Localized arteriole formation directly adjacent to the site of VEGF-Induced angiogenesis in muscle

Abstract

We have shown previously that implantation of myoblasts constitutively expressing the VEGF-A gene into nonischemic mouse skeletal muscle leads to overgrowth of capillary-like blood vessels and hemangioma formation. These aberrant effects occurred directly at the implantation site. We show here that these regions result from angiogenic capillary growth and involve a change in capillary growth pattern and that smooth muscle-coated vessels similar to arterioles form directly adjacent to the implantation site. Myoblasts genetically engineered to produce VEGF were implanted into mouse leg muscles. Implantation sites were surrounded by a zone of dense capillary-sized vessels, around which was a second zone of muscle containing larger, smooth-muscle-covered vessels but few capillaries, and an outer zone of muscle exhibiting normal capillary density. The lack of capillaries in the middle region suggests that the preexisting capillaries adjacent to the implantation site underwent enlargement and/or fusion and recruited a smooth muscle coat. Capillaries at the implantation site were frequently wrapped around VEGF-producing muscle fibers and were continuous with the circulation and were not observed to include bone-marrow-derived endothelial cells. In contrast with the distant arteriogenesis resulting from VEGF delivery described in previous studies, we report here that highly localized arterioles also form adjacent to the site of delivery.

Bone marrow cells recruited through the neuropilin-1 receptor promote arterial formation at the sites of adult neoangiogenesis in mice

“…The BM-derived cells that infiltrate the muscles expressing VEGF 165 in our experimental conditions are definitely not incorporated into the newly formed vasculature to become CD31 + endothelial cells or α-SMA + SMCs (25). This is in agreement with several investigations that have exploited other angiogenesis models (14,22,24,36,37). Obviously, we cannot exclude that in other conditions, such as during tumor angiogenesis, a subset of BMderived cells might act as pericyte progenitors that are directly incorporated into the vasculature (38).…”

“…This conclusion is in perfect agreement with the notion that knockout mice expressing only VEGF 120 exhibit specific defects in arterial development (3)(4)(5). In this respect, it is worth mentioning that the difference in arteriogenic potential between VEGF 121 and VEGF 165 has probably escaped previous gene transfer investigations, since the vast majority of studies were performed by exploiting first generation adenoviral vectors (29)(30)(31) or ex vivo-engineered myoblasts (24,32). The former system is highly inflammatory and induces a strong immunogenic response, while the latter leads to VEGF production at such high levels that aberrant vascular structures appear in treated tissues.…”

“…Indeed, we and others have observed that in both conditional transgenic animals (21,22) and animals injected with viral vectors (23) or implanted with engineered cells (24), the sites of prolonged VEGF 165 expression become infiltrated by a large number of cells bearing myeloid markers.…”

Computational Model of VEGF Spatial Distribution in Muscle and Pro-Angiogenic Cell Therapy

“…Areas of BM are identified by intersections between a grid point in ECM and a grid point within a muscle fiber or capillary. The BM thickness is about one-tenth of the grid size, thus its effect is included in the lumped boundary condition (Equations 3-4 and Equations [5][6][7][8][9][10][11][12][13][14]. The model geometry implies that a BM must lie between the two grid points and that every BM in the model is discretized into a number of smaller BM areas equal to the total grid intersections passing through every BM space in the model.…”

“…Because of this domain, only VEGF 164 can bind to the heparan sulfate proteoglycans (HSPG) present in high concentrations in the extracellular matrix (ECM) and basement membrane (BM) spaces, and the two splice variants are responsible for different signaling in both physiological and cancer angiogenesis [6,7]. Furthermore, due to the presence of high concentrations of HSPG in the BM that surrounds VEGF-secreting cells (such as skeletal muscle myocytes), a large amount of VEGF 164 becomes bound and sequestered near sources of VEGF secretion, creating a steep VEGF gradient [8]. The cellular response to VEGF occurs when signaling is initiated by the binding of VEGF to its cell surface receptor tyrosine kinases, VEGFR1 and VEGFR2.…”