Impacts of femoral artery and vein excision versus femoral artery excision on the hindlimb ischemic model in CD-1 mice

Keratose Hydrogel Drives Differentiation of Cardiac Vascular Smooth Muscle Progenitor Cells: Implications in Ischemic Treatment

Peripheral artery disease (PAD) is a common vascular disorder in the extremity of limbs with limited clinical treatments. Stem cells hold great promise for the treatment of PAD, but their therapeutic efficiency is limited due to multiple factors, such as poor engraftment and non-optimal selection of cell type. To date, stem cells from a variety of tissue sources have been tested, but little information is available regarding vascular smooth muscle cells (VSMCs) for PAD therapy. The present study examines the effects of keratose (KOS) hydrogels on c-kit+/CD31- cardiac vascular smooth muscle progenitor cell (cVSMPC) differentiation and the therapeutic potential of the resultant VSMCs in a mouse hindlimb ischemic model of PAD. The results demonstrated that KOS but not collagen hydrogel was able to drive the majority of cVSMPCs into functional VSMCs in a defined Knockout serum replacement (SR) medium in the absence of differentiation inducers. This effect could be inhibited by TGF-β1 antagonists. Further, KOS hydrogel increased expression of TGF-β1-associated proteins and modulated the level of free TGF-β1 during differentiation. Finally, transplantation of KOS-driven VSMCs significantly increased blood flow and vascular densities of ischemic hindlimbs. These findings indicate that TGF-β1 signaling is involved in KOS hydrogel-preferred VSMC differentiation and that enhanced blood flow are likely resulted from angiogenesis and/or arteriogenesis induced by transplanted VSMCs.

Inhibition of transient receptor potential cation channel 6 promotes capillary arterialization during post-ischaemic blood flow recovery

BACKGROUND AND PURPOSE

Capillary arterialization, characterized by the coverage of pre-existing or nascent capillary vessels with vascular smooth muscle cells (VSMCs), is critical for the development of collateral arterioles to improve post-ischaemic blood flow. We previously demonstrated that the inhibition of transient receptor potential 6 subfamily C, member 6 (TRPC6) channels facilitate contractile differentiation of VSMCs under ischaemic stress. We here investigated whether TRPC6 inhibition promotes post-ischaemic blood flow recovery through capillary arterialization in vivo.

EXPERIMENTAL APPROACH

Mice were subjected to hindlimb ischaemia by ligating left femoral artery. The recovery rate of peripheral blood flow was calculated by the ratio of ischaemic left leg to non-ischaemic right one. The number and diameter of blood vessels were analysed by immunohistochemistry. Expression and phosphorylation levels of TRPC6 proteins were determined by western blotting and immunohistochemistry.

KEY RESULTS

Although the post-ischaemic blood flow recovery is reportedly dependent on endothelium-dependent relaxing factors, systemic TRPC6 deletion significantly promoted blood flow recovery under the condition that nitric oxide or prostacyclin production were inhibited, accompanying capillary arterialization. Cilostazol, a clinically approved drug for peripheral arterial disease, facilitates blood flow recovery by inactivating TRPC6 via phosphorylation at Thr69 in VSMCs. Furthermore, inhibition of TRPC6 channel activity by pyrazole-2 (Pyr2; BTP2; YM-58483) promoted post-ischaemic blood flow recovery in Apolipoprotein E-knockout mice.

CONCLUSION AND IMPLICATIONS

Suppression of TRPC6 channel activity in VSMCs could be a new strategy for the improvement of post-ischaemic peripheral blood circulation.

Mesenchymal Stromal Cells Combined With Elastin-Like Recombinamers Increase Angiogenesis In Vivo After Hindlimb Ischemia

Hindlimb ischemia is an unmet medical need, especially for those patients unable to undergo vascular surgery. Cellular therapy, mainly through mesenchymal stromal cell (MSC) administration, may be a potentially attractive approach in this setting. In the current work, we aimed to assess the potential of the combination of MSCs with a proangiogenic elastin-like recombinamer (ELR)–based hydrogel in a hindlimb ischemia murine model. Human bone marrow MSCs were isolated from four healthy donors, while ELR biomaterials were genetically engineered. Hindlimb ischemia was induced through ligation of the right femoral artery, and mice were intramuscularly injected with ELR biomaterial, 0.5 × 10⁶ MSCs or the combination, and also compared to untreated animals. Tissue perfusion was monitored using laser Doppler perfusion imaging. Histological analysis of hindlimbs was performed after hematoxylin and eosin staining. Immunofluorescence with anti–human mitochondria antibody was used for human MSC detection, and the biomaterial was detected by elastin staining. To analyze the capillary density, immunostaining with an anti–CD31 antibody was performed. Our results show that the injection of MSCs significantly improves tissue reperfusion from day 7 (p = 0.0044) to day 21 (p = 0.0216), similar to the infusion of MSC + ELR (p = 0.0038, p = 0.0014), without significant differences between both groups. After histological evaluation, ELR hydrogels induced minimal inflammation in the injection sites, showing biocompatibility. MSCs persisted with the biomaterial after 21 days, both in vitro and in vivo. Finally, we observed a higher blood vessel density when mice were treated with MSCs compared to control (p<0.0001), but this effect was maximized and significantly different to the remaining experimental conditions when mice were treated with the combination of MSCs and the ELR biomaterial (p < 0.0001). In summary, the combination of an ELR-based hydrogel with MSCs may improve the angiogenic effects of both strategies on revascularization of ischemic tissues.

Effects of STAT3 on aging-dependent neovascularization impairment following limb ischemia: from bedside to bench

Aging is a major risk factor for ischemic hypoxia-related diseases, including peripheral artery diseases (PADs). Signal transducer and activator of transcription 3 (STAT3) is a critical transcription activator in angiogenesis. Nevertheless, the effect of aging on endothelial cells and their responses to hypoxia are not well studied. Using a hindlimb hypoxic/ischemic model of aged mice, we found that aged mice (80-100-week-old) expressed significantly lower levels of angiogenesis than young mice (10-week-old). In our in vitro study, aged endothelial cells (≥30 passage) showed a significant accumulation of β-galactosidase and a high expression of aging-associated genes, including p16, p21, and hTERT compared with young cells (<10 passage). After 24 hours of hypoxia exposure, proliferation, migration and tube formation were significantly impaired in aged cells compared with young cells. Notably, STAT3 and angiogenesis-associated proteins such as PI3K/AKT were significantly downregulated in aged mouse limb tissues and aged cells. Further, using STAT3 siRNA, we found that suppressing STAT3 expression in endothelial cells impaired proliferation, migration and tube formation under hypoxia. Correspondingly, in patients with limb ischemia we also observed a higher expression of circulating STAT3, associated with a lower rate of major adverse limb events (MALEs). Collectively, STAT3 could be a biomarker reflecting the development of MALE in patients and also a regulator of age-dependent angiogenesis post limb ischemia. Additional studies are required to elucidate the clinical applications of STAT3.

Deletion of MicroRNA-21 Impairs Neovascularization Following Limb Ischemia: From Bedside to Bench

With an increasing prevalence, peripheral arterial disease (PAD), cause by atherosclerosis is a new threat to public health beyond coronary artery disease and involves aberrant vascular endothelial cell proliferation and angiogenesis. The degree of vascular remodeling is influenced by the processes described. MicroRNA-21 (miR-21) has been found to play a critical role in cellular functions, including angiogenesis. Nevertheless, the effect of miR-21 on endothelial cells in response to hypoxia is largely unknown. Using wild-type C57BL/6J and miR-21^–/– mice, we compared the capability of angiogenesis in response to hindlimb hypoxic/ischemia. In an in vitro study, we further studied whether overexpression of miR-21 mitigates hypoxia-induced apoptosis and impaired angiogenesis. Also, we prospectively collected the sera of patients with limb ischemia and followed the clinical information, including major adverse limb events (MALEs). Using laser Doppler perfusion imaging and CD31 staining, compared with miR-21^–/– mice, wild-type mice expressed a significantly higher capability of angiogenesis and less apoptosis following 28 days of hindlimb hypoxic/ischemic surgery. In our in vitro study, after 24 h of hypoxia, proliferation, migration, and tube formation were significantly impaired in cells treated with the miR-21 inhibitor but rescued by the miR-21 mimic. Mechanistically, by suppressing PTEN/PI3K/AKT, miR-21 promoted angiogenesis and suppressed apoptosis in endothelial cells post hypoxia. In patients with limb ischemia, the high expression of circulating miR-21 was associated with less subsequent MALE. Collectively, miR-21 could be a biomarker associated with the endogenous ability of angiogenesis and reflect subsequent MALE in patients. Additionally, abolishing miR-21 impairs angiogenesis and promotes apoptosis post limb ischemia. Further studies are required to elucidate the clinical applications of miR-21.

Effect of intentional restriction of venous return on tissue oxygenation in a porcine model of acute limb ischemia

INTRODUCTION

A sufficient oxygen supply to ischemic limb tissue is the most important requirement for wound healing and limb salvage. We investigated whether partial venous occlusion in the common iliac vein (CIV) causes a further increase of venous oxygenation in a porcine model of acute hindlimb ischemia.

MATERIALS AND METHODS

In 7 pigs, the model of acute hindlimb ischemia was created with intra-vascular embolization of the common iliac artery (CIA). The arterial and venous oxygen saturation was evaluated at different moments. Oxygen saturation was evaluated at baseline (T0), just after the arterial embolization (T1), at 10 minutes (T2), at 20 minutes (T3), and at 40 minutes (T4). Next, an intentional partial venous occlusion was achieved by inflating the vascular balloon at the level of the right CIV. Then, blood sampling was repeated at 5 minutes (T5), at 15 minutes (T6), and at 25 minutes (T7).

RESULTS

The arterial oxygen saturation in the right SFA was similar during all phases. In contrast, after arterial embolization, an immediate reduction of venous oxygen saturation was observed (from 85.57 ± 1.72 at T0 to 71.86 ± 7.58 at T4). After the partial venous occlusion, interestingly, the venous oxygen saturations (T5-T7) were significantly increased, again. The venous oxygen saturations evaluated in the hindlimb ischemia with partial venous occlusion and in the control limb (without partial venous occlusion) were significantly over time. Venous oxygen saturations in the experimental limbs were higher than those in the control limbs (79.28 ± 4.82 vs 59.00 ± 2.82, p-value <0.001, 79.71 ± 4.78 vs 60.00 ± 4.24 at T7, p-value <0.001).

CONCLUSIONS

Partial venous occlusion results in an increase of venous oxygen saturation in the ischemic limb, while significant changes in venous oxygen saturation are not observed in the control limb. An explanation for this may be that the oxygen consumption in the limb tissue is increased because it gets congested with the partial venous occlusion in the right CIV.

Surface Tethering of Inflammation-Modulatory Nanostimulators to Stem Cells for Ischemic Muscle Repair

Stem cell transplantation has been a promising treatment for peripheral arterial diseases in the past decade. Stem cells act as living bioreactors of paracrine factors that orchestrate tissue regeneration. Prestimulated adipose-derived stem cells (ADSCs) have been proposed as potential candidates but have been met with challenges in activating their secretory activities for clinical use. Here, we propose that tethering the ADSC surface with nanoparticles releasing tumor necrosis factor α (TNFα), named nanostimulator, would stimulate cellular secretory activity in situ. We examined this hypothesis by complexing octadecylamine-grafted hyaluronic acid onto a liposomal carrier of TNFα. Hyaluronic acid increased the liposomal stability and association to CD44 on ADSC surface. ADSCs tethered with these TNFα carriers exhibited up-regulated secretion of proangiogenic vascular endothelial growth factor and immunomodulatory prosteoglandin E2 (PGE₂) while decreasing secretion of antiangiogenic pigment epithelium-derived factors. Accordingly, ADSCs tethered with nanostimulators promoted vascularization in a 3D microvascular chip and enhanced recovery of perfusion, walking, and muscle mass in a murine ischemic hindlimb compared to untreated ADSCs. We propose that this surface tethering strategy for in situ stimulation of stem cells would replace the costly and cumbersome preconditioning process and expedite clinical use of stem cells for improved treatments of various injuries and diseases.

Consensus guidelines for the use and interpretation of angiogenesis assays

The formation of new blood vessels, or angiogenesis, is a complex process that plays important roles in growth and development, tissue and organ regeneration, as well as numerous pathological conditions. Angiogenesis undergoes multiple discrete steps that can be individually evaluated and quantified by a large number of bioassays. These independent assessments hold advantages but also have limitations. This article describes in vivo, ex vivo, and in vitro bioassays that are available for the evaluation of angiogenesis and highlights critical aspects that are relevant for their execution and proper interpretation. As such, this collaborative work is the first edition of consensus guidelines on angiogenesis bioassays to serve for current and future reference.