br Results br Discussion The clinical success of

Results
Discussion The clinical success of haematopoietic stem/progenitor cell (HSPC) therapy for large bowel disorders is poor, partly due to their limited recruitment following systemic administration. However, cellular therapy may be made effective if systemically transplanted Purmorphamine cost are targeted directly to the colon. This is highly desirable for local treatment of a variety of inflammatory bowel diseases such as ulcerative colitis and Crohn\'s disease. The colon is highly susceptible in humans (and mice) to inflammatory bowel disorders, with approximately 60% of patients with Crohn\'s disease suffering from colonic involvement (Mills and Stamos, 2007). Although the colon is a site affected by many inflammatory disorders, the dynamics of HSPC recruitment within the colonic microcirculation has not previously been imaged experimentally. This study therefore determined whether pre-treating a purified immortalised HSC-like line with factors released during or at injury sites could enhance their adhesion within the murine colon. These pre-treatments were tested in two different inflammatory injuries. Our novel data provides the first evidence that immortalised HSC-like HPC-7 adhesion within the injured colon microvessels can occur almost immediately after their systemic infusion. Within the colon, we show that recruitment is not a passive event but is actively regulated by injury specific surface receptors, namely CD18 and/or CD49d. More importantly, recruitment achieved by injury alone was not maximal as pre-treatment strategies could enhance the local presence of HPC7s. Indeed, both chemical (H2O2) and biological (PES) pre-treatment strategies enhanced HPC7 adhesion in vitro, but only to the colitis colon in vivo. These approaches were utilised as both H2O2 generation and PMP formation are known to be elevated following intestinal IR and colitis injury (Fraticelli et al., 1996; Kavanagh et al., 2013a; Chamouard et al., 2005). However, while PMPs are elevated in both these injuries, only PES was effective in increasing HPC7 adhesion whereas PMPs were not. The development of strategies that enhance colon homing through modulation of HPC7 integrin affinity (or avidity/expression) may be a worthwhile clinical pursuit if associated with improved therapeutic benefit. Increased HPC7 adhesion within IR and colitis injured colon was observed on both frozen tissue sections and in vivo when compared with un-injured colon. Increased adhesion observed in vivo was not due to a reactive hyperaemia, an increased blood perfusion, often associated with tissue injury. Interestingly, blood flow within the exposed colonic mucosa was significantly reduced to a similar degree following both injuries as determined by laser speckle microscopy. In similar experimental models of DSS-induced colitis in mice, a modest decrease in blood flow within the resistance arterioles of the colon submucosa has been demonstrated at days 4 and 6 post-DSS (Mori et al., 2005b). However, the current study is the first to demonstrate that the mucosal lining of the colon also undergoes a significant reduction in blood flow post-injury. Since preservation of the gut lumenal lining is essential to ensure nutrient absorption and prevent bacterial translocation, it was reassuring to observe that systemically infused HPC7s could still be recruited to the mucosa despite the poor perfusion in this region. This has important clinical implications as many inflamed organs suffer from poor blood flow. Indeed, in ulcerative colitis patients, a reduction in flow is often detected in the chronically inflamed and remodelled colon (Hulten et al., 1977). It is possible that this reduced perfusion resulted in increased HPC7 adhesion due to lower shear rates. Reduced blood flow in injury sites may be more conducive to adhesive stem-endothelial cell interactions taking place. Therefore, systemically delivered SCs may have advantages over pharmacological drugs for the targeted treatment of inflammatory diseases of the colon.