Anti-Inflammatory and Anti-Thrombogenic Properties of Arterial Elastic Laminae.

Elastic laminae, an elastin-based, layered extracellular matrix structure in the media of arteries, can inhibit leukocyte adhesion and vascular smooth muscle cell proliferation and migration, exhibiting anti-inflammatory and anti-thrombogenic properties. These properties prevent inflammatory and thrombogenic activities in the arterial media, constituting a mechanism for the maintenance of the structural integrity of the arterial wall in vascular disorders. The biological basis for these properties is the elastin-induced activation of inhibitory signaling pathways, involving the inhibitory cell receptor signal regulatory protein α (SIRPα) and Src homology 2 domain-containing protein tyrosine phosphatase 1 (SHP1). The activation of these molecules causes deactivation of cell adhesion- and proliferation-regulatory signaling mechanisms. Given such anti-inflammatory and anti-thrombogenic properties, elastic laminae and elastin-based materials have potential for use in vascular reconstruction.

Hepatic cell mobilization for protection against ischemic myocardial injury.

The heart is capable of activating protective mechanisms in response to ischemic injury to support myocardial survival and performance. These mechanisms have been recognized primarily in the ischemic heart, involving paracrine signaling processes. Here, we report a distant cardioprotective mechanism involving hepatic cell mobilization to the ischemic myocardium in response to experimental myocardial ischemia-reperfusion (MI-R) injury. A parabiotic mouse model was generated by surgical skin-union of two mice and used to induce bilateral MI-R injury with unilateral hepatectomy, establishing concurrent gain- and loss-of-hepatic cell mobilization conditions. Hepatic cells, identified based on the cell-specific expression of enhanced YFP, were found in the ischemic myocardium of parabiotic mice with intact liver (0.2 ± 0.1%, 1.1 ± 0.3%, 2.7 ± 0.6, and 0.7 ± 0.4% at 1, 3, 5, and 10 days, respectively, in reference to the total cell nuclei), but not significantly in the ischemic myocardium of parabiotic mice with hepatectomy (0 ± 0%, 0.1 ± 0.1%, 0.3 ± 0.2%, and 0.08 ± 0.08% at the same time points). The mobilized hepatic cells were able to express and release trefoil factor 3 (TFF3), a protein mitigating MI-R injury as demonstrated in TFF3-/- mice (myocardium infarcts 17.6 ± 2.3%, 20.7 ± 2.6%, and 15.3 ± 3.8% at 1, 5, and 10 days, respectively) in reference to wildtype mice (11.7 ± 1.9%, 13.8 ± 2.3%, and 11.0 ± 1.8% at the same time points). These observations suggest that MI-R injury can induce hepatic cell mobilization to support myocardial survival by releasing TFF3.

Changes in Muscle Stress and Sarcomere Adaptation in Mice Following Ischemic Stroke.

While abnormal muscle tone has been observed in people with stroke, how these changes in muscle tension affect sarcomere morphology remains unclear. The purpose of this study was to examine time-course changes in passive muscle fiber tension and sarcomeric adaptation to these changes post-ischemic stroke in a mouse model by using a novel in-vivo force microscope. Twenty-one mice were evenly divided into three groups based on the time point of testing: 3 days (D3), 10 days (D10), and 20 days (D20) following right middle cerebral artery ligation. At each testing time, the muscle length, width, and estimated volume of the isolated soleus muscle were recorded, subsequently followed by in-vivo muscle tension and sarcomere length measurement. The mass of the soleus muscle was measured at the end of testing to calculate muscle density. Two-way ANOVA with repeated measures was used to examine the differences in each of the dependent variable among the three time-point groups and between the two legs. The passive muscle stress of the impaired limbs in the D3 group (27.65 ± 8.37 kPa) was significantly lower than the less involved limbs (42.03 ± 18.61 kPa; p = 0.05) and the impaired limbs of the D10 (48.92 ± 14.73; p = 0.03) and D20 (53.28 ± 20.54 kPa; p = 0.01) groups. The soleus muscle density of the impaired limbs in the D3 group (0.69 ± 0.12 g/cm3) was significantly lower than the less involved limbs (0.80 ± 0.09 g/cm3; p = 0.04) and the impaired limbs of the D10 (0.87 ± 0.12 g/cm3; p = 0.02) and D20 (1.00 ± 0.14 g/cm3; p < 0.01) groups. The D3 group had a shorter sarcomere length (2.55 ± 0.26 µm) than the D10 (2.83 ± 0.20 µm; p = 0.03) and D20 group (2.81 ± 0.15 µm; p = 0.04). These results suggest that, while ischemic stroke may cause considerable changes in muscle tension and stress, sarcomere additions under increased mechanical loadings may be absent or disrupted post-stroke, which may contribute to muscle spasticity and/or joint contracture commonly observed in patients following stroke.

Cardiac Protective Engineering.

Cardioprotective engineering is an emerging bioengineering discipline aiming to develop engineering strategies to optimize cardioprotective actions against cardiac injuries and disorders. Although there exist innate cardioprotective mechanisms capable of supporting cardiomyocyte survival in response to an insult, not all these mechanisms are optimized in promptness and effectiveness, suggesting the necessity of cardioprotective engineering. Various cardioprotective strategies have been developed and used in experimental and clinical investigations; however, few of these strategies have exerted a significant clinical impact. There are two major challenges in cardioprotective engineering-understanding the innate cardioprotective mechanisms and developing engineering strategies for precise control of the types, levels, timing, and coordination of cardioprotective actions to facilitate recovery from injuries and disorders. Understanding the innate mechanisms is the foundation for developing cardioprotective engineering strategies. Here, ischemic myocardial injury is used as an example to demonstrate the concept of cardioprotective engineering.

Activation of the Renin-Angiotensin System Promotes Colitis Development.

The renin-angiotensin system (RAS) plays pathogenic roles in renal and cardiovascular disorders, but whether it is involved in colitis is unclear. Here we show that RenTgMK mice that overexpress active renin from the liver developed more severe colitis than wild-type controls. More than 50% RenTgMK mice died whereas all wild-type mice recovered. RenTgMK mice exhibited more robust mucosal TH17 and TH1/TH17 responses and more profound colonic epithelial cell apoptosis compared to wild-type controls. Treatment with aliskiren (a renin inhibitor), but not hydralazine (a smooth muscle relaxant), ameliorated colitis in RenTgMK mice, although both drugs normalized blood pressure. Chronic infusion of angiotensin II into wild-type mice mimicked the severe colitic phenotype of RenTgMK mice, and treatment with losartan [an angiotensin type 1 receptor blocker (ARB)] ameliorated colitis in wild-type mice, confirming a colitogenic role for the endogenous RAS. In human biopsies, pro-inflammatory cytokines were suppressed in patients with inflammatory bowel disease who were on ARB therapy compared to patients not receiving ARB therapy. These observations demonstrate that activation of the RAS promotes colitis in a blood pressure independent manner. Angiotensin II appears to drive colonic mucosal inflammation by promoting intestinal epithelial cell apoptosis and mucosal TH17 responses in colitis development.

Chronic Activation of the Renin-Angiotensin System Induces Lung Fibrosis.

Pulmonary fibrosis is a serious lung disorder that can lead to respiratory failure. Here we show that transgenic mice expressing active renin from the liver (RenTgMK) developed progressive pulmonary fibrosis leading to impaired pulmonary function. Histological analyses revealed a marked increase in extracellular matrix (ECM) deposition and decrease in alveolar size in the lungs of RenTgMK mice compared to wild-type (WT) littermates, accompanied with increased expression of ECM proteins and fibrogenic factors. The increase in lung fibrosis led to a substantial decrease in respiratory system compliance. Two-week treatment with aliskiren (renin inhibitor) or losartan (AT1 antagonist) ameliorated pulmonary ECM deposition, blocked the induction of ECM proteins and fibrogenic factors and improved respiratory compliance in RenTgMK mice, confirming a critical role of the renin-Ang II-AT1 cascade in promoting pulmonary fibrogenesis. However, when RenTgMK mice were treated with hydralazine (a smooth muscle relaxant), the blood pressure was normalized but the lung fibrotic abnormalities, fibrogenic gene induction and pulmonary elasticity were not corrected. Moreover, intratracheal instillation of lipopolysaccharide induced more severe lung injury in RenTgMK mice compared to WT littermates. These observations demonstrate that the renin-angiotensin system is a key mediator of lung fibrosis, and its pro-fibrotic effect is independent of blood pressure.

Fabrication and Short-Term in Vivo Performance of a Natural Elastic Lamina-Polymeric Hybrid Vascular Graft.

Although significant advances have been made in the development of artificial vascular grafts, small-diameter grafts still suffer from excessive platelet activation, thrombus formation, smooth muscle cell intimal hyperplasia, and high occurrences of restenosis. Recent discoveries demonstrating the excellent blood-contacting properties of the natural elastic lamina have raised the possibility that an acellular elastic lamina could effectively serve as a patent blood-contacting surface in engineered vascular grafts. However, the elastic lamina alone lacks the requisite mechanical properties to function as a viable vascular graft. Here, we have screened a wide range of biodegradable and biostable medical-grade polymers for their ability to adhere to the outer surface of the elastic lamina and allow cellular repopulation following engraftment in the rat abdominal aorta. We demonstrate a novel method for the fabrication of elastic lamina-polymeric hybrid small-diameter vascular grafts and identify poly(ether urethane) (PEU 1074A) as ideal for this purpose. In vivo results demonstrate graft patency over 21 days, with low thrombus formation, mild inflammation, and the general absence of smooth muscle cell hyperplasia on the graft's luminal surface. The results provide a new direction for developing small-diameter vascular grafts that are mass-producible, shelf-stable, and universally compatible due to a lack of immune response and inhibit the in-graft restenosis response that is common to nonautologous materials.

Trans-system mechanisms against ischemic myocardial injury.

A mammalian organism possesses a hierarchy of naturally evolved protective mechanisms against ischemic myocardial injury at the molecular, cellular, and organ levels. These mechanisms comprise regional protective processes, including upregulation and secretion of paracrine cell-survival factors, inflammation, angiogenesis, fibrosis, and resident stem cell-based cardiomyocyte regeneration. There are also interactive protective processes between the injured heart, circulation, and selected remote organs, defined as trans-system protective mechanisms, including upregulation and secretion of endocrine cell-survival factors from the liver and adipose tissue as well as mobilization of bone marrow, splenic, and hepatic cells to the injury site to mediate myocardial protection and repair. The injured heart and activated remote organs exploit molecular and cellular processes, including signal transduction, gene expression, cell proliferation, differentiation, migration, mobilization, and/or extracellular matrix production, to establish protective mechanisms. Both regional and trans-system cardioprotective mechanisms are mediated by paracrine and endocrine messengers and act in coordination and synergy to maximize the protective effect, minimize myocardial infarction, and improve myocardial function, ensuring the survival and timely repair of the injured heart. The concept of the trans-system protective mechanisms may be generalized to other organ systems-injury in one organ may initiate regional as well as trans-system protective responses, thereby minimizing injury and ensuring the survival of the entire organism. Selected trans-system processes may serve as core protective mechanisms that can be exploited by selected organs in injury. These naturally evolved protective mechanisms are the foundation for developing protective strategies for myocardial infarction and injury-induced disorders in other organ systems.

Trefoil factor 3 as an endocrine neuroprotective factor from the liver in experimental cerebral ischemia/reperfusion injury.

Cerebral ischemia, while causing neuronal injury, can activate innate neuroprotective mechanisms, minimizing neuronal death. In this report, we demonstrate that experimental cerebral ischemia/reperfusion injury in the mouse causes upregulation of the secretory protein trefoil factor 3 (TFF3) in the hepatocyte in association with an increase in serum TFF3. Partial hepatectomy (~60% liver resection) immediately following cerebral injury significantly lowered the serum level of TFF3, suggesting a contribution of the liver to the elevation of serum TFF3. Compared to wild-type mice, TFF3(-/-) mice exhibited a significantly higher activity of caspase 3 and level of cell death in the ischemic cerebral lesion, a larger fraction of cerebral infarcts, and a smaller fraction of the injured cerebral hemisphere, accompanied by severer forelimb motor deficits. Intravenous administration of recombinant TFF3 reversed changes in cerebral injury and forelimb motor function due to TFF3 deficiency. These observations suggest an endocrine neuroprotective mechanism involving TFF3 from the liver in experimental cerebral ischemia/reperfusion injury.

Endocrine protection of ischemic myocardium by FGF21 from the liver and adipose tissue.

Myocardial ischemia, while causing cardiomyocyte injury, can activate innate protective processes, enhancing myocardial tolerance to ischemia. Such processes are present in not only the heart, but also remote organs. In this investigation, we demonstrated a cardioprotective process involving FGF21 from the liver and adipose tissue. In response to myocardial ischemia/reperfusion injury in the mouse, FGF21 was upregulated and released from the hepatic cells and adipocytes into the circulation and interacted with FGFR1 in cardiomyocytes under the mediation of the cell membrane protein ß-Klotho, inducing FGFR1 phosphorylation. This action caused phosphorylation of the signaling molecules PI3K p85, Akt1, and BAD, thereby reducing caspase 3 activity, cell death, and myocardial infarction in association with improvement of myocardial function. These observations suggest that FGF21 is upregulated and released from the liver and adipose tissue in myocardial injury, contributing to myocardial protection by the mediation of the FGFR1/ß-Klotho-PI3K-Akt1-BAD signaling network.

Cardioprotective proteins upregulated in the liver in response to experimental myocardial ischemia.

Myocardial ischemia (MI) activates innate cardioprotective mechanisms, enhancing cardiomyocyte tolerance to ischemia. Here, we report a MI-activated liver-dependent mechanism for myocardial protection. In response to MI in the mouse, hepatocytes exhibited 6- to 19-fold upregulation of genes encoding secretory proteins, including α-1-acid glycoprotein (AGP)2, bone morphogenetic protein-binding endothelial regulator (BMPER), chemokine (C-X-C motif) ligand 13, fibroblast growth factor (FGF)21, neuregulin (NRG)4, proteoglycan 4, and trefoil factor (TFF)3. Five of these proteins, including AGP2, BMPER, FGF21, NRG4, and TFF3, were identified as cardioprotective proteins since administration of each protein significantly reduced the fraction of myocardial infarcts (37 ± 9%, 34 ± 7%, 32 ± 8%, 39 ± 6%, and 31 ± 7%, respectively, vs. 48 ± 7% for PBS at 24 h post-MI). The serum level of the five proteins elevated significantly in association with protein upregulation in hepatocytes post-MI. Suppression of a cardioprotective protein by small interfering (si)RNA-mediated gene silencing resulted in a significant increase in the fraction of myocardial infarcts, and suppression of all five cardioprotective proteins with siRNAs further intensified myocardial infarction. While administration of a single cardioprotective protein mitigated myocardial infarction, administration of all five proteins furthered the beneficial effect, reducing myocardial infarct fractions from PBS control values from 46 ± 6% (5 days), 41 ± 5% (10 days), and 34 ± 4% (30 days) to 35 ± 5%, 28 ± 5%, and 24 ± 4%, respectively. These observations suggest that the liver contributes to cardioprotection in MI by upregulating and releasing protective secretory proteins. These proteins may be used for the development of cardioprotective agents.

Vitamin D receptor signaling inhibits atherosclerosis in mice.

Although vitamin D has been implicated in cardiovascular protection, few studies have addressed the role of vitamin D receptor (VDR) in atherosclerosis. Here we investigate the effect of inactivation of the VDR signaling on atherogenesis and the antiatherosclerotic mechanism of vitamin D. Low density lipoprotein receptor (LDLR)(-/-)/VDR(-/-) mice exhibited site-specific accelerated atherogenesis, accompanied by increases in adhesion molecules and proinflammatory cytokines in the aorta and cholesterol influx in macrophages. Macrophages showed marked renin up-regulation in the absence of VDR, and inhibition of renin by aliskiren reduced atherosclerosis in LDLR(-/-)/VDR(-/-) mice, suggesting that the renin-angiotensin system (RAS) promotes atherosclerosis in the absence of VDR. LDLR(-/-) mice receiving LDLR(-/-)/VDR(-/-) BMT developed larger lesions than LDLR(-/-) BMT controls. Moreover, LDLR(-/-) mice receiving Rag-1(-/-)/VDR(-/-) BMT, which were unable to generate functional T and B lymphocytes, still had more severe atherosclerosis than Rag-1(-/-) BMT controls, suggesting a critical role of macrophage VDR signaling in atherosclerotic suppression. Aliskiren treatment eliminated the difference in lesions between Rag-1(-/-)/VDR(-/-) BMT and Rag-1(-/-) BMT recipients, indicating that local RAS activation in macrophages contributes to the enhanced atherogenesis seen in Rag-1(-/-)/VDR(-/-) BMT mice. Taken together, these observations provide evidence that macrophage VDR signaling, in part by suppressing the local RAS, inhibits atherosclerosis in mice.

Cardioprotective mechanisms activated in response to myocardial ischemia.

Myocardial ischemia, a disorder causing myocardial infarction and malfunction, can activate various adaptive mechanisms that protect cardiomyocytes from ischemic injury. During the early hours post myocardial ischemia, injured cardiac cells can release several molecules, including adenosine, opioids, and bradykinin, which promote myocardial survival by activating the G protein signaling pathways. During a later phase about several days, myocardial ischemia induces upregulation of growth factors and cytokines, including VEGF, ILGF, HGF, and SDF-1, in the injured myocardium, contributing to cardioprotection. In addition to the injured heart, the liver participates in cardioprotection. In response to myocardial ischemia, the liver upregulates and releases secretory proteins, including FGF21 and TFF3, both of which promote cardiomyocyte survival. The liver also provides a reservoir of hepatic cells that mobilize to the site of myocardial ischemia, potentially contributing to cardioprotection. Taken together, the early and late mechanisms act coordinately in a time-dependent manner, ensuring effective cardioprotection post myocardial infarction. Investigations on these innate cardioprotective mechanisms have provided insights into the development of cardioprotective strategies for treating myocardial infarction. In this article, the authors review the innate mechanisms of cardioprotection in myocardial ischemia.

Elastic laminae in vascular development and disease.

The activities of vascular cells, including adhesion, proliferation, and migration, are mediated by extracellular matrix components, including collagen matrix and elastic fibers or laminae. Whereas the collagen matrix stimulates vascular cell adhesion, proliferation, and migration, the elastic laminae inhibit these activities. Coordinated regulation of cell activities by these matrix components is an essential process for controlling the development and remodeling of the vascular system. This article summarizes recent development on the role of arterial elastic laminae in regulating the development of smooth muscle-like cells from bone marrow-derived progenitor cells as well as in mediating cell adhesion, proliferation, and migration with a focus on the molecular mechanisms and physiological significance.

Therapeutic effects of vitamin D analogs on cardiac hypertrophy in spontaneously hypertensive rats.

Vitamin D inhibits renin expression and blocks the compensatory induction of renin associated with the use of renin-angiotensin system inhibitors. Here we test the therapeutic effects of two commonly used vitamin D analogs and their combination with losartan on the development of left ventricular hypertrophy. One-month-old male spontaneously hypertensive rats were treated with vehicle, losartan, paricalcitol, doxercalciferol, a combination of losartan and paricalcitol, or a combination of losartan and doxercalciferol for 2 months. Blood pressure was markedly reduced by losartan, but not by paricalcitol or doxercalciferol alone. Echocardiograpy demonstrated a 65 to 80% reduction in left ventricular wall thickness with losartan, paricalcitol, or doxercalciferol monotherapy and almost complete prevention of left ventricular hypertrophy with the combination therapies. Attenuation of cardiac and cardiomyocyte hypertrophy, and suppression of atrial and brain natriuretic peptides, were most marked in the combination therapy groups. These changes were well correlated with left ventricular gene and microRNA expression profiles in the different treatment groups. Renal and cardiac renin expression was markedly increased in losartan-treated animals, but nearly normalized with combination therapy. The same vitamin D analogs suppressed plasma renin activity in patients receiving chronic hemodialysis. These data demonstrate that vitamin D analogs have potent antihypertrophic activity in part via suppression of renin in the kidney and heart, and combination of these analogs with losartan achieves much better therapeutic effects because of the blockade of the compensatory renin increase.

Characterization of spasticity in cerebral palsy: dependence of catch angle on velocity.

AIM: To evaluate spasticity under controlled velocities and torques in children with cerebral palsy (CP) using a manual spasticity evaluator. METHOD: The study involved 10 children with spastic CP (six males, four females; mean age 10 y 1 mo, SD 2 y 9 mo, range 7-16 y; one with quadriplegia, six with right hemiplegia, three with left hemiplegia; Gross Motor Function Classification System levels I [n=2], II [n=3], III [n=2], IV [n=2], and V [n=1]; Manual Ability Classification System levels II [n=5], III [n=4], and V [n=1]) and 10 typically developing participants (four males, six females; mean age 10 y 3 mo, SD 2 y 7 mo, range 7-15 y). Spasticity and catch angle were evaluated using joint position, resistance torque, and torque rate at velocities of 90 degrees, 180 degrees, and 270 degrees per second, controlled using real-time audio-visual feedback. Biomechanically, elbow range of motion (ROM), stiffness, and energy loss were determined during slow movement (30 degrees/s) and under controlled terminal torque. RESULTS: Compared with typically developing children, children with CP showed higher reflex-mediated torque (p<0.001) and the torque increased more rapidly with increasing velocity (p<0.001). Catch angle was dependent on velocity and occurred later with increasing velocity (p=0.005). Children with CP showed smaller ROM (p<0.05), greater stiffness (p<0.001), and more energy loss (p=0.003). INTERPRETATION: Spasticity with velocity dependence may also be position-dependent. The delayed catch angle at higher velocities indicates that the greater resistance felt by the examiner at higher velocities was also due to position change, because the joint was moved further to a stiffer position at higher velocities.

Liver cell-mediated alleviation of acute ischemic myocardial injury.

Cardiomyocyte injury occurs in myocardial ischemia, resulting in impairment of cardiac function. As the endogenous protective function of adult cardiomyocytes is limited, nonmyocytic cells may be activated to protect myocardium from ischemic injury. In this investigation, we demonstrated in a mouse model of myocardial ischemia that the liver was able to respond to myocardial ischemia to upregulate a number of genes encoding secreted proteins, mobilize its cells, and release cell contents into the circulatory system. These naturally occurring mechanisms suggested a possible cardioprotective role for myocardial ischemia-conditioned liver cells and inspired us to develop cardioprotective therapies based on these mechanisms. We demonstrated that administration of liver cell extract derived from myocardial ischemic mice, but not sham control mice, resulted in a significant reduction in acute myocardial infarction as well as the density of TUNEL+ cells in ischemic myocardium compared to administration of PBS at 2, 6, 12, and 24 hrs. These observations suggest that liver cells may respond to myocardial ischemia to express cardioprotective factors, which may be identified and used for alleviating myocardial infarction.

Ultrasonic evaluations of Achilles tendon mechanical properties poststroke.

Spasticity, contracture, and muscle weakness are commonly observed poststroke in muscles crossing the ankle. However, it is not clear how biomechanical properties of the Achilles tendon change poststroke, which may affect functions of the impaired muscles directly. Biomechanical properties of the Achilles tendon, including the length and cross-sectional area, in the impaired and unimpaired sides of 10 hemiparetic stroke survivors were evaluated using ultrasonography. Elongation of the Achilles tendon during controlled isometric ramp-and-hold and ramping up then down contractions was determined using a block-matching method. Biomechanical changes in stiffness, Young's modulus, and hysteresis of the Achilles tendon poststroke were investigated by comparing the impaired and unimpaired sides of the 10 patients. The impaired side showed increased tendon length (6%; P = 0.04), decreased stiffness (43%; P < 0.001), decreased Young's modulus (38%; P = 0.005), and increased mechanical hysteresis (1.9 times higher; P < 0.001) compared with the unimpaired side, suggesting Achilles tendon adaptations to muscle spasticity, contracture, and/or disuse poststroke. In vivo quantitative characterizations of the tendon biomechanical properties may help us better understand changes of the calf muscle-tendon unit as a whole and facilitate development of more effective treatments.

Targeted vitamin D receptor expression in juxtaglomerular cells suppresses renin expression independent of parathyroid hormone and calcium.

Previously, we showed that vitamin D receptor gene knockout leads to hyperreninemia independent of calcium metabolism; however, the contribution of parathyroid hormone to renin upregulation remained unclear. Here we separated the role of vitamin D and parathyroid hormone in the regulation of renin expression in vivo by generating transgenic mice that overexpressed the human vitamin D receptor in renin-producing cells using the 4.1 kb Ren-1c gene promoter. Targeting of human vitamin D receptor to the juxtaglomerular cells of the mice was confirmed by immunohistochemistry. Renal renin mRNA levels and plasma renin activity were decreased in these transgenic mice by about 50% and 30%, respectively, with no significant change in blood pressure, calcium, or parathyroid hormone levels. Moreover using vitamin D receptor knockout mice, we found that expression of the human receptor in their juxtaglomerular cells reduced renin expression in these mice without affecting calcium or parathyroid hormone status. Our study shows that suppression of renin expression by 1,25-dihydroxyvitamin D in vivo is independent of parathyroid hormone and calcium.

Formation of smooth muscle alpha actin filaments in CD34+ bone marrow cells on arterial elastic laminae: potential role of SH2 domain-containing protein tyrosine phosphatase-1.

Arterial smooth muscle cells (SMCs) are present in the elastic lamina-containing media, suggesting that the elastic laminae may regulate the development of SMCs. Here, we investigated the role of elastic laminae in regulating the formation of SM alpha actin filaments in mouse CD34+ bone marrow cells and the role of a protein tyrosine phosphatase, SH2 domain-containing protein tyrosine phosphatase (SHP)-1, in the mediation of this process. Mouse CD34+ bone marrow cells were isolated by magnetic separation and used for assessing the influence of elastic laminae and collagen matrix on the formation of SM alpha actin filaments. CD34+ cells with transgenic SHP-1 knockout or siRNA-mediated SHP-1 knockdown were used to assess the role of SHP-1 in mediating the formation of SM alpha actin filaments. In cell culture tests, elastic laminae, but not collagen matrix, stimulated the formation of SM alpha actin filaments in CD34+ cells. The phosphatase SHP-1 mediated the stimulatory effect of elastic laminae. The interaction of CD34+ cells with elastic laminae, but not with collagen matrix, induced activation of SHP-1. The suppression of SHP-1 by transgenic SHP-1 knockout or siRNA-mediated SHP-1 knockdown significantly reduced the formation of SM alpha actin filaments in CD34+ cells cultured on elastic laminae. The in vitro observations were confirmed by using an in vivo model of implantation of elastic lamina and collagen matrix scaffolds into the aorta. These observations suggest that elastic laminae stimulate the formation of SM alpha actin filaments in CD34+ bone marrow cells and SHP-1 mediates the stimulatory effect of elastic laminae.