Mechanotransduction via the Piezo1-Akt pathway underlies Sost suppression in osteocytes

Osteocytes function as critical regulators of bone homeostasis by coordinating the functions of osteoblasts and osteoclasts, and are constantly exposed to mechanical force. However, the molecular mechanism underlying the mechanical signal transduction in osteocytes is not well understood. Here, we found that Yoda1, a selective Piezo1 agonist, increased intracellular calcium mobilization and dose-dependently decreased the expression of Sost (encoding Sclerostin) in the osteocytic cell line IDG-SW3. We also demonstrated that mechanical stretch of IDG-SW3 suppressed Sost expression, a result which was abrogated by treatment with the Piezo1 inhibitor GsMTx4, and the deficiency of Piezo1. Furthermore, the suppression of Sost expression was abolished by treatment with an Akt inhibitor. Taken together, these results indicate that the activation of the Piezo1-Akt pathway in osteocytes is required for mechanical stretch-induced downregulation of Sost expression.     

The Expression of Fn14 via Mechanical Stress-activated JNK Contributes to Apoptosis Induction in Osteoblasts

Bone mass is maintained by the balance between the activities of bone-forming osteoblasts and bone-resorbing osteoclasts. It is well known that adequate mechanical stress is essential for the maintenance of bone mass, whereas excess mechanical stress induces bone resorption. However, it has not been clarified how osteoblasts respond to different magnitudes of mechanical stress. Here we report that large-magnitude (12%) cyclic stretch induced Ca²⁺ influx, which activated reactive oxygen species generation in MC3T3-E1 osteoblasts. Reactive oxygen species then activated the ASK1-JNK/p38 pathways. The activated JNK led to transiently enhanced expression of FGF-inducible 14 (Fn14, a member of the TNF receptor superfamily) gene. Cells with enhanced expression of Fn14 subsequently acquired sensitivity to the ligand of Fn14, TNF-related weak inducer of apoptosis, and underwent apoptosis. On the other hand, the ASK1-p38 pathway induced expression of the monocyte chemoattractant protein 3 (MCP-3) gene, which promoted chemotaxis of preosteoclasts. In contrast, the ERK pathway was activated by small-magnitude stretching (1%) and induced expression of two osteogenic genes, collagen Ia (Col1a) and osteopontin (OPN). Moreover, activated JNK suppressed Col1a and OPN induction in large-magnitude mechanical stretch-loaded cells. The enhanced expression of Fn14 and MCP-3 by 12% stretch and the enhanced expression of Col1a and OPN by 1% stretch were also observed in mouse primary osteoblasts. These results suggest that differences in the response of osteoblasts to varying magnitudes of mechanical stress play a key role in switching the mode of bone metabolism between formation and resorption.     

Dysregulated Gene Expression in the Primary Osteoblasts and Osteocytes Isolated from Hypophosphatemic Hyp Mice

Osteocytes express multiple genes involved in mineral metabolism including PHEX, FGF23, DMP1 and FAM20C. In Hyp mice, a murine model for X-linked hypophosphatemia (XLH), Phex deficiency results in the overproduction of FGF23 in osteocytes, which leads to hypophosphatemia and impaired vitamin D metabolism. In this study, to further clarify the abnormality in osteocytes of Hyp mice, we obtained detailed gene expression profiles in osteoblasts and osteocytes isolated from the long bones of 20-week-old Hyp mice and wild-type (WT) control mice. The expression of Fgf23, Dmp1, and Fam20c was higher in osteocytic cells than in osteoblastic cells in both genotypes, and was up-regulated in Hyp cells. Interestingly, the up-regulation of these genes in Hyp bones began before birth. On the other hand, the expression of Slc20a1 encoding the sodium/phosphate (Na⁺/Pi) co-transporter Pit1 was increased in osteoblasts and osteocytes from adult Hyp mice, but not in Hyp fetal bones. The direct effects of extracellular Pi and 1,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃] on isolated osteoblastic and osteocytic cells were also investigated. Twenty-four-hour treatment with 10⁻⁸ M 1,25(OH)₂D₃ increased the expression of Fgf23 in WT osteoblastic cells but not in osteocytic cells. Dmp1 expression in osteocytic cells was increased due to the 24-hour treatment with 10 mM Pi and was suppressed by 10⁻⁸ M 1,25(OH)₂D₃ in WT osteocytic cells. We also found the up-regulation of the genes for FGF1, FGF2, their receptors, and Egr-1 which is a target of FGF signaling, in Hyp osteocytic cells, suggesting the activation of FGF/FGFR signaling. These results implicate the complex gene dysregulation in osteoblasts and osteocytes of Hyp mice, which might contribute to the pathogenesis.     

Cyclic stretch enhances reorientation and differentiation of 3-D culture model of human airway smooth muscle

Activation of airway smooth muscle (ASM) cells plays a central role in the pathophysiology of asthma. Because ASM is an important therapeutic target in asthma, it is beneficial to develop bioengineered ASM models available for assessing physiological and biophysical properties of ASM cells. In the physiological condition in vivo, ASM cells are surrounded by extracellular matrix (ECM) and exposed to mechanical stresses such as cyclic stretch. We utilized a 3-D culture model of human ASM cells embedded in type-I collagen gel. We further examined the effects of cyclic mechanical stretch, which mimics tidal breathing, on cell orientation and expression of contractile proteins of ASM cells within the 3-D gel. ASM cells in type-I collagen exhibited a tissue-like structure with actin stress fiber formation and intracellular Ca²⁺ mobilization in response to methacholine. Uniaxial cyclic stretching enhanced alignment of nuclei and actin stress fibers of ASM cells. Moreover, expression of mRNAs for contractile proteins such as α-smooth muscle actin, calponin, myosin heavy chain 11, and transgelin of stretched ASM cells was significantly higher than that under the static condition. Our findings suggest that mechanical force and interaction with ECM affects development of the ASM tissue-like construct and differentiation to the contractile phenotype in a 3-D culture model.     

E11/gp38 selective expression in osteocytes: regulation by mechanical strain and role in dendrite elongation

Within mineralized bone, osteocytes form dendritic processes that travel through canaliculi to make contact with other osteocytes and cells on the bone surface. This three-dimensional syncytium is thought to be necessary to maintain viability, cell-to-cell communication, and mechanosensation. E11/gp38 is the earliest osteocyte-selective protein to be expressed as the osteoblast differentiates into an osteoid cell or osteocyte, first appearing on the forming dendritic processes of these cells. Bone extracts contain large amounts of E11, but immunostaining only shows its presence in early osteocytes compared to more deeply embedded cells, suggesting epitope masking by mineral. Freshly isolated primary osteoblasts are negative for E11 expression but begin to express this protein in culture, and expression increases with time, suggesting differentiation into the osteocyte phenotype. Osteoblast-like cell lines 2T3 and Oct-1 also show increased expression of E11 with differentiation and mineralization. E11 is highly expressed in MLO-Y4 osteocyte-like cells compared to osteoblast cell lines and primary osteoblasts. Differentiated, mineralized 2T3 cells and MLO-Y4 cells subjected to fluid flow shear stress show an increase in mRNA for E11. MLO-Y4 cells show an increase in dendricity and elongation of dendrites in response to shear stress that is blocked by small interfering RNA specific to E11. In vivo, E11 expression is also increased by a mechanical load, not only in osteocytes near the bone surface but also in osteocytes more deeply embedded in bone. Maximal expression is observed not in regions of maximal strain but in a region of potential bone remodeling, suggesting that dendrite elongation may be occurring during this process. These data suggest that osteocytes may be able to extend their cellular processes after embedment in mineralized matrix and have implications for osteocytic modification of their microenvironment.     

Osteogenesis in vitro: from pre-osteoblasts to osteocytes

Murine calvariae pre-osteoblasts (MC3T3-E1), grown in a novel bioreactor, proliferate into a mineralizing 3D osteoblastic tissue that undergoes progressive phenotypic maturation into osteocyte-like cells. Initially, the cells are closely packed (high cell/matrix ratio), but transform into a more mature phenotype (low cell/matrix ratio) after about 5 mo, a process that recapitulates stages of bone development observed in vivo. The cell morphology concomitantly evolves from spindle-shaped pre-osteoblasts through cobblestone-shaped osteoblasts to stellate-shaped osteocyte-like cells interconnected by many intercellular processes. Gene-expression profiles parallel cell morphological changes, up-to-and-including increased expression of osteocyte-associated genes such as E11, DMP1, and sclerostin. X-ray scattering and infrared spectroscopy of contiguous, square centimeter-scale macroscopic mineral deposits are consistent with bone hydroxyapatite, showing that bioreactor conditions can lead to ossification reminiscent of bone formation. Thus, extended-term osteoblast culture (≤10 mo) in a bioreactor based on the concept of simultaneous growth and dialysis captures the full continuum of bone development otherwise inaccessible with conventional cell culture, resulting in an in vitro model of osteogenesis and a source of terminally differentiated osteocytes that does not require demineralization of fully formed bone.     

三维回转骨细胞条件培养基对成骨细胞功能的调节作用

骨细胞是骨组织中主要的力学感受器.研究失重条件下骨细胞对效应细胞的调控作用对于揭示失重引起的骨丢失机制具有重要意义.本研究拟采用三维回转器模拟失重,探讨模拟失重骨细胞条件培养基(RCM)对成骨功能的调节作用.小鼠骨细胞系MLO-Y4三维回转培养72h后,收集回转条件培养基(RCM)和未回转对照组的条件培养基(CCM),用四甲基偶氮唑盐比色(MTT)法、对硝基苯磷酸(pNPP)法和流式细胞术(FCM)分别检测RCM对小鼠成骨样细胞系MC3T3-E1增殖、周期及细胞分泌碱性磷酸酶(ALP)活性的影响.采用RT-PCR方法检测RCM对MC3T3-E1成骨相关基因表达的影响.结果显示,三维随机回转72h后的MLO-Y4RCM可促进MC3T3-E1增殖:条件培养基培养MC3T3-E124h和48h后,50%RCM组比CCM组分别增加了1.62和1.60倍,差异显著(*P0.05),培养72h后,100%RCM组比CCM组增加了1.69倍,差异显著(*P0.05);细胞周期检测结果表明,条件培养基培养24、48和72h后,RCM组部分恢复CCM引起的MC3T3-E1细胞周期阻滞;MC3T3-E1的ALP活性在RCM组和CCM组之间无差异;RT-PCR检测结果表明,100%MLO-Y4条件培养基培养MC3T3-E148h后,降低了成骨相关基因ALP、Runx2、OPN、OC的表达.差异显著(*P0.05,**P0.01,***P0.001).实验结果表明,三维随机回转模拟失重培养骨细胞72h后的条件培养基促进了成骨细胞增殖,抑制了成骨相关基因表达.     

TGF-β-activated kinase 1 mediates mechanical stress-induced IL-6 expression in osteoblasts

Mechanical stress plays a key role in bone remodeling. Previous studies showed that loading of mechanical stretch induces a rapid Ca²⁺ influx and subsequent activation of stress-activated protein kinase pathways in osteoblasts. However, the activation mechanism and its significance in bone remodeling have not been fully elucidated. Here we show that TAK1 MAPKKK was activated by cyclic stretch loading of MC3T3-E1 cells. Knockdown of TAK1 attenuated the stretch-induced activation of JNK, p38, and NF-κB. Extracellular (EGTA) or intracellular (BAPTA/AM) Ca²⁺ chelator prevented the stretch-induced activation of TAK1. Activation of TAK1 and its associated downstream signaling pathways were also suppressed by CaMKII inhibitors (KN-93 and KN-62). Furthermore, TAK1-mediated downstream pathways cooperatively induced the expression of IL-6 mRNA in the stretched MC3T3-E1 cells. We also confirmed that TAK1 mediates cyclic stretch-induced IL-6 protein synthesis in the cells using immunoblotting and ELISA. Finally, stretch loading of murine primary osteoblasts induced the expression of IL-6 mRNA via TAK1. Collectively, these data suggest that stretch-dependent Ca²⁺ influx activates TAK1 via CaMKII, leading to the enhanced expression of IL-6 through JNK, p38, and NF-κB pathways in osteoblasts.     

Increased Expression of Matrix Extracellular Phosphoglycoprotein (MEPE) in Cortical Bone of the Rat Tibia after Mechanical Loading: Identification by Oligonucleotide Microarray

Skeletal integrity in humans and animals is maintained by daily mechanical loading. It has been widely accepted that osteocytes function as mechanosensors. Many biochemical signaling molecules are involved in the response of osteocytes to mechanical stimulation. The aim of this study was to identify genes involved in the translation of mechanical stimuli into bone formation. The four-point bending model was used to induce a single period of mechanical loading on the right tibia, while the contra lateral left tibia served as control. Six hours after loading, the effects of mechanical loading on gene-expression were determined with microarray analysis. Protein expression of differentially regulated genes was evaluated with immunohistochemistry. Nine genes were found to exhibit a significant differential gene expression in LOAD compared to control. MEPE, Garnl1, V2R2B, and QFG-TN1 olfactory receptor were up-regulated, and creatine kinase (muscle form), fibrinogen-B beta-polypeptide, monoamine oxidase A, troponin-C and kinesin light chain-C were down-regulated. Validation with real-time RT-PCR analysis confirmed the up-regulation of MEPE and the down-regulation of creatine kinase (muscle form) and troponin-C in the loaded tibia. Immunohistochemistry showed that the increase of MEPE protein expression was already detectable six hours after mechanical loading. In conclusion, these genes probably play a role during translation of mechanical stimuli six hours after mechanical loading. The modulation of MEPE expression may indicate a connection between bone mineralization and bone formation after mechanical stimulation.     

Shear stress inhibits while disuse promotes osteocyte apoptosis

Cell apoptosis operates as an organizing mechanism in biology in addition to removing effete cells. We have recently proposed that during bone remodeling, osteocyte apoptosis steers osteonal alignment in relation to mechanical loading of the whole bone [J. Biomech. 36 (2003) 1453]. Here we present evidence that osteocyte apoptosis in cell culture is modulated by shear stress. Under static culture conditions, serum starved osteocytes exposed phosphatidylserine (PS) on their cell membrane 6x more often than periosteal fibroblasts and 3x more often than osteoblasts. Treatment with shear stress reduced the number of osteocytes that exposed PS by 90%, but did not affect the other cell types. Fluid shear stress of increasing magnitude, dose-dependently stimulated Bcl-2 mRNA expression in human bone cells, while shear stress did not change Bax expression. These data suggest that disuse promotes osteocyte apoptosis, while mechanical stimulation by fluid shear stress promotes osteocyte survival, by modulating the Bcl-2/Bax expression ratio.     

Mechanical-Stretch of C2C12 Myoblasts Inhibits Expression of Toll-Like Receptor 3 (TLR3) and of Autoantigens Associated with Inflammatory Myopathies

Recent studies in patients suffering from inflammatory autoimmune myopathies suggested that moderate exercise training improves or at least stabilizes muscle strength and function without inducing disease flares. However, the precise mechanisms involved in this beneficial effect have not been extensively studied. Here we used a model of in vitro stretched C2C12 myoblasts to investigate whether mechanical stretch could influence myoblast proliferation or the expression of proinflammatory genes. Our results demonstrated that cyclic mechanical stretch stimulated C2C12 cell cycling and early up-regulation of the molecules related to mechanical-stretch pathway in muscle (calmodulin, nNOS, MMP-2, HGF and c-Met). Unexpectedly, mechanical stretch also reduced the expression of TLR3 and of proteins known to represent autoantigens in inflammatory autoimmune myopathies (Mi-2, HRS, DNA-PKcs, U1-70). Interestingly, stimulation or inhibition of calmodulin, NOS, HGF or c-Met molecules in vitro affected the expression of autoantigens and TLR3 proteins confirming their role in the inhibition of autoantigens and TLR3 during mechanical stretch. Overall, this study demonstrates for the first time that mechanical stretch could be beneficial by reducing expression of muscle autoantigens and of pro-inflammatory TLR3 and may provide new insight to understand how resistance training can reduce the symptoms associated with myositis.     

Osteocytes but not osteoblasts directly build mineralized bone structures

Bone-forming osteoblasts have been a cornerstone of bone biology for more than a century. Most research toward bone biology and bone diseases center on osteoblasts. Overlooked are the 90% of bone cells, called osteocytes. This study aims to test the hypothesis that osteocytes but not osteoblasts directly build mineralized bone structures, and that defects in osteocytes lead to the onset of hypophosphatemia rickets. The hypothesis was tested by developing and modifying multiple imaging techniques, including both in vivo and in vitro models plus two types of hypophosphatemia rickets models (Dmp1-null and Hyp, Phex mutation mice), and Dmp1-Cre induced high level of β-catenin models. Our key findings were that osteocytes (not osteoblasts) build bone similar to the construction of a high-rise building, with a wire mesh frame (i.e., osteocyte dendrites) and cement (mineral matrices secreted from osteocytes), which is a lengthy and slow process whose mineralization direction is from the inside toward the outside. When osteoblasts fail to differentiate into osteocytes but remain highly active in Dmp-1-null or Hyp mice, aberrant and poor bone mineralization occurs, caused by a sharp increase in Wnt-β-catenin signaling. Further, the constitutive expression of β-catenin in osteocytes recaptures a similar osteomalacia phenotype as shown in Dmp1 null or Hyp mice. Thus, we conclude that osteocytes directly build bone, and osteoblasts with a short life span serve as a precursor to osteocytes, which challenges the existing dogma.     

Activation of HIFa Pathway in Mature Osteoblasts Disrupts the Integrity of the Osteocyte/Canalicular Network

The hypoxia-inducible factors (HIFs), HIF-1α and HIF-2α, are the central mediators of the homeostatic response that enables cells to survive and differentiate in low-oxygen conditions. Previous studies indicated that disruption of the von Hippel-Lindau gene (Vhl) coincides with the activation of HIFα signaling. Here we show that inactivation of Vhl in mature osteoblasts/osteocytes induces their apoptosis and disrupts the cell/canalicular network. VHL-deficient (ΔVHL) mice exhibited a significantly increased cortical bone area resulting from enhanced proliferation and osteogenic differentiation of the bone marrow stromal cells (BMSCs) by inducing the expression of β-catenin in the BMSC. Our data suggest that the VHL/HIFα pathway in mature osteoblasts/osteocytes plays a critical role in the bone cell/canalicular network and that the changes of osteocyte morphology/function and cell/canalicular network may unleash the bone formation, The underlying mechanism of which was the accumulation of β-catenin in the osteoblasts/osteoprogenitors of the bone marrow.     

Stretch-Induced Stress Fiber Remodeling and the Activations of JNK and ERK Depend on Mechanical Strain Rate,but Not FAK

Background

Cells within tissues are subjected to mechanical forces caused by extracellular matrix deformation. Cells sense and dynamically respond to stretching of the matrix by reorienting their actin stress fibers and by activating intracellular signaling proteins, including focal adhesion kinase (FAK) and the mitogen-activated proteins kinases (MAPKs). Theoretical analyses predict that stress fibers can relax perturbations in tension depending on the rate of matrix strain. Thus, we hypothesized stress fiber organization and MAPK activities are altered to an extent dependent on stretch frequency.

Principal Findings

Bovine aortic endothelial cells and human osteosarcoma cells expressing GFP-actin were cultured on elastic membranes and subjected to various patterns of stretch. Cyclic stretching resulted in strain rate-dependent increases in stress fiber alignment, cell retraction, and the phosphorylation of the MAPKs JNK, ERK and p38. Transient step changes in strain rate caused proportional transient changes in the levels of JNK and ERK phosphorylations without affecting stress fiber organization. Disrupting stress fiber contractile function with cytochalasin D or Y27632 decreased the levels of JNK and ERK phosphorylation. Previous studies indicate that FAK is required for stretch-induced cell alignment and MAPK activations. However, cyclic uniaxial stretching induced stress fiber alignment and the phosphorylation of JNK, ERK and p38 to comparable levels in FAK-null and FAK-expressing mouse embryonic fibroblasts.

Conclusions

These results indicate that cyclic stretch-induced stress fiber alignment, cell retraction, and MAPK activations occur as a consequence of perturbations in fiber strain. These findings thus shed new light into the roles of stress fiber relaxation and reorganization in maintenance of tensional homeostasis in a dynamic mechanical environment.     

Extracellular NO signalling from a mechanically stimulated osteocyte

Bone remodelling is a dynamic process that requires the coordinated interaction of osteocytes, osteoblasts, and osteoclasts, collaborating in basic multicellular units (BMUs). Communication between these cells can be by extracellular soluble molecules as well as directly propagating intercellular signalling molecules. Key to the understanding of bone remodelling is osteocyte mechanosensing and chemical signalling to the surrounding cells, since osteocytes are believed to be the mechanosensors of bone, responding to mechanical stresses. Nitric oxide (NO) is an important parameter to study osteocyte activation following mechanical loading. It is a small short-lived molecule, which makes its real-time, quantitative monitoring difficult. However, recently we demonstrated that DAR-4M AM chromophore can be used for real-time quantitative monitoring of intracellular NO production in individual cells following mechanical loading. Here we studied if a single mechanically stimulated osteocyte communicates with, and thus activates its surrounding cells via extracellular soluble factors. We monitored quantitatively intracellular NO production in the stimulated osteocyte and in its surrounding osteocytes, which were not interconnected. Mechanical stimulation by microneedle of a single-MLO-Y4 osteocyte-like cell upregulated the average intracellular NO production by 94% in the stimulated cell, and by 31-150% in the surrounding osteocytes. In conclusion, a single osteocyte can disseminate a mechanical stimulus to its surrounding osteocytes via extracellular soluble signalling factors. This reinforces the putative mechanosensory role of osteocytes, and demonstrates a possible mechanism by which a single mechanically stimulated osteocyte can communicate with other cells in a BMU, which might help to better understand the intricacies of intercellular interactions in BMUs and thus bone remodelling.     

Osteocytes,not Osteoblasts or Lining Cells,are the Main Source of the RANKL Required for Osteoclast Formation in Remodeling Bone

The cytokine receptor activator of nuclear factor kappa B ligand (RANKL), encoded by the Tnfsf11 gene, is essential for osteoclastogenesis and previous studies have shown that deletion of the Tnfsf11 gene using a Dmp1-Cre transgene reduces osteoclast formation in cancellous bone by more than 70%. However, the Dmp1-Cre transgene used in those studies leads to recombination in osteocytes, osteoblasts, and lining cells making it unclear whether one or more of these cell types produce the RANKL required for osteoclast formation in cancellous bone. Because osteoblasts, osteocytes, and lining cells have distinct locations and functions, distinguishing which of these cell types are sources of RANKL is essential for understanding the orchestration of bone remodeling. To distinguish between these possibilities, we have now created transgenic mice expressing the Cre recombinase under the control of regulatory elements of the Sost gene, which is expressed in osteocytes but not osteoblasts or lining cells in murine bone. Activity of the Sost-Cre transgene in osteocytes, but not osteoblast or lining cells, was confirmed by crossing Sost-Cre transgenic mice with tdTomato and R26R Cre-reporter mice, which express tdTomato fluorescent protein or LacZ, respectively, only in cells expressing the Cre recombinase or their descendants. Deletion of the Tnfsf11 gene in Sost-Cre mice led to a threefold decrease in osteoclast number in cancellous bone and increased cancellous bone mass, mimicking the skeletal phenotype of mice in which the Tnfsf11 gene was deleted using the Dmp1-Cre transgene. These results demonstrate that osteocytes, not osteoblasts or lining cells, are the main source of the RANKL required for osteoclast formation in remodeling cancellous bone.     

Suppressed nuclear envelope proteins activate autophagy of vascular smooth muscle cells during cyclic stretch application

Dysfunctions of vascular smooth muscle cells (VSMCs) play crucial roles in vascular remodeling in hypertension, which correlates with pathologically elevated cyclic stretch due to increased arterial pressure. Recent researches reported that autophagy, a life-sustaining process, was increased in hypertension. However, the mechanobiological mechanism of VSMC autophagy and its potential roles in vascular remodeling are still unclear. Using renal hypertensive rats in vivo and FX5000 stretch application Unit in vitro, the autophagy of VSMCs was detected. The results showed that LC3II remarkably enhanced in hypertensive rats and 15% cyclic stretch (mimic the pathologically increased mechanical stretch in hypertension), and the activity of mammalian target of rapamycin (mTOR) was suppressed in 15% cyclic stretch. Administration of autophagy inhibitors, bafilomycin A1 and chloroquine, repressed VSMC proliferation efficiently, but did not affect the degradation of two important nuclear envelope (NE) proteins, lamin A/C and emerin. Using RNA interference to decline the expression of lamin A/C and emerin, respectively, we discovered that autophagy was upregulated under both static and 5% cyclic stretch conditions, accompanying with the decreased mTOR activity. During 15% cyclic stretch application, mTOR inhibition was responsible for autophagy elevation. Chloroquine administration in vivo inhibited the expression of PCNA (marker of proliferation) of abdominal aorta in hypertensive rats. Altogether, these results demonstrated that pathological cyclic stretch suppresses the expression of lamin A/C and emerin which subsequently represses mTOR pathway so as to induce autophagy activation. Blocking autophagic flux may be a practicable way to relieve the pathological vascular remodeling in hypertensive.