br Materials Methods br Results br Discussion The

Materials & Methods
Results
Discussion The plasticity of glial na+/ca2+ exchanger and pericytes has been shown in injuries occurring to the central nervous system and pancreatic islets in diseases with progressive lesion formation such as Alzheimer\'s disease and insulitis in experimental type 1 diabetes (Beach et al., 1989; Tang et al., 2013) and in acute conditions such as stroke, traumatic central nervous system injury, and islet injury induced by streptozotocin injection (Goritz et al., 2011; Pekny and Nilsson, 2005; Tang et al., 2013; Teitelman et al., 1998). In this research, we demonstrate the adaptability of islet Schwann (glial) cells and pericytes in response to islet transplantation, in which the Schwann cell network and the pericyte population reestablished at the graft exterior and interior boundaries, re-associating with the engrafted islets. We traced the donor Schwann cells and pericytes using the nestin-GFP+ transgenic islets to confirm their contribution to the regeneration. The 3-D graft microstructure, vasculature, and Schwann cell network were presented with high definition to facilitate qualitative and quantitative analyses of the tissue networks to characterize the graft neurovascular regeneration. The classic view of the graft neurovascular regeneration is the in-growth of blood vessels and nerves from the host tissue to the transplanted islets (Jansson and Carlsson, 2002; Persson-Sjogren et al., 2000; Vajkoczy et al., 1995). Although Nyqvist et al. (2005) reported that the donor islet endothelial cells also participate in the formation of the graft microvessels after islet transplantation under the kidney capsule, the donor endothelial cells seems to cover only a limited area of the graft vasculature, indicating that the endothelial cells from the host kidney are the major contributor to the graft angiogenesis. In this research, however, we show that the Schwann cells and pericytes derived from the donor islets were the major contributors to the Schwann cell sheath and the perivascular pericyte population of the grafts (Figs. 4 and 6): both were abundantly associated with the engrafted islets, a sharp contrast to the intrinsic densities of the two cell types in the kidney (Fig. 2C and D and Supplemental Figs. S1 and S2). The prominent presence of Schwann cells and pericytes and their known functions of releasing the neurotrophic and angiogenic factors suggest the roles of the two cell types in attracting the nerves and blood vessels to facilitate graft neurovascular regeneration, despite prior research focusing mainly on the transplanted endocrine cells in the recruiting process (Brissova et al., 2006; Jansson and Carlsson, 2002; Myrsen et al., 1996; Persson-Sjogren et al., 2000; Vasir et al., 1998). Although the survival of β-cells accounts for the success of islet transplantation, other cell types transplanted with the islets have also been described to correlate with the outcome of transplantation. For example, Street et al. (2004) reported a positive correlation between the long-term metabolic success of the islet recipients and the number of the ductal cells transplanted with the islets following the Edmonton Protocol. In this research, we used the mouse model to reveal the participation of the donor islet Schwann cells and pericytes in the process of transplantation. Although the roles of the human islet Schwann cells and pericytes in islet transplantation remain to be established, we suggest two of their potential impacts on the engraftment process: first, the neurovascular regeneration (as discussed earlier) and second, the host immunological response, due to the immunogenicity of the donor Schwann cells and pericytes (both of which are the antigen-presenting cells; Balabanov et al., 1999; Gulati, 1998; Lilje, 2002; Thomas, 1999) and their presence at the graft boundaries. The technical advance of the islet graft 3-D histology with tissue clearing (Juang et al., 2014) has made possible the visualization of the graft Schwann cell network and pericyte population with high definition. Without tissue clearing, the kidney and pancreatic islets are intrinsically opaque because of the higher refractive index of the tissue constituents such as the phospholipids and proteins than that of the water molecules, leading to scattering when light enters the tissue matrix in optical microscopy. Tissue clearing substantially reduces light scattering by replacing the surrounding fluids with a solution of high refractive index, thereby matching the optical properties between the tissue constituents and the immersion solution to improve light transmission for different optical applications such as the optical coherence tomography (OCT) imaging (Khan et al., 2004) and confocal and two-photon microscopy (Chung and Deisseroth, 2013; Erturk et al., 2012; Genina et al., 2010; Ke et al., 2013; Marx, 2014).