Intramuscular VEGF repairs the failing heart: role of host-derived growth factors and mobilization of progenitor cells

Skeletal muscle produces a myriad of mitogenic factors possessing cardiovascular regulatory effects that can be explored for cardiac repair. Given the reported findings that VEGF may modulate muscle regeneration, we investigated the therapeutic effects of chronic injections of low doses of human recombinant VEGF-A165 (0.1–1 μg/kg) into the dystrophic hamstring muscle in a hereditary hamster model of heart failure and muscular dystrophy. In vitro, VEGF stimulated proliferation, migration, and growth factor production of cultured C2C12 skeletal myocytes. VEGF also induced production of HGF, IGF2, and VEGF by skeletal muscle. Analysis of skeletal muscle revealed an increase in myocyte nuclear [531 ± 12 VEGF 1 μg/kg vs. 364 ± 19 for saline (number/mm2) saline] and capillary [591 ± 80 VEGF 1 μg/kg vs. 342 ± 21 for saline (number/mm2)] densities. Skeletal muscle analysis revealed an increase in Ki67+ nuclei in the VEGF 1 μg/kg group compared with saline. In addition, VEGF mobilized c-kit+, CD31+, and CXCR4+ progenitor cells. Mobilization of progenitor cells was consistent with higher SDF-1 concentrations found in hamstring, plasma, and heart in the VEGF group. Echocardiogram analysis demonstrated improvement in left ventricular ejection fraction (0.60 ± 0.02 VEGF 1 μg/kg vs. 0.45 ± 0.01 mm for saline) and an attenuation in ventricular dilation [5.59 ± 0.12 VEGF 1 μg/kg vs. 6.03 ± 0.09 for saline (mm)] 5 wk after initiating therapy. Hearts exhibited higher cardiomyocyte nuclear [845 ± 22 VEGF 1 μg/kg vs. 519 ± 40 for saline (number/mm2)] and capillary [2,159 ± 119 VEGF 1 μg/kg vs. 1,590 ± 66 for saline (number/mm2)] densities. Myocardial analysis revealed ∼2.5 fold increase in Ki67+ cells and ∼2.8-fold increase in c-kit+ cells in the VEGF group, which provides evidence for cardiomyocyte regeneration and progenitor cell expansion. This study provides novel evidence of a salutary effect of VEGF in the cardiomyopathic hamster via induction of myogenic growth factor production by skeletal muscle and mobilization of progenitor cells, which resulted in attenuation of cardiomyopathy and repair of the heart

Activation of host tissue trophic factors through JAK-STAT3 signaling: a mechanism of mesenchymal stem cell-mediated cardiac repair

We recently demonstrated a cardiac therapeutic regimen based on injection of bone marrow mesenchymal stem cells (MSCs) into the skeletal muscle. Although the injected MSCs were trapped in the local musculature, the extracardiac cell delivery approach repaired the failing hamster heart. This finding uncovers a tissue repair mechanism mediated by trophic factors derived from the injected MSCs and local musculature that can be explored for minimally invasive stem cell therapy. However, the trophic factors involved in cardiac repair and their actions remain largely undefined. We demonstrate here a role of MSC-derived IL-6-type cytokines in cardiac repair through engagement of the skeletal muscle JAK-STAT3 axis. The MSC IL-6-type cytokines activated JAK-STAT3 signaling in cultured C2C12 skeletal myocytes and caused increased expression of the STAT3 target genes hepatocyte growth factor (HGF) and VEGF, which was inhibited by glycoprotein 130 (gp130) blockade. These in vitro findings were corroborated by in vivo studies, showing that the MSC-injected hamstrings exhibited activated JAK-STAT3 signaling and increased growth factor/cytokine production. Elevated host tissue growth factor levels were also detected in quadriceps, liver, and brain, suggesting a possible global trophic effect. Paracrine actions of these host tissue-derived factors activated the endogenous cardiac repair mechanisms in the diseased heart mediated by Akt, ERK, and JAK-STAT3. Administration of the cell-permeable JAK-STAT inhibitor WP1066 abrogated MSC-mediated host tissue growth factor expression and functional improvement. The study illustrates that the host tissue trophic factor network can be activated by MSC-mediated JAK-STAT3 signaling for tissue repair