Improving the therapeutic efficacy of mesenchymal stromal cells to restore perfusion in critical limb ischemia through pulsed focused ultrasound

Abstract

Mesenchymal stem cells (MSC) are promising therapeutics for critical limb ischemia (CLI). Mechanotransduction from pulsed focused ultrasound (pFUS) upregulates local chemoattractants to enhance homing of intravenously (IV)-infused MSC and improve outcomes. This study investigated whether pFUS exposures to skeletal muscle would improve local homing of iv-infused MSCs and their therapeutic efficacy compared to iv-infused MSCs alone. CLI was induced by external iliac arterial cauterization in 10–12-month-old mice. pFUS/MSC treatments were delayed 14 days, when surgical inflammation subsided. Mice were treated with iv-saline, pFUS alone, IV-MSC, or pFUS and IV-MSC. Proteomic analyses revealed pFUS upregulated local chemoattractants and increased MSC tropism to CLI muscle. By 7 weeks post-treatment, pFUS + MSC significantly increased perfusion and CD31 expression, while reducing fibrosis compared to saline. pFUS or MSC alone reduced fibrosis, but did not increase perfusion or CD31. Furthermore, MSCs homing to pFUS-treated CLI muscle expressed more vascular endothelial growth factor (VEGF) and interleukin-10 (IL-10) than MSCs homing to non-pFUS-treated muscle. pFUS + MSC improved perfusion and vascular density in this clinically-relevant CLI model. The molecular effects of pFUS increased both MSC homing and MSC production of VEGF and IL-10, suggesting microenvironmental changes from pFUS also increased potency of MSCs in situ to further enhance their efficacy.

Mesenchymal stromal cell potency to treat acute kidney injury increased by ultrasound‐activated interferon‐γ/interleukin‐10 axis

“…While this study elucidates the mechanism behind combination therapy of pFUS and MSCs for cisplatin‐induced AKI, there are wide‐ranging implications for this noninvasive approach to improve other cellular therapies used in regenerative medicine. For example, we demonstrated a potential link between pFUS and cell potency in a model of critical limb ischaemia . To our knowledge, pFUS represents the first demonstration of an in vivo stem cell conditioning tool.…”

“…We have extensively investigated the molecular effects of pFUS and employed pFUS to improve MSC tropism and outcomes in several disease models . When MSCs are not stimulated by the pFUS‐altered renal microenvironment (ie.…”

“…shockwaves) into the parenchyma. The pFUS sonications described here have been applied to renal and muscle tissue without significant cellular damage—a likely necessity for regenerative medicine approaches . Interestingly, it has been reported that diagnostic ultrasound to the spleen stimulates cholinergic anti‐inflammatory pathways through haematopoietic nicotinic acetylcholine receptors to reduce inflammation and improve the specific duration of ischaemic reperfusion induced AKI …”

“…For example, we demonstrated a potential link between pFUS and cell potency in a model of critical limb ischaemia. 34 homing of MSC and improved renal function in rats following mercuric chloride injury. 44 In that study, ultrasound interaction with F I G U R E 4 IDO expression is up-regulated in mesenchymal stromal cells (MSC) that home to AKI kidneys, but the increased renal IFNγ following pFUS does not further up-regulate IDO expression.…”

“…We have extensively investigated the molecular effects of pFUS [18][19][20][21]33 and employed pFUS to improve MSC tropism and outcomes in several disease models. 17,20,34 When MSCs are not stimulated by the pFUS-altered renal microenvironment (ie. in the IFNγ-KO mouse or using IL-10-silenced MSC), despite increased tropism in the pFUS-treated groups, the additional cells did not improve AKI outcomes.…”