E3 Ligase RNF126 Directly Ubiquitinates Frataxin, Promoting Its Degradation: Identification of a Potential Therapeutic Target for Friedreich Ataxia.

Friedreich ataxia (FRDA) is a severe genetic neurodegenerative disease caused by reduced expression of the mitochondrial protein frataxin. To date, there is no therapy to treat this condition. The amount of residual frataxin critically affects the severity of the disease; thus, attempts to restore physiological frataxin levels are considered therapeutically relevant. Frataxin levels are controlled by the ubiquitin-proteasome system; therefore, inhibition of the frataxin E3 ligase may represent a strategy to achieve an increase in frataxin levels. Here, we report the identification of the RING E3 ligase RNF126 as the enzyme that specifically mediates frataxin ubiquitination and targets it for degradation. RNF126 interacts with frataxin and promotes its ubiquitination in a catalytic activity-dependent manner, both in vivo and in vitro. Most importantly, RNF126 depletion results in frataxin accumulation in cells derived from FRDA patients, highlighting the relevance of RNF126 as a new therapeutic target for Friedreich ataxia.

GIFT-1, a phase IIa clinical trial to test the safety and efficacy of IFNγ administration in FRDA patients.

Friedreich's ataxia is an autosomal recessive progressive degenerative disorder caused by deficiency of the protein frataxin. The most common genetic cause is a homozygotic expansion of GAA triplets within intron 1 of the frataxin gene leading to impaired transcription. Preclinical in vivo and in vitro studies have shown that interferon gamma (IFNγ) is able to up-regulate the expression of frataxin gene in multiple cell types. We designed a phase IIa clinical trial, the first in Italy, aimed at assessing both safety and tolerability of IFNγ in Friedreich's patients and ability to increase frataxin levels in peripheral blood mononuclear cells. Nine patients (6 female and 3 males aged 21-38 years) with genetically confirmed disease were given 3 subcutaneous escalating doses (100, 150 and 200 µg) of IFNγ (human recombinant interferon 1 b gamma, trade name IMUKIN(®)), over 4 weeks. The primary end-point was the assessment of the safety and tolerability of IFNγ by means of standard clinical and hematological criteria. The secondary end-point was the detection of changes of frataxin levels in peripheral blood mononuclear cells after each single escalating dose of the drug. IFNγ was generally well tolerated, the main adverse event was hyperthermia/fever. Although, increases in frataxin levels could be detected in a minority of patients, these changes were not significant. A large phase III multicenter, randomized clinical trial with IFNγ in Friedreich's ataxia patients is currently ongoing. This study is expected to conclusively address the clinical efficacy of IFNγ therapy in patients with Friedreich's ataxia.

Src inhibitors modulate frataxin protein levels.

Defective expression of frataxin is responsible for the inherited, progressive degenerative disease Friedreich's Ataxia (FRDA). There is currently no effective approved treatment for FRDA and patients die prematurely. Defective frataxin expression causes critical metabolic changes, including redox imbalance and ATP deficiency. As these alterations are known to regulate the tyrosine kinase Src, we investigated whether Src might in turn affect frataxin expression. We found that frataxin can be phosphorylated by Src. Phosphorylation occurs primarily on Y118 and promotes frataxin ubiquitination, a signal for degradation. Accordingly, Src inhibitors induce accumulation of frataxin but are ineffective on a non-phosphorylatable frataxin-Y118F mutant. Importantly, all the Src inhibitors tested, some of them already in the clinic, increase frataxin expression and rescue the aconitase defect in frataxin-deficient cells derived from FRDA patients. Thus, Src inhibitors emerge as a new class of drugs able to promote frataxin accumulation, suggesting their possible use as therapeutics in FRDA.

Vitamin A, cancer treatment and prevention: the new role of cellular retinol binding proteins.

Retinol and vitamin A derivatives influence cell differentiation, proliferation, and apoptosis and play an important physiologic role in a wide range of biological processes. Retinol is obtained from foods of animal origin. Retinol derivatives are fundamental for vision, while retinoic acid is essential for skin and bone growth. Intracellular retinoid bioavailability is regulated by the presence of specific cytoplasmic retinol and retinoic acid binding proteins (CRBPs and CRABPs). CRBP-1, the most diffuse CRBP isoform, is a small 15 KDa cytosolic protein widely expressed and evolutionarily conserved in many tissues. CRBP-1 acts as chaperone and regulates the uptake, subsequent esterification, and bioavailability of retinol. CRBP-1 plays a major role in wound healing and arterial tissue remodelling processes. In the last years, the role of CRBP-1-related retinoid signalling during cancer progression became object of several studies. CRBP-1 downregulation associates with a more malignant phenotype in breast, ovarian, and nasopharyngeal cancers. Reexpression of CRBP-1 increased retinol sensitivity and reduced viability of ovarian cancer cells in vitro. Further studies are needed to explore new therapeutic strategies aimed at restoring CRBP-1-mediated intracellular retinol trafficking and the meaning of CRBP-1 expression in cancer patients' screening for a more personalized and efficacy retinoid therapy.

Highly specific ubiquitin-competing molecules effectively promote frataxin accumulation and partially rescue the aconitase defect in Friedreich ataxia cells.

Friedreich ataxia is an inherited neurodegenerative disease that leads to progressive disability. There is currently no effective treatment and patients die prematurely. The underlying genetic defect leads to reduced expression of the mitochondrial protein frataxin. Frataxin insufficiency causes mitochondrial dysfunction and ultimately cell death, particularly in peripheral sensory ganglia. There is an inverse correlation between the amount of residual frataxin and the severity of disease progression; therefore, therapeutic approaches aiming at increasing frataxin levels are expected to improve patients' conditions. We previously discovered that a significant amount of frataxin precursor is degraded by the ubiquitin/proteasome system before its functional mitochondrial maturation. We also provided evidence for the therapeutic potential of small molecules that increase frataxin levels by docking on the frataxin ubiquitination site, thus preventing frataxin ubiquitination and degradation. We called these compounds ubiquitin-competing molecules (UCM). By extending our search for effective UCM, we identified a set of new and more potent compounds that more efficiently promote frataxin accumulation. Here we show that these compounds directly interact with frataxin and prevent its ubiquitination. Interestingly, these UCM are not effective on the ubiquitin-resistant frataxin mutant, indicating their specific action on preventing frataxin ubiquitination. Most importantly, these compounds are able to promote frataxin accumulation and aconitase rescue in cells derived from patients, strongly supporting their therapeutic potential.

Antioxidant treatment prevents serum deprivation- and TNF-α-induced endothelial dysfunction through the inhibition of NADPH oxidase 4 and the restoration of ß-oxidation.

AIMS: Oxidative stress plays a pivotal role in the impaired endothelial function occurring in vascular diseases. Antioxidant strategies induce a clinical advantage in patients with endothelial dysfunction and atherosclerosis and protect from oxidative damage, but the underlying molecular mechanisms have been poorly evaluated. The aim of this study was to analyze the effects and mechanisms of action of antioxidant regimens on endothelial function. METHODS AND RESULTS: Antioxidant efficacy of N-acetylcysteine, ascorbic acid and propionyl-L-carnitine was evaluated in serum-deprived and TNF-α-stimulated human umbilical vein endothelial cells in vitro. Cell adhesion molecule (CAM) expression was evaluated by blot and real-time PCR, and inflammatory cytokine secretion was evaluated by ELISA; leukocyte adhesion and reactive oxygen species assays and NADPH oxidase 4 isoform (Nox4) expression analyses by blots were also performed. Antioxidant pretreatment restored serum-deprived and TNF-α-induced impaired mitochondrial ß-oxidation by reducing flavin adenine dinucleotide level and counteracting increased CAM and Nox4 expression, leukocyte adhesion and inflammatory cytokine secretion. Specific inhibition by plumbagin and siNox4 prevented TNF-α- and serum deprivation-induced detrimental effects, confirming that endothelial oxidative stress and inflammation were Nox4 dependent. CONCLUSIONS: Our findings documented Nox4 as a main actor in oxidative stress-induced endothelial dysfunction and further clarify the molecular basis of antioxidant treatment efficacy.

Ageing and microvasculature.

A decline in the function of the microvasculature occurs with ageing. An impairment of endothelial properties represents a main aspect of age-related microvascular alterations. Endothelial dysfunction manifests itself through a reduced angiogenic capacity, an aberrant expression of adhesion molecules and an impaired vasodilatory function. Increased expression of adhesion molecules amplifies the interaction with circulating factors and inflammatory cells. The latter occurs in both conduit arteries and resistance arterioles. Age-related impaired function also associates with phenotypic alterations of microvascular cells, such as endothelial cells, smooth muscle cells and pericytes. Age-related morphological changes are in most of cases organ-specific and include microvascular wall thickening and collagen deposition that affect the basement membrane, with the consequent perivascular fibrosis. Data from experimental models indicate that decreased nitric oxide (NO) bioavailability, caused by impaired eNOS activity and NO inactivation, is one of the causes responsible for age-related microvascular endothelial dysfunction. Consequently, vasodilatory responses decline with age in coronary, skeletal, cerebral and vascular beds. Several therapeutic attempts have been suggested to improve microvascular function in age-related end-organ failure, and include the classic anti-atherosclerotic and anti-ischemic treatments, and also new innovative strategies. Change of life style, antioxidant regimens and anti-inflammatory treatments gave the most promising results. Research efforts should persist to fully elucidate the biomolecular basis of age-related microvascular dysfunction in order to better support new therapeutic strategies aimed to improve quality of life and to reduce morbidity and mortality among the elderly patients.

High insulin-induced down-regulation of Erk-1/IGF-1R/FGFR-1 signaling is required for oxidative stress-mediated apoptosis of adipose-derived stem cells.

Homeostasis of adipose tissue requires highly coordinated response between circulating factors and cell population. Human adult adipose-derived stem cells (ASCs) display multiple differentiation properties and are sensitive to insulin stimulation. Insulin resistance and high level of circulating insulin characterize patients with type 2 diabetes and obesity. At physiological concentration, insulin promoted proliferation and survival of ASCs in vitro, whereas high insulin level induced their dose-dependent proliferative arrest and apoptosis. Insulin-induced apoptotic commitment depended on the down-regulation of Erk-1, insulin growth factor-1 receptor (IGF-1R), and fibroblast growth factor receptor-1 (FGFR-1)-mediated signaling. Specific inhibition of Erk-1/2, IGF-1R, and FGFR activity promoted ASC apoptosis but did not increase insulin effects, whereas EGFR and ErbB2 inhibition potentiated insulin-induced apoptosis. FGFRs and EGFR inhibition reduced ASC adipogenic differentiation, whereas Erk-1/2 and IGF-1R inhibition was ineffective. Insulin-induced apoptosis associated to reactive oxygen species (ROS) accumulation and inhibition of NADPH oxidase 4 (Nox4) activity prevented ASC apoptosis. Moreover, specific inhibition of Erk-1/2, IGF-1R, and FGFR-1 activity promoted ROS generation and this effect was not cumulative with that of insulin alone. Our data indicate that insulin concentration is a critical regulatory switch between proliferation and survival of ASCs. High insulin level-induced apoptotic machinery involves Nox4-generated oxidative stress and the down-regulation of a complex receptor signaling, partially distinct from that influencing adipogenic differentiation of ASCs.

Propionyl-L-Carnitine is Efficacious in Ulcerative Colitis Through its Action on the Immune Function and Microvasculature.

OBJECTIVES: Microvascular endothelial dysfunction characterizes ulcerative colitis (UC), the most widespread form of inflammatory bowel disease. Intestinal mucosal microvessels in UC display aberrant expression of cell adhesion molecules (CAMs) and increased inflammatory cell recruitment. Propionyl-L-carnitine (PLC), an ester of L-carnitine required for the mitochondrial transport of fatty acids, ameliorates propionyl-CoA bioavailability and reduces oxidative stress in ischemic tissues. The present study aimed to document the efficacy of anti-oxidative stress properties of PLC in counteracting intestinal microvascular endothelial dysfunction and inflammation. METHODS: To evaluate the efficacy in vivo, we analyzed the effects in intestinal biopsies of patients with mild-to-moderate UC receiving oral PLC co-treatment and in rat TNBS-induced colitis; in addition, we investigated antioxidant PLC action in TNF-α-stimulated human intestinal microvascular endothelial cells (HIMECs) in vitro. RESULTS: Four-week PLC co-treatment reduced intestinal mucosal polymorph infiltration and CD4(+) lymphocytes, ICAM-1(+) and iNOS(+) microvessels compared with placebo-treated patients with UC. Oral and intrarectal administration of PLC but not L-carnitine or propionate reduced intestinal damage and microvascular dysfunction in rat TNBS-induced acute and reactivated colitis. In cultured TNF-α-stimulated HIMECs, PLC restored ß-oxidation and counteracted NADPH oxidase 4-generated oxidative stress-induced CAM expression and leukocyte adhesion. Inhibition of ß-oxidation by L-aminocarnitine increased reactive oxygen species production and PLC beneficial effects on endothelial dysfunction and leukocyte adhesion. Finally, PLC reduced iNOS activity and nitric oxide accumulation in rat TNBS-induced colitis and in HIMEC cultures. CONCLUSIONS: Our results show that the beneficial antioxidant effect of PLC targeting intestinal microvasculature restores endothelial ß-oxidation and function, and reduces mucosal inflammation in UC patients.

Sortilin expression is essential for pro-nerve growth factor-induced apoptosis of rat vascular smooth muscle cells.

BACKGROUND: Sortilin, a member of the Vps10p-domain receptor family, has been demonstrated a key regulator in mediating cellular response to pro-neurotrophins. In the present study, we investigated the role of sortilin in the apoptotic pathway of vascular smooth muscle cells. METHODS AND PRINCIPAL FINDINGS: Immunohistochemistry revealed that sortilin was barely detectable in human and rat normal young vessels, while its expression was increased in human fibroatheromatous plaques. Sortilin immunodetection was also marked in the neointima of the rat aorta fifteen days after ballooning.In vitro, rat aortic intimal cells expressed higher sortilin levels than normal media SMCs; sortilin was distributed in the cytoplasm and in correspondence of the cell membrane. After 48 h, pro-nerve growth factor (proNGF) induced the strong dose-dependent increase of intimal cell apoptosis and the accumulation of sortilin protein. ProNGF was a more potent apoptotic inducer than equimolar or even higher concentration of NGF, whereas brain derived neutrotrophic factor was ineffective. Targeted interfering RNA-mediated sortilin reduction counteracted proNGF-induced apoptosis without affecting p75(NTR) expression. ProNGF-induced apoptosis was associated to NF-κB down-regulation and bax increase. Inhibition of NF-κB activity increased intimal cell apoptosis that did not further increase with the addition of proNGF. CONCLUSIONS: Our results indicate that sortilin expression characterizes human atheromatous lesions and rat aortic post-injury neointima, and suggest that sortilin represents an important regulator of proNGF-induced SMC apoptosis and arterial remodeling.

Transglutaminase 2 as a biomarker of osteoarthritis: an update.

Osteoarthritis is a progressive joint disease characterized by cartilage degradation and bone remodelling. Under physiologic conditions, articular cartilage displays a stable chondrocyte phenotype, whereas in osteoarthritis a chondrocyte hypertrophy develops near the sites of cartilage surface damage and associates to the pathologic expression of type X collagen. Transglutaminases (TGs) include a family of Ca(2+)-dependent enzymes that catalyze the formation of γ-glutamyl cross-links. Their substrates include a variety of intracellular and extracellular macromolecular components. TGs are ubiquitously and abundantly expressed and implicated in a variety of physiopathological processes. TGs activity is modulated by inflammatory cytokines. TG2 (also known as tissue transglutaminase) mediates the hypertrophic differentiation of joint chondrocytes and interleukin-1-induced calcification. Histomorphometrical and biomolecular investigations document increased TG2 expression in human and experimental osteoarthritis. Consequently, the level of TG2 expression may represent an adjuvant additional marker to monitor tissue remodelling occurring in osteoarthritic joint tissue. Experimental induction of osteoarthritis in TG2 knockout mice is followed from reduced cartilage destruction and increased osteophyte formation compared to wild-type mice, suggesting a different influence on joint bone and cartilage remodelling. The capacity of transamidation by TG2 to regulate activation of latent TGF-ß seems to have a potential impact on the regulation of inflammatory response in osteoarthritic tissues. Additional studies are needed to define TG2-regulated pathways that are differently modulated in osteoblasts and chondrocytes during osteoarthritis.

Insulin-degrading enzyme (IDE): a novel heat shock-like protein.

Insulin-degrading enzyme (IDE) is a highly conserved zinc metallopeptidase that is ubiquitously distributed in human tissues, and particularly abundant in the brain, liver, and muscles. IDE activity has been historically associated with insulin and ß-amyloid catabolism. However, over the last decade, several experimental findings have established that IDE is also involved in a wide variety of physiopathological processes, including ubiquitin clearance and Varicella Zoster Virus infection. In this study, we demonstrate that normal and malignant cells exposed to different stresses markedly up-regulate IDE in a heat shock protein (HSP)-like fashion. Additionally, we focused our attention on tumor cells and report that (i) IDE is overexpressed in vivo in tumors of the central nervous system (CNS); (ii) IDE-silencing inhibits neuroblastoma (SHSY5Y) cell proliferation and triggers cell death; (iii) IDE inhibition is accompanied by a decrease of the poly-ubiquitinated protein content and co-immunoprecipitates with proteasome and ubiquitin in SHSY5Y cells. In this work, we propose a novel role for IDE as a heat shock protein with implications in cell growth regulation and cancer progression, thus opening up an intriguing hypothesis of IDE as an anticancer target.

Age-related increase of stem marker expression influences vascular smooth muscle cell properties.

OBJECTIVE: Aging represents a major risk factor for vascular disease development. With aging, changes of the biological properties of vascular smooth muscle cells (SMCs) are observed. Stem marker expression characterizes SMCs during developmental growth and atherosclerosis, but the contribution of SMCs with stem features to the age-related arterial remodeling remains largely unknown. METHODS AND RESULTS: Immunostaining revealed rare vascular growth factor receptor-1(+) (flt-1(+)) and c-kit(+) cells in tunica media of grossly normal human young (17-30 years old) large arteries and 2-month old rat aorta, whereas CD133(+) cells were absent. In large arteries of human aged donors (64-77 years), flt-1(+) and c-kit(+) cell number increased in the intimal thickening and tunica media. Double immunofluorescence revealed that 30.6 ± 3% of flt-1(+) intimal cells co-expressed α-smooth muscle actin. Immunostaining, blots and RT-PCR documented the increased expression of flt-1 and c-kit in 20-24-month old rat aortic media. In vitro, old rat aortic SMCs proliferated and migrated more with greater flt-1, c-kit, NF-κB, VCAM-1, IAP-1 and MCP-1 levels and less α-smooth muscle actin and myosin compared to young SMCs. Old SMCs were also more susceptible to all-trans retinoic and NF-κB inhibition-induced apoptosis compared to young SMCs. Anti-flt-1 blocking antibody reduced migration and placental growth factor-induced but not serum and PDGF-BB-stimulated proliferation of old SMCs. CONCLUSIONS: The increase of flt-1(+) and c-kit(+) SMCs characterizes large arteries of aged donors; the blocking of flt-1 signaling influences the behavior of old SMCs, suggesting that the accumulation of SMCs with a stem phenotype contributes to the age-dependent adverse arterial remodeling.

Interferon gamma upregulates frataxin and corrects the functional deficits in a Friedreich ataxia model.

Friedreich's ataxia (FRDA) is the most common hereditary ataxia, affecting ∼3 in 100 000 individuals in Caucasian populations. It is caused by intronic GAA repeat expansions that hinder the expression of the FXN gene, resulting in defective levels of the mitochondrial protein frataxin. Sensory neurons in dorsal root ganglia (DRG) are particularly damaged by frataxin deficiency. There is no specific therapy for FRDA. Here, we show that frataxin levels can be upregulated by interferon gamma (IFNγ) in a variety of cell types, including primary cells derived from FRDA patients. IFNγ appears to act largely through a transcriptional mechanism on the FXN gene. Importantly, in vivo treatment with IFNγ increases frataxin expression in DRG neurons, prevents their pathological changes and ameliorates the sensorimotor performance in FRDA mice. These results disclose new roles for IFNγ in cellular metabolism and have direct implications for the treatment of FRDA.

Preventing the ubiquitin-proteasome-dependent degradation of frataxin, the protein defective in Friedreich's ataxia.

Friedreich's ataxia (FRDA) is a devastating orphan disease, with no specific treatment. The disease is caused by reduced expression of the protein frataxin, which results in mitochondrial defects and oxidative damage. Levels of residual frataxin critically affect onset and progression of the disease. Understanding the molecular mechanisms that regulate frataxin stability and degradation may, therefore, be exploited for the design of effective therapeutics. Here we show that frataxin is degraded by the ubiquitin-proteasome system and that K(147) is the critical residue responsible for frataxin ubiquitination and degradation. Accordingly, a K(147)R substitution generates a more stable frataxin. We then disclose a set of lead compounds, computationally selected to target the molecular cleft harboring K(147), that can prevent frataxin ubiquitination and degradation, and increase frataxin levels in cells derived from FRDA patients. Moreover, treatment with these compounds induces substantial recovery of aconitase activity and adenosine-5'-triphosphate levels in FRDA cells. Thus, we provide evidence for the therapeutic potential of directly interfering with the frataxin degradation pathway.

Propionyl-L-carnitine improves postischemic blood flow recovery and arteriogenetic revascularization and reduces endothelial NADPH-oxidase 4-mediated superoxide production.

OBJECTIVE: The beneficial effect of the natural compound propionyl-l-carnitine (PLC) on intermittent claudication in patients with peripheral arterial disease is attributed to its anaplerotic function in ischemic tissues, but inadequate information is available concerning action on the vasculature. METHODS AND RESULTS: We investigated the effects of PLC in rabbit hind limb collateral vessels after femoral artery excision, mouse dorsal air pouch, chicken chorioallantoic membrane, and vascular cells by angiographic, Doppler flow, and histomorphometrical and biomolecular analyses. PLC injection accelerated hind limb blood flow recovery after 4 days (P<0.05) and increased angiographic quadriceps collateral vascularization after 7 days (P<0.001) Histomorphometry confirmed the increased vascular area (P<0.05), with unchanged intramuscular capillary density. PLC-induced dilatative adaptation, and growth was found associated with increased inducible nitric oxide synthase and reduced arterial vascular endothelial growth factor and intracellular adhesion molecule-1 expression. PLC also increased vascularization in air pouch and chorioallantoic membrane (P<0.05), particularly in large vessels. PLC increased endothelial and human umbilical vascular endothelial cell proliferation and rapidly reduced inducible nitric oxide synthase and NADPH-oxidase 4-mediated reactive oxygen species production in human umbilical vascular endothelial cells; NADPH-oxidase 4 also regulated NF-kappaB-independent intracellular adhesion molecule-1 expression. CONCLUSIONS: Our results provided strong evidence that PLC improves postischemic flow recovery and revascularization and reduces endothelial NADPH-oxidase-related superoxide production. We recommend that PLC should be included among therapeutic interventions that target endothelial function.

Flt-1 expression influences apoptotic susceptibility of vascular smooth muscle cells through the NF-kappaB/IAP-1 pathway.

AIMS: Flt-1 is an fms-like tyrosine kinase receptor which binds to vascular endothelial growth factor (VEGF) and placental growth factor (PlGF). Ligand activation and blocking of flt-1 influence several vascular smooth muscle cell (SMC) functions, including apoptotic susceptibility. However, downstream signal transduction pathways by which flt-1 regulates SMC apoptosis have still to be investigated. METHODS AND RESULTS: Flt-1 expression and apoptosis in Wistar rat aortic intimal cells 15 days after ballooning were studied by immunohistochemistry, cytometry, cell sorting, western blotting, and PCR. Anti-flt1 blocking antibody effects were compared with those of anti-PlGF and anti-VEGF antibodies. Rat aortic intimal cells 15 days after injury exhibited increased flt-1 protein and mRNA and lower smooth muscle markers compared with normal media SMCs. Immunoreactivity for flt-1 protein was also observed in apoptotic intimal cells. Anti-flt-1 (EC(50) = 16.5 ng/mL) and anti-PlGF (EC(50) = 20.5 ng/mL) antibodies added to intimal cultures reduced serum-deprived apoptosis but not serum- and PDGF-BB-induced proliferation; the anti-VEGF antibody was ineffective. Sorted flt-1(+) cells were more clonogenic than flt-1(-) and whole intimal SMC populations. Increased nuclear factor-kappaB (NF-kappaB) and inhibitor of apoptosis protein-1 (IAP-1) and reduced bax levels associated with the anti-flt-1-induced increase of intimal SMC survival; the latter was prevented by NF-kappaB activity inhibitor and IAP-1 interfering RNA (RNAi). Blocking of NF-kappaB activity reduced IAP-1 expression and prevented IAP-1 RNAi effects. Increased flt-1 immunoreaction was also documented in human atheromatous lesions. CONCLUSION: Our results show that anti-flt-1 blocking reduces apoptosis through NF-kappaB and the downstream IAP-1 pathway. The close link between flt-1, PlGF, and apoptotic susceptibility of intimal SMCs suggests new potential strategies aimed at influencing post-injury arterial remodelling.

Stem cell marker expression and proliferation and apoptosis of vascular smooth muscle cells.

Vascular endothelial Flt-1 and other stem cell markers are variably expressed in vascular smooth muscle cells (SMCs) during normal and pathological conditions, but their biological role remains uncertain. In normal rat aorta, rare flt-1+ and c-kit+ SMCs were detected. Fifteen days after injury, 61.8 +/- 3.8, 45.7 +/- 3% of the intimal cells resulted flt-1+ and c-kit+ and expressed low level of alpha-smooth muscle actin; CD133+ cells were 5.6 +/- 0.7%. BrDU+/flt-1+ largely predominated in the neointima, whereas BrDU+/CD133+ cells were rare. Forty-five and sixty days after injury, intimal proliferation such as BrDU+ cells was greatly reduced. After sixty days, intimal stem marker expression had almost disappeared whereas alpha-smooth muscle actin was restored. Flk-1 and Oct-4 SMC immunodection was consistently negative. In vitro, intimal cells obtained fifteen days after injury exhibited an epithelioid phenotype and increased flt-1 and c-kit protein and mRNA and low smooth muscle markers compared to spindle-shaped medial and intimal SMCs obtained after sixty days. Epithelioid clones, independently from layer of origin, were similar in stem cell marker expression. The anti-flt-1 blocking antibody added to epithelioid SMC cultures reduced serum-deprived apoptosis and migration but not PDGF-BB-induced proliferation, and increased cell-populated collagen lattice contraction. In conclusion, vascular SMC stem marker expression was variable, chronologically modulated and prevalent in epithelioid populations and clones; among stem markers, flt-1 expression critically regulates intimal SMC response to microenviromental changes.