Gaia Spinetti

Deregulation of microRNA-503 Contributes to Diabetes Mellitus–Induced Impairment of Endothelial Function and Reparative Angiogenesis After Limb Ischemia

Background— Diabetes mellitus impairs endothelial cell (EC) function and postischemic reparative neovascularization by molecular mechanisms that are not fully understood. microRNAs negatively regulate the expression of target genes mainly by interaction in their 3′ untranslated region. Methods and Results— We found that microRNA-503 (miR-503) expression in ECs is upregulated in culture conditions mimicking diabetes mellitus (high D-glucose) and ischemia-associated starvation (low growth factors). Under normal culture conditions, lentivirus-mediated miR-503–forced expression inhibited EC proliferation, migration, and network formation on Matrigel (comparisons versus lentivirus.GFP control). Conversely, blocking miR-503 activity by either adenovirus-mediated transfer of a miR-503 decoy (Ad.decoymiR-503) or by antimiR-503 (antisense oligonucleotide) improved the functional capacities of ECs cultured under high D-glucose/low growth factors. We identified CCNE1 and cdc25A as direct miR-503 targets which are downregulated by high glucose/low growth factors in ECs. Next, we obtained evidence that miR-503 expression is increased in ischemic limb muscles of streptozotocin-diabetic mice and in ECs enriched from these muscles. Moreover, Ad.decoymiR-503 delivery to the ischemic adductor of diabetic mice corrected diabetes mellitus–induced impairment of postischemic angiogenesis and blood flow recovery. We finally investigated miR-503 and target gene expression in muscular specimens from the amputated ischemic legs of diabetic patients. As controls, calf biopsies of nondiabetic and nonischemic patients undergoing saphenous vein stripping were used. In diabetic muscles, miR-503 expression was remarkably higher, and it inversely correlated with cdc25 protein expression. Plasma miR-503 levels were also elevated in the diabetic individuals. Conclusions— Our data suggest miR-503 as a possible therapeutic target in diabetic patients with critical limb ischemia.

Proinflammatory Profile Within the Grossly Normal Aged Human Aortic Wall

Studies in animal models demonstrate that angiotensin II and its downstream signaling molecules, that is, matrix metalloproteinases and monocyte chemoattractant protein-1, increase within the diffusely thickened intima of central arteries with aging. Whether such age-related changes occur within the human arterial wall is unknown. We harvested “grossly normal thoracic aortas” from 5 young (20±3 years) and 5 old white males (65±6 years) at necropsy, after death from traumatic causes. The intimae of older samples were markedly and diffusely thickened compared with younger intimae and contained increased levels of angiotensin-converting enzyme, angiotensin II, angiotensin II receptor type 1, matrix metalloproteinases 2/9, monocyte chemoattractant protein-1, and collagen I and III proteins. In situ activities of metalloproteinases 2/9 were also significantly enhanced within old, normal aortas. The thickened intima of older aortas also contained a 5-fold increase in the embryonic form of smooth muscle myosin heavy chain–labeled cells than that of younger aortas, and these fetal-type cells were colocalized with angiotensin II protein staining. The ability of isolated smooth muscle cells to invade an artificial basement membrane in response to a monocyte chemoattractant protein-1 gradient increased with age. Furthermore, angiotensin II increased the invasive capacity of young smooth muscle cells, and this effect was reduced by a metalloproteinase inhibitor or an angiotensin II receptor blocker. Thus, in the absence of lipid infiltration, the aged human aortic wall exhibits a proinflammatory profile that renders it a fertile substrate for the development of arterial disease, for example, atherosclerosis and hypertension.

Matrix Metalloproteinase 2 Activation of Transforming Growth Factor-β1 (TGF-β1) and TGF-β1–Type II Receptor Signaling Within the Aged Arterial Wall

Objective—To study matrix metalloproteinase 2 (MMP-2) effects on transforming growth factor-&bgr;1 (TGF-&bgr;1) activation status and downstream signaling during arterial aging. Methods and Results—Western blotting and immunostaining showed that latent and activated TGF-&bgr;1 are markedly increased within the aorta of aged Fisher 344 cross-bred Brown Norway (30 months of age) rats compared with adult (8 months of age) rats. Aortic TGF-&bgr;1–type II receptor (T&bgr;RII), its downstream molecules p-similar to mad-mother against decapentaplegic (SMAD)2/3 and SMAD4, fibronectin, and collagen also increased with age. Moreover, TGF-&bgr;1 staining is colocalized with that of activated MMP-2 within the aged arterial wall and vascular smooth muscle cell (VSMC) in vitro, and this physical association was confirmed by coimmunoprecipitation. Incubation of young aortic rings ex vivo or VSMCs in vitro with activated MMP-2 enhanced active TGF-&bgr;1, collagen, and fibronectin expression to the level of untreated old counterparts, and this effect was abolished via inhibitors of MMP-2. Interestingly, in old untreated rings or VSMCs, the increased TGF-&bgr;1, fibronectin, and collagen were also substantially reduced by inhibition of MMP-2. Conclusions—Active TGF-&bgr;1, its receptor, and receptor-mediated signaling increase within the aortic wall with aging. TGF-&bgr;1 activation is dependent, in part at least, by a concomitant age-associated increase in MMP-2 activity. Thus, MMP-2–activated TGF-&bgr;1, and subsequently T&bgr;RII signaling, is a novel molecular mechanism for arterial aging.

Diabetes Mellitus Induces Bone Marrow Microangiopathy

Objective—The impact of diabetes on the bone marrow (BM) microenvironment was not adequately explored. We investigated whether diabetes induces microvascular remodeling with negative consequence for BM homeostasis. Methods and Results—We found profound structural alterations in BM from mice with type 1 diabetes with depletion of the hematopoietic component and fatty degeneration. Blood flow (fluorescent microspheres) and microvascular density (immunohistochemistry) were remarkably reduced. Flow cytometry verified the depletion of MECA-32+ endothelial cells. Cultured endothelial cells from BM of diabetic mice showed higher levels of oxidative stress, increased activity of the senescence marker &bgr;-galactosidase, reduced migratory and network-formation capacities, and increased permeability and adhesiveness to BM mononuclear cells. Flow cytometry analysis of lineage− c-Kit+ Sca-1+ cell distribution along an in vivo Hoechst-33342 dye perfusion gradient documented that diabetes depletes lineage− c-Kit+ Sca-1+ cells predominantly in the low-perfused part of the marrow. Cell depletion was associated to increased oxidative stress, DNA damage, and activation of apoptosis. Boosting the antioxidative pentose phosphate pathway by benfotiamine supplementation prevented microangiopathy, hypoperfusion, and lineage− c-Kit+ Sca-1+ cell depletion. Conclusion—We provide novel evidence for the presence of microangiopathy impinging on the integrity of diabetic BM. These discoveries offer the framework for mechanistic solutions of BM dysfunction in diabetes.

Angiotensin II activates matrix metalloproteinase type II and mimics age-associated carotid arterial remodeling in young rats.

Increased angiotensin II (Ang II), matrix metalloproteinase type II (MMP2), and sympathetic activity accompany age-associated arterial remodeling. To analyze this relationship, we infused a low subpressor dose of Ang II into young (8 months old) rats. This increased carotid arterial MMP2 transcription, translation, and activation, as well as transforming growth factor-beta1 activity and collagen deposition. A higher Ang II concentration, which increased arterial pressure to that of old (30 months old) untreated rats, produced carotid media thickening and intima infiltration by vascular smooth muscle cells (VSMCs). Ex vivo, Ang II increased MMP2 activity in carotid rings from young rats to that of untreated old rats. Ang II also increased the ability of early passage VSMCs from young rats to invade a synthetic basement membrane, similar to that of untreated VSMCs from old rats. The MMP inhibitor GM6001 and the AT1 receptor antagonist Losartan inhibited these effects. The alpha-adrenoreceptor agonist phenylephrine increased arterial Ang II protein, causing MMP2 activation and intima and media thickening. Exposure of young VSMCs to phenylephrine in vitro increased Ang II protein and MMP2 activity to the levels of old VSMCs; Losartan abolished these effects. Thus, Ang II-induced effects on MMP2, transforming growth factor-beta1, collagen, and VSMCs are central to the arterial remodeling that accompanies advancing age.

Rat Aortic MCP-1 and Its Receptor CCR2 Increase With Age and Alter Vascular Smooth Muscle Cell Function

Objective—With age, rat arterial walls thicken and vascular smooth muscle cells (VSMCs) exhibit enhanced migration and proliferation. Monocyte chemotactic protein-1 (MCP-1) affects these VSMC properties in vitro. Because arterial angiotensin II, which induces MCP-1 expression, increases with age, we hypothesized that aortic MCP-1 and its receptor CCR2 are also upregulated and affect VSMC properties. Methods and Results—Both MCP-1 and CCR2 mRNAs and proteins increased in old (30-month) versus young (8-month) F344×BN rat aortas in vivo. Cellular MCP-1 and CCR2 staining colocalized with that of &agr;-smooth muscle actin in the thickened aortas of old rats and were expressed by early-passage VSMCs isolated from old aortas, which, relative to young VSMCs, exhibited increased invasion, and the age difference was abolished by vCCI, an inhibitor of CCR2 signaling. MCP-1 treatment of young VSMCs induced migration and increased their ability to invade a synthetic basement membrane. The MCP-1–dependent VSMC invasiveness was blocked by vCCI. After MCP-1 treatment, migration and invasion capacities of VSMCs from young aortas no longer differed from those of VSMCs isolated from older rats. Conclusions—Arterial wall and VSMC MCP-1/CCR2 increase with aging. MCP-1 enhances VSMC migration and invasion, and thus, MCP-1/CCR2 signaling may play a role in age-associated arterial remodeling.

MicroRNA-15a and MicroRNA-16 Impair Human Circulating Proangiogenic Cell Functions and Are Increased in the Proangiogenic Cells and Serum of Patients With Critical Limb Ischemia

Rationale: Circulating proangiogenic cells (PACs) support postischemic neovascularization. Cardiovascular disease and diabetes mellitus impair PAC regenerative capacities via molecular mechanisms that are not fully known. We hypothesize a role for microRNAs (miRs). Circulating miRs are currently investigated as potential diagnostic and prognostic biomarkers. Objective: The objectives were the following: (1) to profile miR expression in PACs from critical limb ischemia (CLI) patients; (2) to demonstrate that miR-15a and miR-16 regulate PAC functions; and (3) to characterize circulating miR-15a and miR-16 and to investigate their potential biomarker value. Methods and Results: Twenty-eight miRs potentially able to modulate angiogenesis were measured in PACs from CLI patients with and without diabetes mellitus and controls. miR-15a and miR-16 were further analyzed. CLI-PACs expressed higher level of mature miR-15a and miR-16 and of the primary transcript pri–miR-15a/16-1. miR-15a/16 overexpression impaired healthy PAC survival and migration. Conversely, miR-15a/16 inhibition improved CLI-PAC–defective migration. Vascular endothelial growth factor-A and AKT-3 were validated as direct targets of the 2 miRs, and their protein levels were reduced in miR-15a/16–overexpressing healthy PACs and in CLI-PACs. Transplantation of healthy PACs ex vivo–engineered with anti–miR-15a/16 improved postischemic blood flow recovery and muscular arteriole density in immunodeficient mice. miR-15a and miR-16 were present in human blood, including conjugated to argonaute-2 and in exosomes. Both miRs were increased in the serum of CLI patients and positively correlated with amputation after restenosis at 12 months postrevascularization of CLI type 2 diabetes mellitus patients. Serum miR-15a additionally correlated with restenosis at follow-up. Conclusions: Ex vivo miR-15a/16 inhibition enhances PAC therapeutic potential, and circulating miR-15a and miR-16 deserves further investigation as a prognostic biomarker in CLI patients undergoing revascularization.

Diabetes and vessel wall remodelling: from mechanistic insights to regenerative therapies

Over the past two decades, extensive research has focused on arterial remodelling in both physiological and pathological ageing. The concept now describes the growth as well as the rearrangement of cellular components and extracellular matrix, resulting in either reduction or increase in vessel lumen. In diabetes, remodelling extends to capillaries, microvascular beds, and arteries of different calibre. This process is paralleled by accelerated atherosclerosis and accounts for an increased incidence of ischaemic complications. The incapacity of pre-existing and de novo formed collaterals to bypass atherosclerotic occlusions, combined with a decline in tissue capillary density, is responsible for the delayed recovery from ischaemia and ultimately leads to organ failure. The mechanisms of vascular remodelling are incompletely understood, but metabolic and mechanical factors seem to play an important role. Hyperglycaemia represents the main factor responsible for the fast progression of atherosclerosis as well as microangiopathy. However, intensive blood glucose control alone is insufficient to reduce the risk of macrovascular complications. Pharmacological control of oxidative stress and stimulation of nitric oxide release have proved to exert beneficial effects on vascular remodelling in experimental diabetic models. New approaches of regenerative medicine using vascular progenitor cells for the treatment of ischaemic disease have been shown to be safe and are now being tested for efficacy in pre-clinical and clinical trials.

Role of kinin B2 receptor signaling in the recruitment of circulating progenitor cells with neovascularization potential

Reduced migratory function of circulating angiogenic progenitor cells (CPCs) has been associated with impaired neovascularization in patients with cardiovascular disease (CVD). Previous findings underline the role of the kallikrein-kinin system in angiogenesis. We now demonstrate the involvement of the kinin B2 receptor (B2R) in the recruitment of CPCs to sites of ischemia and in their proangiogenic action. In healthy subjects, B2R was abundantly present on CD133+ and CD34+ CPCs as well as cultured endothelial progenitor cells (EPCs) derived from blood mononuclear cells (MNCs), whereas kinin B1 receptor expression was barely detectable. In transwell migration assays, bradykinin (BK) exerts a potent chemoattractant activity on CD133+ and CD34+ CPCs and EPCs via a B2R/phosphoinositide 3-kinase/eNOS-mediated mechanism. Migration toward BK was able to attract an MNC subpopulation enriched in CPCs with in vitro proangiogenic activity, as assessed by Matrigel assay. CPCs from cardiovascular disease patients showed low B2R levels and decreased migratory capacity toward BK. When injected systemically into wild-type mice with unilateral limb ischemia, bone marrow MNCs from syngenic B2R-deficient mice resulted in reduced homing of sca-1+ and cKit+flk1+ progenitors to ischemic muscles, impaired reparative neovascularization, and delayed perfusion recovery as compared with wild-type MNCs. Similarly, blockade of the B2R by systemic administration of icatibant prevented the beneficial effect of bone marrow MNC transplantation. BK-induced migration represents a novel mechanism mediating homing of circulating angiogenic progenitors. Reduction of BK sensitivity in progenitor cells from cardiovascular disease patients might contribute to impaired neovascularization after ischemic complications.

MicroRNA-15a and MicroRNA-16 Impair Human Circulating Pro-Angiogenic Cell (PAC) Functions and are Increased in the PACs and Serum of Patients with Critical Limb Ischemia

Rationale: Circulating proangiogenic cells (PACs) support postischemic neovascularization. Cardiovascular disease and diabetes mellitus impair PAC regenerative capacities via molecular mechanisms that are not fully known. We hypothesize a role for microRNAs (miRs). Circulating miRs are currently investigated as potential diagnostic and prognostic biomarkers. Objective: The objectives were the following: (1) to profile miR expression in PACs from critical limb ischemia (CLI) patients; (2) to demonstrate that miR-15a and miR-16 regulate PAC functions; and (3) to characterize circulating miR-15a and miR-16 and to investigate their potential biomarker value. Methods and Results: Twenty-eight miRs potentially able to modulate angiogenesis were measured in PACs from CLI patients with and without diabetes mellitus and controls. miR-15a and miR-16 were further analyzed. CLI-PACs expressed higher level of mature miR-15a and miR-16 and of the primary transcript pri–miR-15a/16-1. miR-15a/16 overexpression impaired healthy PAC survival and migration. Conversely, miR-15a/16 inhibition improved CLI-PAC–defective migration. Vascular endothelial growth factor-A and AKT-3 were validated as direct targets of the 2 miRs, and their protein levels were reduced in miR-15a/16–overexpressing healthy PACs and in CLI-PACs. Transplantation of healthy PACs ex vivo–engineered with anti–miR-15a/16 improved postischemic blood flow recovery and muscular arteriole density in immunodeficient mice. miR-15a and miR-16 were present in human blood, including conjugated to argonaute-2 and in exosomes. Both miRs were increased in the serum of CLI patients and positively correlated with amputation after restenosis at 12 months postrevascularization of CLI type 2 diabetes mellitus patients. Serum miR-15a additionally correlated with restenosis at follow-up. Conclusions: Ex vivo miR-15a/16 inhibition enhances PAC therapeutic potential, and circulating miR-15a and miR-16 deserves further investigation as a prognostic biomarker in CLI patients undergoing revascularization.