The role of cellular senescence in aortic dissection

Background

Aortic dissection (AD) is a catastrophic disease that occurs suddenly. The acute mortality is high and those who survived frequently suffer from serious complications such as aneurysm formation and distal ischemia due to progressive destruction of the aortic walls. Currently, no predictor of AD onset is available nor therapeutic intervention to specifically prevent the progressive destruction in AD, because the molecular pathogenesis is largely unknown. Clinical and experimental studies highlighted the importance of inflammation in AD, although the regulatory mechanism of inflammation remains unclear. Recently, we found that cell proliferation precedes the inflammatory response in AD. Because cell proliferation causes cellular senescence that can induce inflammatory response, we hypothesized that cellular senescence participates in AD pathogenesis.

Objective

We investigated if cellular senescence contributes to AD development and progression in mouse AD model.

Methods and results

A mouse AD model was created by continuous infusion of beta-aminopropionitrile and angiotensin II (BAPN+AngII), where AD starts to develop in 3 days and occurs to most of the mice in 14 days accompanied by frequent AD rupture and death. Infusion of BAPN+AngII resulted in the induction of senescence markers Ink4a from day 3 before AD onset and persisted for the 14 days of the observational period.

Cellular senescence, as demonstrated by the expression of senescence-associated beta-galactosidase, was evident in intimal endothelial cells, medial smooth muscle cells, adventitial macrophages and fibroblasts. We examined the role of cellular senescence in AD pathogenesis by oral administration of ABT263 which is known as “senolytics” that eliminates senescent cells. ABT263 treatment reduced the expression of the senescence marker, prevented the death by AD rupture, and ameliorated the severity of AD lesion compared to the vehicle treatment. Transcriptome analysis revealed that ABT treatment suppressed the immune and inflammatory response in AD. Quantitative RT-PCR confirmed that ABT treatment prevented the induction of p21Cip1, interleukin-6, several chemokines and their receptors by 3-day infusion of BAPN+AngII.

Conclusions

These findings demonstrated that senescence of multiple cell types precedes AD development, which is likely to induce the inflammatory response. Elimination of senescent cells effectively prevented AD progression and death. Therefore, cellular senescence represents a potential predictor and a therapeutic target for AD.

Funding Acknowledgement

Type of funding sources: None.

The role of cellular senescence in aortic dissection

Background

Aortic dissection (AD) is a catastrophic disease that occurs suddenly. The acute mortality is high and those who survived frequently suffer from serious complications such as aneurysm formation and distal ischemia due to progressive destruction of the aortic walls. Currently, no reliable predictor is available for AD development and surgical intervention is the only therapeutic option to prevent the fatal events after AD development, because the pathogenesis of AD is largely unknown.

Clinical and experimental studies highlighted the importance of inflammation in AD pathogenesis, although the trigger of inflammation remains unclear. Recently, we found that cell proliferation precedes the inflammatory response in AD. Because cell proliferation triggers cellular senescence and senescent cells secrete of proinflammatory cytokines and matrix metalloproteinases, we hypothesized that cellular senescence may participate in AD pathogenesis.

Objective

We investigated if cellular senescence contributes to AD development and progression in a mouse model of AD.

Methods and results

A mouse AD model was created by continuous infusion of beta-aminopropionitrile and angiotensin II (BAPN+AngII), where AD starts to develop in 3 days and occurs to most of the mice in 14 days accompanied by frequent AD rupture and death. Infusion of BAPN+AngII resulted in the appearance of senescent cells that are positive for senescence-associated beta-galactosidase, and expression of senescence markers Arf and Ink4a in the aortic walls. Appearance of cellular senescence occurred in one day of BAPN+AngII infusion and continued throughout the observational period of 14 days. We examined the role of cellular senescence in AD pathogenesis by oral administration of ABT263 which is known as “senolytics” that eliminates senescent cells. ABT263 treatment reduced the expression of the senescence markers. In the vehicle-treated group, the mortality was 66.7% (12/18), whereas that of ABT263-treated group was 35% (14/20, P<0.05 by log-rank test). The severity of AD, as assessed by the lesion length in vehicle group was33.2±3.1 mm, whereas that in ABT263 group was 24.6±1.8 mm (P<0.05).

Conclusions

These findings demonstrated that cellular senescence precedes AD development, and ABT263 effectively prevented AD progression and death, indicating the involvement of cellular senescence in AD pathogenesis. Therefore, cellular senescence represents a potential predictor and a therapeutic target for AD.

Funding Acknowledgement

Type of funding sources: None.

Involvement of FAK in aortic dissection: potential role in aortic interstitial cells

Background

Aortic dissection (AD) is a fatal disease where the intimomedial layer of the aorta suddenly fail. Although it is widely accepted that hemodynamic stress on the aortic wall triggers its destruction that is further promoted by inflammatory response as exemplified by the infiltration of neutrophils and macrophages, molecular mechanism is unknown for the link of aortic wall stress, inflammation and tissue destruction. In general, mechanical stress to the tissue is converted to the cellular response through the cell adhesion molecules and the activation of focal adhesion kinase (Fak). Although it has been reported that Fak is involved in pathogenesis of aortic aneurysm by promoting migration and activation of macrophages, its role in AD is unknown. We hypothesized that Fak may be involved in AD pathogenesis.

Purpose

We investigated the involvement of Fak in AD pathogenesis, focusing on its role in inflammatory cells.

Methods and results

We created a mouse model of AD by continuous infusion of beta-aminopropionitrile, a collagen crosslink inhibitor, and angiotensin II (BAPN + Ang II). Immunostaining for activated Fak revealed that Fak was not activated in normal aorta, but was activated in the infiltrating inflammatory cells and in interstitial cells of the aortic wall after AD development. We examined the role of Fak by oral administration of PND-1186, a specific Fak inhibitor, in mouse AD model. Vehicle-treated group showed 63.6% mortality, whereas PND-1186-treated group showed 20% mortality (P<0.01, n=20 for each group) in 14 days of the observational period. The aortic arch lesion, the most critical part in AD, was improved from 1.96±0.41 mm in vehicle group to 0.66±0.29 mm in PND group (P<0.05). We next examined the cell type-specific role of Fak in AD by creating macrophage and granulocyte-specific deletion of Fak driven by LysM-Cre and floxed Fak system. Unexpectedly, the genetic deletion of Fak in macrophages and granulocytes had no impact on the mortality nor the severity of AD.

Conclusions

These findings proved that Fak plays a critical role in AD progression and death. Because Fak is dispensable for macrophages and granulocytes, other cell types, possibly aortic wall interstitial cells, may be regulated by Fak in AD pathogenesis. Deciphering the role of Fak would provide the fundamental understanding of AD pathogenesis.

Funding Acknowledgement

Type of funding sources: None.

The role of B cells and IgG in aortic dissection

Background

Aortic dissection (AD) is one of the destructive and fatal aortic diseases, for which molecular pathogenesis is largely unknown. Recent studies have highlighted the importance of inflammatory response in AD. We and others reported that B cells and immunoglobulins participate in pathogenesis of abdominal aortic aneurysm, another form of aortic destructive disease, by promoting inflammatory response. It is not known whether and how B cells participate in AD pathogenesis.

Methods and results

Immunohistochemical staining of human AD tissue revealed that B cells were clustered together with T cells, macrophages and neutrophils at the entry site of AD with medial disruption. B cell cluster was also observed at the site of medial disruption in mouse model of AD that was induced by continuous infusion of beta-aminopropionitrile and angiotensin II (BAPN+AngII). In muMT mouse, which is deficient for B cells and immunoglobulins due to genetic deletion of immunoglobulin heavy chain, BAPN+AngII induced significantly less severe AD compared to that in wild type. Depositions of IgG and fibrinogen, one of the endogenous antigen for natural IgG, were observed after BAPN+AngII infusion before and after AD development in wild type mice. Deposition of fibrinogen was also observed in mMT mice after BAPN+AngII infusion. The rate of aortic rupture and sudden death was approximately 42% in wild type mice, while that in muMT mouse was 12% (P<0.05). Administration of mouse normal polyclonal IgG to muMT mice resulted in dramatic increase in aortic rupture and sudden death, starting at day 7 of BAPN+AngII infusion, and reaching 69% of rupture rate, indicating the critical role of IgG in AD.

Conclusion

These findings demonstrated B cells and IgG are critically involved in the destructive inflammation of AD pathogenesis. Further, the deposition of fibrinogen, one of the targets of natural IgG, precedes the development of AD. Our findings may provide the conceptual foundation of the diagnostic strategy for on-going tissue destruction and for the therapeutic opportunities to intervene the progressive tissue destruction in AD.

Funding Acknowledgement

Type of funding source: Public grant(s) – National budget only. Main funding source(s): The Japan Society for the Promotion of Science

P6494Activation of focal adhesion kinase is involved in pathogenesis of aortic dissection in mice

Background

Aortic dissection (AD) is a fatal disease where the media of the aorta suddenly fail. Currently, Molecular pathogenesis of AD is unknown. Recently, we discovered that the activity of MRTF-A, a mechanosensitive transcriptional regulator, promotes AD development. The activity of MRTF-A is regulated by mechanical stress to cells, which is transduced through focal adhesion and actin dynamics. However, it is currently unknown whether the mechanotransduction mechanism is involved in AD pathogenesis.

Purpose

We investigated the role of focal adhesion kinase (FAK), a signaling molecule that transduces mechanostress from focal adhesion to actin dynamics, in AD pathogenesis.

Methods

We created a mouse model of AD with a continuous infusion of beta-aminopropionitrile (150 mg/kg/day), a collagen crosslink inhibitor, and angiotensin II (1,000 ng/kg/min) (BAPN + AngII) by an osmotic pump. This model caused about 60% death in all mice due to AD rupture within 2 weeks. In this model, we examined the severity and mortality rate of aortic dissection after 2 weeks in mice administered with PND-1186, an orally available FAK inhibitor, and in those treated with vehicle (n=20 for each group). We performed immunochemical staining, immunofluorescence staining and Western blot for activated (phosphorylated) FAK (pFAK) to evaluate the activation status of FAK in the aortic tissue. We also performed transcriptome analysis of the aortic tissue in with and without PND-1186 with BAPN + AngII stimulation before AD development.

Results

Immunochemical staining revealed that FAK was inactive in normal mouse aorta, but was strongly activated in the aortic walls after AD development. Immunofluorescence staining showed that FAK was activated mainly in smooth muscle cells after AD development. Western blot analysis also revealed that FAK was activated in 3 days after BAPN + AngII infusion before AD development, followed by transient reduction at day 7, and re-activation after AD at day 14. Significantly, administration of PND-1186 resulted in a significant reduction in the severity of AD in the aortic arch (1.96±0.41 mm in vehicle group, 0.66±0.29 mm in PND group, P<0.05). In addition, survival rate improved from 36.4% to 80.0% by administration of PND-1186 (P<0.01). In immunofluorescence staining, the PND-1186 treated group showed weaker staining of pFAK. Transcriptome analysis showed that genes for hematopoiesis and immune system were suppressed in PND-1186 treated group.

Conclusions

These findings proved that FAK plays a central role in the pathogenesis of AD probably by transmitting pathological stress to the aortic wall to cause tissue destruction. We propose that FAK is a potential therapeutic target for limiting the fatal destruction of the aortic wall of AD.

P6493Syk activation is a defense mechanism in murine model of aortic dissection

Background

Aortic dissection (AD) is a serious clinical condition with unknown etiology that frequently results in fatal outcome. Recent studies showed essential role of inflammatory response both in promoting AD and aortic aneurysm (AA). However, the difference of the molecular pathogenesis between AD and AA is unclear. Previously, we reported that Syk, a tyrosine kinase that regulates differentiation and activation of inflammatory cells, promotes AA formation in a mouse model.

Objective

In the current study, we investigated the role of Syk in AD.

Methods and results

A mouse AD model was created by continuous infusion of beta-aminopropionitrile (125 mg/kg/day) and angiotensin II (1,000 ng/min/kg) (BAPN+AngII), which caused AD in approximately 80% of mice within 14 days. Immunohistochemical staining for activated (phosphorylated) Syk (pSyk) revealed that Syk was inactive in normal mouse aorta, but was activated in the aortic walls after AD development. Double immunofluorescence staining for pSyk and smooth muscle alpha actin showed that Syk was active not only in the infiltrating inflammatory cells, but also in smooth muscle cells in AD tissue. Western blot analysis revealed that BAPN+AngII treatment caused Syk activation at 3 days before AD development, followed by transient suppression, and reactivation at 14 days after AD development. We examined the significance of Syk activation in AD by treating mice with fostamatinib, a specific Syk inhibitor, before and during BAPN+AngII infusion. Notably, fostamatinib-treated group developed more severe AD compared to the vehicle-treated group. The AD lesion length was 3.80±0.86 mm for vehicle group and 8.87±1.69 mm for fostamatinib group (P<0.05, n=12 for each group). In addition, fostamatinib significantly worsened the mortality of mice due to the rupture of the aorta from 0% to 42% (P<0.05, n=12 for each group). Transcriptome analysis revealed that fostamatinib suppressed both positive and negative regulators of immune response, defense response and inflammatory response.

Conclusions

These findings uncovered the previously unrecognized role of Syk for protecting the aortic tissue in AD pathogenesis, and suggested fundamentally different disease mechanisms of AD and AA.

Osteitis fibrosa cystica generalizata with adult T-cell leukaemia: a case report

We report on a 62-year-old female initially suffering from extreme pain in both her lower extremities. Plain radiographs revealed multiple osteolytic lesions. Laboratory analyses indicated high levels of serum calcium and parathyroid hormone related protein (PTHrP) and detected HTLV-1 antibody. Histological examination of biopsied specimens which were obtained from osteolytic lesions indicated osteitis fibrosa cystica (OFC) without tumour cells. After the initial biopsy, a subcutaneous mass developed in the left thigh. Microsections of the biopsied mass disclosed adult T-cell leukaemia (ATL) neoplastic cells. Immunohistochemical findings revealed that PTHrP secreted from ATL neoplastic cells induced the OFC.

Vascular occlusion and cartilage disorders in osteonecrosis of the femoral head in rats

The aim of our study was to clarify the role of lateral epiphyseal vessels in the development of femoral head osteonecrosis in rats. We did this by performing histological and immunological studies on rats at the age that they are most prone to spontaneous osteonecrosis. We observed that obstruction of the lateral epiphyseal vessels occurred at the site of cartilage penetration. This obstruction preceded the development of osteonecrosis in adjacent areas of the femoral head. We propose that a similar mechanism may be responsible, in part, for the development of Perthes disease in man.

Characteristics of blood vessels feeding the femoral head liable to osteonecrosis in spontaneously hypertensive rats

In order to elucidate the cause of osteonecrosis of the femoral head in spontaneously hypertensive rats (SHRs), which resembles the osteonecrosis of Perthes' disease, we observed the three-dimensional structure of vascular casts of the blood vessels feeding the femoral head using both optical and scanning electron microscopes. During the period of 9-15 weeks after birth, when osteonecrosis of the femoral heads in SHRs occurred frequently, the lateral epiphyseal vessels (LEVs), which were the main feeding vessels, entered from the lateral of the femoral heads. Anastomosing branches of LEVs between the epiphysis and the femoral neck were scarce even in the femoral heads showing normal ossification. It seemed that the development of LEVs in SHRs did not proceed normally in this period. Furthermore, remarkable segmental stenosis and the obstruction of LEVs were often recognized near the lateral of the femoral heads. These results suggest that LEVs in growing SHRs have the vascular structure that could cause an interruption of the blood supply to the femoral heads.

The effect of formycin on the processing of transfer RNA precursors in the posterior silk gland of Bombyx mori

Formycin, an adenosine analog, was used in studies of RNA synthesis by silk glands of silkworms in organ culture. Formycin has been shown to inhibit preferentially the incorporation of [3H]uridine into low molecular weight RNA in the cytoplasm. When silk glands were pulse-chase labeled with [3H]uridine in the presence of formycin, the synthesis of 4.5S tRNA precursors was not affected, as determined by gel electrophoresis. However, the accumulation of mature 4S tRNA was greatly reduced in the formycin-treated system, although the precursors synthesized disappeared from the 4.5S region on chase at the same rate as in the control system. [14C]Formycin was incorporated into the 4.5S precursors but not into 4S tRNA. These findings suggest that the inhibition of tRNA synthesis by formycin is due to the existence of some degradation mechanisms of formycin-containing 4.5S precursor RNA's and the failure to process them into normal 4S tRNA.

The biosynthesis of transfer RNA in insects. II. Isolation of transfer RNA precursors from the posterior silk gland of Bombyx mori

The occurrence of precursors to tRNA in the post-polysomal fraction of the posterior silk gland of Bombyx mori was demonstrated by pulse-chase labeling and DNA-RNA hybridization competition experiments. These precursors had molecular sizes ranging from 4S to 5S on polyacrylamide gel electrophoresis. Analysis of the incorporation of the methyl group from [methyl-14C]methionine revealed that a radioactive peak on polyacrylamide gel appeared in the 4.5S region during brief labeling. This suggested that some methylation occurred at the 4.5S precursor step.

The biosynthesis of transfer RNA in insects. I. Increase of amino acid acceptor activity of specific tRNA's utilized for silk protein biosynthesis in the silk gland of Bombyx mori

1) To detect the quantitative changes of amino acid acceptor activity of tRNA's from the posterior and middle silk glands of Bombyx mori at various ages, a relatively simple and rapid method was established using a mixture of radioactive amino acids in Chlorella hydrolysate. 2) The acceptor activities of silk gland tRNA for 15 amino acids tested seemed to be almost on the same level at the end of the 4th moult stage. During the 5th instar, however, characteristic increases were observed in glycine, alanine, and serine acceptor activities in both silk glands. 3) In the posterior silk gland, which produces fibroin, the acceptor activities for glycine and alanine increased more than that for serine. In the middle silk gland, which produces sericine, the acceptor activity for serine increased more than those for glycine and alanine. 4) In the light of observations on the increase of corresponding aminoacyl-tRNA synthetase activities in the silk glands, a functional adaptation of tRNA synthesis in the tissue is discussed.