L/L‐ApoE^−/− mice compared with ApoE^−/− mice, and was accompanied by decreased accumulation of macrophages. To address the relative contribution of BubR1 on bone marrow–derived cells compared with non‐bone marrow–derived cells, we performed bone marrow transplantation in ApoE^−/− and BubR1^L/L‐ApoE^−/− mice. Decreased BubR1 in bone marrow cells and non‐bone marrow–derived cells decreased the atherosclerotic burden. In vitro assays indicated that decreased BubR1 expression impaired proliferation, but not migration, of bone marrow–derived macrophages.

Conclusions

BubR1 may represent a promising new target for regulating atherosclerosis.

BubR1 Insufficiency Impairs Liver Regeneration in Aged Mice after Hepatectomy through Intercalated Disc Abnormality

A delay in liver regeneration after partial hepatectomy (PHx) leads to acute liver injury, and such delays are frequently observed in aged patients. BubR1 (budding uninhibited by benzimidazole-related 1) controls chromosome mitotic segregation through the spindle assembly checkpoint, and BubR1 down-regulation promotes aging-associated phenotypes. In this study we investigated the effects of BubR1 insufficiency on liver regeneration in mice. Low-BubR1-expressing mutant (BubR1^L/L) mice had a delayed recovery of the liver weight-to-body weight ratio and increased liver deviation enzyme levels after PHx. Microscopic observation of BubR1^L/L mouse liver showed an increased number of necrotic hepatocytes and intercalated disc anomalies, resulting in widened inter-hepatocyte and perisinusoidal spaces, smaller hepatocytes and early-stage microvilli atrophy. Up-regulation of desmocollin-1 (DSC1) was observed in wild-type, but not BubR1^L/L, mice after PHx. In addition, knockdown of BubR1 expression caused down-regulation of DSC1 in a human keratinocyte cell line. BubR1 insufficiency results in the impaired liver regeneration through weakened microstructural adaptation against PHx, enhanced transient liver failure and delayed hepatocyte proliferation. Thus, our data suggest that a reduction in BubR1 levels causes failure of liver regeneration through the DSC1 abnormality.

BubR1 alterations that reinforce mitotic surveillance act against aneuploidy and cancer

BubR1 is a key component of the spindle assembly checkpoint (SAC). Mutations that reduce BubR1 abundance cause aneuploidization and tumorigenesis in humans and mice, whereas BubR1 overexpression protects against these. However, how supranormal BubR1 expression exerts these beneficial physiological impacts is poorly understood. Here, we used Bub1b mutant transgenic mice to explore the role of the amino-terminal (BubR1^N) and internal (BubR1^I) Cdc20-binding domains of BubR1 in preventing aneuploidy and safeguarding against cancer. BubR1^N was necessary, but not sufficient to protect against aneuploidy and cancer. In contrast, BubR1 lacking the internal Cdc20-binding domain provided protection against both, which coincided with improved microtubule-kinetochore attachment error correction and SAC activity. Maximal SAC reinforcement occurred when both the Phe- and D-box of BubR1^I were disrupted. Thus, while under- or overexpression of most mitotic regulators impairs chromosome segregation fidelity, certain manipulations of BubR1 can positively impact this process and therefore be therapeutically exploited.

DOI:http://dx.doi.org/10.7554/eLife.16620.001

Human DNA is organized into 46 chromosomes, which must be duplicated before a cell divides and are then shared equally between the two new cells. When this process goes awry, the new cells either have too many or too few chromosomes. This situation – known as aneuploidy – frequently occurs in cancer cells, and is thought to cause cells to gain extra copies or lose copies of genes that promote or prevent cancer, respectively.

Cells have several ways to prevent aneuploidy. One of these safeguards, known as the spindle assembly checkpoint (SAC), involves a protein called BubR1, which acts at the stage when the duplicated chromosomes need to be equally divided into each daughter cell. Mouse models show that low levels of the BubR1 protein result in aneuploidy and increased predisposition to cancer. High levels of BubR1, on the other hand, allow the mice to stay healthier for longer and can stop tumors from forming. However, it was not known exactly how high amounts of BubR1 protect against cancer.

To address this question, Weaver et al. set out to determine which parts, or domains, of the BubR1 protein protect against cancer. Mice with high levels of the full-length BubR1 protein were compared with mice that made mutant versions of BubR1 lacking certain domains. These experiments revealed that a small portion of the beginning of the protein was necessary to protect against tumor formation, but removing a large region in the middle of BubR1 still protected mice against lung cancer and aneuploidy. Additional experiments performed on mouse cells grown in the laboratory revealed that whole BubR1 protein and the mutant protein lacking the middle region might prevent aneuploidy in multiple ways. For example, both systems had stronger SAC signaling, which could serve to make segregating the chromosomes more accurate.

In the future, it will be important to find out whether BubR1 acts in the same way in human cells and cancers. Lastly, since it is not possible to over-produce BubR1 in humans, other methods will need to be investigated to use this knowledge to treat cancer.

DOI:http://dx.doi.org/10.7554/eLife.16620.002

Oncological miR-182-3p, a Novel Smooth Muscle Cell Phenotype Modulator, Evidences From Model Rats and Patients

OBJECTIVE

Vascular smooth muscle cell (VSMC) phenotype change is a hallmark of vascular remodeling, which contributes to atherosclerotic diseases and can be regulated via microRNA-dependent mechanisms. We recently identified that asymmetrical dimethylarginine positively correlates to vascular remodeling-based diseases. We hypothesized that asymmetrical dimethylarginine induces smooth muscle cell (SMC) phenotypic change via a microRNA-dependent mechanism.

APPROACH AND RESULTS

Microarray analysis enabled the identification of downregulation of miR-182-3p in asymmetrical dimethylarginine-treated human aortic artery SMCs. The myeloid-associated differentiation marker (MYADM) was identified as the downstream target of miR-182-3p and implicated to contribute to miR-182-3p knockdown-mediated SMC phenotype change, which was evidenced by the increased proliferation and migration and reduced expression levels of phenotype-related genes in human aortic artery SMCs through the ERK/MAP (extracellular signal-regulated kinase/mitogen-activated protein) kinase-dependent mechanism. When inhibiting MYADM in the presence of miR-182-3p inhibitor or overexpressing MYADM in the presence of pre-miR-182-3p, human aortic artery SMCs were reversed to the differentiation phenotype. In vivo, adeno-miR-182-3p markedly suppressed carotid neointimal formation by using balloon-injured rat carotid artery model, specifically via decreased MYADM expression, whereas adeno-miR-182-3p inhibitor significantly promoted neointimal formation. Atherosclerotic lesions from patients with high asymmetrical dimethylarginine plasma levels exhibited decreased miR-182-3p expression levels and elevated MYADM expression levels.

CONCLUSIONS

miR-182-3p is a novel SMC phenotypic modulator by targeting MYADM.