In this study we investigated the homing ability

In this study, we investigated the homing ability and retention of transplanted BMSCs in diabetic kidneys and explored the local effects on kidney morphology and its functional profile induced by microbubble-mediated diagnostic ultrasound irradiation. Moreover, treating the right kidney allows the contralateral kidney to serve as an internal control. The number of RFP-labeled BMSCs in treated diabetic kidneys was much larger than that in contralateral control kidneys 24, 48 and 72 h post-treatment. An ideal stem cell homing strategy capitalizes on enhanced BMSC engraftment generated without tissue damage. Histologic examination revealed that diagnostic ultrasound-mediated microbubble destruction did not change kidney architecture or induce hyperemia, disfiguration or cell apoptosis in the treated kidney. Only slight renal cell swelling, mild renal hemorrhage and slight inflammatory infiltration were observed transiently and were recoverable 48 h post-treatment. Blood chemical analysis indicated that MB-mediated diagnostic ultrasound irradiation did not affect renal clearance of BUN and Scr in the treated diabetic kidneys, indicating no renal function was changed. These results suggested that the use of diagnostic ultrasound-mediated microbubble destruction was effective and tolerable in improving BMSC homing to diabetic kidney parenchyma. We hypothesized that it was largely because of the relatively low acoustic intensity of the diagnostic ultrasound apparatus (maximum acoustic intensity of 4 P1 transducer: ISPTA ≤ 539 mW/cm2).
To assess potential mechanisms underlying the enhanced ability of BMSCs to home to diabetic kidneys, we explored the local kidney micro-environmental changes by determining the levels of BYL719 of four representative cytokines (VEGF, SDF-1, VCAM-1 and E-selectin), which had already been proved helpful in improving the tropism of BMSCs injected into targeted tissues (Klyachkin et al. 2014). Immunohistochemistry and Western blot analysis revealed increased expression of VCAM-1 and E-selectin in the kidney vasculature and increased expression of VEGF and SDF-1 in kidneys 24 and 48 h post-treatment, as compared with the contralateral controls. The levels returned to normal by 72 h post-treatment.
The expression of different types of mediators secreted by inflamed tissues plays a vital role in mediating the homing of specific BMSCs to targeted tissues, including IL-1 α, IL-2, IL-3, IL-10, IFN-γ, TNF-α and MCP-1 (Kielian et al. 2002; Ponte et al. 2007). ELISA-based cytokine array indicated increased expression of some cytokines (IL-1 α, IL-2, IL-3, IFN-γ, TNF-α and MCP-1) in targeted diabetic kidneys 24 and 48 h post-treatment compared with the contralateral controls. These levels returned to normal by 72 h post-treatment. All of these results indicated that MB-mediated diagnostic ultrasound irradiation may enhance engrafted stem cell homing by changing the local renal micro-environment by increasing the expression of adhesion molecules, trophic factors and inflammatory cytokines.
In this study, TEM was used to observe the ultrastructural changes of capillary walls in kidney tissues subjected to MB-mediated diagnostic ultrasound irradiation. We found that part of the renal interstitial vascular walls became ruptured, discontinuous and roughened, in agreement with previously reported results. This proved that capillary walls in sonicated DN areas were ruptured under the mediation of diagnostic ultrasound and microbubbles. Thus, we hypothesize that the potential mechanism may lie in the fact that the ruptured capillaries, injured cells and subsequent inflammatory response caused by acoustic cavitation in the sonicated diabetic kidneys can promote the attachment of stem cells to the injured endothelial BYL719 layer, and some of the increased cytokines and trophic factors may be helpful in improving stem cell homing (Burks et al. 2013).