Pharmacologic recruitment of regulatory T cells as a therapy for ischemic acute kidney injury

Mesenchymal stem cells attenuate ischemic acute kidney injury by inducing regulatory T cells through splenocyte interactions

The mechanism of mesenchymal stem cell therapy in acute kidney injury remains uncertain. Previous studies indicated that mesenchymal stem cells could attenuate inflammation-related organ injury by induction of regulatory T cells. Whether regulatory T-cell induction is a potential mechanism of mesenchymal stem cell therapy in ischemic acute kidney injury and how these induced regulatory T cells orchestrate local inflammation are unknown. Here we found that mesenchymal stem cells decrease serum creatinine and urea nitrogen levels, improve tubular injury, and downregulate IFN-γ production of T cells in the ischemic kidney. In addition to the lung, mesenchymal stem cells persisted mostly in the spleen. Mesenchymal stem cells increased the percentage of regulatory T cells in the spleen and the ischemic kidney. Antibody-dependent depletion of regulatory T cells blunted the therapeutic effect of mesenchymal stem cells, while coculture of splenocytes with mesenchymal stem cells caused an increase in the percentage of regulatory T cells. Splenectomy abrogated attenuation of ischemic injury, and downregulated IFN-γ production and the induction of regulatory T cells by mesenchymal stem cells. Thus, mesenchymal stem cells ameliorate ischemic acute kidney injury by inducing regulatory T cells through interactions with splenocytes. Accumulated regulatory T cells in ischemic kidney might be involved in the downregulation of IFN-γ production.

Ischemic preconditioning in the liver is independent of regulatory T cell activity

Ischemic preconditioning (IPC) protects organs from ischemia reperfusion injury (IRI) through unknown mechanisms. Effector T cell populations have been implicated in the pathogenesis of IRI, and T regulatory cells (Treg) have become a putative therapeutic target, with suggested involvement in IPC. We explored the role of Treg in hepatic IRI and IPC in detail. IPC significantly reduced injury following ischemia reperfusion insults. Treg were mobilized rapidly to the circulation and liver after IRI, but IPC did not further increase Treg numbers, nor was it associated with modulation of circulating pro-inflammatory chemokine or cytokine profiles. We used two techniques to deplete Treg from mice prior to IRI. Neither Treg depleted FoxP3.LuciDTR mice, nor wildtyoe mice depleted of Tregs with PC61, were more susceptible to IRI compared with controls. Despite successful enrichment of Treg in the liver, by adoptive transfer of both iTreg and nTreg or by in vivo expansion of Treg with IL-2/anti-IL-2 complexes, no protection against IRI was observed.We have explored the role of Treg in IRI and IPC using a variety of techniques to deplete and enrich them within both the liver and systemically. This work represents an important negative finding that Treg are not implicated in IPC and are unlikely to have translational potential in hepatic IRI.

Endothelial pentraxin 3 contributes to murine ischemic acute kidney injury

Toll-like receptor 4 (TLR4), a receptor for damage-associated molecular pattern molecules and also the lipopolysaccharide receptor, is required for early endothelial activation leading to maximal inflammation and injury during murine ischemic acute kidney injury. DNA microarray analysis of ischemic kidneys from TLR4-sufficient and -deficient mice showed that pentraxin 3 (PTX3) was upregulated only on the former while transgenic knockout of PTX3 ameliorated acute kidney injury. PTX3 was expressed predominantly on peritubular endothelia of the outer medulla of the kidney in control mice. Acute kidney injury increased PTX3 protein in the kidney and the plasma where it may be a biomarker of the injury. Stimulation by hydrogen peroxide, or the TLR4 ligands recombinant human high-mobility group protein B1 or lipopolysaccharide, induced PTX3 expression in the Mile Sven 1 endothelial cell line and in primary renal endothelial cells, suggesting that endothelial PTX3 was induced by pathways involving TLR4 and reactive oxygen species. This increase was inhibited by conditional endothelial knockout of myeloid differentiation primary response gene 88, a mediator of a TLR4 intracellular signaling pathway. Compared to wild-type mice, PTX3 knockout mice had decreased endothelial expression of cell adhesion molecules at 4 h of reperfusion, possibly contributing to a decreased early maladaptive inflammation in the kidneys of knockout mice. At 24 h of reperfusion, PTX3 knockout increased expression of endothelial adhesion molecules when regulatory and reparative leukocytes enter the kidney. Thus, endothelial PTX3 plays a pivotal role in the pathogenesis of ischemic acute kidney injury.

Autocrine adenosine signaling promotes regulatory T cell-mediated renal protection

Regulatory T cells (Tregs) suppress the innate inflammation associated with kidney ischemia-reperfusion injury (IRI), but the mechanism is not well understood. Tregs express CD73, the final enzyme involved in the production of extracellular adenosine, and activation of the adenosine 2A receptor (A(2A)R) on immune cells suppresses inflammation and preserves kidney function after IRI. We hypothesized that Treg-generated adenosine is required to block innate immune responses in kidney IRI and that the Treg-generated adenosine would signal through A(2A)Rs on inflammatory cells and, in an autocrine manner, on Tregs themselves. We found that adoptively transferred wild-type Tregs protected wild-type mice from kidney IRI, but the absence of adenosine generation (CD73-deficient Tregs) or adenosine responsiveness (A(2A)R-deficient Tregs) led to inhibition of Treg function. Pharmacologic stimulation of A(2A)R before adoptive transfer augmented the ability of wild-type and CD73-deficient Tregs to suppress kidney IRI. Microarray analysis and flow cytometry revealed that A(2A)R activation enhanced surface PD-1 expression on Tregs in the absence of any other activation signal. Treatment of Tregs with a PD-1 blocking antibody before adoptive transfer reversed their protective effects, even if pretreated with an A(2A)R agonist. Taken together, these results demonstrate that the simultaneous ability to generate and respond to adenosine is required for Tregs to suppress innate immune responses in IRI through a PD-1-dependent mechanism.