MicroRNA-16 and MicroRNA-424 Regulate Cell-Autonomous Angiogenic Functions in Endothelial Cells via Targeting Vascular Endothelial Growth Factor Receptor-2 and Fibroblast Growth Factor Receptor-1

Prediction of miRNA Targets That Regulate Cell-Intrinsic Angiogenic Activity of ECs

We investigated the possible role of miR-16 and miR-424 in cell-intrinsic angiogenic activity of ECs. A direct effect of these miRNAs as regulators of angiogenesis in ECs has not been studied so far. miR-15a, -15b, -16 (including 16-1 and 16-2, which have the same whole mature sequence), -195, -497, and -424 have different genomic locations but possess the same seed sequence nucleotides 2 to 8 at their 5′ end (Supplemental Figure IA and IB), which implies that these miRNAs share most of their target genes.^{13,26–29,37} Therefore, to simplify, here we refer to these targets as “miR-16 predicted targets.” Perfect sequence complementarity to nucleotides 2 to 8 at the 5′ end of the miRNA, called the seed sequence, is the strongest characteristic for targeting activity and holds true for the majority of targets characterized to date.³⁸ Other characteristics, such as site location within the 3′UTR, flanking region, and conservation across multiple species, greatly increase the probability of a predicted target site being real.¹³ By combining these characteristics, numerous computational approaches have been developed to predict miRNA targets.^13,38 By using these bioinformatic tools, we determined whether miR-16 predicted targets were preferentially connected to any specific biological process (Supplemental Material and Methods, Bioinformatic Analysis). We saw enrichment for genes implicated in the control of transcription, as well as in important cellular functions, such as proliferation, cycle progression, and apoptosis, the last 2 of which were in agreement with the predictions and validated target genes reported by others.^26,27,29 Interestingly, we also observed enrichment for genes regulating angiogenesis and its related functions (proliferation, cell migration, cell differentiation, and morphogenesis, as well as relevant transcriptional regulators). Analysis of the predicted targets involved in angiogenesis revealed that the majority of them (81%) were positive regulators of angiogenesis (Supplemental Figure II). Among the predicted targets found, of note were VEGFR2 (also known as KDR) and FGFR1 because of their important role in the regulation of angiogenic functions of ECs.⁸ These 2 genes, along with VEGF, which was previously reported to be a target for miR-16,^30,39 were selected for further analysis.

miR-16 and miR-424 Regulate VEGFR2, FGFR1, and VEGF Expression by Targeting the VEGFR2, FGFR1, and VEGF 3′UTRs

First, we analyzed the expression of the selected miRNAs (ie, miR-16 and miR-424) in ECs. As shown in Supplemental Figure IIIA, the relative levels of these miRNAs in human primary ECs (HUVECs and human aortic ECs) were very similar to those of other human primary cells, such as vascular smooth muscle cells and fibroblasts, but they were very highly expressed in HeLa cells (a highly proliferative tumor cell line). Because these miRNAs play very important roles in regulating cell and cell cycle progression,²⁶ the reduced levels of miR-16/424 would allow HeLa cells to maintain a highly proliferative state with respect to the primary cell lines analyzed, including ECs.

We then analyzed whether “miR-16-like miRNAs” participate in the regulation of VEGFR2, FGFR1, and VEGF. Specifically, we analyzed the effect of miR-16 and miR-424 on VEGFR2, FGFR1, and VEGF. miR-16 was chosen as a representative member of miR-15 family. miR-424, although not a member of miR-15 family, was chosen because it shares the seed sequence with all the members of the miR-15 family but has a more divergent 3′ end (Supplemental Figure IB). We identified a putative binding site in the 3′UTR of VEGFR2 (Figure 1A). The miR-16/-424 predicted site is a canonical 7mer-m8 site (Supplemental Figure IC). In the specific case of miR-424, this site is supported by an additional 3′ pairing optimally centered on miRNA nucleotides 13 to 18¹³ (Supplemental Figure IC). The seed region of miR-16/-424 complementary to the sequence in the VEGFR2 3′UTR is conserved across species (not shown) and extends in humans from nucleotides 44 to 50 (Figure 1A and Supplemental Figure IC). In the FGFR1 3′UTR, we found 3 predicted sites for miR-16/-424, the first of which is a conserved canonical 7mer-m8 located in the center of the FGFR1 3′UTR (Figure 1A and Supplemental Figure IC). This site is supported by an additional 3′ pairing for miR-16 but not for miR-424 (Supplemental Figure IC). The second site is located at the end of the FGFR1 3′UTR (Figure 1A and Supplemental Figure IC) and is a 7mer-8m8 for both miR-16 and miR-424 (Supplemental Figure IC). The third site is a 3′ compensatory site, or an imperfect match to the seed¹³; however, we did not consider this site in our studies. The site predicted in the 3′UTR of VEGFA was previously reported^30,39 (Figure 1A) and is a conserved 8mer with an additional 3′ pairing for miR-16 but not for miR-424 (Supplemental Figure IC).

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Figure 1.

MicroRNA (miR)-16 and miR-424 regulate vascular endothelial growth factor receptor-2 (VEGFR2), fibroblast growth factor receptor-1 (FGFR1), and vascular endothelial growth factor (VEGF) expression by targeting the VEGFR2, FGFR1, and VEGF 3′ untranslated regions (UTRs). A, Predicted target sites (indicated in blue) for miR-16 and miR-424 in the 3′UTRs of human VEGFR2, FGFR1, and VEGF 3′UTR. PM (indicated in red) indicates mutation of the predicted miR-16/-424 seed region in the 3′UTRs of human VEGFR2, FGFR1, and VEGF 3′UTR. B to D, COS-7 cells were cotransfected with the indicated constructs (containing or not containing the above-mentioned PM) and with 30 nmol/L of miR-16, miR-424, or control mimic (CM). Data are expressed as relative luciferase activity to control samples cotransfected with an equal concentration of CM and correspond to the mean±SEM of 3 experiments performed in duplicate. *Significantly different from cells cotransfected with CM, #significantly different from cells cotransfected with miR-16 or miR-424 and control 3′UTR (P≤0.05). ORF indicates open reading frame.

To validate the predicted miRNA/mRNA interactions, the VEGFR2, FGFR1, and VEGF 3′UTRs were subcloned in a luciferase reporter vector. The resultant constructs were cotransfected into COS cells along with miR-16 or miR-424 mimic oligonucleotides or a nontargeting control mimic. Transfection with the control luciferase reporter without any 3′UTR (empty vector) did not affect luciferase activity (data not shown). Interestingly, the relative luciferase activity was significantly reduced (≈20%) when cells were cotransfected with VEGFR2 3′UTR and miR-16 or miR-424 but not with control mimic (Figure 1B). Both miR-16 or miR-424 markedly repressed FGFR1 (Figure 1C) 3′UTR activity (≈50%); this effect was likely due to the presence of 3 binding sites.¹³ Our data also indicate that miR-16, as well as miR-424, significantly reduced (≈20%) VEGF 3′UTR activity (Figure 1D), in agreement with previous reports.^30,39 In all cases, when the miRNAs were transfected together, there was no difference in the overall luciferase activity as compared with their individual effect (data not shown). This is likely due to the identical seed sequences displayed by these miRNAs. Confirming the initial results, mutation of the miR-16/-424 site abrogated the repression of VEGFR2, and VEGF 3′UTR activity, consistent with a direct interaction of miR-16/-424 with the studied sites (Figure 1B–1D). As indicated in Figure 1A, we found 3 predicted sites for miR-16/-424 in the FGFR1 3′UTR. Two of them had perfect sequence complementarities to the seed sequence, which is the strongest characteristic for targeting activity¹³ and more likely to provide the strongest effects. Mutation of these sites (sites 1 and 2) produced a partial recovery of luciferase activity, therefore indicating that the effect of site 3 was not eliminated.

We further examined the effects of miR-16/-424 on VEGFR2, FGFR1, and VEGF expression in ECs (Figure 2 and Supplemental Figure IV). We first analyzed miRNA levels after transfection with miRNA mimics or inhibitors to measure transfection efficiency in ECs. As shown in Supplemental Figure IIIB, overexpression with both miR-16 and miR-424 mimics in HUVECs efficiently increased the levels of these miRNAs, and more importantly, overexpression of one of them did not affect the expression of the other. Furthermore, inhibition of endogenous miR-16 and miR-424 with specific inhibitors reduced their intracellular levels in a specific manner (Supplemental Figure IIIC). Finally, we analyzed the effect of miR-16/-424 on VEGFR2, FGFR1, and VEGF expression. HUVECs were transfected with miR-16 or miR-424 mimics, and the effects on protein and mRNA levels were analyzed 36 hours posttransfection. As shown in Figure 2A to 2C, both miR-16 and miR-424 significantly decreased VEGFR2, FGFR1, and VEGF protein and mRNA levels. Importantly, inhibition of endogenous miR-16 or miR-424 increased the expression of VEGFR2, FGFR1, and VEGF at both the protein and mRNA levels (Figure 2B–2D). The targeting activity of these miRNAs on VEGFR2 and FGFR1 was also relevant for human aortic ECs (data not shown), a human adult EC type from a different vascular bed than HUVECs. In addition, and consistent with the conservation of these sites across species, similar results were obtained using bovine aortic ECs (Supplemental Figure IV).

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Figure 2.

MicroRNA (miR)-16 and miR-424 modulate vascular endothelial growth factor receptor-2 (VEGFR2), fibroblast growth factor receptor-1 (FGFR1), and vascular endothelial growth factor (VEGF) expression in endothelial cells (ECs). Human umbilical vascular ECs (HUVECs) were transfected for 12 hours with miR-16, miR-424, or control mimic (CM) (A and C) or with inhibitor miR-16 (I-miR-16), inhibitor miR-424 (I-miR-424), or control inhibitor (CI) (B and D). In both cases, cells were harvested 36 hours posttransfection. A and B, Protein levels of VEGFR2, FGFR1, and VEGF were detected by Western blot. Heat shock protein-90 (HSP-90) was used as a loading control. In the quantification (right graphs), data are expressed as relative total protein levels and correspond to mean±SEM of 3 experiments. C and D, mRNA expression of VEGFR2, FGFR1, and VEGF was quantified by quantitative reverse transcription–polymerase chain reaction. Data are expressed as relative expression and correspond to mean±SEM of 3 experiments. *Significantly different from cells transfected with CM or CI, P≤0.05.

VEGF- and bFGF-Regulated Expression of miR-16 and miR-424 Is Relevant for the Targeting of VEGFR2 and FGFR1 in ECs

It has been well established that both the VEGFR2 and FGFR1 signaling pathways play crucial roles in angiogenesis. Interestingly, accumulating evidence has now implicated endothelial miRNAs in this process. To examine the potential relationship between VEGFR2 and FGFR1 signaling and miR-16 or miR-424, we asked whether VEGF or bFGF modulated the cell-intrinsic expression of miR-16/-424 in HUVECs. As shown in Figure 3A, both cytokines regulated the expression of the mature form of miR-16 and miR-424. To identify whether these cytokines regulated the expression of these miRNAs at the transcriptional level, we examined the expression of primary transcripts containing the stem loop of the miRNA of interest. As shown in Figure 3B, both VEGF and bFGF increased the expression of pri-miR-16-1 (detects stem loops of miR-15b and miR-16-1 transcribed from chromosome 13) and, modestly, pri-miR-16-2 (detects stem loops of miR-15b and miR-16-1 transcribed from chromosome 3), suggesting a transcriptional regulation of these 2 clusters by these cytokines. In contrast, the expression of pri-miR-424 remained essentially unchanged, suggesting that VEGF and bFGF likely modulate the processing of miR-424 from the preexisting primary transcript (ie, the increase in the mature form, Figure 3A) without affecting its transcriptional expression.

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Figure 3.

Vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) regulate microRNA (miR)-16 and miR-424 expression in endothelial cells. A and B, Human umbilical vascular endothelial cells (HUVECs) were starved (0.1% bovine serum albumin [BSA]) for 12 hours and then treated with VEGF (50 ng/mL), bFGF (25 ng/mL) or non treated (NT) for the indicated times. Mature miR-16 and miR-424 (A) and primary transcript (pri-miR)-16-1/-2 and pri-miR-424 (B) expression was quantified by quantitative reverse transcription–polymerase chain reaction. Data are expressed as relative expression and correspond to mean±SEM of 3 experiments. *Significantly different from cells without treatment, P≤0.05. C, HUVECs were transfected for 6 hours with empty vector, vascular endothelial growth factor receptor-2 (VEGFR2), or fibroblast growth factor receptor-1 (FGFR1) 3′ untranslated region (UTR) construct; 12 hours posttransfection, cells were starved (0.1% BSA) for 12 hours and then treated with VEGF for the indicated times. D, HUVECs were transfected as above in the presence or not of 60 nmol/L inhibitor miR-16 (I-miR-16), inhibitor miR-424 (I-miR-424), or control inhibitor (CI). Thirty-six hours posttransfection, cells were starved (0.1% BSA) for 12 hours and then treated with VEGF for the indicated times. Data are expressed as luciferase activity relative to control samples cotransfected with an equal concentration CI and correspond to the mean±SEM of 3 experiments performed in duplicate. *Significantly different from cells cotransfected with CI and VEGF 3′UTR, #significantly different from cells cotransfected with CI and VEGF 3′UTR plus VEGF treatment, P≤0.05.

Regardless of whether the effect is at the transcriptional or posttranscriptional level, both VEGF and bFGF have similar effects (stimulation) on miR-16 and miR-424 mature expression. We then investigated whether VEGF directly regulated VEGFR2 or FGFR1 3′UTRs via miR-16 in ECs. For these experiments, we used the luciferase reporter assay, described above, directly in HUVECs. As shown in Figure 3C, stimulation of HUVECs with VEGF reduced both VEGFR2 and FGFR1 3′UTR activity, whereas no effect was observed when cells were transfected with the empty vector control, indicating that some endogenous miRNAs involved in the regulation of VEGFR2 and FGFR1 were induced to regulate their expression under stimulated conditions. Interestingly, endogenous inhibition of miR-16 or miR-424 before VEGF stimulation restored VEGFR2 and FGFR1 3′UTR activity (Figure 3D), indicating that these effects are likely to be mediated by miR-16 and miR-424 upregulation in ECs.

miR-16 and miR-424 Reduce Proliferation and Migration and Impair EC Cord Formation

Next, we tested whether the effects observed on VEGFR2, FGFR1, and VEGF expression were functional. To this end, we examined the effects of miR-16 and miR-424 on 3 angiogenic phenotypes of ECs, namely proliferation, migration, and morphogenesis (cord formation). Previous results have shown that both miR-16 and miR-424 regulate cell proliferation in different cell types.^26–28,33 In agreement with these data, we observed that miR-16 or miR-424 had a negative effect on cell proliferation. As seen in Figure 4A, overexpression of miR-16 or miR-424 reduced cell proliferation in HUVECs without a significant induction of apoptosis assessed by induction of caspase-3 cleavage or increase in sub-G₀/G₁ population by flow cytometry (Supplemental Figure VA and VB, respectively). Moreover, under stress conditions, such as prolonged serum starvation,⁴⁰ both miR-16 and miR-424 further reduced the number of cells assessed by crystal violet staining (Figure 4B). Interestingly, 9 additional hours in the absence of VEGF diminished the cell number in both control mimic and miRNA-overexpressing cells. Treatment with exogenous VEGF produced partial rescue in control cells without affecting miRNA-overexpressing cells (Figure 4B), suggesting an altered response to VEGF in cells overexpressing miR-16 or miR-424. Next, we examined the effects of these miRNAs on EC migration. Overexpression of miR-16 or miR-424 reduced basal migration, as well as VEGF- or bFGF-induced migration, in bovine aortic ECs (Figure 4C). miR-16 and miR-424 overexpression in HUVECs also resulted in significant impairment of cord formation under basal conditions and following stimulation with VEGF or bFGF (Figure 4D). Converse effects on migration and cord formation were obtained when the endogenous levels of these miRNAs were inhibited (Supplemental Figure VI). Importantly, we also overexpressed either VEGFR2 or FGFR1 cDNA together with a miR-16 mimic in HUVECs and evaluated their effect on EC migration in response to VEGF or bFGF (Supplemental Figure VII). As shown in Supplemental Figure VIIA, transfection of HUVECs with VEGFR2 or FGFR1 cDNA (without the respective 3′UTR) for 24 hours was very efficient, and in both cases, high levels of VEGFR2 and FGFR1 were obtained. Interestingly, VEGFR2 or FGFR1 overexpression rescued the inhibitory effect of miR-16 in EC migration. Altogether, these data indicate that miR-16/-424 regulates cell-intrinsic angiogenic responses in vitro and are consistent with their targeting activity on VEGFR2, FGFR1, and VEGF in ECs.

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Figure 4.

MicroRNA (miR)-16 and miR-424 reduce proliferation and migration and impair endothelial cell cord formation. A, Human umbilical vascular endothelial cells (HUVECs) were transfected for 12 hours with miR-16, miR-424, or control mimic (CM). Cells were harvested and counted 36 hours posttransfection. Data are expressed as relative number of cells and correspond to mean±SEM of 3 experiments performed in duplicate. B, HUVECs were transfected as indicated in A. Thirty-six hours posttransfection, cells were starved (0.1% bovine serum albumin [BSA]) for 16 hours and then treated or not with vascular endothelial growth factor (VEGF) for an additional 9 hours. Cells were washed and stained by crystal violet as indicated in the Materials and Methods section. Data are expressed as cell survival and correspond to mean±SEM of 3 experiments. C, Bovine aortic endothelial cells (BAECs) were transfected as indicated in A. Thirty-six hours posttransfection, migration in response to VEGF or basic fibroblast growth factor (bFGF) was quantified as described in the Materials and Methods section. The average number of cells from 5 randomly chosen fields on the lower side of the membrane of each well was counted. Data are expressed as migrated cells and correspond to mean±SEM of 3 experiments performed in duplicate. D, HUVECs were transfected as indicated in A. Thirty-six hours posttransfection, cells were counted and seeded on growth factor–reduced Matrigel in the presence of 0.1% FBS (basal, left), 0.1% FBS+VEGF (VEGF stimulated, middle), and 0.1% FBS+bFGF (bFGF stimulated, right). Cumulative sprout length of capillary-like structures was measured by light microscopy after 12 hours. Representative micrographs and quantification are shown. Scale bars=100 μmol/L. Data are expressed as cumulative tube lengths and correspond to mean±SEM of 3 experiments performed in duplicate. *Significantly different from cells transfected with CM, #significantly different from basal conditions, P≤0.05.

miR-16 and miR-424 Regulate VEGF and bFGF Signaling Through VEGFR2 and FGR1

To test the potential involvement of these miRNAs on VEGFR2 and FGFR1 signaling more directly, we examined the effect of the reduction of VEGFR2 and FGFR1 via miR-16 overexpression on v-akt murine thymoma viral oncogene (Akt) and tracellular signal-regulated kinase 1/2 (ERK1/2) activation because these downstream effectors (namely the phosphatidylinositol 3-kinase/Akt and Ras/Raf/Erk pathways) are activated after VEGF or bFGF stimulation in ECs. As seen in Figure 5A and 5B, Akt and ERK1/2 phosphorylation were reduced in response to VEGF or bFGF stimulation (Figure 5A and 5B, respectively) in ECs transfected with miR-16. Similar results were obtained when cells were transfected with miR-424 (Supplemental Figure VIII). Interestingly, when cells were stimulated with sphingosine-1-phosphate, which signals primarily through a family of 5 G-protein-coupled receptors (EDG receptors),⁴¹ Akt and ERK1/2 activation was not significantly affected by miR-16 overexpression (Figure 5C). Altogether, these data suggest that these miRNAs are likely to control proliferation, migration, and differentiation of ECs by regulation of VEGF and bFGF signaling through VEGFR2 and FGFR1.

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Figure 5.

MicroRNA (miR)-16 modulates vascular endothelial growth factor (VEGF) signaling. Bovine aortic endothelial cells (BAECs) were transfected for 12 hours with miR-16 or control mimic (CM). Thirty-six hours posttransfection, cells were starved (0.1% bovine serum albumin) for 12 hours and then treated with VEGF (50 ng/mL) (A), basic fibroblast growth factor (bFGF) (25 ng/mL) (B), or sphingosine-1-phosphate (S1P) (400 nmol/L) (C) for the indicated times. Phospho (P)-v-akt murine thymoma viral oncogene homolog (AKT) (Ser-473) and phospho-tracellular signal-regulated kinase (ERK) (Thr202/Tyr204) protein levels were detected by Western blot. Blots for vascular endothelial growth factor receptor-2 (VEGFR2) and fibroblast growth factor receptor-1 (FGFR1) are shown as control of miR-16 action. Heat shock protein-90 (HSP-90) was used as loading control. In the quantification (graphs, right) data are expressed as fold activation over control and correspond to mean±SEM of 3 experiments. *Significantly different from cells without VEGF or bFGF treatment, P≤0.05.

miR-16 Reduces Blood Vessel Formation In Vivo

In a final series of experiments, we evaluated the effect of miR-16 on the ability of human ECs to form capillary-like structures in vivo using a previously described model for forming tubes within a 3-dimensional gel with cultured HUVECs.^34,42 We used lentiviral vectors to manipulate the levels of miRNAs in vivo as reported previously.⁴³ HUVECs were efficiently transduced with a miR-16 lentiviral vector or scr-miR (Figure 6A) and then suspended in collagen-fibronectin protein gels.^34,36,42 These gels were then implanted into the abdominal wall of immunocompetent mice. Consistent with previous reports, HUVEC-derived cords formed in vitro survive and evolve into tubes that inosculated with the host microcirculation.^34,42 Grafts were explanted for evaluation at 14 and 21 days. Interestingly, 7 days after implantation, HUVECs transduced with either scr-miR or miR-16 that were kept in culture in parallel maintained green fluorescent protein expression (Figure 6B). Moreover, miR-16 transduced HUVECs presented increased levels of miR-16 (Figure 6C) and, as expected, a concomitant decrease in the expression of VEGFR2, FGFR1, and VEGF (Figure 6D). Gross visualization of constructs harvested 14 days after implantation appeared to be blood-perfused by mouse circulation; however, those containing miR-16 transduced HUVECs seemed to be, in general, less efficiently perfused and cellularized and slightly smaller than scr-miR implants (Figure 6). Moreover, miR-16 implants contained significantly fewer capillary structures (Figure 6F), as assessed by both human platelet endothelial cell adhesion molecule-1 or Ulex europaeus agglutinin-1 lectin staining (reacts with the blood group ABH expressed on human EC) for detection of human EC-lined vessels within engrafted protein gels, respectively. In both cases, the majority of the structures were wholly composed of human ECs, as anti-mouse platelet endothelial cell adhesion molecule-1 antibodies reacted with fewer than 1% of the vascular profiles within the constructs (data not shown), confirming that the vessel-like structures detected were not formed by mouse neovascularization of the gel and consistent with previous reports of this model.⁴² After 21 days of implantation, platelet endothelial cell adhesion molecule-1-positive structures were present throughout the collagen-fibronectin gel of scr-miR implants; however, they were largely absent in the gels containing miR16-HUVECs (Supplemental Figure IX). Altogether, these data indicate that miR-16 participates in the regulation of neovascularization in vivo by controlling the cell-intrinsic angiogenic activity of ECs.

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Figure 6.

MicroRNA (miR)-16 reduces microvessel formation in vivo. A, Human umbilical vascular endothelial cells (HUVECs) were transduced with miR-16 or scrambled miRNA (scr-miR) as indicated in Material and Methods section. Green fluorescent protein (GFP) expression (FL1-H) was analyzed by flow cytometry prior gel implantation. B to D, HUVECs that were transduced with either miR-16 and scr-miR as above indicated were kept in culture 7 days after implantation. B, Representative fluorescence micrographs of GFP detection are shown. Magnification ×20. C and D, Mature miR-16 (C) and mRNA expression of vascular endothelial growth factor receptor-2 (VEGFR2), fibroblast growth factor receptor-1 (FGFR1), and vascular endothelial growth factor (VEGF) (D) was quantified by quantitative reverse transcription–polymerase chain reaction. Data are expressed as relative expression and correspond to mean±SEM *Significantly different from cells transduced with scr-miRNA, P≤0.05. Grafts from miR-16 or scr-miR-transduced HUVECs were isolated 14 days after implantation. E, Representative micrographs of the gel implants and hematoxylin/eosin staining are shown. Magnification ×0.5 (left) and ×10 (right). F, Grafts from miR-16- or scr-miR-transduced HUVECs were isolated 14 days after implantation. Representative platelet endothelial cell adhesion molecule-1 (PECAM-1) and Ulex europaeus agglutinin (UEA)-1 staining is shown. Scale bars=100 μmol/L. In the quantification, data are expressed as PECAM-1- or UEA-1-positive capillary structures of 2 to 4 images from 5 sections per animal and correspond to mean±SEM (n=5 animals per group). *Significantly different from cells transduced with scr-miRNA, P≤0.05.