Genetically engineered mesenchymal stem cells as a nitric oxide reservoir for acute kidney injury therapy

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    This important study combines engineered mesenchymal stem cells together with mouse models of kidney injury to determine the ability of these cells to reduce kidney damage upon acute kidney injury. The evidence supporting the claims is solid, although the inclusion of more than one type of stem cell and the use of male mice which are more prone to acute kidney injury, would strengthen the study. This work will be of interest to both basic scientists and clinicians working on mechanisms of kidney injury and repair.

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Abstract

Nitric oxide (NO), as a gaseous therapeutic agent, shows great potential for the treatment of many kinds of diseases. Although various NO delivery systems have emerged, the immunogenicity and long-term toxicity of artificial carriers hinder the potential clinical translation of these gas therapeutics. Mesenchymal stem cells (MSCs), with the capacities of self-renewal, differentiation, and low immunogenicity, have been used as living carriers. However, MSCs as gaseous signaling molecule (GSM) carriers have not been reported. In this study, human MSCs were genetically modified to produce mutant β-galactosidase (β-GAL H363A ). Furthermore, a new NO prodrug, 6-methyl-galactose-benzyl-oxy NONOate (MGP), was designed. MGP can enter cells and selectively trigger NO release from genetically engineered MSCs (eMSCs) in the presence of β-GAL H363A . Moreover, our results revealed that eMSCs can release NO when MGP is systemically administered in a mouse model of acute kidney injury (AKI), which can achieve NO release in a precise spatiotemporal manner and augment the therapeutic efficiency of MSCs. This eMSC and NO prodrug system provides a unique and tunable platform for GSM delivery and holds promise for regenerative therapy by enhancing the therapeutic efficiency of stem cells.

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  1. eLife assessment

    This important study combines engineered mesenchymal stem cells together with mouse models of kidney injury to determine the ability of these cells to reduce kidney damage upon acute kidney injury. The evidence supporting the claims is solid, although the inclusion of more than one type of stem cell and the use of male mice which are more prone to acute kidney injury, would strengthen the study. This work will be of interest to both basic scientists and clinicians working on mechanisms of kidney injury and repair.

  2. Reviewer #1 (Public Review):

    For a gaseous therapeutic agent such as NO, delivery to the site and release to the injured area are both required for efficacy. Previous work has focused on hydrogels for delivery. The authors engineered a combined gene/cell therapy plus a pharmaceutical approach to NO delivery. Engineered MSC produced a mutant beta-galactosidase (B-GALH363A) that when a prodrug is administered, will release NO locally.

    One can imagine applications involving such a novel concept for gaseous signaling molecule delivery to include other kinds of cells, other prodrugs, other gaseous agents, and other injury types. In this elegant study, the concept has been explored deeply in one potential application, making it a landmark contribution to the field of regenerative medicine.

    Limitations of the current study are that the mice utilized were C57/Bl6 females, the most resistant sex and strain to kidney injury. Another limitation is the use of human placental MSCs only; as such we do not know if other MSCs will perform equally well.

  3. Reviewer #2 (Public Review):

    In this Manuscript, Huang et al generated engineered MSC (eMSC) to produce mutant b-GALH363A, and when stimulated with a pro-drug (MGP) they can release NO. These cells were tested in vivo in a mouse model of AKI. When MGP is systemically administrated in AKI mice, it can induce eMSC to release NO in a precise and spatiotemporal manner, possibly enhancing the therapeutic efficacy of these stem cells.

    The authors have conducted a very interesting study. The results are likely of interest to the renal scientific community, especially in the context of acute kidney injury.

    Weaknesses are present. Methods (animals, groups, time points, cell lines, bulk RNA-seq, etc.) are not clearly described and details are missing. Legends are not clear, and some Figures do not clearly represent the results discussed.

  4. Reviewer #3 (Public Review):

    Mesenchymal stem cells have been shown to have potent immunomodulatory and regenerative properties and have been tested and tried in kidney transplantation. In a previous paper, the authors of this paper reviewed the beneficial actions of nitric oxide (NO) on the beneficial action of MSC. In this manuscript, they describe a method to generate NO in the therapeutic MSC. While NO donors like the short-acting nitrates have been used for angina pectoris patients few therapeutic approaches have been published aiming at the local delivery of NO to specific tissues or organs like the kidney. Gene therapy with adenoviral vectors, overexpressing the eNOS gene itself failed due to the fact that the eNOS enzyme, when overexpressed quickly runs out of sufficient co-factors like BH4. As a consequence, the enzyme uncouples and becomes cytotoxic due to the generation of peroxynitrate. Hence, the current strategy to generate NO in the MSC itself is novel and interesting.

    The authors first describe the cryoprotective effects and antioxidant effects of NO generation in MSC in vitro and subsequently in vivo in a mouse model of ischemia-reperfusion injury that may reflect acute kidney injury (or ischemia associated with kidney transplantation) in patients. While the MSC are transplanted intracortical on a local position in the kidneys, the manuscript describes surprising effectivity on serum creatinine, ureum, casts, and protection of brush border. Also, upon immunohistochemical analyses, fibrosis, and kidney injury markers decrease. Most likely there is a strong paracrine effect. It is unfortunate that the control "PBS + MGP" is lacking to exclude some low-grade background conversion of the compound with subsequent release of NO. MGP only is tested however, studies in kidney sections with state-of-the-art EPR, give the authors the wanted control.

    The paper provides an interesting proof of concept for a novel therapeutic approach. However, in the clinical arena, some questions remain involving the survival of the MSC after transplantation and the introduction of novel antigens associated with the engineered cells