Linoleic acid blunts early osteoblast differentiation and impairs oxidative phosphorylation in vitro.

BACKGROUND: Linoleic acid (LNA), an essential polyunsaturated fatty acid (PUFA), plays a crucial role in cellular functions. However, excessive intake of LNA, characteristic of Western diets, can have detrimental effects on cells and organs. Human observational studies have shown an inverse relationship between plasma LNA concentrations and bone mineral density. The mechanism by which LNA impairs the skeleton is unclear, and there is a paucity of research on the effects of LNA on bone-forming osteoblasts. METHODS: The effect of LNA on osteoblast differentiation, cellular bioenergetics, and production of oxidized PUFA metabolites in vitro, was studied using primary mouse bone marrow stromal cells (BMSC) and MC3T3-E1 osteoblast precursors. RESULTS: LNA treatment decreased alkaline phosphatase activity, an early marker of osteoblast differentiation, but had no effect on committed osteoblasts or on mineralization by differentiated osteoblasts. LNA suppressed osteoblast commitment by blunting the expression of Runx2 and Osterix, key transcription factors involved in osteoblast differentiation, and other key osteoblast-related factors involved in bone formation. LNA treatment was associated with increased production of oxidized LNA- and arachidonic acid-derived metabolites and blunted oxidative phosphorylation, resulting in decreased ATP production. CONCLUSION: Our results show that LNA inhibited early differentiation of osteoblasts and this inhibitory effect was associated with increased production of oxidized PUFA metabolites that likely impaired energy production via oxidative phosphorylation.

Loss of Ptpmt1 limits mitochondrial utilization of carbohydrates and leads to muscle atrophy and heart failure in tissue-specific knockout mice.

While mitochondria in different tissues have distinct preferences for energy sources, they are flexible in utilizing competing substrates for metabolism according to physiological and nutritional circumstances. However, the regulatory mechanisms and significance of metabolic flexibility are not completely understood. Here, we report that the deletion of Ptpmt1, a mitochondria-based phosphatase, critically alters mitochondrial fuel selection - the utilization of pyruvate, a key mitochondrial substrate derived from glucose (the major simple carbohydrate), is inhibited, whereas the fatty acid utilization is enhanced. Ptpmt1 knockout does not impact the development of the skeletal muscle or heart. However, the metabolic inflexibility ultimately leads to muscular atrophy, heart failure, and sudden death. Mechanistic analyses reveal that the prolonged substrate shift from carbohydrates to lipids causes oxidative stress and mitochondrial destruction, which in turn results in marked accumulation of lipids and profound damage in the knockout muscle cells and cardiomyocytes. Interestingly, Ptpmt1 deletion from the liver or adipose tissue does not generate any local or systemic defects. These findings suggest that Ptpmt1 plays an important role in maintaining mitochondrial flexibility and that their balanced utilization of carbohydrates and lipids is essential for both the skeletal muscle and the heart despite the two tissues having different preferred energy sources.

Cells are powered by mitochondria, a group of organelles that produce chemical energy in the form of molecules called ATP. This energy is derived from the breakdown of carbohydrates, fats, and proteins. The number of mitochondria in a cell and the energy source they use to produce ATP varies depending on the type of cell. Mitochondria can also switch the molecules they use to produce energy when the cell is responding to stress or disease. The heart and the skeletal muscles ­ which allow movement ­ are two tissues that require large amounts of energy, but it remained unknown whether disrupting mitochondrial fuel selection affects how these tissues work. To answer these questions, Zheng, Li, Li et al. investigated the role of an enzyme found in mitochondria called Ptpmt1. Genetically deleting Ptpmt1 in the heart and skeletal muscle of mice showed that while the development of these organs was not affected, mitochondria in these cells switched from using carbohydrates to using fats as an energy source. Over time, this shift damaged both the mitochondria and the tissues, leading to muscle wasting, heart failure, and sudden death in the mice. This suggests that balanced use of carbohydrates and fats is essential for the muscles and heart. These findings imply that long-term use of medications that alter the fuel that mitochondria use may be detrimental to patients' health and could cause heart dysfunction. This may be important for future drug development, as well as informing decisions about medication taken in the clinic.

Cyclic Adenosine Monophosphate (cAMP)-Dependent Phosphodiesterase Inhibition Promotes Bone Anabolism Through CD8+ T Cell Wnt-10b Production in Mice.

Cyclic adenosine monophosphate (cAMP)-dependent phosphodiesterase (PDE) inhibitors such as pentoxifylline (PTX) suppress cAMP degradation and promote cAMP-dependent signal transduction. PDE inhibitors increase bone formation and bone mass in preclinical models and are used clinically to treat psoriatic arthritis by targeting inflammatory mediators including activated T cells. T cell activation requires two signals: antigen-dependent CD3-activation, which stimulates cAMP production; and CD28 co-stimulation, which downregulates cAMP-signaling, through PDE activation. PDE-inhibitors consequently suppress T cell activation by disrupting CD28 co-stimulation. Interestingly, we have reported that when CD8+ T cells are activated in the absence of CD28 co-stimulation, they secrete Wnt-10b, a bone anabolic Wnt ligand that promotes bone formation. In the present study, we investigated whether the bone anabolic activity of the PDE-inhibitor PTX, has an immunocentric basis, involving Wnt-10b production by CD8+ T cells. When wild-type (WT) mice were administered PTX, biochemical markers of both bone resorption and formation were significantly increased, with net bone gain in the axial skeleton, as quantified by micro-computed tomography (µCT). By contrast, PTX increased only bone resorption in T cell knockout (KO) mice, causing net bone loss. Reconstituting T cell-deficient mice with WT, but not Wnt-10b knockout (KO) CD8+ T cells, rescued bone formation and prevented bone loss. To study the role of cAMP signaling in Wnt-10b expression, reverse-transcription polymerase chain reaction (RT-PCR) and luciferase-reporter assays were performed using primary T cells. PDE inhibitors intensified Wnt-10b promoter activity and messenger RNA (mRNA) accumulation in CD3 and CD28 activated CD8+ T cells. In contrast, inhibiting the cAMP pathway mediators protein kinase A (PKA) and cAMP response element-binding protein (CREB), suppressed Wnt-10b expression by T cells activated in the absence of CD28 co-stimulation. In conclusion, the data demonstrate a key role for Wnt-10b production by CD8+ T cells in the bone anabolic response to PDE-inhibitors and reveal competing T cell-independent pro-resorptive properties of PTX, which dominate under T cell-deficient conditions. Selective targeting of CD8+ T cells by PDE inhibitors may be a beneficial approach for promoting bone regeneration in osteoporotic conditions. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Immune Reconstitution Bone Loss Exacerbates Bone Degeneration Due to Natural Aging in a Mouse Model.

BACKGROUND: Immune reconstitution bone loss (IRBL) is a common side-effect of antiretroviral therapy (ART) in people with human immunodeficiency virus (PWH). Immune reconstitution bone loss acts through CD4+ T-cell/immune reconstitution-induced inflammation and is independent of antiviral regimen. Immune reconstitution bone loss may contribute to the high rate of bone fracture in PWH, a cause of significant morbidity and mortality. Although IRBL is transient, it remains unclear whether bone recovers, or whether it is permanently denuded and further compounds bone loss associated with natural aging. METHODS: We used a validated IRBL mouse model involving T-cell reconstitution of immunocompromised mice. Mice underwent cross-sectional bone phenotyping of femur and/or vertebrae between 6 and 20 months of age by microcomputed tomography (µCT) and quantitative bone histomorphometry. CD4+ T cells were purified at 20 months to quantify osteoclastogenic/inflammatory cytokine expression. RESULTS: Although cortical IRBL in young animals recovered with time, trabecular bone loss was permanent and exacerbated skeletal decline associated with natural aging. At 20 months of age, reconstituted CD4+ T cells express enhanced osteoclastogenic cytokines including RANKL, interleukin (IL)-1ß, IL-17A, and tumor necrosis factor-α, consistent with elevated osteoclast numbers. CONCLUSIONS: Immune reconstitution bone loss in the trabecular compartment is permanent and further exacerbates bone loss due to natural aging. If validated in humans, interventions to limit IRBL may be important to prevent fractures in aging PWH.

Overexpression of myeloid angiotensin-converting enzyme (ACE) reduces atherosclerosis.

BACKGROUND: Macrophages are ubiquitous in all stages of atherosclerosis, exerting tremendous impact on lesion progression and plaque stability. Because macrophages in atherosclerotic plaques express angiotensin-converting enzyme (ACE), current dogma posits that local myeloid-mediated effects worsen the disease. In contrast, we previously reported that myeloid ACE overexpression augments macrophage resistance to various immune challenges, including tumors, bacterial infection and Alzheimer's plaque deposition. Here, we sought to assess the impact of myeloid ACE on atherosclerosis. METHODS: A mouse model in which ACE is overexpressed in myelomonocytic lineage cells, called ACE10, was generated and sequentially crossed with ApoE-deficient mice to create ACE10/10ApoE-/- (ACE10/ApoE). Control mice were ACEWT/WTApoE-/- (WT/ApoE). Atherosclerosis was induced using an atherogenic diet alone, or in combination with unilateral nephrectomy plus deoxycorticosterone acetate (DOCA) salt for eight weeks. RESULTS: With an atherogenic diet alone or in combination with DOCA, the ACE10/ApoE mice showed significantly less atherosclerotic plaques compared to their WT/ApoE counterparts (p < 0.01). When recipient ApoE-/- mice were reconstituted with ACE10/10 bone marrow, these mice showed significantly reduced lesion areas compared to recipients reconstituted with wild type bone marrow. Furthermore, transfer of ACE-deficient bone marrow had no impact on lesion area. CONCLUSION: Our data indicate that while myeloid ACE may not be required for atherosclerosis, enhanced ACE expression paradoxically reduced disease progression.

Reduced bone formation in males and increased bone resorption in females drive bone loss in hemophilia A mice.

Hemophilia A (HA), a rare X-linked recessive genetic disorder caused by insufficient blood clotting factor VIII, leaves affected individuals susceptible to spontaneous and traumatic hemorrhage. Although males generally exhibit severe symptoms, due to variable X inactivation, females can also be severely impacted. Osteoporosis is a disease of the skeleton predisposing patients to fragility fracture, a cause of significant morbidity and mortality and a common comorbidity in HA. Because the causes of osteoporosis in HA are unclear and in humans confounded by other traditional risk factors for bone loss, in this study, we phenotyped the skeletons of F8 total knockout (F8 TKO) mice, an animal model of severe HA. We found that trabecular bone accretion in the axial and appendicular skeletons of male F8 TKO mice lagged significantly between 2 and 6 months of age, with more modest cortical bone decline. By contrast, in female mice, diminished bone accretion was mostly limited to the cortical compartment. Interestingly, bone loss was associated with a decline in bone formation in male mice but increased bone resorption in female mice, a possible result of sex steroid insufficiency. In conclusion, our studies reveal a sexual dimorphism in the mechanism driving bone loss in male and female F8 TKO mice, preventing attainment of peak bone mass and strength. If validated in humans, therapies aimed at promoting bone formation in males but suppressing bone resorption in females may be indicated to facilitate attainment of peak mass in children with HA to reduce the risk for fracture later in life.

Osteopontin isoforms differentially promote arteriogenesis in response to ischemia via macrophage accumulation and survival.

Osteopontin (OPN) is critical for ischemia-induced neovascularization. Unlike rodents, humans express three OPN isoforms (a, b, and c); however, the roles of these isoforms in post-ischemic neovascularization and cell migration remain undefined. Our objective was to determine if OPN isoforms differentially affect post-ischemic neovascularization and to elucidate the mechanisms underlying these differences. To investigate if human OPN isoforms exert divergent effects on post-ischemic neovascularization, we utilized OPN-/- mice and a loss-of-function/gain-of-function approach in vivo and in vitro. In this study OPN-/- mice underwent hindlimb ischemia surgery and 1.5 × 106 lentivirus particles were administered intramuscularly to overexpress OPNa, OPNb, or OPNc. OPNa and OPNc significantly improved limb perfusion 30.4% ± 0.8 and 70.9% ± 6.3, respectively, and this translated to improved functional limb use, as measured by voluntary running wheel utilization. OPNa- and OPNc-treated animals exhibited significant increases in arteriogenesis, defined here as the remodeling of existing arterioles into larger conductance arteries. Macrophages play a prominent role in the arteriogenesis process and OPNa- and OPNc-treated animals showed significant increases in macrophage accumulation in vivo. In vitro, OPN isoforms did not affect macrophage polarization, whereas all three isoforms increased macrophage survival and decreased macrophage apoptosis. However, OPN isoforms exert differential effects on macrophage migration, where OPNa and OPNc significantly increased macrophage migration, with OPNc serving as the most potent isoform. In conclusion, human OPN isoforms exert divergent effects on neovascularization through differential effects on arteriogenesis and macrophage accumulation in vivo and on macrophage migration and survival, but not polarization, in vitro. Altogether, these data support that human OPN isoforms may represent novel therapeutic targets to improve neovascualrization and preserve tissue function in patients with obstructive artery diseases.

The cofilin phosphatase slingshot homolog 1 restrains angiotensin II-induced vascular hypertrophy and fibrosis in vivo.

The dual specificity phosphatase slingshot homolog 1 (SSH1) contributes to actin remodeling by dephosphorylating and activating the actin-severing protein cofilin. The reorganization of the actin cytoskeleton has been implicated in chronic hypertension and the subsequent mechano-adaptive rearrangement of vessel wall components. Therefore, using a novel Ssh1-/- mouse model, we investigated the potential role of SSH1 in angiotensin II (Ang II)-induced hypertension, and vascular remodeling. We found that loss of SSH1 did not produce overt phenotypic changes and that baseline blood pressures as well as heart rates were comparable between Ssh1+/+ and Ssh1-/- mice. Although 14 days of Ang II treatment equally increased systolic blood pressure in both genotypes, histological assessment of aortic samples indicated that medial thickening was exacerbated by the loss of SSH1. Consequently, reverse-transcription quantitative PCR analysis of the transcripts from Ang II-infused animals confirmed increased aortic expression levels of fibronectin, and osteopontin in Ssh1-/- when compared to wild-type mice. Mechanistically, our data suggest that fibrosis in SSH1-deficient mice occurs by a process that involves aberrant responses to Ang II-induced TGFß1. Taken together, our work indicates that Ang II-dependent fibrotic gene expression and vascular remodeling, but not the Ang II-induced pressor response, are modulated by SSH1-mediated signaling pathways and SSH1 activity is protective against Ang II-induced remodeling in the vasculature.

CTLA-4Ig (abatacept) balances bone anabolic effects of T cells and Wnt-10b with antianabolic effects of osteoblastic sclerostin.

Activated lymphocytes promote inflammation and bone destruction in rheumatoid arthritis (RA), making T cells and B cells therapeutic targets. Indeed, pharmacological blockade of CD28 costimulation using CTLA-4Ig (abatacept), approved for amelioration of RA, renders T cells dormant (anergic). CTLA-4Ig also promotes bone accretion in healthy mice; surprisingly, however, this effect is driven exclusively through upregulation of bone formation, rather than anti-inflammatory effects on resorption. In the study presented here, we utilized T cell receptor ß gene and Wnt-10b gene knockout mice to investigate the roles of T cells and Wnt-10b in CTLA-4Ig-induced bone anabolism. Ablation of either T cells or Wnt-10b not only abolished CTLA-4Ig-induced bone anabolism but also, paradoxically, suppressed bone formation leading to bone loss. Stalled bone formation was accompanied by bone marrow stromal cell expression of the Wnt pathway inhibitor sclerostin. Our data suggest that an immunoskeletal pivot may promote or suppress bone formation, depending on the net outcome of CTLA-4Ig action directed independently on T cells and osteoblast-linage cells that counter Wnt-10b-induced bone anabolism, by secretion of sclerostin. While CTLA-4Ig action is tipped in favor of bone formation under physiological conditions, pathological immunodeficiency may lead to suppressed bone formation and skeletal damage.

Impaired Collateral Vessel Formation in Sickle Cell Disease.

OBJECTIVE: The adaptive response to vascular injury is the formation of functional collateral vessels to maintain organ integrity. Many of the clinical complications associated with sickle cell disease can be attributed to repeated bouts of vascular insufficiency, yet the detailed mechanisms of collateral vessel formation after injury are largely unknown in sickle cell disease. Here, we characterize postischemic neovascularization in sickle cell disease and the role of neutrophils in the production of reactive oxygen species. APPROACH AND RESULTS: We induced hindlimb ischemia by ligation of the femoral artery in Townes SS (sickle cell) mice compared with AA (wild type) mice. Perfusion recovery, ascertained using LASER (light amplification by stimulated emission of radiation) Doppler perfusion imaging, showed significant diminution in collateral vessel formation in SS mice after hindlimb ischemia (76±13% AA versus 34±10% in SS by day 28; P<0.001; n=10 per group). The incidence of amputation (25% versus 5%) and foot necrosis (80% versus 15%) after hindlimb ischemia was significantly increased in the SS mice. Motor function recovery evaluation by the running wheel assay was also impaired in SS mice (36% versus 97% at 28 days post-hindlimb ischemia; P<0.001). This phenotype was associated with persistent and excessive production of reactive oxygen species by neutrophils. Importantly, neutrophil depletion or treatment with the antioxidant N-acetylcysteine reduced oxidative stress and improved functional collateral formation in the SS mice. CONCLUSIONS: Our data suggest dysfunctional collateral vessel formation in SS mice after vascular injury and provide a mechanistic basis for the multiple vascular complications of sickle cell disease.

The receptor for advanced glycation end products impairs collateral formation in both diabetic and non-diabetic mice.

Diabetics often have poor perfusion in their limbs as a result of peripheral artery disease and an impaired ability to generate collateral vessels. The receptor for advanced glycation end products (RAGE) is one protein that is thought to play a detrimental role in collateral development in diabetics due to increased levels of advanced glycation end products (AGE), one of its ligands, in diabetes. Thus, the aim of this study was to investigate the role of RAGE in both diabetic and non-diabetic settings in a model of collateral formation in mice. Streptozotocin was used to induce diabetes in both wild type and RAGE knockout mice. Increased levels of the AGE, Nɛ-(carboxymethyl) lysine (CML), were confirmed via an ELISA. A hindlimb ischemia model, in which the femoral artery is ligated, was used to drive collateral growth and reperfusion was assessed using laser Doppler perfusion imaging and histological analysis of vessels in the muscle. Both of these measurements showed impaired collateral growth in diabetic compared with wild-type mice as well as improved collateral growth in both diabetic and non-diabetic RAGE knockout mice when compared their wild-type counterparts. Distance on a freely accessed running wheel, used as a measure of perfusion recovery, showed that wild-type diabetic mice had functionally impaired recovery compared with their wild-type counterparts. Immunohistochemistry and immunoblotting showed that HMGB-1 (high-mobility group box 1), another RAGE ligand, was increased in the ischemic leg compared with the non-ischemic leg in all mice. This increase in HMGB-1 may explain improvement in animals lacking RAGE and its subsequent signaling. In conclusion, this study shows that RAGE impairs collateral growth in a diabetic setting and also in a non-diabetic setting. This demonstrates the importance of RAGE and alternate RAGE ligands in the setting of collateral vessel growth.

Cyclic Strain and Hypertension Increase Osteopontin Expression in the Aorta.

Hypertension has a direct impact on vascular hypertrophy and is a known risk factor for the development of atherosclerosis. Osteopontin (OPN) has emerged as an important protein mediator of inflammation and remodeling of large arteries. However, its role and mechanism of regulation in the setting of hypertension is still unknown. Our objectives for this study were therefore to investigate the role of OPN in hypertension-induced vascular remodeling and inflammation. OPN Knockout (KO) and wild type (WT) mice were made hypertensive with angiotensin II (Ang II) infusion for seven days. We observed that OPN KO aortas were protected against Ang II-induced medial hypertrophy and inflammation, despite comparable increases in systolic blood pressure (SBP) in both groups. OPN expression was increased in WT aortas from hypertensive mice (induced by either Ang II or norepinephrine). OPN expression was increased in aortic smooth muscle cells (SMCs) subjected to cyclic mechanical strain suggesting that mechanical deformation of the aortic wall is responsible in part for the increased OPN expression induced by hypertension. Finally, we utilized hypertensive transgenic smooth muscle cell-specific catalase overexpressing (TgSMC-Cat) mice to determine the role of H2O2 in mediating hypertension-induced increases in OPN expression. We also found that the hypertension-induced increase in OPN expression was inhibited in transgenic smooth muscle cell-specific catalase overexpressing (TgSMC-Cat) mice, suggesting that H2O2, plays a vital role in mediating the hypertension-induced increase in OPN expression. Taken together, these results define a potentially important role for OPN in the pathophysiology of hypertension.

Alginate microencapsulation of human mesenchymal stem cells as a strategy to enhance paracrine-mediated vascular recovery after hindlimb ischaemia.

Stem cell-based therapies hold great promise as a clinically viable approach for vascular regeneration. Preclinical studies have been very encouraging and early clinical trials have suggested favourable outcomes. However, significant challenges remain in terms of optimizing cell retention and maintenance of the paracrine effects of implanted cells. To address these issues, we have proposed the use of a cellular encapsulation approach to enhance vascular regeneration. We contained human mesenchymal stem cells (hMSCs) in biocompatible alginate microcapsules for therapeutic treatment in the setting of murine hindlimb ischaemia. This approach supported the paracrine pro-angiogenic activity of hMSCs, prevented incorporation of hMSCs into the host tissue and markedly enhanced their therapeutic effect. While injection of non-encapsulated hMSCs resulted in a 22 ± 10% increase in vascular density and no increase in perfusion, treatment with encapsulated hMSCs resulted in a 70 ± 8% increase in vascular density and 21 ± 7% increase in perfusion. The described cellular encapsulation strategy may help to better define the mechanisms responsible for the beneficial effects of cell-based therapies and provide a therapeutic strategy for inducing vascular growth in the adult. As hMSCs are relatively easy to isolate from patients, and alginate is biocompatible and already used in clinical applications, therapeutic cell encapsulation for vascular repair represents a highly translatable platform for cell-based therapy in humans.

CD163 interacts with TWEAK to regulate tissue regeneration after ischaemic injury.

Macrophages are an essential component of the immune response to ischaemic injury and play an important role in promoting inflammation and its resolution, which is necessary for tissue repair. The type I transmembrane glycoprotein CD163 is exclusively expressed on macrophages, where it acts as a receptor for haemoglobin:haptoglobin complexes. An extracellular portion of CD163 circulates in the blood as a soluble protein, for which no physiological function has so far been described. Here we show that during ischaemia, soluble CD163 functions as a decoy receptor for TWEAK, a secreted pro-inflammatory cytokine of the tumour necrosis factor family, to regulate TWEAK-induced activation of canonical nuclear factor-κB (NF-κB) and Notch signalling necessary for myogenic progenitor cell proliferation. Mice with deletion of CD163 have transiently elevated levels of TWEAK, which stimulate muscle satellite cell proliferation and tissue regeneration in their ischaemic and non-ischaemic limbs. These results reveal a role for soluble CD163 in regulating muscle regeneration after ischaemic injury.

PET imaging of bacterial infections with fluorine-18-labeled maltohexaose.

A positron emission tomography (PET) tracer composed of (18)F-labeled maltohexaose (MH(18)F) can image bacteria in vivo with a sensitivity and specificity that are orders of magnitude higher than those of fluorodeoxyglucose ((18)FDG). MH(18)F can detect early-stage infections composed of as few as 10(5) E. coli colony-forming units (CFUs), and can identify drug resistance in bacteria in vivo. MH(18)F has the potential to improve the diagnosis of bacterial infections given its unique combination of high specificity and sensitivity for bacteria.

Polymerase δ-interacting protein 2 promotes postischemic neovascularization of the mouse hindlimb.

OBJECTIVE: Collateral vessel formation can functionally compensate for obstructive vascular lesions in patients with atherosclerosis. Neovascularization processes are triggered by fluid shear stress, hypoxia, growth factors, chemokines, proteases, and inflammation, as well as reactive oxygen species, in response to ischemia. Polymerase δ-interacting protein 2 (Poldip2) is a multifunctional protein that regulates focal adhesion turnover and vascular smooth muscle cell migration and modifies extracellular matrix composition. We, therefore, tested the hypothesis that loss of Poldip2 impairs collateral formation. APPROACH AND RESULTS: The mouse hindlimb ischemia model has been used to understand mechanisms involved in postnatal blood vessel formation. Poldip2(+/-) mice were subjected to femoral artery excision, and functional and morphological analysis of blood vessel formation was performed after injury. Heterozygous deletion of Poldip2 decreased the blood flow recovery and spontaneous running activity at 21 days after injury. H2O2 production, as well as the activity of matrix metalloproteinases-2 and -9, was reduced in these animals compared with Poldip2(+/+) mice. Infiltration of macrophages in the peri-injury muscle was also decreased; however, macrophage phenotype was similar between genotypes. In addition, the formation of capillaries and arterioles was impaired, as was angiogenesis, in agreement with a decrease in proliferation observed in endothelial cells treated with small interfering RNA against Poldip2. Finally, regression of newly formed vessels and apoptosis was more pronounced in Poldip2(+/-) mice. CONCLUSIONS: Together, these results suggest that Poldip2 promotes ischemia-induced collateral vessel formation via multiple mechanisms that likely involve reactive oxygen species-dependent activation of matrix metalloproteinase activity, as well as enhanced vascular cell growth and survival.

Semi-degradable poly(ß-amino ester) networks with temporally controlled enhancement of mechanical properties.

Biodegradable polymers are clinically used in numerous biomedical applications, and classically show a loss of mechanical properties within weeks of implantation. This work demonstrates a new class of semi-degradable polymers that show an increase in mechanical properties through degradation via a controlled shift in a thermal transition. Semi-degradable polymer networks, poly(ß-amino ester)-co-methyl methacrylate, were formed from a low glass transition temperature crosslinker, poly(ß-amino ester), and high glass transition temperature monomer, methyl methacrylate, which degraded in a manner dependent upon the crosslinker chemical structure. In vitro and in vivo degradation revealed changes in mechanical behavior due to the degradation of the crosslinker from the polymer network. This novel polymer system demonstrates a strategy to temporally control the mechanical behavior of polymers and to enhance the initial performance of smart biomedical devices.

Overexpression of catalase in vascular smooth muscle cells prevents the formation of abdominal aortic aneurysms.

OBJECTIVE: Elevated levels of oxidative stress have been reported in abdominal aortic aneurysms (AAA), but which reactive oxygen species promotes the development of AAA remains unclear. Here, we investigate the effect of hydrogen peroxide (H2O2)-degrading enzyme catalase on the formation of AAA. APPROACH AND RESULTS: AAA were induced with the application of calcium chloride (CaCl2) on mouse infrarenal aortas. The administration of PEG-catalase, but not saline, attenuated the loss of tunica media and protected against AAA formation (0.91 ± 0.1 versus 0.76 ± 0.09 mm). Similarly, in a transgenic mouse model, catalase overexpression in the vascular smooth muscle cells preserved the thickness of tunica media and inhibited aortic dilatation by 50% (0.85 ± 0.14 versus 0.57 ± 0.08 mm). Further studies showed that injury with CaCl2 decreased catalase expression and activity in the aortic wall. Pharmacological administration or genetic overexpression of catalase restored catalase activity and subsequently decreased matrix metalloproteinase activity. In addition, a profound reduction in inflammatory markers and vascular smooth muscle cell apoptosis was evident in aortas of catalase-overexpressing mice. Interestingly, as opposed to infusion of PEG-catalase, chronic overexpression of catalase in vascular smooth muscle cells did not alter the total aortic H2O2 levels. CONCLUSIONS: The data suggest that a reduction in aortic wall catalase activity can predispose to AAA formation. Restoration of catalase activity in the vascular wall enhances aortic vascular smooth muscle cell survival and prevents AAA formation primarily through modulation of matrix metalloproteinase activity.

Magnetic targeting of human mesenchymal stem cells with internalized superparamagnetic iron oxide nanoparticles.

Cell therapies offer exciting new opportunities for effectively treating many human diseases. However, delivery of therapeutic cells by intravenous injection, while convenient, relies on the relatively inefficient process of homing of cells to sites of injury. To address this limitation, a novel strategy has been developed to load cells with superparamagnetic iron oxide nanoparticles (SPIOs), and to attract them to specific sites within the body by applying an external magnetic field. The feasibility of this approach is demonstrated using human mesenchymal stem cells (hMSCs), which may have a significant potential for regenerative cell therapies due to their ease of isolation from autologous tissues, and their ability to differentiate into various lineages and modulate their paracrine activity in response to the microenvironment. The efficient loading of hMSCs with polyethylene glycol-coated SPIOs is achieved, and it is found that SPIOs are localized primarily in secondary lysosomes of hMSCs and are not toxic to the cells. Further, the key stem cell characteristics, including the immunophenotype of hMSCs and their ability to differentiate, are not altered by SPIO loading. Through both experimentation and mathematical modeling, it is shown that, under applied magnetic field gradients, SPIO-containing cells can be localized both in vitro and in vivo. The results suggest that, by loading SPIOs into hMSCs and applying appropriate magnetic field gradients, it is possible to target hMSCs to particular vascular networks.

Anti-inflammatory and antiatherogenic role of BMP receptor II in endothelial cells.

OBJECTIVE: Atherosclerosis is an inflammatory disease with multiple underlying metabolic and physical risk factors. Bone morphogenic protein 4 (BMP4) expression is increased in endothelium in atherosclerosis-prone regions and is known to induce endothelial inflammation, endothelial dysfunction, and hypertension. BMP actions are mediated by 2 different types of BMP receptors (BMPRI and BMPRII). Here, we show a surprising finding that loss of BMPRII expression causes endothelial inflammation and atherosclerosis. APPROACH AND RESULTS: Using BMPRII siRNA and BMPRII(+/-) mice, we found that specific knockdown of BMPRII, but not other BMP receptors (Alk1, Alk2, Alk3, Alk6, ActRIIa, and ActRIIb), induced endothelial inflammation in a ligand-independent manner by mechanisms mediated by reactive oxygen species, nuclear factor-KappaB, and reduced nicotinamide adenine dinucleotide phosphate oxidases. Further, BMPRII(+/-)ApoE(-/-) mice developed accelerated atherosclerosis compared with BMPRII(+/+)ApoE(-/-) mice. Interestingly, we found that multiple proatherogenic stimuli, such as hypercholesterolemia, disturbed flow, prohypertensive angiotensin II, and the proinflammatory cytokine (tumor necrosis factor-α), downregulated BMPRII expression in endothelium, whereas antiatherogenic stimuli, such as stable flow and statin treatment, upregulated its expression in vivo and in vitro. Moreover, BMPRII expression was significantly diminished in human coronary advanced atherosclerotic lesions. Also, we were able to rescue the endothelial inflammation induced by BMPRII knockdown by overexpressing the BMPRII wild type, but not by the BMPRII short form lacking the carboxyl-terminal tail region. CONCLUSIONS: These results suggest that BMPRII is a critical, anti-inflammatory, and antiatherogenic protein that is commonly targeted by multiple pro- and antiatherogenic factors. BMPRII may be used as a novel diagnostic and therapeutic target in atherosclerosis.