HIF-1α Dependent Wound Healing Angiogenesis In Vivo Can Be Controlled by Site-Specific Lentiviral Magnetic Targeting of SHP-2

Abstract

Hypoxia promotes vascularization by stabilization and activation of the hypoxia inducible factor 1α (HIF-1α), which constitutes a target for angiogenic gene therapy. However, gene therapy is hampered by low gene delivery efficiency and non-specific side effects. Here, we developed a gene transfer technique based on magnetic targeting of magnetic nanoparticle-lentivirus (MNP-LV) complexes allowing site-directed gene delivery to individual wounds in the dorsal skin of mice. Using this technique, we were able to control HIF-1α dependent wound healing angiogenesis in vivo via site-specific modulation of the tyrosine phosphatase activity of SHP-2. We thus uncover a novel physiological role of SHP-2 in protecting HIF-1α from proteasomal degradation via a Src kinase dependent mechanism, resulting in HIF-1α DNA-binding and transcriptional activity in vitro and in vivo. Excitingly, using targeting of MNP-LV complexes, we achieved simultaneous expression of constitutively active as well as inactive SHP-2 mutant proteins in separate wounds in vivo and hereby specifically and locally controlled HIF-1α activity as well as the angiogenic wound healing response in vivo. Therefore, magnetically targeted lentiviral induced modulation of SHP-2 activity may be an attractive approach for controlling patho-physiological conditions relying on hypoxic vessel growth at specific sites.

Keywords: HIF-1α; SHP-2; angiogenesis; magnetic nanoparticles; magnetic targeting; wound healing.

Graphical abstract

Figure 1

SHP-2 Inactivation Inhibits Hypoxia-Induced Angiogenesis and HIF-1α Accumulation and Activity In Vitro (A) Overexpression of SHP-2 WT, SHP-2 CS (dominant negative mutant), or SHP-2 E76A (constitutively active mutant) was achieved by lentiviral transduction (see Figure S1). Proliferation of endothelial cells expressing the different SHP-2 constructs upon 24 hr hypoxia treatment was assessed by MTT reduction 96 hr post transduction (*p < 0.05, n = 5 in triplicates). The enhanced proliferation in SHP-2 E76A cells was inhibited by treatment with 10 ng/mL echinomycin (Ecm) (p < 0.05, n = 5 in triplicates). (B) Formation of capillary like structures in Matrigel during hypoxia (24 hr) in SHP-2 WT, CS, and E76A expressing endothelial cells (*p < 0.05, n = 5 each, 4 fields of view). The Matrigel assay was performed 96 hr after lentiviral transduction. (C) Vessel sprouting from aortic rings ex vivo expressing SHP-2 WT, CS, or E76A and exposed to hypoxia (24 hr) (*p < 0.05, n = 4–5). The isolated vessels were immediately transduced using magnetic targeting of MNP-LV complexes to the vessel wall. At 48 hr later, aortas were cut into rings, embedded in Matrigel, and exposed to hypoxia. (D) Hypoxia-induced (4 hr) VEGF production from SHP-2 WT, CS, or E76A expressing endothelial cells, as assessed by ELISA 96 hr after transduction (*p < 0.05, n = 3–6). (E) Analysis of hypoxia-induced (4 hr) HIF-1α accumulation in endothelial cells lentivirally transduced with SHP-2 WT, CS, E76A, or Y2F. The graph shows protein band densities of HIF-1α normalized to actin (*p < 0.05, n = 6). (F) HIF-1 DNA binding activity in nuclear extracts of cells expressing SHP-2 WT or CS upon hypoxia (4 hr) was measured using a HIF-1 transcription factor assay kit 96 hr post transduction (*p < 0.05, n = 3 in duplicates). (G) HIF-1α activity upon hypoxia (4 hr) in endothelial cells expressing SHP-2 WT or CS was detected 72 hr upon co-transduction of SHP-2 WT or CS in combination with the HIF1-TRE-Luc or Control-Luc reporter construct (*p < 0.05, n = 5). All of the quantitative data are represented as mean ± SEM.

Figure 2

SHP-2 Inhibits HIF-1α Degradation via Activation of the Src Kinase (A) Hypoxic (4 hr) HIF-1α mRNA expression in cells overexpressing SHP-2 WT, CS, or E76A was assessed by qRT-PCR 96 hr post transduction (n = 3 in duplicates). (B) Live cell HIF-1α mRNA detection in hypoxic (4 hr) cells expressing SHP-2 WT-IRES-eGFP, CS-IRES-eGFP, or E76A-IRES-eGFP, using HIF-1α or scramble (control) SmartFlare probes and flow cytometry 96 hr post transduction (n = 3 in duplicates). The graph shows HIF-1α mRNA in GFP positive cells. (C) MG132 (10 μM) or epoxomicin (1 μM) treatment increased HIF-1α levels in SHP-2 CS expressing cells (lanes 7–9) to the same extent as in SHP-2 WT cells under hypoxia (4 hr) (lanes 4–6) (*p < 0.05, n = 3–7), as assessed by western blot. (D) HIF-1α levels in DFO treated (100 μM) SHP-2 WT or CS expressing cells during hypoxia (4 hr) (*p < 0.05, n = 4). (E) Prolyl-hydroxylated HIF-1α (Pro564) was analyzed in SHP-2 WT, CS, and E76A cells after hypoxia (4 hr) and MG132 (10 μM) treatment by western blot (*p < 0.05, n = 3). The graphs below blots show protein band densities of HIF-1α normalized to actin. (F) Hydroxylation of HIF-1α in endothelial cells during hypoxia (4 hr) upon treatment with Src inhibitor (100 nM PP2) and exposure to MG132 (10 μM) (*p < 0.05, n = 3) was detected using western blot. The graph shows protein band densities of hydroxy-HIF-1α normalized to actin. (G) Hypoxia- (4 hr) induced Src phosphorylation in cells expressing SHP-2 WT, CS, or SHP-2 E76A was analyzed by western blot 96 hr post transduction (*p < 0.05, n = 4–7). The graph shows protein band densities of phospho-Src normalized to actin. See also Figure S2. (H) The influence of hypoxia (4 hr) on SHP-2 phosphatase activity was measured by dephosphorylation of pNPP in SHP-2 precipitates (**p < 0.01, n = 6). All of the quantitative data are represented as mean ± SEM.

Figure 3

Magnetic Mediated MNP-LV Gene Delivery Allows for Gene Expression in Wounds in the Dorsal Skin of Mice (A) Time course of wound closure of the subcutaneous layer in the mouse dorsal skinfold chamber model (*p < 0.05 versus time point of first measurement, n = 3 animals). The dorsal skin of mice was wounded using a hot probe and wound size was detected by FITC-Dextran injection and fluorescent intravital microscopy at denoted time points. The representative intravital microscopy images of wounds after FITC-Dextran injection for visualization of vessel growth into wounds are shown (right). The white dotted line marks initial wound area as measured on day 3 (first measurement). The bar in photos represents 500 μm. (B) Application of luciferase expressing lentiviral particles (Luc LV) associated to MNP resulted in local luciferase expression only when a magnetic field (MF) was applied to the dorsal skinfold chamber (right). The total photon flux (TF) (photons/sec) was determined using region of interest (ROI) measurements. The bioluminescence measurements by intraperitoneal luciferin injection were performed 6 days post transduction. See also Figure S3. (C) Comparison in wound healing response between non-treated (no MNP-LV; white bars) wounds and wounds with magnetic targeting of MNP associated to lentivirus expressing SHP-2 WT (gray bars). The fluorescent intravital microscopy was performed 3 and 9 days post transduction, respectively, by injection of FITC-Dextran. The wound closure at day 9 was normalized to day 3 of the respective wound. ns: not significant, n = 3–7. The representative intravital microscopy images of wounds after FITC-Dextran injection are shown (right). The white dotted line marks the initial wound area as measured on day 3 (first measurement). The bar in photos represents 500 μm. (D) Magnetic targeting of MNP associated to different lentiviral particle amounts (VP) of luciferase expressing lentivirus to defined areas of the same dorsal skinfold chamber correlates with the respective different luciferase expression strength. The bioluminescence measurements by intraperitoneal luciferin injection were performed 6 days post transduction. (1) application of 1 × 10⁶ VP; (2) application of 5 × 10⁶ VP; and (3) application of 1 × 10⁷ VP. (E) Magnetic targeting of MNP associated to a luciferase expressing lentivirus to a wound induces expression of the transgene 6 days after transduction, whereas no expression was detected in other wounds of the same dorsal skinfold chamber treated with only sodium chloride solution and exposed to the magnetic field (MF). The dotted circles mark the wounds. (F) Intravital microscopy images of wounds after FITC-Dextran injection (green) and magnetic targeting of MNP associated to lentivirus expressing SHP-2 WT and td Tomato via an IRES element showing transgene expression in the wound (red) 6 days after transduction. The bar in photos represents 500 μm. All of the quantitative data are represented as mean ± SEM.

Figure 4

Scheme of Site-Specific Expression of SHP-2 Mutants and HIF1-TRE-Luc in Wounds in the Dorsal Skinfold Chamber in Mice Day 1: Preparation of the dorsal skinfold chamber on C57BL/6J mice. Day 0: Up to three wounds were induced within the observation window using a heated wire. Day 1: Lentiviral vectors carrying expression vectors for SHP-2 mutants (WT, CS, and E76A), HIF1-TRE-Luc, or Control-Luc, respectively, were associated to magnetic nanoparticles and individually applied to the wounds under magnetic field exposure. Day 3: First measurement of wound size and vessel growth within the wound by intravenous injection of FITC-Dextran and intravital microscopy. Day 6: Measurement of wound size and vessel growth within the wound by intravenous injection of FITC-Dextran and intravital microscopy (SHP-2 WT, CS, and E76A) or detection of bioluminescence in wounds (HIF1-TRE-Luc and Control-Luc).

Figure 5

SHP-2 Activity Is Necessary for HIF-1α Dependent Angiogenesis In Vivo (A) HIF-1α expression and activity in wounds were detected by local expression of a lentiviral HIF-1 transcriptional luciferase reporter construct (HIF1-TRE-Luc) in the wound and compared to transduction of a control luciferase reporter construct missing the HIF1-TRE (Control-Luc) (*p < 0.05, n = 8 animals). The representative bioluminescence image of luciferase activity in wounds of the dorsal skinfold chamber after magnetic assisted transduction with HIF1-TRE-Luc and Control-Luc, respectively, is shown (right). 1: HIF1-TRE-Luc transduction without wounding; 2: Control-Luc transduction of wound; and 3: HIF1-TRE-Luc transduction of wound. (B) Influence of SHP-2 WT, CS, and E76A expression in the wound area on vessel growth and wound closure (*p < 0.05, n = 5 animals). The expression of SHP-2 constructs was achieved using magnetic targeting of MNP-LV complexes. The wound sizes were normalized to respective wounds from day 3. The representative intravital microscopy images taken after intravenous injection of FITC-Dextran at day 3 and 6 after wounding showing the vessel growth into the wounds of one animal simultaneously expressing different SHP-2 constructs in separate wounds are shown (right). The white dotted lines mark the initial wound area of the respective wound as measured on day 3. The bar in photos represents 500 μm. (C) Luciferase expression and thus HIF-1α transcriptional activity 6 days post co-transduction of HIF1-TRE-Luc and different SHP-2 mutant constructs in wounds in the mouse dorsal skinfold chamber by magnetic targeting of MNP-LV complexes (*p < 0.05, n = 4 animals). The representative bioluminescence images next to the graph show wounds transduced with control-Luc (left) or HIF1-TRE-Luc (right) vectors in combination with SHP-2 WT and mutant constructs, respectively. (D) mRNA expression of VEGF-A, PDGF-B, and MMP-2 was measured in wounds and healthy tissue of the mouse dorsal skin by qRT-PCR (left graph) (*p < 0.05, n = 5), as well as in wounds expressing SHP-2 WT or SHP-2 CS (right graph) (*p < 0.05, n = 3–5). All of the quantitative data are represented as mean ± SEM.