CD54+ rabbit adipose-derived stem cells overexpressing HIF-1α facilitate vascularized fat flap regeneration

Advanced platelet-rich fibrin promotes the paracrine function and proliferation of adipose-derived stem cells and contributes to micro-autologous fat transplantation by modulating HIF-1α and VEGF

Background

The micro-autologous fat transplantation (MAFT) technique has demonstrated its feasibility in multiple medical fields, such as facial rejuvenation. Advanced platelet-rich fibrin (APRF), an autologous platelet concentrated on a fibrin membrane without added external factors, has shown significant potential for tissue restoration. However, the role of APRF in the modulation of MAFT remains unclear. Here, we aimed to explore the effect of APRF on MAFT.

Methods

Adipose-derived stem cells (ASCs) were isolated from human gastric subcutaneous fat and treated with APRF. ELISA assays measured cytokines. The proliferation of ASCs was analyzed by CCK-8 assays. The levels of hypoxia-inducible factor-1α (HIF-1α), heat shock protein 70 (HSP70), insulin like growth factor 2 (IGF-2), interleukin-6 (IL-6), interleukin-8 (IL-8), and vascular endothelial growth factor (VEGF) were measured by ELISA assays, quantitative reverse transcription-PCR (qRT-PCR), and Western blot analysis. The effect of APRF/HIF-1α/VEGF on MAFT in vivo was analyzed in Balb/c nude mice. The BALB/c mice were subcutaneously co-transplanted with fat, APRF, and control shRNA, HIF-1α shRNA, or VEGF shRNA into the dorsal area. The serum and protein levels of the above cytokines were analyzed by ELISA assays and Western blot analysis. Lipid accumulation was measured by Oil Red O staining. The expression of CD34 was assessed by immunohistochemical staining.

Results

APRF continuously secreted multiple cytokines, including epidermal growth factor (EGF), FGF-2, insulin like growth factor 1 (IGF-1), interleukin-1beta (IL-1β), interleukin-4 (IL-4), platelet-derived growth factor alpha polypeptide b (PDGF-AB), platelet-derived growth factor beta polypeptide b (PDGF-BB), transforming growth factor-beta (TGF-β), and VEGF. APRF was able to promote the proliferation of ASCs. APRF dose-dependently activated the expression of HIF-1α, HSP70, IGF-2, IL-6, IL-8, and VEGF in ASCs. APRF regulated the paracrine function of ASCs by modulating HIF-1α and VEGF.APRF increased the survival of MAFT by modulating HIF-1α and VEGF in vivo.

Conclusions

APRF promotes the paracrine function and proliferation of ASCs and contributes to MAFT by modulating HIF-1α and VEGF. Our findings provide new insights into the mechanism by which APRF regulates MAFT.

Non-viral gene delivery of HIF-1α promotes angiogenesis in human adipose-derived stem cells

Stable and mature vascular formation is a current challenge in engineering functional tissues. Transient, non-viral gene delivery presents a unique platform for delivering genetic information to cells for tissue engineering purposes and to restore blood flow to ischemic tissue. The formation of new blood vessels can be induced by upregulation of hypoxia-inducible factor-1α (HIF-1), among other factors. We hypothesized that biodegradable polymers could be used to efficiently deliver the HIF-1α gene to human adipose-derived stromal/stem cells (hASCs) and that this treatment could recruit an existing endogenous endothelial cell population to induce angiogenesis in a 3D cell construct in vitro. In this study, end-modified poly(β-amino ester) (PBAE) nanocomplexes were first optimized for transfection of hASCs and a new biodegradable polymer with increased hydrophobicity and secondary amine structures, N'-(3-aminopropyl)-N,N-dimethylpropane-1,3-diamine end-modified poly(1,4-butanediol diacrylate-co-4-amino-1-butanol), was found to be most effective. Optimal PBAE nanocomplexes had a hydrodynamic diameter of approximately 140 nm and had a zeta potential of 30 mV. The PBAE polymer self-assembled with HIF-1α plasmid DNA and treatment of hASCs with these nanocomplexes induced 3D vascularization. Cells transfected with this polymer-DNA complex were found to have 106-fold upregulation HIF-1α expression, an approximately 2-fold increase in secreted VEGF, and caused the formation of vessel tubules compared to an untransfected control. These gene therapy biomaterials may be useful for regenerative medicine. STATEMENT OF SIGNIFICANCE: Not only is the formation of stable vasculature a challenge for engineering human tissues in vitro, but it is also of valuable interest to clinical applications such as peripheral artery disease. Previous studies using HIF-1α to induce vascular formation have been limited by the necessity of hypoxic chambers. It would be advantageous to simulate endogenous responses to hypoxia without the need for physical hypoxia. In this study, 3D vascular formation was shown to be inducible through non-viral gene delivery of HIF-1α with new polymeric nanocomplexes. A biodegradable polymer N'-(3-aminopropyl)-N,N-dimethylpropane-1,3-diamine end-modified poly(1,4-butanediol diacrylate-co-4-amino-1-butanol) demonstrates improved transfection of human adipose-derived stem cells. This nanobiotechnology could be a promising strategy for the creation of vasculature for tissue engineering and clinical applications.

Adipose tissue and the vascularization of biomaterials: Stem cells, microvascular fragments and nanofat-a review

Tissue defects in the human body after trauma and injury require precise reconstruction to regain function. Hence, there is a great demand for clinically translatable approaches with materials that are both biocompatible and biodegradable. They should also be able to adequately integrate within the tissue through sufficient vascularization. Adipose tissue is abundant and easily accessible. It is a valuable tissue source in regenerative medicine and tissue engineering, especially with regard to its angiogenic potential. Derivatives of adipose tissue, such as microfat, nanofat, microvascular fragments, stromal vascular fraction and stem cells, are commonly used in research, but also clinically to enhance the vascularization of implants and grafts at defect sites. In plastic surgery, adipose tissue is harvested via liposuction and can be manipulated in three ways (macro-, micro- and nanofat) in the operating room, depending on its ultimate use. Whereas macro- and microfat are used as a filling material for soft tissue injuries, nanofat is an injectable viscous extract that primarily induces tissue remodeling because it is rich in growth factors and stem cells. In contrast to microfat that adds volume to a defect site, nanofat has the potential to be easily combined with scaffold materials due to its liquid and homogenous consistency and is particularly attractive for blood vessel formation. The same is true for microvascular fragments that are easily isolated from adipose tissue through collagenase digestion. In preclinical animal models, it has been convincingly shown that these vascular fragments inosculate with host vessels and subsequently accelerate scaffold perfusion and host tissue integration. Adipose tissue is also an ideal source of stem cells. It yields larger quantities of cells than any other source and is easier to access for both the patient and doctor compared with other sources such as bone marrow. They are often used for tissue regeneration in combination with biomaterials. Adipose-derived stem cells can be applied unmodified or as single cell suspensions. However, certain pretreatments, such as cultivation under hypoxic conditions or three-dimensional spheroids production, may provide substantial benefit with regard to subsequent vascularization in vivo due to induced growth factor production. In this narrative review, derivatives of adipose tissue and the vascularization of biomaterials are addressed in a comprehensive approach, including several sizes of derivatives, such as whole fat flaps for soft tissue engineering, nanofat or stem cells, their secretome and exosomes. Taken together, it can be concluded that adipose tissue and its fractions down to the molecular level promote, enhance and support vascularization of biomaterials. Therefore, there is a high potential of the individual fat component to be used in regenerative medicine.