MFG-E8 mediates arterial aging by promoting the proinflammatory phenotype of vascular smooth muscle cells

Contribution of circulating Mfge8 to human T2DM and cardiovascular disease

MFGE8 is a major exosome (EV) protein known to mediate inflammation and atherosclerosis in type 2 diabetes mellitus (T2DM) in animal studies. The pathophysiological role of this protein in obesity, T2DM, and cardiovascular disease is less investigated in humans. Earlier we reported a rare Asian Indian population-specific missense variant (rs371227978; Arg148His) in the MFGE8 gene associated with increased circulating Mfge8 and T2DM. We have further investigated the role of Mfge8 with T2DM risk in additional Asian Indians (n = 4897) and Europeans and other multiethnic cohorts from UK Biobank (UKBB) (n = 455,808) and the US (n = 1150). We also evaluated the exposure of Mfge8-enriched human EVs in zebrafish (ZF) for their impact on cardiometabolic organ system. Most individual carriers of Arg148His variant not only had high circulating Mfge8 but also revealed a positive significant correlation with glucose (r = 0.42; p = 4.9 × 10-04), while the non-carriers showed a negative correlation of Mfge8 with glucose (r = -0.38; p = 0.001) in Asian Indians. The same variant was monomorphic in non-South Asian ethnicities. Even without the variant, serum Mfge8 correlated significantly with blood glucose in other non-South Asian ethnicities (r = 0.47; p = 2.2 × 10-13). Since Mfge8 is an EV marker, we tested the exposure of Mfge8-enriched human EVs to ZF larvae as an exploratory study. The ZF larvae showed rapid effects on insulin-sensitive organs, developing fatty liver disease, heart hypertrophy and exhibiting redundant growth with poor muscular architecture with and without the high-fat diet (HFD). In contrast, the control group fishes developed fatty liver disease and heart hypertrophy only after the HFD feeding. Backed with strong support from animal studies on the role of Mfge8 in obesity, insulin resistance, and atherosclerosis, the current research suggests that circulating Mfge8 may become a potential marker for predicting the risk of T2DM and cardiovascular disease in humans.

The regulation of MFG-E8 on the mitophagy in diabetic sarcopenia via the HSPA1L-Parkin pathway and the effect of D-pinitol

BACKGROUND

Diabetic sarcopenia is a disease-related skeletal muscle disorder that causes progressive symptoms. The complete understanding of its pathogenesis is yet to be unravelled, which makes it difficult to develop effective therapeutic strategies. This study investigates how MFG-E8 affects mitophagy and the protective role of D-pinitol (DP) in diabetic sarcopenia.

METHODS

In vivo, streptozotocin-induced diabetic SAM-R1 (STZ-R1) and SAM-P8 (STZ-P8) mice (16-week-old) were used, and STZ-P8 mice were administrated of DP (150 mg/kg per day) for 6 weeks. Gastrocnemius muscles were harvested for histological analysis including transmission electron microscopy. Proteins were evaluated via immunohistochemistry (IHC), immunofluorescence (IF), and western blotting (WB) assay. In vitro, advanced glycation end products (AGEs) induced diabetic and D-galactose (DG) induced senescent C2C12 models were established and received DP, MFG-E8 plasmid (Mover)/siRNA (MsiRNA), or 3-MA/Torin-1 intervention. Proteins were evaluated by IF and WB assay. Immunoprecipitation (IP) and co-immunoprecipitation (CO-IP) were used for hunting the interacted proteins of MFG-E8.

RESULTS

In vivo, sarcopenia, mitophagy deficiency, and up-regulated MFG-E8 were confirmed in the STZ-P8 group. DP exerted protective effects on sarcopenia and mitophagy (DP + STZ-P8 vs. STZ-P8; all P < 0.01), such as increased lean mass (8.47 ± 0.81 g vs. 7.08 ± 1.64 g), grip strength (208.62 ± 39.45 g vs. 160.87 ± 26.95 g), rotarod tests (109.7 ± 11.81 s vs. 59.3 ± 20.97 s), muscle cross-sectional area (CSA) (1912.17 ± 535.61 μm2 vs. 1557.19 ± 588.38 μm2), autophagosomes (0.07 ± 0.02 per μm2 vs. 0.02 ± 0.01 per μm2), and cytolysosome (0.07 ± 0.03 per μm2 vs. 0.03 ± 0.01 per μm2). DP down-regulated MFG-E8 in both serum (DP + STZ-P8: 253.19 ± 34.75 pg/mL vs. STZ-P8: 404.69 ± 78.97 pg/mL; P < 0.001) and gastrocnemius muscle (WB assay. DP + STZ-P8: 0.39 ± 0.04 vs. STZ-P8: 0.55 ± 0.08; P < 0.01). DP also up-regulated PINK1, Parkin and LC3B-II/I ratio, and down-regulated P62 in gastrocnemius muscles (all P < 0.01). In vitro, mitophagy deficiency and MFG-E8 up-regulation were confirmed in diabetic and senescent models (all P < 0.05). DP and MsiRNA down-regulated MFG-E8 and P62, and up-regulated PINK1, Parkin and LC3B-II/I ratio to promote mitophagy as Torin-1 does (all P < 0.05). HSPA1L was confirmed as an interacted protein of MFG-E8 in IP and CO-IP assay. Mover down-regulated the expression of Parkin via the HSPA1L-Parkin pathway, leading to mitophagy inhibition. MsiRNA up-regulated the expression of PINK1 via SGK1, FOXO1, and STAT3 phosphorylation pathways, leading to mitophagy stimulation.

CONCLUSIONS

MFG-E8 is a crucial target protein of DP and plays a distinct role in mitophagy regulation. DP down-regulates the expression of MFG-E8, reduces mitophagy deficiency, and alleviates the symptoms of diabetic sarcopenia, which could be considered a novel therapeutic strategy for diabetic sarcopenia.

The Role of Endothelial Cells in Atherosclerosis: Insights from Genetic Association Studies

Endothelial cells (ECs) mediate several biological functions that are relevant to atherosclerosis and coronary artery disease (CAD), regulating an array of vital processes including vascular tone, wound healing, reactive oxygen species, shear stress response, and inflammation. Although which of these functions is linked causally with CAD development and/or progression is not yet known, genome-wide association studies have implicated more than 400 loci associated with CAD risk, among which several have shown EC-relevant functions. Given the arduous process of mechanistically interrogating single loci to CAD, high-throughput variant characterization methods, including pooled Clustered Regularly Interspaced Short Palindromic Repeats screens, offer exciting potential to rapidly accelerate the discovery of bona fide EC-relevant genetic loci. These discoveries in turn will broaden the therapeutic avenues for CAD beyond lipid lowering and behavioral risk modification to include EC-centric modalities of risk prevention and treatment.

Eugenol Inhibits Ox-LDL-Induced Proliferation and Migration of Human Vascular Smooth Muscle Cells by Inhibiting the Ang II/MFG-E8/MCP-1 Signaling Cascade

Objective

In this study, we investigated the effect and mechanism of action of eugenol on oxidized low-density lipoprotein (ox-LDL)-induced abnormal proliferation and migration of human vascular smooth muscle cells (HVSMCs).

Methods

HVSMCs were treated with 100 ug/mL ox-LDL for 24 hours to establish a cell model. After 1-hour pretreatment, eugenol at concentrations of 5, 25, and 50 uM was added. Cell viability was assessed using an MTT assay, PCNA expression was detected using Western blot, cell cycle distribution was analyzed using flow cytometry, and cell migration ability was evaluated using wound healing and Transwell migration assays. To investigate the mechanisms, Ang II receptors were inhibited by 1000 nM valsartan, MFG-E8 was knocked down by shRNA, MCP-1 was inhibited by siRNA, and MFG-E8 was overexpressed using plasmids.

Results

The findings from this study elucidated the stimulatory impact of ox-LDL on the proliferation and functionality of HVSMCs. Different concentrations of eugenol effectively mitigated the enhanced activity of HVSMCs induced by ox-LDL, with 50 uM eugenol exhibiting the most pronounced inhibitory effect. Flow cytometry and Western blot results showed ox-LDL reduced G1 phase cells and increased PCNA expression, while 50 uM eugenol inhibited ox-LDL-induced HVSMC proliferation. In wound healing and Transwell migration experiments, the ox-LDL group showed larger cell scratch filling and migration than the control group, both of which were inhibited by 50 uM eugenol. Inhibiting the Ang II/MFG-E8/MCP-1 signaling cascade mimicked eugenol's effects, while MFG-E8 overexpression reversed eugenol's inhibitory effect.

Conclusion

Eugenol can inhibit the proliferation and migration of ox-LDL-induced HVSMCs by inhibiting Ang II/MFG-E8/MCP-1 signaling cascade, making it a potential therapeutic drug for atherosclerosis.

Remodeling of the Cardiac Extracellular Matrix Proteome During Chronological and Pathological Aging

Impaired extracellular matrix (ECM) remodeling is a hallmark of many chronic inflammatory disorders that can lead to cellular dysfunction, aging, and disease progression. The ECM of the aged heart and its effects on cardiac cells during chronological and pathological aging are poorly understood across species. For this purpose, we first used mass spectrometry-based proteomics to quantitatively characterize age-related remodeling of the left ventricle (LV) of mice and humans during chronological and pathological (Hutchinson-Gilford progeria syndrome (HGPS)) aging. Of the approximately 300 ECM and ECM-associated proteins quantified (named as Matrisome), we identified 13 proteins that were increased during aging, including lactadherin (MFGE8), collagen VI α6 (COL6A6), vitronectin (VTN) and immunoglobulin heavy constant mu (IGHM), whereas fibulin-5 (FBLN5) was decreased in most of the data sets analyzed. We show that lactadherin accumulates with age in large cardiac blood vessels and when immobilized, triggers phosphorylation of several phosphosites of GSK3B, MAPK isoforms 1, 3, and 14, and MTOR kinases in aortic endothelial cells (ECs). In addition, immobilized lactadherin increased the expression of pro-inflammatory markers associated with an aging phenotype. These results extend our knowledge of the LV proteome remodeling induced by chronological and pathological aging in different species (mouse and human). The lactadherin-triggered changes in the proteome and phosphoproteome of ECs suggest a straight link between ECM component remodeling and the aging process of ECs, which may provide an additional layer to prevent cardiac aging.

Human cell-expressed tag-free rhMFG-E8 as an effective radiation mitigator

Human milk fat globule epidermal growth factor-factor VIII (MFG-E8) functions as a bridging molecule to promote the removal of dying cells by professional phagocytes. E. coli-expressed histidine-tagged recombinant human MFG-E8 (rhMFG-E8) is protective in various disease conditions. However, due to improper recombinant protein glycosylation, misfolding and the possibility of antigenicity, E. coli-expressed histidine-tagged rhMFG-E8 is unsuitable for human therapy. Therefore, we hypothesize that human cell-expressed, tag-free rhMFG-E8 will have suitable structural and functional properties to be developed as a safe and effective novel biologic to treat inflammatory diseases including radiation injury. We produced a new tag-free rhMFG-E8 protein by cloning the human MFG-E8 full-length coding sequence without any fusion tag into a mammalian vector and expressed it in HEK293-derived cells. The construct includes the leader sequence of cystatin S to maximize secretion of rhMFG-E8 into the culture medium. After purification and confirmation of the protein identity, we first evaluated its biological activity in vitro. We then determined its efficacy in vivo utilizing an experimental rodent model of radiation injury, i.e., partial body irradiation (PBI). HEK293 cell supernatant containing tag-free rhMFG-E8 protein was concentrated, purified, and rhMFG-E8 was verified by SDS-PAGE with the standard human MFG-E8 loaded as control and, mass spectrometry followed by analysis using MASCOT for peptide mass fingerprint. The biological activity of human cell-expressed tag-free rhMFG-E8 was superior to that of E. coli-expressed His-tagged rhMFG-E8. Toxicity, stability, and pharmacokinetic studies indicate that tag-free rhMFG-E8 is safe, highly stable after lyophilization and long-term storage, and with a terminal elimination half-life in circulation of at least 1.45 h. In the 15 Gy PBI model, a dose-dependent improvement of the 30-day survival rate was observed after tag-free rhMFG-E8 treatment with a 30-day survival of 89%, which was significantly higher than the 25% survival in the vehicle group. The dose modification factor (DMF) of tag-free rhMFG-E8 calculated using probit analysis was 1.058. Tag-free rhMFG-E8 also attenuated gastrointestinal damage after PBI suggesting it as a potential therapeutic candidate for a medical countermeasure for radiation injury. Our new human cell-expressed tag-free rhMFG-E8 has proper structural and functional properties to be further developed as a safe and effective therapy to treat victims of severe acute radiation injury.

Milk Fat Globule Epidermal Growth Factor VIII Fragment Medin in Age-Associated Arterial Adverse Remodeling and Arterial Disease

Medin, a small 50-amino acid peptide, is an internal cleaved product from the second discoidin domain of milk fat globule epidermal growth factor VIII (MFG-E8) protein. Medin has been reported as the most common amylogenic protein in the upper part of the arterial system, including aortic, temporal, and cerebral arterial walls in the elderly. Medin has a high affinity to elastic fibers and is closely associated with arterial degenerative inflammation, elastic fiber fragmentation, calcification, and amyloidosis. In vitro, treating with the medin peptide promotes the inflammatory phenotypic shift of both endothelial cells and vascular smooth muscle cells. In vitro, ex vivo, and in vivo studies demonstrate that medin enhances the abundance of reactive oxygen species and reactive nitrogen species produced by both endothelial cells and vascular smooth muscle cells and promotes vascular endothelial dysfunction and arterial stiffening. Immunostaining and immunoblotting analyses of human samples indicate that the levels of medin are increased in the pathogenesis of aortic aneurysm/dissection, temporal arteritis, and cerebrovascular dementia. Thus, medin peptide could be targeted as a biomarker diagnostic tool or as a potential molecular approach to curbing the arterial degenerative inflammatory remodeling that accompanies aging and disease.

Discovery and systematic characterization of risk variants and genes for coronary artery disease in over a million participants

The discovery of genetic loci associated with complex diseases has outpaced the elucidation of mechanisms of disease pathogenesis. Here we conducted a genome-wide association study (GWAS) for coronary artery disease (CAD) comprising 181,522 cases among 1,165,690 participants of predominantly European ancestry. We detected 241 associations, including 30 new loci. Cross-ancestry meta-analysis with a Japanese GWAS yielded 38 additional new loci. We prioritized likely causal variants using functionally informed fine-mapping, yielding 42 associations with less than five variants in the 95% credible set. Similarity-based clustering suggested roles for early developmental processes, cell cycle signaling and vascular cell migration and proliferation in the pathogenesis of CAD. We prioritized 220 candidate causal genes, combining eight complementary approaches, including 123 supported by three or more approaches. Using CRISPR-Cas9, we experimentally validated the effect of an enhancer in MYO9B, which appears to mediate CAD risk by regulating vascular cell motility. Our analysis identifies and systematically characterizes >250 risk loci for CAD to inform experimental interrogation of putative causal mechanisms for CAD.

How vascular smooth muscle cell phenotype switching contributes to vascular disease

Vascular smooth muscle cells (VSMCs) are the most abundant cell in vessels. Earlier experiments have found that VSMCs possess high plasticity. Vascular injury stimulates VSMCs to switch into a dedifferentiated type, also known as synthetic VSMCs, with a high migration and proliferation capacity for repairing vascular injury. In recent years, largely owing to rapid technological advances in single-cell sequencing and cell-lineage tracing techniques, multiple VSMCs phenotypes have been uncovered in vascular aging, atherosclerosis (AS), aortic aneurysm (AA), etc. These VSMCs all down-regulate contractile proteins such as α-SMA and calponin1, and obtain specific markers and similar cellular functions of osteoblast, fibroblast, macrophage, and mesenchymal cells. This highly plastic phenotype transformation is regulated by a complex network consisting of circulating plasma substances, transcription factors, growth factors, inflammatory factors, non-coding RNAs, integrin family, and Notch pathway. This review focuses on phenotypic characteristics, molecular profile and the functional role of VSMCs phenotype landscape; the molecular mechanism regulating VSMCs phenotype switching; and the contribution of VSMCs phenotype switching to vascular aging, AS, and AA. Video Abstract.

Arctigenin Attenuates Vascular Inflammation Induced by High Salt through TMEM16A/ESM1/VCAM-1 Pathway

Salt-sensitive hypertension is closely related to inflammation, but the mechanism is barely known. Transmembrane member 16A (TMEM16A) is the Ca2+-activated chloride channel in epithelial cells, smooth muscle cells, and sensory neurons. It can promote inflammatory responses by increasing proinflammatory cytokine release. Here, we identified a positive role of TMEM16A in vascular inflammation. The expression of TMEM16A was increased in high-salt-stimulated vascular smooth muscle cells (VSMCs), whereas inhibiting TMEM16A or silencing TMEM16A with small interfering RNA (siRNA) can abolish this effect in vitro or in vivo. Transcriptome analysis of VSMCs revealed some differential downstream genes of TMEM16A related to inflammation, such as endothelial cell-specific molecule 1 (ESM1) and CXC chemokine ligand 16 (CXCL16). Overexpression of TMEM16A in VSMCs was accompanied by high levels of ESM1, CXCL16, intercellular adhesion molecule-1 (ICAM-1), and vascular adhesion molecule-1 (VCAM-1). We treated VSMCs cultured with high salt and arctigenin (ARC), T16Ainh-A01 (T16), and TMEM16A siRNA (siTMEM16A), leading to greatly decreased ESM1, CXCL16, VCAM-1, and ICAM-1. Beyond that, silencing ESM1, the expression of VCAM-1 and ICAM-1, and CXCL16 was attenuated. In conclusion, our results outlined a signaling scheme that increased TMEM16 protein upregulated ESM1, which possibly activated the CXCL16 pathway and increased VCAM-1 and ICAM-1 expression, which drives VSMC inflammation. Beyond that, arctigenin, as a natural inhibitor of TMEM16A, can reduce the systolic blood pressure (SBP) of salt-sensitive hypertension mice and alleviate vascular inflammation.

RGMa promotes dedifferentiation of vascular smooth muscle cells into a macrophage-like phenotype in vivo and in vitro

Repulsive guidance molecule a (RGMa) is a glycosylphosphatidylinositol-anchored glycoprotein that has been demonstrated to influence inflammatory-related diseases in addition to regulating neuronal differentiation and survival during brain development. However, any function or mechanism of RGMa in dedifferentiation of contractile vascular smooth muscle cells (VSMCs) during inflammatory-related atherosclerosis is poorly understood. In the current study, we found that RGMa is expressed in VSMCs-derived macrophage-like cells from the fibrous cap of type V atherosclerotic plaques and the neointima of ligated carotid artery in ApoE^-/- mice. We determined levels of RGMa mRNA and protein increased in oxidized LDL (ox-LDL)-induced VSMCs. Knockdown of RGMa, both in vivo and in vitro, inhibited the dedifferentiation of ox-LDL-induced VSMCs and their ability to proliferate and migrate, reduced the thickness of the neointima after ligation of the left common carotid artery in ApoE^-/- mice. Additionally, we show RGMa promoted the dedifferentiation of VSMCs via enhancement of the role of transcription factor Slug. Slug knockdown reversed the dedifferentiation of ox-LDL-induced VSMCs promoted by RGMa overexpression. Thus, inhibition of RGMa may constitute a therapeutic strategy for atherosclerotic plaques prone to rupture and restenosis following mechanical injury.

Inflammatory Role of Milk Fat Globule-Epidermal Growth Factor VIII in Age-Associated Arterial Remodeling

Background

Age‐associated aortic remodeling includes a marked increase in intimal medial thickness (IMT), associated with signs of inflammation. Although aortic wall milk fat globule–epidermal growth factor VIII (MFG‐E8) increases with age, and is associated with aortic inflammation, it is not known whether MFG‐E8 is required for the age‐associated increase in aortic IMT. Here, we tested whether MFG‐E8 is required for the age‐associated increase in aortic IMT.

Methods and Results

To determine the role of MFG‐E8 in the age‐associated increase of IMT, we compared aortic remodeling in adult (20‐week) and aged (96‐week) MFG‐E8 (−/−) knockout and age matched wild‐type (WT) littermate mice. The average aortic IMT increased with age in the WT from 50±10 to 70±20 μm (P<0.0001) but did not significantly increase with age in MFG‐E8 knockout mice. Because angiotensin II signaling is implicated as a driver of age‐associated increase in IMT, we infused 30‐week‐old MFG‐E8 knockout and age‐matched littermate WT mice with angiotensin II or saline via osmotic mini‐pumps to determine whether MFG‐E8 is required for angiotensin II–induced aortic remodeling. (1) In WT mice, angiotensin II infusion substantially increased IMT, elastic lamina degradation, collagen deposition, and the proliferation of vascular smooth muscle cells; in contrast, these effects were significantly reduced in MFG‐E8 KO mice; (2) On a molecular level, angiotensin II treatment significantly increased the activation and expression of matrix metalloproteinase type 2, transforming growth factor beta 1, and its downstream signaling molecule phosphorylated mother against decapentaplegic homolog 2, and collagen type I production in WT mice; however, in the MFG‐E8 knockout mice, these molecular effects were significantly reduced; and (3) in WT mice, angiotensin II increased levels of aortic inflammatory markers phosphorylated nuclear factor‐kappa beta p65, monocyte chemoattractant protein 1, tumor necrosis factor alpha, intercellular adhesion molecule 1, and vascular cell adhesion molecule 1 molecular expression, while in contrast, these inflammatory markers did not change in knockout mice.

Conclusions

Thus, MFG‐E8 is required for both age‐associated proinflammatory aortic remodeling and also for the angiotensin II–dependent induction in younger mice of an aortic inflammatory phenotype observed in advanced age. Targeting MFG‐E8 would be a novel molecular approach to curb adverse arterial remodeling.

MFG-E8 promotes osteogenic transdifferentiation of smooth muscle cells and vascular calcification by regulating TGF-β1 signaling

Vascular calcification occurs in arterial aging, atherosclerosis, diabetes mellitus, and chronic kidney disease. Transforming growth factor-β1 (TGF-β1) is a key modulator driving the osteogenic transdifferentiation of vascular smooth muscle cells (VSMCs), leading to vascular calcification. We hypothesize that milk fat globule–epidermal growth factor 8 (MFG-E8), a glycoprotein expressed in VSMCs, promotes the osteogenic transdifferentiation of VSMCs through the activation of TGF-β1-mediated signaling. We observe that the genetic deletion of MFG-E8 prevents calcium chloride-induced vascular calcification in common carotid arteries (CCAs). The exogenous application of MFG-E8 to aged CCAs promotes arterial wall calcification. MFG-E8-deficient cultured VSMCs exhibit decreased biomineralization and phenotypic transformation to osteoblast-like cells in response to osteogenic medium. MFG-E8 promotes β1 integrin–dependent MMP2 expression, causing TGF-β1 activation and subsequent VSMC osteogenic transdifferentiation and biomineralization. Thus, the established molecular link between MFG-E8 and vascular calcification suggests that MFG-E8 can be therapeutically targeted to mitigate vascular calcification.

A molecular link between the milk fat globule–epidermal growth factor 8 (MFG-E8), activation of vascular calcification driver TGF-β1 and osteogenic differentiation of vascular smooth muscle cells suggests that MFG-E8 could be a therapeutic target for vascular calcification.

Increased MFG-E8 at neuromuscular junctions is an exacerbating factor for sarcopenia-associated denervation

Sarcopenia is an important health problem associated with adverse outcomes. Although the etiology of sarcopenia remains poorly understood, factors apart from muscle fibers, including humoral factors, might be involved. Here, we used cytokine antibody arrays to identify humoral factors involved in sarcopenia and found a significant increase in levels of milk fat globule epidermal growth factor 8 (MFG‐E8) in skeletal muscle of aged mice, compared with young mice. We found that the increase in MFG‐E8 protein at arterial walls and neuromuscular junctions (NMJs) in muscles of aged mice. High levels of MFG‐E8 at NMJs and an age‐related increase in arterial MFG‐E8 have also been identified in human skeletal muscle. In NMJs, MFG‐E8 is localized on the surface of terminal Schwann cells, which are important accessory cells for the maintenance of NMJs. We found that increased MFG‐E8 at NMJs precedes age‐related denervation and is more prominent in sarcopenia‐susceptible fast‐twitch than in sarcopenia‐resistant slow‐twitch muscle. Comparison between fast and slow muscles further revealed that arterial MFG‐E8 can be uncoupled from sarcopenic phenotype. A genetic deficiency in MFG‐E8 attenuated age‐related denervation of NMJs and muscle weakness, providing evidence of a pathogenic role of increased MFG‐E8. Thus, our study revealed a mechanism by which increased MFG‐E8 at NMJs leads to age‐related NMJ degeneration and suggests that targeting MFG‐E8 could be a promising therapeutic approach to prevent sarcopenia.

Dynamic Crosstalk between Vascular Smooth Muscle Cells and the Aged Extracellular Matrix

Vascular aging is accompanied by the fragmentation of elastic fibers and collagen deposition, leading to reduced distensibility and increased vascular stiffness. A rigid artery facilitates elastin to degradation by MMPs, exposing vascular cells to greater mechanical stress and triggering signaling mechanisms that only exacerbate aging, creating a self-sustaining inflammatory environment that also promotes vascular calcification. In this review, we highlight the role of crosstalk between smooth muscle cells and the vascular extracellular matrix (ECM) and how aging promotes smooth muscle cell phenotypes that ultimately lead to mechanical impairment of aging arteries. Understanding the underlying mechanisms and the role of associated changes in ECM during aging may contribute to new approaches to prevent or delay arterial aging and the onset of cardiovascular diseases.

MFG-E8 (LACTADHERIN): a novel marker associated with cerebral amyloid angiopathy

Brain accumulation of amyloid-beta (Aβ) is a crucial feature in Alzheimer´s disease (AD) and cerebral amyloid angiopathy (CAA), although the pathophysiological relationship between these diseases remains unclear. Numerous proteins are associated with Aβ deposited in parenchymal plaques and/or cerebral vessels. We hypothesized that the study of these proteins would increase our understanding of the overlap and biological differences between these two pathologies and may yield new diagnostic tools and specific therapeutic targets. We used a laser capture microdissection approach combined with mass spectrometry in the APP23 transgenic mouse model of cerebral-β-amyloidosis to specifically identify vascular Aβ-associated proteins. We focused on one of the main proteins detected in the Aβ-affected cerebrovasculature: MFG-E8 (milk fat globule-EGF factor 8), also known as lactadherin. We first validated the presence of MFG-E8 in mouse and human brains. Immunofluorescence and immunoblotting studies revealed that MFG-E8 brain levels were higher in APP23 mice than in WT mice. Furthermore, MFG-E8 was strongly detected in Aβ-positive vessels in human postmortem CAA brains, whereas MFG-E8 was not present in parenchymal Aβ deposits. Levels of MFG-E8 were additionally analysed in serum and cerebrospinal fluid (CSF) from patients diagnosed with CAA, patients with AD and control subjects. Whereas no differences were found in MFG-E8 serum levels between groups, MFG-E8 concentration was significantly lower in the CSF of CAA patients compared to controls and AD patients. Finally, in human vascular smooth muscle cells MFG-E8 was protective against the toxic effects of the treatment with the Aβ40 peptide containing the Dutch mutation. In summary, our study shows that MFG-E8 is highly associated with CAA pathology and highlights MFG-E8 as a new CSF biomarker that could potentially be used to differentiate cerebrovascular Aβ pathology from parenchymal Aβ deposition.

MicroRNA-199a-5p aggravates angiotensin II-induced vascular smooth muscle cell senescence by targeting Sirtuin-1 in abdominal aortic aneurysm

Vascular smooth muscle cells (VSMCs) senescence contributes to abdominal aortic aneurysm (AAA) formation although the underlying mechanisms remain unclear. This study aimed to investigate the role of miR-199a-5p in regulating VSMC senescence in AAA. VSMC senescence was determined by a senescence-associated β-galactosidase (SA-β-gal) assay. RT-PCR and Western blotting were performed to measure miRNA and protein level, respectively. The generation of reactive oxygen species (ROS) was evaluated by H2DCFDA staining. Dual-luciferase reporter assay was used to validate the target gene of miR-199a-5p. VSMCs exhibited increased senescence in AAA tissue relative to healthy aortic tissue from control donors. Compared with VSMCs isolated from control donors (control-VSMCs), those derived from patients with AAA (AAA-VSMCs) exhibited increased cellular senescence and ROS production. Angiotensin II (Ang II) induced VSMC senescence by promoting ROS generation. The level of miR-199a-5p expression was upregulated in the plasma from AAA patients and Ang II-treated VSMCs. Mechanistically, Ang II treatment significantly elevated miR-199a-5p level, thereby stimulating ROS generation by repressing Sirt1 and consequent VSMC senescence. Nevertheless, Ang II-induced VSMC senescence was partially attenuated by a miR-199a-5p inhibitor or Sirt1 activator. Our study revealed that miR-199a-5p aggravates Ang II-induced VSMC senescence by targeting Sirt1 and that miR-199a-5p is a potential therapeutic target for AAA.

ClC-3: A Novel Promising Therapeutic Target for Atherosclerosis

Chloride channel 3 (ClC-3), a Cl^-/H⁺ antiporter, has been well established as a member of volume-regulated chloride channels (VRCCs). ClC-3 may be a crucial mediator for activating inflammation-associated signaling pathways by regulating protein phosphorylation. A growing number of studies have indicated that ClC-3 overexpression plays a crucial role in mediating increased plasma low-density lipoprotein levels, vascular endothelium dysfunction, pro-inflammatory activation of macrophages, hyper-proliferation and hyper-migration of vascular smooth muscle cells (VSMCs), as well as oxidative stress and foam cell formation, which are the main factors responsible for atherosclerotic plaque formation in the arterial wall. In the present review, we summarize the molecular structures and classical functions of ClC-3. We further discuss its emerging role in the atherosclerotic process. In conclusion, we explore the potential role of ClC-3 as a therapeutic target for atherosclerosis.

MFG-E8 Regulates Vascular Smooth Muscle Cell Migration Through Dose-Dependent Mediation of Actin Polymerization

Background Migration of vascular smooth muscle cells (VSMCs) is the main contributor to neointimal formation. The Arp2/3 (actin-related proteins 2 and 3) complex activates actin polymerization and is involved in lamellipodia formation during VSMC migration. Milk fat globule-epidermal growth factor 8 (MFG-E8) is a glycoprotein expressed in VSMCs. We hypothesized that MFG-E8 regulates VSMC migration through modulation of Arp2/3-mediated actin polymerization. Methods and Results To determine whether MFG-E8 is essential for VSMC migration, a model of neointimal hyperplasia was induced in the common carotid artery of wild-type and MFG-E8 knockout mice, and the extent of neointimal formation was evaluated. Genetic deletion of MFG-E8 in mice attenuated injury-induced neointimal hyperplasia. Cultured VSMCs deficient in MFG-E8 exhibited decreased cell migration. Immunofluorescence and immunoblotting revealed decreased Arp2 but not Arp3 expression in the common carotid arteries and VSMCs deficient in MFG-E8. Exogenous administration of recombinant MFG-E8 biphasically and dose-dependently regulated the cultured VSMCs. At a low concentration, MFG-E8 upregulated Arp2 expression. By contrast, MFG-E8 at a high concentration reduced the Arp2 level and significantly attenuated actin assembly. Arp2 upregulation mediated by low-dose MFG-E8 was abolished by treating cultured VSMCs with β1 integrin function-blocking antibody and Rac1 inhibitors. Moreover, treatment of the artery with a high dose of recombinant MFG-E8 diminished injury-induced neointimal hyperplasia and reduced VSMC migration. Conclusions MFG-E8 plays a critical role in VSMC migration through dose-dependent regulation of Arp2-mediated actin polymerization. These findings suggest that high doses of MFG-E8 may have therapeutic potential for treating vascular occlusive diseases.

Single-Cell Epigenomics and Functional Fine-Mapping of Atherosclerosis GWAS Loci

Supplemental Digital Content is available in the text.

Genome-wide association studies have identified hundreds of loci associated with coronary artery disease (CAD). Many of these loci are enriched in cisregulatory elements but not linked to cardiometabolic risk factors nor to candidate causal genes, complicating their functional interpretation.

Age-associated proinflammatory elastic fiber remodeling in large arteries

Elastic fibers are the main components of the extracellular matrix of the large arterial wall. Elastic fiber remodeling is an intricate process of synthesis and degradation of the core elastin protein and microfibrils accompanied by the assembly and disassembly of accessory proteins. Age-related morphological, structural, and functional proinflammatory remodeling within the elastic fiber has a profound effect upon the integrity, elasticity, calcification, amyloidosis, and stiffness of the large arterial wall. An age-associated increase in arterial stiffness is a major risk factor for the pathogenesis of diseases of the large arteries such as hypertensive and atherosclerotic vasculopathy. This mini review is an update on the key molecular, cellular, functional, and structural mechanisms of elastic fiber proinflammatory remodeling in large arteries with aging. Targeting structural and functional integrity of the elastic fiber may be an effective approach to impede proinflammatory arterial remodeling with advancing age.

Inflammation, Nitro-Oxidative Stress, Impaired Autophagy, and Insulin Resistance as a Mechanistic Convergence Between Arterial Stiffness and Alzheimer's Disease

The average age of the world's elderly population is steadily increasing. This unprecedented rise in the aged world population will increase the prevalence of age-related disorders such as cardiovascular disease (CVD) and neurodegeneration. In recent years, there has been an increased interest in the potential interplay between CVDs and neurodegenerative syndromes, as several vascular risk factors have been associated with Alzheimer's disease (AD). Along these lines, arterial stiffness is an independent risk factor for both CVD and AD. In this review, we discuss several inflammaging-related disease mechanisms including acute tissue-specific inflammation, nitro-oxidative stress, impaired autophagy, and insulin resistance which may contribute to the proposed synergism between arterial stiffness and AD.

Roles and mechanisms of MFG-E8 in vascular aging-related diseases

The aging of the vasculature plays a crucial role in the pathological progression of various vascular aging-related diseases. As endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) are essential parts in the inner and medial layers of vessel wall, respectively, the structural and functional alterations of ECs and VSMCs are the major causes of vascular aging. Milk fat globule-epidermal growth factor 8 (MFG-E8) is a multifunctional glycoprotein which exerts a regulatory role in the intercellular interactions involved in a variety of biological and pathological processes. Emerging evidence suggests that MFG-E8 is a novel and outstanding modulator for vascular aging via targeting at ECs and VSMCs. In this review, we will summarise the cumulative roles and mechanisms of MFG-E8 in vascular aging and vascular aging-related diseases with special emphasis on the functions of ECs and VSMCs. In addition, we also aim to focus on the promising diagnostic function as a biomarker and the potential therapeutic application of MFG-E8 in vascular aging and the clinical evaluation of vascular aging-related diseases.

Medin aggregation causes cerebrovascular dysfunction in aging wild-type mice

Medin is the most common amyloid known in humans, as it can be found in blood vessels of the upper body in virtually everybody over 50 years of age. However, it remains unknown whether deposition of Medin plays a causal role in age-related vascular dysfunction. We now report that aggregates of Medin also develop in the aorta and brain vasculature of wild-type mice in an age-dependent manner. Strikingly, genetic deficiency of the Medin precursor protein, MFG-E8, eliminates not only vascular aggregates but also prevents age-associated decline of cerebrovascular function in mice. Given the prevalence of Medin aggregates in the general population and its role in vascular dysfunction with aging, targeting Medin may become a novel approach to sustain healthy aging.

[Olmesartan inhibits age-associated migration and invasion of human aortic vascular smooth muscle cells by upregulating miR-3133 axis]

OBJECTIVE

To explore the effects of olmesartan on age-associated migration and invasion capacities and microRNA (miRAN) axis in human aortic vascular smooth muscle cells (HA-VSMCs).

METHODS

Cultured HA-VSMCs were divided into control group, bleomycin-mediated senescence (BLM) group and bleomycin + olmesartan treatment group. Wound-healing assay and Boyden chambers invasion assay were used to assess the changes in migration and invasion of the cells, gelatin zymography was used to analyze matrix metalloproteinase-2 (MMP-2) activation in the cells. The differentially expressed miRNAs were identified by miRNA microarray assay and validated by quantitative real-time PCR. MiR-3133 inhibitor was used to examine the effects of molecular manipulation of olmesartan on age-associated migration and invasion and MMP-2 activation in the cells.

RESULTS

Compared with those of the control group, the percentage of the repopulated cells and the number of cells crossing the basement membrane increased significantly in BLM group [(78.43±12.76)% vs (42.47±7.22)%, P &lt; 0.05; 33.33±5.51 vs 13.00±4.36, P &lt; 0.05]. A significant increase of MMP-2 activation was found in BLM group as compared with the control group (1.66 ± 0.27 vs 0.87 ± 0.13, P &lt; 0.05). Olmesartan significantly inhibited BLM-induced enhancement of cell migration and invasion and MMP-2 secretion in the cells. MiR-3133 was significantly downregulated in BLM group and upregulated in olmesartan group. Transfection with miR-3133 inhibitor significantly reversed the effects of olmesartan on age-associated migration and invasion of the cells [(85.87±7.39)% vs (49.77±3.05)%; 34.67±2.31 vs 20.00±4.58, P &lt; 0.05] and MMP-2 activation in the cells (1.76±0.19 vs 0.94±0.10, P &lt; 0.05).

CONCLUSIONS

Olmesartan inhibits the migration and invasion of ageassociated HA-VSMCs probably by upregulating of the miR-3133 axis.

Proinflammation, profibrosis, and arterial aging

Aging is a major risk factor for quintessential cardiovascular diseases, which are closely related to arterial proinflammation. The age-related alterations of the amount, distribution, and properties of the collagen fibers, such as cross-links and degradation in the arterial wall, are the major sequelae of proinflammation. In the aging arterial wall, collagen types I, II, and III are predominant,  and are mainly produced by stiffened vascular smooth muscle cells (VSMCs) governed by proinflammatory signaling, leading to profibrosis. Profibrosis is regulated by an increase in the proinflammatory molecules angiotensin II, milk fat globule-EGF-VIII, and transforming growth factor-beta 1 (TGF-β1) signaling and a decrease in the vasorin signaling cascade. The release of these proinflammatory factors triggers the activation of matrix metalloproteinase type II (MMP-2) and activates profibrogenic TGF-β1 signaling, contributing to profibrosis. The age-associated increase in activated MMP-2 cleaves latent TGF-β and subsequently increases TGF-β1 activity leading to collagen deposition in the arterial wall. Furthermore, a blockade of the proinflammatory signaling pathway alleviates the fibrogenic signaling, reduces profibrosis, and prevents arterial stiffening with aging. Thus, age-associated proinflammatory-profibrosis coupling is the underlying molecular mechanism of arterial stiffening with advancing age.