Introduction: Dendritic cells (DC) are critical initiators of innate immunity in the kidney and orchestrate inflammation subsequent to ischemia-reperfusion injury (IRI). The role of mammalian/mechanistic target of rapamycin (mTOR) in the pathophysiology of renal IRI has been poorly characterized; furthermore, the influence of DC-based alterations in mTOR signaling has not been investigated.
Methods: We initially evaluated activation of the mTORC1/2 pathway in sham-operated and post kidney IRI C57BL/6 mice. Ex vivo isolated bone marrow-derived mTORC2 deficient (Rictor-/-) or wild-type (WT) DC underwent hypoxia-reoxygenation and then were analysed by flow cytometry. Adoptive transfer of WT or Rictor-/- DC to C57BL/6 mice followed by unilateral renal IRI was used to assess migratory capacity. Age- and gender-matched DC-specific Rictor-/- mice or littermate controls underwent bilateral renal IRI followed by assessment of renal function, histopathology, bio-molecular and cell infiltration analysis.
Results: Protein expression of phosphorylated S6K that is a downstream of mTORC1 was upregulated, but conversely, phosphorylated Akt S473 that is a downstream of mTORC2 was decreased in whole kidney tissue in response to IRI. Rictor-/- DC express more CD80/CD86 but less programed death ligand-1 (PDL1) which can be enhanced by hypoxia-reoxygenation, and demonstrate increased migration to the injured kidney. Following IRI, Rictor-/- DC mice develop higher serum creatinine, more severe histologic damage and greater pro-inflammatory mRNA transcript profiles of IL-1β, IL-6 and TNF-α compared to littermate controls. After IRI challenge, Rictor-/- DC show a trend towards increased TNF-α production, but significantly reduced IL-10 secretion compared to WT DC. A greater influx of both neutrophils and T cells was also seen in Rictor-/- DC mice, in addition to CD11c+MHCII+CD11bhiF4/80+ renal DC, which expressed more CD86 but less PDL1.
Conclusion: These novel data suggest that mTORC2 signaling in renal DC negatively regulates acute kidney injury. Thus, DC-targeted elimination of Rictor enhances inflammatory and migratory responses to the injured kidney, highlighting the regulatory roles of both DC and Rictor in the pathophysiology of renal IRI.