This study tested whether late-life aerobic exercise influences sex differences in rats. We hypothesized that exercise, when started late in life, would reduce sex-differences in muscle function and inflammatory markers. Methods: 21-month-old male (n=11) and female (n=13) Fischer 344 rats were randomly assigned to sedentary (SED; 5M,7F) or exercise (EX; 6M,6F) groups. Trained animals ran at 60% maximal speed, 10° incline, 50 min/day, 5 days/week for 8 weeks. Exercise tolerance was assessed by maximal treadmill tests before and after training. At the end of the study, body composition was measured by echoMRI, in vivo muscle function by electrical stimulation, and blood, plantar flexor muscles, and spleen collected. Blood samples were analyzed for total white blood cells, relative immune cell composition, and tumor necrosis factor-alpha (TNF-α). Differences between groups were analyzed using two-way ANOVAs, followed by a Tukey’s post hoc test when appropriate, and Pearson’s correlations. Statistical significance was set at p < 0.05. Results: There was a significant effect of exercise (p < 0.0001) on body composition, with no significant effects of sex or exercise x sex interaction. Exercise tolerance was influenced by both sex (p < 0.001) and exercise (p < 0.001), with higher exercise tolerance in females and trained rats. We observed a significant exercise x sex interaction for skeletal muscle function, measured as maximal torque at 120 Hz. Specifically, maximal torque was higher in female SED than in male SED, and lower in male SED compared to male EX (p < 0.05). Both plantar flexors and spleen mass, normalized to body mass, showed a significant effect of sex. Males had a significantly larger spleen (p = 0.001), and females had greater skeletal muscle mass (p = 0.001). Since spleen enlargement reflects systemic inflammation, which can suppress muscle growth, we measured inflammatory markers. Plasma TNF-α levels were significantly higher in males than in females (p < 0.001). Total white blood cell counts showed a significant effect of sex, with males exhibiting higher counts (p = 0.004). The relative abundance of immune cell types was similar across sexes and training status, except for monocytes, which displayed a significant exercise x sex interaction (p = 0.001): male SED had higher percentages than female SED, and exercise appeared to normalize this difference. Relative monocytes were negatively correlated with both skeletal muscle mass (r = -0.70, p = 0.0004) and muscle torque (r = -0.55, p = 0.011). Conclusions: Our data show that aged male rats had larger spleen, higher TNF-α and white blood cell counts, and elevated monocyte percentages compared to females. Inflammatory markers were negatively associated with skeletal muscle mass and function. Late-life aerobic exercise improved skeletal muscle function, exercise tolerance, and immune profile, and appeared to mitigate sex differences in aged rats. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

Aging is an independent risk factor for cardiovascular disease. Preventing age-induced arterial dysfunction and the associated risk of cardiovascular disease remains a significant clinical challenge. Aerobic exercise, which induces a temporary increase in both blood flow and pressure in active tissue, has been shown to reduce macroscale arterial stiffening in humans. This study investigates the effects of mechanical stimuli on improving aging pathophysiology of vascular smooth muscle (VSM) cells isolated from soleus feed arteries (SFA). We hypothesized that age-induced impairment of VSM contractility can be rescued by mechanical stimulation that enhances formation of smooth muscle alpha-actin (SMα-actin) fibers and cell-matrix adhesions in aged VSM cells. Ex-vivo functional studies were used to assess myogenic contractility of VSM in isolated SFA from young (4 months) and old (24 months) Fischer 344 rats. These data indicated that pre-treatment of isolated aged SFA with a short-duration increase in intraluminal pressure rescued contractility. The mechanical stretch-induced remodeling of the cellular architecture was assessed in VSM cells isolated from young and old SFA. To dissect the mechanisms involved, the structural and functional properties of VSM cells were assessed by using mechanical stimulation combined with fluorescence confocal microscopy. Results showed that aged VSM cells respond faster than young cells to 2D biaxial cyclic stretch by increasing actin stress fiber formation and vinculin recruitment at cell-matrix adhesions. In addition, hydrostatic pressure treatment applied to aged VSM cells plated on stiffer substrates restored actin fibers and integrin β1 recruitment. Taken together, these findings suggest that discrete VSM cell mechanical properties and their ability to adapt to external mechanical signals are key in restoring VSM contractility in aging. These results are significant because they provide a novel understanding of the mechanisms by which mechanical stimulation improves VSM contractility in aged resistance arteries. Our results provide new insights into the role of VSM in vascular aging and highlight a new direction for mitigating age-related effects via mechanical stimulation-induced VSM remodeling.

EDITORIAL article Front. Physiol., 04 January 2024Sec. Vascular Physiology Volume 14 - 2023 | https://doi.org/10.3389/fphys.2023.1339619

Arterial aging is associated with increased stiffness and decreased arterial contractility, which alters mechanosensitive responses to external mechanical stimuli in aged vascular smooth muscle (VSM) cells. Real-time measurements of mechanosensitive events at the sub-cellular level in response to physiologically relevant mechanical stimulation are a critical component in understanding mechanically-induced cellular remodeling. Relatively little is known about how cells sense and integrate mechanical forces at the molecular level to induce intracellular signaling. This study investigates the effect of pressure-induced extracellular mechanical signaling on integrin-mediated cell adhesions and actin cytoskeleton in VSM cells isolated from soleus feed arteries from young and old Fischer 344 rats. Cells were plated on fibronectin functionalized soft (4 kPa) and stiff (100 kPa) substrates and then subjected to an acute high-pressure treatment (160 cmH2O) for 30 min to mimic the pressure present in soleus feed arteries during exercise. Cells were fixed and further stained for integrin beta1 and smooth muscle alpha-actin followed by high-resolution imaging using confocal microscopy. Non-pressurized cells were used as control. Quantitative analysis of fluorescence images showed that for old cells plated on stiffer substrates, smooth muscle alpha-actin and integrin beta1 protein expressions were significantly reduced compared with young cells in the control condition. However, pressure treatment induced a significant increase in both integrin beta1 and smooth muscle alpha-actin in old but not young VSM cells. Pressure treatment had no effect on old cells plated on soft substrates. In addition, soft substrates almost abolished the age-induced differences in protein expression. These findings suggest that short-duration pressure treatment induces a matrix stiffness-dependent beneficial effect in aging.

The intima, comprising the endothelium and the subendothelial matrix, plays a crucial role in atherosclerosis pathogenesis. The mechanical stress arising from disturbed blood flow (d-flow) and the stiffening of the arterial wall contributes to endothelial dysfunction. However, the specific impacts of these physical forces on the mechanical environment of the intima remain undetermined. Here, we investigated whether inhibiting collagen crosslinking could ameliorate the detrimental effects of persistent d-flow on the mechanical properties of the intima. Partial ligation of the left carotid artery (LCA) was performed in C57BL/6J mice, inducing d-flow. The right carotid artery (RCA) served as an internal control. Carotids were collected 2 days and 2 weeks after surgery to study acute and chronic effects of d-flow on the mechanical phenotype of the intima. The chronic effects of d-flow were decoupled from the ensuing arterial wall stiffening by administration of β-aminopropionitrile (BAPN), an inhibitor of collagen crosslinking by lysyl oxidase (LOX) enzymes. Atomic force microscopy (AFM) was used to determine stiffness of the endothelium and the denuded subendothelial matrix in en face carotid preparations. The stiffness of human aortic endothelial cells (HAEC) cultured on soft and stiff hydrogels was also determined. Acute exposure to d-flow caused a slight decrease in endothelial stiffness in male mice but had no effect on the stiffness of the subendothelial matrix in either sex. Regardless of sex, the intact endothelium was softer than the subendothelial matrix. In contrast, exposure to chronic d-flow led to a substantial increase in the endothelial and subendothelial stiffness in both sexes. The effects of chronic d-flow were largely prevented by concurrent BAPN administration. In addition, HAEC displayed reduced stiffness when cultured on soft vs. stiff hydrogels. We conclude that chronic d-flow results in marked stiffening of the arterial intima, which can be effectively prevented by inhibition of collagen crosslinking.

Stress fibers are actomyosin bundles that regulate cellular mechanosensation and force transduction. Interacting with the extracellular matrix through focal adhesion complexes, stress fibers are highly dynamic structures regulated by myosin motors and crosslinking proteins. Under external mechanical stimuli such as tensile forces, the stress fiber remodels its architecture to adapt to external cues, displaying properties of viscoelastic materials. How the structural remodeling of stress fibers is related to the generation of contractile force is not well understood. In this work, we simulate mechanochemical dynamics and force generation of stress fibers using the molecular simulation platform MEDYAN. We model stress fiber as two connecting bipolar bundles attached at the ends to focal adhesion complexes. The simulated stress fibers generate contractile force that is regulated by myosin motors and α -actinin crosslinkers. We find that stress fibers enhance contractility by reducing the distance between actin filaments to increase crosslinker binding, and this structural remodeling ability depends on the crosslinker turnover rate. Under tensile pulling force, the stress fiber shows an instantaneous increase of the contractile forces followed by a slow relaxation into a new steady state. While the new steady state contractility after pulling depends only on the overlap between actin bundles, the short-term contractility enhancement is sensitive to the tensile pulling distance. We further show that this mechanical response is also sensitive to the crosslinker turnover rate. Our results provide new insights into the stress fiber mechanics that have significant implications for understanding cellular adaptation to mechanical signaling.

Background The intima, comprising the endothelium and the subendothelial matrix, plays a crucial role in the development of atherosclerotic plaques, especially in bifurcations and curved segments of arteries. The mechanical stress arising from disturbed blood flow (d-flow) and the stiffening of the arterial wall contributes to endothelial dysfunction. However, the specific impacts of these physical forces on the mechanical environment of the intima remain undetermined. To address this gap in knowledge, we investigated whether inhibiting collagen crosslinking could ameliorate the detrimental effects of persistent d-flow on the mechanical properties of the intima. Methods To explore this hypothesis, we performed partial ligation (PCL) of the left carotid artery (LCA) in male and female C57BL/6J mice, inducing d-flow. The right carotid artery (RCA) served as an internal control. Carotids were collected two days and two weeks after PCL to study acute and chronic effects of d-flow on the mechanical phenotype of the intima. To decouple the chronic effects of d-flow from the ensuing arterial wall stiffening, we used subcutaneous implants delivering either phosphate-buffered saline (Saline) or 150 mg/kg/day of β-aminopropionitrile (BAPN), an inhibitor of elastin and collagen crosslinking lysyl oxidase (LOX) and LOX-like (LOXL) enzymes. Atomic force microscopy (AFM) measurements allowed us to determine stiffness of the endothelium and the denuded subendothelial matrix in en face carotid preparations. In addition, we determined the stiffness of human aortic endothelial cells (HAEC) cultured on soft and stiff hydrogels. Results Acute exposure to d-flow caused a slight decrease in endothelial stiffness in male mice but had no effect on the stiffness of the subendothelial matrix in either sex. Regardless of sex, the intact endothelium was softer than the subendothelial matrix. In contrast, exposure to chronic d-flow led to a substantial increase in the endothelial and subendothelial stiffness in both sexes. The effects of chronic d-flow were largely prevented by concurrent BAPN administration. Notably, the subendothelial matrix of ligated, BAPN-treated arteries was softer than that of unligated, saline-treated counterparts. Furthermore, HAEC displayed reduced stiffness when cultured on soft vs. stiff hydrogels. Conclusions Exposure to chronic d-flow results in marked stiffening of arterial intima, which can be effectively prevented by pharmacological inhibition of LOX/LOXL enzymes. Highlights Acute exposure to d-flow slightly softens the endothelium in males. Chronic exposure to d-flow causes stiffening of the arterial intima. Inhibition of LOX/LOXL enzymes prevents intimal stiffening arising from chronic d-flow.

Age–related impairments of skeletal muscle resistance arteries are associated with alterations in vascular smooth muscle cell (VSMC) contractility. Aerobic exercise is an effective intervention for reversing the impacts of aging on vascular contractility. In addition, we have shown that arterial wall-stretch, induced by a short-duration increase in intraluminal pressure in cannulated soleus muscle feed arteries (SFA), attenuates age-related changes in VSM contractility. The mechanisms responsible for the beneficial effect of wall stretch on contractility are not fully understood. Purpose: VSMC respond to extracellular mechanical signals by dynamic remodeling of actin fibers and cell-matrix adhesions. In this study, we investigated the impact of in vitro cyclic stretch on attenuating the age–induced alterations in VSMCs contractility by evaluating changes in vinculin, as a marker for cell-matrix adhesions, and smooth muscle α-actin (SMα-actin) fiber formation. Methods: VSMC isolated from SFA of young (4 month) and old (24 month) male F344 rats were cultured on fibronectin–functionalized silicon membranes. Equibiaxial cyclic stretch (10%) at 0.25 Hz frequency was applied to both young and old cells for 2 or 5 min. Static condition (no stretch) was used as control. At the end of the study, cells were fixed in their stretched or static state with 2% paraformaldehyde and stained for SMα-actin and vinculin. Dual color confocal imaging was performed using Olympus Fluoview 3000 microscope, and SlideBook software was used to analyze the data. Results: Young and old VSMC respond differently to stretch-induced mechanical stimulation. Results showed an increase in actin stress fibers formation in old VSMC for both time points when compared to young cells or old cells at rest. Similarly, vinculin recruitment at cell-matrix adhesion was increased in old VSMC. No differences were found between young and old cells in the static condition for any of the proteins. Conclusion: Taken together, these data show that stretch-induced mechanical stimulation increases actin stress fiber and integrin-based adhesions contributing to improved aged VSM cells contractility. Sydney and J.L. Huffines Institute for Sports Medicine and Human Performance This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Thoracic aortic aneurysm is found in patients with ACTA2 pathogenic variants. ACTA2 missense variants are associated with impaired aortic smooth muscle cell (SMC) contraction. This study tested the hypothesis that the Acta2R149C/+ variant alters actin isoform expression and decreases integrin recruitment, thus, reducing aortic contractility. Stress relaxation measurements in thoracic aortic rings showed two functional regimes with a reduction of stress relaxation in the aorta from Acta2R149C/+ mice at low tension, but not at high tension values. Contractile responses to phenylephrine and potassium chloride were 50% lower in Acta2R149C/+ mice than in wild-type (WT) mice. Additionally, SMC were immunofluorescently labeled for specific proteins and imaged by confocal or total internal reflection fluorescence microscopy. The quantification of protein fluorescence of Acta2R149C/+ SMC showed a downregulation in smooth muscle α-actin (SMα-actin) and a compensatory upregulation of smooth muscle γ-actin (SMγ-actin) compared to WT cells. These results suggest that downregulation of SMα-actin leads to reduced SMC contractility, while upregulation of SMγ-actin may lead to increased SMC stiffness. Decreased α5β1 and α2β1 integrin recruitment at cell-matrix adhesions further reduce the ability of mutant cells to participate in cell-matrix crosstalk. Collectively, the results suggest that mutant Acta2R149C/+ aortic SMC have reduced contractility and interaction with the matrix, which are potential long-term contributing factors to thoracic aortic aneurysms.

Taken together, these data suggest that aging leads to integrin dysfunction, which contributes to decreased contractile properties of vascular smooth muscle in SFA.

Arterial aging results in a progressive reduction in elasticity of the vessel wall and an impaired ability of aged blood vessels to control local blood flow and pressure. Recently, a new concept has emerged that the stiffness and decreased contractility of vascular smooth muscle (VSM) cells are important contributors to age-induced arterial dysfunction. This study investigated the hypothesis that aging alters integrin function in a matrix stiffness-dependent manner, which contributes to decreased VSM contractility in aged soleus muscle feed arteries (SFA). The effect of RGD-binding integrins on contractile function of cannulated SFA isolated from young (4 months) and old (24 months) Fischer 344 rats was assessed by measuring constrictor responses to norepinephrine, phenylephrine, and angiotensin II. Results indicated that constrictor responses in presence of RGD were impaired in old compared to young SFA. VSM cells isolated from young and old SFA were used for functional experiments using atomic force microscopy and high-resolution imaging. Aging was associated with a modulation of integrin β1 recruitment at cell-matrix adhesions that was matrix and substrate stiffness dependent. Our data showed that substrate stiffening drives altered integrin β1 expression in aging, while soft substrates abolish age-induced differences in overall integrin β1 expression. In addition, substrate stiffness and matrix composition contribute to the modulation of SMα-actin cytoskeleton architecture with soft substrates reducing age effects. Our results provide new insights into age-induced structural changes at VSM cell level that translates to decreased functionality of aged resistance soleus feed arteries.

A better understanding of endothelial dysfunction holds promise for more effective interventions for atherosclerosis prevention and treatment. Endothelial signaling by the non-catalytic region of the tyrosine kinase (NCK) family of adaptors, consisting of NCK1 and NCK2, has been implicated in cardiovascular development and postnatal angiogenesis but its role in vascular disease remains incompletely understood. Here, we report stage- and sex-dependent effects of endothelial NCK2 signaling on arterial wall inflammation and atherosclerosis development. Male and female Nck1 -null atheroprone mice enabling inducible, endothelial-specific Nck2 inactivation were fed a high fat diet (HFD) for 8 or 16 weeks to model atherosclerosis initiation and progression, respectively. Analysis of aorta preparations en face during disease progression, but not initiation, showed a significant reduction in plaque burden in males, but not females, lacking endothelial NCK2 relative to controls. Markers of vascular inflammation were reduced by endothelial NCK2 deficiency in both males and females during atherosclerosis progression but not initiation. At advanced stages of disease, plaque size and severity of atherosclerotic lesions were reduced by abrogation of endothelial NCK2 signaling only in males. Collectively, our results demonstrate stage- and sex-dependent modulation of atherosclerosis development by endothelial NCK2 signaling.

Arterial aging is associated with decreased arterial contractility and altered mechanosensitive response to external stimuli in vascular smooth muscle cells. This study investigates the effect of lysophosphatidic acid (LPA) on integrin-mediated cell adhesion and actin fiber formation in aged cells. Vascular smooth muscle cells were isolated from soleus feed arteries from young (4 months) and old (24 months) male Fischer 344 rats. To test the effect of LPA on integrin recruitment at cell-matrix adhesions and actin stress fiber formation, cells were plated on cell culture dishes functionalized with fibronectin and collagen-I.

Introduction Vasoconstrictor responses decline with age in soleus muscle feed arteries (SFA). Previous data from our laboratory revealed that alterations in integrin signaling contributed to the impaired constrictor responses. Whether the impaired constrictor responses resulted from integrin signaling in endothelial cells or vascular smooth muscle (VSM) cells is unknown. Thus, the purpose of the study was to test the hypothesis that aging alters VSM contractility due to impaired VSM integrin signaling in SFA. Method Soleus muscle feed arteries (SFA) were isolated from young (4 mo) and old (24 mo) male Fischer 344 rats. SFA were cannulated with glass micropipettes and pressurized to 90 cm H2O for assessment of vasoconstrictor function. To isolate the role of smooth muscle in constrictor responses, endothelial cells were removed (denuded) by passing 5 ml of air through the lumen of the artery. Vasoconstrictor responses were assessed using increasing whole log doses of norepinephrine (NE; 10-9-10-4 M), angiotensin II (Ang II; 10-11-10-7 M), and phenylephrine (PE; 10-9-10-4 M) in the presence or absence of RGD, an integrin inhibitory peptide, and RGE, as control. Results Vasoconstrictor responses to NE, PE, and Ang II were less in old denuded SFA when compared to young SFA. In the presence of RGD, the constrictor response to Ang II (not NE or PE) was significantly reduced in both young and old SFA. RGE did not alter the constrictor responses to any of the agonists. Conclusion The results of this study indicate that VSM contractility declines with age in SFA. In addition, our results suggest that RGD binding integrin-mediated constrictor function declines with age in denuded SFA.

Understanding cellular remodeling in response to mechanical stimuli is a critical step in elucidating mechanical activation of biochemical signaling pathways. Experimental evidence indicates that external stress-induced subcellular adaptation is accomplished through dynamic cytoskeletal reorganization. To study the interactions between subcellular structures involved in transducing mechanical signals, we combined experimental data and computational simulations to evaluate real-time mechanical adaptation of the actin cytoskeletal network. Actin cytoskeleton was imaged at the same time as an external tensile force was applied to live vascular smooth muscle cells using a fibronectin-functionalized atomic force microscope probe. Moreover, we performed computational simulations of active cytoskeletal networks under an external tensile force. The experimental data and simulation results suggest that mechanical structural adaptation occurs before chemical adaptation during filament bundle formation: actin filaments first align in the direction of the external force by initializing anisotropic filament orientations, then the chemical evolution of the network follows the anisotropic structures to further develop the bundle-like geometry. Our findings present an alternative two-step explanation for the formation of actin bundles due to mechanical stimulation and provide new insights into the mechanism of mechanotransduction.

ObjectiveWe tested the hypothesis that vascular smooth muscle (VSM) myogenic constrictor responses decline with age in soleus muscle feed arteries (SFA). In addition, we asked whether pre‐treatment of SFA with a short duration (1 h) increase in intraluminal pressure, to mimic pressure associated with a bout of exercise, would have beneficial effects on myogenic responses in SFA.MethodsSFA from young (4 mo) and old (24 mo) Fischer 344 rats were cannulated with glass micropipettes and endothelial cells were removed (denuded) by passing 5 ml of air through the lumen of the vessel. SFA were then pressurized to 90 cmH2O (p90) or 130 cmH2O (p130) for 1 h. At the end of the 1 h treatment, intraluminal pressure in all arteries was set to 90 cmH2O for examination of VSM myogenic constrictor function. After stable tone was achieved, myogenic contractile responses were assessed using step‐increases in intraluminal pressure from 90 cmH2O to 135 cmH2O in 15 cmH2O increments followed by step‐decreases down to 45 cmH2O.ResultsMyogenic responses of denuded old SFA (p90) was not different from denuded young SFA (p90). Pre‐treatment of SFA with increased pressure for 1 h improved myogenic constriction in young SFA (p130) but not in old (p130).ConclusionVSM myogenic responses were not altered with age in denuded SFA. Pressure treatment contributed to enhanced myogenic constrictor responses in young SFA.Support or Funding InformationNIH grant R03AG064551, Sydney and J.L. Huffines Institute of Sports Medicine and Human Performance, and CEHD Research Fellowship, Texas A&M University

Mutations in ACTA2, encoding smooth muscle α-actin, are a frequent cause of heritable thoracic aortic aneurysm and dissections. These mutations are associated with impaired vascular smooth muscle cell function, which leads to decreased ability of the cell to sense matrix-mediated mechanical stimuli. This study investigates how loss of smooth muscle α-actin affects cytoskeletal tension development and cell adhesion using smooth muscle cells explanted from aorta of mice lacking smooth muscle α-actin. We tested the hypothesis that reduced vascular smooth muscle contractility due to a loss of smooth muscle α-actin decreases cellular mechanosensing by dysregulating cell adhesion to the matrix. Assessment of functional mechanical properties of the aorta by stress relaxation measurements in thoracic aortic rings suggested two functional regimes for Acta2 −/− mice. Lower stress relaxation was recorded in aortic rings from Acta2 −/− mice at tensions below 10 mN compared with wild type, likely driven by cytoskeletal-dependent contractility. However, no differences were recorded between the two groups above the 10 mN threshold, since at higher tension the matrix-dependent contractility may be predominant. In addition, our results showed that at any given level of stretch, transmural pressure is lower in aortic rings from Acta2 −/− mice than wild type mice. In addition, a three-dimensional collagen matrix contractility assay showed that collagen pellets containing Acta2 −/− smooth muscle cells contracted less than the pellets containing the wild type cells. Moreover, second harmonic generation non-linear microscopy revealed that Acta2 −/− cells locally remodeled the collagen matrix fibers to a lesser extent than wild type cells. Quantification of protein fluorescence measurements in cells also showed that in absence of smooth muscle α-actin, there is a compensatory increase in smooth muscle γ-actin. Moreover, specific integrin recruitment at cell–matrix adhesions was reduced in Acta2 −/− cells. Thus, our findings suggest that Acta2 −/− cells are unable to generate external forces to remodel the matrix due to reduced contractility and interaction with the matrix. Impact statement Thoracic aneurysm formation is characterized by progressive enlargement of the ascending aorta, which predisposes the aorta to acute aortic dissection that can lead to sudden death. SMCs in the aorta play an integral role in regulating vessel wall contractility and matrix deposition in the medial layer. Recent studies show that mutations in genes associated with actomyosin apparatus reduce SMC contractility, increasing susceptibility to TAAD. Single-cell experiments enable discrete measurements of transient microscopic events that may be masked by a macroscopic average tissue behavior. Biophysical methods combined with microscopy techniques aid in understanding the specific roles of adhesion and cytoskeletal proteins in regulating SMC mechanosensing when SMα-actin is disrupted. Our findings suggest that Acta2 − / − cells have increased SMγ-actin and decreased integrin recruitment at cell–matrix adhesion, hence a synthetic phenotype with reduced cellular mechanosensing.

Vascular smooth muscle cells (VSMC) are now considered important contributors to the pathophysiological and biophysical mechanisms underlying arterial stiffening in aging. Here, we review mechanisms whereby VSMC stiffening alters vascular function and contributes to the changes in vascular stiffening observed in aging and cardiovascular disease. Vascular stiffening in arterial aging was historically associated with changes in the extracellular matrix; however, new evidence suggests that endothelial and vascular smooth muscle cell stiffness also contribute to overall blood vessel stiffness. Furthermore, VSMC play an integral role in regulating matrix deposition and vessel wall contractility via interaction between the actomyosin contractile unit and adhesion structures that anchor the cell within the extracellular matrix. Aged-induce phenotypic modulation of VSMC from a contractile to a synthetic phenotype is associated with decreased cellular contractility and increased cell stiffness. Aged VSMC also display reduced mechanosensitivity and adaptation to mechanical signals from their microenvironment due to impaired intracellular signaling. Finally, evidence for decreased contractility in arteries from aged animals demonstrate that changes at the cellular level result in decreased functional properties at the tissue level.