Ultrastructural and three-dimensional analysis of the contractile cells of the cutaneous microvasculature

3D Bioprinting of Vascularized Tissues for in vitro and in vivo Applications

With a limited supply of organ donors and available organs for transplantation, the aim of tissue engineering with three-dimensional (3D) bioprinting technology is to construct fully functional and viable tissue and organ replacements for various clinical applications. 3D bioprinting allows for the customization of complex tissue architecture with numerous combinations of materials and printing methods to build different tissue types, and eventually fully functional replacement organs. The main challenge of maintaining 3D printed tissue viability is the inclusion of complex vascular networks for nutrient transport and waste disposal. Rapid development and discoveries in recent years have taken huge strides toward perfecting the incorporation of vascular networks in 3D printed tissue and organs. In this review, we will discuss the latest advancements in fabricating vascularized tissue and organs including novel strategies and materials, and their applications. Our discussion will begin with the exploration of printing vasculature, progress through the current statuses of bioprinting tissue/organoids from bone to muscles to organs, and conclude with relevant applications for in vitro models and drug testing. We will also explore and discuss the current limitations of vascularized tissue engineering and some of the promising future directions this technology may bring.

Pericyte mechanics and mechanobiology

Pericytes are mural cells of the microvasculature, recognized by their thin processes and protruding cell body. Pericytes wrap around endothelial cells and play a central role in regulating various endothelial functions, including angiogenesis and inflammation. They also serve as a vascular support and regulate blood flow by contraction. Prior reviews have examined pericyte biological functions and biochemical signaling pathways. In this Review, we focus on the role of mechanics and mechanobiology in regulating pericyte function. After an overview of the morphology and structure of pericytes, we describe their interactions with both the basement membrane and endothelial cells. We then turn our attention to biophysical considerations, and describe contractile forces generated by pericytes, mechanical forces exerted on pericytes, and pericyte responses to these forces. Finally, we discuss 2D and 3D engineered in vitro models for studying pericyte mechano-responsiveness and underscore the need for more evolved models that provide improved understanding of pericyte function and dysfunction.

Three Dimensional Bioprinting of a Vascularized and Perfusable Skin Graft Using Human Keratinocytes, Fibroblasts, Pericytes, and Endothelial Cells

Multilayered skin substitutes comprising allogeneic cells have been tested for the treatment of nonhealing cutaneous ulcers. However, such nonnative skin grafts fail to permanently engraft because they lack dermal vascular networks important for integration with the host tissue. In this study, we describe the fabrication of an implantable multilayered vascularized bioengineered skin graft using 3D bioprinting. The graft is formed using one bioink containing human foreskin dermal fibroblasts (FBs), human endothelial cells (ECs) derived from cord blood human endothelial colony-forming cells (HECFCs), and human placental pericytes (PCs) suspended in rat tail type I collagen to form a dermis followed by printing with a second bioink containing human foreskin keratinocytes (KCs) to form an epidermis. In vitro, KCs replicate and mature to form a multilayered barrier, while the ECs and PCs self-assemble into interconnected microvascular networks. The PCs in the dermal bioink associate with EC-lined vascular structures and appear to improve KC maturation. When these 3D printed grafts are implanted on the dorsum of immunodeficient mice, the human EC-lined structures inosculate with mouse microvessels arising from the wound bed and become perfused within 4 weeks after implantation. The presence of PCs in the printed dermis enhances the invasion of the graft by host microvessels and the formation of an epidermal rete. Impact Statement Three Dimensional printing can be used to generate multilayered vascularized human skin grafts that can potentially overcome the limitations of graft survival observed in current avascular skin substitutes. Inclusion of human pericytes in the dermal bioink appears to improve both dermal and epidermal maturation.

Medical Treatment for Epistaxis in Hereditary Hemorrhagic Telangiectasia: A Meta-analysis

Objectives

The aim of this study (PROSPERO ID: CRD42017081952) was to evaluate medical treatment for epistaxis from hereditary hemorrhagic telangiectasia (HHT).

Data Sources

PubMed, Embase, Scopus, and Cochrane Library databases were interrogated from their inceptions to November 2017.

Review Methods

Randomized clinical trials comparing medical treatment with placebo for epistaxis of HHT were included. We used a random-effects model to synthesize overall effects. Heterogeneity was evaluated with the I2 statistic.

Results

Eight studies were identified after systematic searching. The use of bevacizumab (BV), tranexamic acid, and estrogen, regardless of the route of administration, had no significant influence on frequency of episodes. Tamoxifen was superior to placebo in both frequency and severity of epistaxis. For duration of epistaxis, nasal spray BV, oral or nasal spray tranexamic acid, and nasal spray estrogen had no significant differences versus placebo, but patients receiving submucosal BV showed lower duration of epistaxis (mean difference: −219.00 min/mo, 95% CI: −271.90 to −166.10). Medical treatment for HHT had no significant changes of mean hemoglobin concentration (pooled mean difference: −0.23 mg/dL, 95% CI: −0.65 to 0.20, I2 = 0%) or quality of life (pooled standardized mean difference: 0.07, 95% CI: −0.16 to 0.30, I2 = 0%).

Conclusions

Only limited evidence provides a benefit on frequency of epistaxis by treatment with tamoxifen and duration of epistaxis by treatment with submucosal BV among patients with HHT. Mean hemoglobin concentration and quality of life were not influenced by medical treatment.

Dermal Contributions to Human Interfollicular Epidermal Architecture and Self-Renewal

The human interfollicular epidermis is renewed throughout life by populations of proliferating basal keratinocytes. Though interfollicular keratinocyte stem cells have been identified, it is not known how self-renewal in this compartment is spatially organized. At the epidermal-dermal junction, keratinocytes sit atop a heterogeneous mix of dermal cells that may regulate keratinocyte self-renewal by influencing local tissue architecture and signalling microenvironments. Focusing on the rete ridges and complementary dermal papillae in human skin, we review the identity and organisation of abundant dermal cells types and present evidence for interactions between the dermal microenvironment and the interfollicular keratinocytes.

Combined immunologic and anti-angiogenic therapy reduces hepatic micrometastases in a murine ocular melanoma model

PURPOSE

To evaluate the combined effect of neoadjuvant intracameral interferon alpha -2b and adjuvant low-dose angiostatin in reducing the number of hepatic micrometastases in a murine model of ocular melanoma.

METHODS

The posterior compartments of the right eyes of C57BL6 mice were inoculated with 5 x 10(5) cells/2.5 microl of cells from the Queens, B16F10, or B16LS9 melanoma cell lines. The right eyes were enucleated at 7 days, and the mice were sacrificed at 28 days postinoculation, respectively. Hepatic micrometastases were counted. There were four treatment groups (n = 15 each) for each cell line as follows: group 1, intraperitoneal injections of 20 KIU interferon alpha -2b for 4 days prior to enucleation; group 2, intramuscular injections of 100 microl 0.1 microg/microl murine angiostatin every day for 14 days starting on day 1 after enucleation; group 3, treatment of group 1 and group 2 combined; group 4, intraperitoneal and intramuscular injections of equal volumes of phosphate-buffered saline (PBS) (control group).

RESULTS

Results showed decreased micrometastases for groups 1 through 3 compared with group 4, with the greatest reduction in group 3 (p < 0.006).

CONCLUSIONS

This study suggests that combined neoadjuvant interferon alpha -2b and adjuvant low-dose angiostatin therapy act synergistically to decrease hepatic micrometastases in a murine ocular melanoma model.

Mechanism of the delay phenomenon: tissue protection is mediated by heme oxygenase-1

Induction of the “delay phenomenon” by chronic ischemia is an established clinical procedure, but the mechanisms conferring tissue protection are still incompletely understood. To elucidate the role of heme oxygenase-1 [HO-1 or heat shock protein-32 (HSP-32)] in delay, we examined in the skin-flap model of the ear of the hairless mouse, 1) whether chronic ischemia (delay) is capable to induce expression of HO-1, and 2) whether delay-induced HO-1 affects skin-flap microcirculation and survival by either its carbon monoxide-associated vasodilatory action or its biliverdin-associated anti-oxidative mechanism. Chronic ischemia was induced by transsection of the central feeding vessel of the ear 7 days before flap creation. The flap was finally raised by an incision through four-fifths of the base of the ear. Microcirculatory dysfunction and tissue necrosis were studied with the use of laser Doppler fluxmetry and intravital fluorescence microscopy. HO-1 protein expression was determined with Western blot analysis. Seven days of chronic ischemia (delay) induced a marked expression of HO-1. This was paralleled by a significant improvement ( P < 0.05) of microvascular perfusion and a reduction ( P < 0.05) of flap necrosis when compared with nondelayed controls. Importantly, blockade of HO-1 activity by tin protoporhyrin-IX completely blunted the protection of microcirculation and the improvement of tissue survival. Additional administration of the vitamin E analog trolox after blockade of HO-1 to mimic exclusively the anti-oxidative action of the heat shock protein did not restore the HO-1-associated microcirculatory improvement and only transiently attenuated the manifestation of flap necrosis. Thus our data indicate that the delay-induced protection from tissue necrosis is mediated by HO-1, predominantly through its carbon monoxide-associated action of adequately maintaining nutritive capillary perfusion.

The cutaneous microcirculation

The cutaneous microcirculation is organized as two horizontal plexuses. One is situated 1-1.5 mm below the skin surface and the other is at the dermal-subcutaneous junction. Ascending arterioles and descending venules are paired as they connect the two plexuses. From the upper layer, arterial capillaries rise to form the dermal papillary loops that represent the nutritive component of the skin circulation. There are sphincter-like smooth muscle cells at the point where the ascending arterioles divide to form the arteriolar component of the upper horizontal plexus. At the dermal-subcutaneous junction, there are collecting veins with two cusped valves that are oriented to prevent the retrograde flow of blood. Laser Doppler flowmetry has demonstrated vasomotion of red cell flux localized to the sites of ascending arterioles. The simultaneous recording by laser Doppler flowmetry of red cell flux and the concentration of moving red blood cells from individual sites allows one to construct topographic maps of these two values. These two maps, based on initial studies using correlative skin biopsies, can define 1 mm3 volumes of skin that are predominantly arteriolar in composition, venular in composition, or essentially devoid of all microvascular elements. The electron and light microscopic features that define the microvascular segments, when coupled with that ability of laser Doppler flowmetry to define the predominant microvascular segments under the probe, allow one to study both the mechanisms of normal physiologic states and the pathogenetic mechanisms underlying pathologic skin disorders in which the microvasculature plays a predominant role.

Three-dimensional analysis of vacuoles and surface invaginations of capillary endothelia in the eel rete mirabile

One layer of attenuated endothelia of continuous capillaries provides a partially selective diffusion barrier between the blood and the interstitium. Ultrastructures of membrane specialization without the known physiologic functions have been found in blood vessel endothelia. The vacuolar profiles or vacuole-like, membrane-bound structures, which are larger than plasmalemmal vesicles, have been observed routinely in normal endothelial cytoplasm or in blood vessels challenged by insults in electron microscopic studies. Three-dimensional information from serial sections is required to understand the organization and functions of vacuole-like structures in capillary endothelium. The capillaries in eel retia mirabile were perfused with electron-dense tracers, glutaraldehyde in buffer, and were processed for transmission electron microscopy. Ribbons of serial thin sections without counterstaining were examined under a transmission electron microscope. The vacuolar profiles inside endothelial cytoplasm were investigated with the techniques of serial section analysis and three-dimensional reconstruction from serial sections. The vacuole-like structures inside endothelial cytoplasm either were connected to extracellular (luminal, abluminal) compartments or existed as isolated vacuoles from serial section analysis. In the eight series examined in this study, six of ten vacuole-like structures were classified as isolated vacuoles inside endothelia, and their diameters ranged between 186 nm and 266 nm. Two of ten vacuole-like structures were found to extend to the luminal surface of capillaries as luminal, pocket-like invaginations. One of ten vacuole-like structures was found to be connected to the albuminal compartment, and another one existed as an extracellular compartment surrounded by endothelia. Three-dimensional projection of the vacuolar compartments from serial sections showed that endothelial cytoplasm of sheet shape protruded and folded over adjacent endothelium. Three-dimensional information from serial sections reveals the organization of vacuolar profiles and pocket-like invaginations from the cell surfaces in capillary endothelium. The vacuolar profiles in capillary endothelia in two-dimensional electron photomicrographs may represent the extracellular compartments surrounded by the endothelial finger-like extensions. The results indicate that the luminal and abluminal surfaces of the capillary lumen are not smooth or static, and endothelia may change their shape in three dimensions through cytoplasmic protrusions when the tissue environment changes.

What dermatologists should know about digital imaging

The digital imaging revolution that swept other medical specialties in the late 1970s and early 1980s is beginning to find new and important roles in dermatology. This technology has a wide range of educational, clinical, and research applications. Dermatologists should understand certain basic concepts about images and imaging techniques to take advantage of progress in this field and eventually apply it to their own research and/or clinical practice.

Correlation of laser Doppler wave patterns with underlying microvascular anatomy

Laser Doppler velocimetry (LDV) was performed on the chest, back, and abdomen of four healthy volunteers. As the probe was moved over distances of 2-6 mm, the red-cell flux varied by 100%, but was associated with three distinctive wave patterns. Correlative skin biopsies showed that a high flux, pulsatile pattern superimposed on vasomotor activity was found when the probe was directly over an ascending elastic arteriole with its immediate branches; low flux, pulsatile flow with minimal or no vasomotor activity was found when the probe was off center relative to the ascending arteriole and its branches; and a low flux, non-pulsatile pattern occurred when the probe window was situated between ascending arterioles over an area in the upper horizontal plexus composed primarily of capillaries and post-capillary venules.