Hongtao Sun

Renal ischemia-reperfusion injury (IRI) can result in acute renal failure with mortality rates of 50% in severe cases. NK cells are important participants in early-stage innate immune responses. However, their role in renal tubular epithelial cell (TEC) injury in IRI is currently unknown. Our data indicate that NK cells can kill syngeneic TEC in vitro. Apoptotic death of TEC in vitro is associated with TEC expression of the NK cell ligand Rae-1, as well as NKG2D on NK cells. In vivo following IRI, there was increased expression of Rae-1 on TEC. FACS analyses of kidney cell preparations indicated a quantitative increase in NKG2D-bearing NK cells within the kidney following IRI. NK cell depletion in wild-type C57BL/6 mice was protective, while adoptive transfer of NK cells worsened injury in NK, T, and B cell-null Rag2(-/-)gamma(c)(-/-) mice with IRI. NK cell-mediated kidney injury was perforin (PFN)-dependent as PFN(-/-) NK cells had minimal capacity to kill TEC in vitro compared with NK cells from wild-type, FasL-deficient (gld), or IFN-gamma(-/-) mice. Taken together, these results demonstrate for the first time that NK cells can directly kill TEC and that NK cells contribute substantially to kidney IRI. NK cell killing may represent an important underrecognized mechanism of kidney injury in diverse forms of inflammation, including transplantation.

BACKGROUND: The role of the innate immune system in the development of thrombotic microangiopathy (TM) after alpha1,3-galactosyltransferase gene-knockout (GTKO) pig organ transplantation in primates is uncertain. METHODS: Twelve organs (nine hearts, three kidneys) from GTKO pigs were transplanted into baboons that received no immunosuppressive therapy, partial regimens, or a full regimen based on costimulation blockade. After graft failure, histologic and immunohistologic examinations were carried out. RESULTS: Graft survival of less than 1 day was prolonged to 2 to 12 days with partial regimens (acute humoral xenograft rejection) and to 5 and 8 weeks with the full regimen (TM). Clinical or laboratory features of consumptive coagulopathy occurred in 7 of 12 baboons. Immunohistochemistry demonstrated IgM, IgG, and complement deposition in most cases. Histopathology demonstrated neutrophil and macrophage infiltrates, intravascular fibrin deposition, and platelet aggregation (TM). Grafts showed expression of primate tissue factor (TF), with increased mRNA levels, and TF was also expressed on baboon macrophages/monocytes infiltrating the graft. CONCLUSIONS: Our data suggest that (1) irrespective of the presence or absence of the adaptive immune response, early or late xenograft rejection is associated with activation of the innate immune system; and (2) porcine endothelial cell activation and primate TF expression by recipient innate immune cells may both contribute to the development of TM.

Necroptosis, a novel type of programmed cell death, is involved in stroke-induced ischemic brain injury. Although studies have sought to explore the mechanisms of necroptosis, its signaling pathway has not yet to be completely elucidated. Thus, we used oxygen-glucose deprivation (OGD) and middle cerebral artery occlusion (MCAO) models mimicking ischemic stroke (IS) conditions to investigate mechanisms of necroptosis. We found that OGD and MCAO induced cell death, local brain ischemia and neurological deficit, while zVAD-fmk (zVAD, an apoptotic inhibitor), GSK'872 (a receptor interacting protein kinase-3 (RIP3) inhibitor), and combined treatment alleviated cell death and ischemic brain injury. Moreover, OGD and MCAO upregulated protein expression of the triggers of necroptosis: receptor interacting protein kinase-1 (RIP1), RIP3 and mixed lineage kinase domain-like protein (MLKL). The upregulation of these proteins was inhibited by GSK'872, combination treatments and RIP3 siRNA but not zVAD treatment. Intriguingly, hypoxia-inducible factor-1 alpha (HIF-1α), an important transcriptional factor under hypoxic conditions, was upregulated by OGD and MCAO. Similar to their inhibitory effects on aforementioned proteins upregulation, GSK'872, combination treatments and RIP3 siRNA decreased HIF-1α protein level. These findings indicate that necroptosis contributes to ischemic brain injury induced by OGD and MCAO and implicate HIF-1α, RIP1, RIP3, and MLKL in necroptosis.