Renal ischemia-reperfusion injury: renal dendritic cells loudly sound the alarm

Rapamycin Alternatively Modifies Mitochondrial Dynamics in Dendritic Cells to Reduce Kidney Ischemic Reperfusion Injury

Dendritic cells (DCs) are unique immune cells that can link innate and adaptive immune responses and Immunometabolism greatly impacts their phenotype. Rapamycin is a macrolide compound that has immunosuppressant functions and is used to prevent graft loss in kidney transplantation. The current study evaluated the therapeutic potential of ex-vivo rapamycin treated DCs to protect kidneys in a mouse model of acute kidney injury (AKI). For the rapamycin single (S) treatment (Rapa-S-DC), Veh-DCs were treated with rapamycin (10 ng/mL) for 1 h before LPS. In contrast, rapamycin multiple (M) treatment (Rapa-M-DC) were exposed to 3 treatments over 7 days. Only multiple ex-vivo rapamycin treatments of DCs induced a persistent reprogramming of mitochondrial metabolism. These DCs had 18-fold more mitochondria, had almost 4-fold higher oxygen consumption rates, and produced more ATP compared to Veh-DCs (Veh treated control DCs). Pathway analysis showed IL10 signaling as a major contributing pathway to the altered immunophenotype after Rapamycin treatment compared to vehicle with significantly lower cytokines Tnfa, Il1b, and Il6, while regulators of mitochondrial content Pgc1a, Tfam, and Ho1 remained elevated. Critically, adoptive transfer of rapamycin-treated DCs to WT recipients 24 h before bilateral kidney ischemia significantly protected the kidneys from injury with a significant 3-fold improvement in kidney function. Last, the infusion of DCs containing higher mitochondria numbers (treated ex-vivo with healthy isolated mitochondria (10 µg/mL) one day before) also partially protected the kidneys from IRI. These studies demonstrate that pre-emptive infusion of ex-vivo reprogrammed DCs that have higher mitochondria content has therapeutic capacity to induce an anti-inflammatory regulatory phenotype to protect kidneys from injury.

FTY720 Regulates Mitochondria Biogenesis in Dendritic Cells to Prevent Kidney Ischemic Reperfusion Injury

Dendritic cells (DCs) are central in regulating immune responses of kidney ischemia-reperfusion injury (IRI), and strategies to alter DC function may provide new therapeutic opportunities. Sphingosine 1-phosphate (S1P) modulates immunity through binding to its receptors (S1P1-5), and protection from kidney IRI occurs in mice treated with S1PR agonist, FTY720 (FTY). We tested if ex vivo propagation of DCs with FTY could be used as cellular therapy to limit the off-target effects associated with systemic FTY administration in kidney IRI. DCs have the ability of regulate innate and adaptive responses and we posited that treatment of DC with FTY may underlie improvements in kidney IRI. Herein, it was observed that treatment of bone marrow derived dendritic cells (BMDCs) with FTY induced mitochondrial biogenesis, FTY-treated BMDCs (FTY-DCs) showed significantly higher oxygen consumption rate and ATP production compared to vehicle treated BMDCs (Veh-DCs). Adoptive transfer of FTY-DCs to mice 24 h before or 4 h after IRI significantly protected the kidneys from injury compared to mice treated with Veh-DCs. Additionally, allogeneic adoptive transfer of C57BL/6J FTY-DCs into BALB/c mice equally protected the kidneys from IRI. FTY-DCs propagated from S1pr1-deficient DCs derived from CD11cCreS1pr1^fl/fl mice as well as blunting mitochondrial oxidation in wildtype (WT) FTY-DCs prior to transfer abrogated the protection observed by FTY-DCs. We queried if DC mitochondrial content alters kidney responses after IRI, a novel but little studied phenomenon shown to be integral to regulation of the immune response. Transfer of mitochondria rich FTY-DCs protects kidneys from IRI as transferred FTY-DCs donated their mitochondria to recipient splenocytes (i.e., macrophages) and prior splenectomy abrogated this protection. Adoptive transfer of FTY-DCs either prior to or after ischemic injury protects kidneys from IRI demonstrating a potent role for donor DC-mitochondria in FTY's efficacy. This is the first evidence, to our knowledge, that DCs have the potential to protect against kidney injury by donating mitochondria to splenic macrophages to alter their bioenergetics thus making them anti-inflammatory. In conclusion, the results support that ex vivo FTY720-induction of the regulatory DC phenotype could have therapeutic relevance that can be preventively infused to reduce acute kidney injury.

Sphingosine 1-Phosphate Receptor 3-Deficient Dendritic Cells Modulate Splenic Responses to Ischemia-Reperfusion Injury

The plasticity of dendritic cells (DCs) permits phenotypic modulation ex vivo by gene expression or pharmacologic agents, and these modified DCs can exert therapeutic immunosuppressive effects in vivo through direct interactions with T cells, either inducing T regulatory cells (T(REG)s) or causing anergy. Sphingosine 1-phosphate (S1P) is a sphingolipid and the natural ligand for five G protein-coupled receptors (S1P1, S1P2, S1P3, S1P4, and S1P5), and S1PR agonists reduce kidney ischemia-reperfusion injury (IRI) in mice. S1pr3(-/-)mice are protected from kidney IRI, because DCs do not mature. We tested the therapeutic advantage of S1pr3(-/-) bone marrow-derived dendritic cell (BMDC) transfers in kidney IRI. IRI produced a rise in plasma creatinine (PCr) levels in mice receiving no cells (NCs) and mice pretreated with wild-type (WT) BMDCs. However, S1pr3(-/-) BMDC-pretreated mice were protected from kidney IRI. S1pr3(-/-) BMDC-pretreated mice had significantly higher numbers of splenic T(REG)s compared with NC and WT BMDC-pretreated mice. S1pr3(-/-) BMDCs did not attenuate IRI in splenectomized, Rag-1(-/-), or CD11c(+) DC-depleted mice. Additionally, S1pr3(-/-) BMDC-dependent protection required CD169(+)marginal zone macrophages and the macrophage-derived chemokine CCL22 to increase splenic CD4(+)Foxp3(+) T(REG)s. Pretreatment with S1pr3(-/-) BMDCs also induced T(REG)-dependent protection against IRI in an allogeneic mouse model. In summary, adoptively transferred S1pr3(-/-) BMDCs prevent kidney IRI through interactions within the spleen and expansion of splenic CD4(+)Foxp3(+) T(REG)s. We conclude that genetically induced deficiency of S1pr3 in allogenic BMDCs could serve as a therapeutic approach to prevent IRI-induced AKI.

Dendritic Cells in Kidney Transplant Biopsy Samples Are Associated with T Cell Infiltration and Poor Allograft Survival

Progress in long-term renal allograft survival continues to lag behind the progress in short-term transplant outcomes. Dendritic cells are the most efficient antigen-presenting cells, but surprisingly little attention has been paid to their presence in transplanted kidneys. We used dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin as a marker of dendritic cells in 105 allograft biopsy samples from 105 kidney transplant recipients. High dendritic cell density was associated with poor allograft survival independent of clinical variables. Moreover, high dendritic cell density correlated with greater T cell proliferation and poor outcomes in patients with high total inflammation scores, including inflammation in areas of tubular atrophy. We then explored the association between dendritic cells and histologic variables associated with poor prognosis. Multivariate analysis revealed an independent association between the densities of dendritic cells and T cells. In biopsy samples with high dendritic cell density, electron microscopy showed direct physical contact between infiltrating lymphocytes and cells that have the ultrastructural morphologic characteristics of dendritic cells. The origin of graft dendritic cells was sought in nine sex-mismatched recipients using XY fluorescence in situ hybridization. Whereas donor dendritic cells predominated initially, the majority of dendritic cells in late allograft biopsy samples were of recipient origin. Our data highlight the prognostic value of dendritic cell density in allograft biopsy samples, suggest a new role for these cells in shaping graft inflammation, and provide a rationale for targeting dendritic cell recruitment to promote long-term allograft survival.

Investigation of association between donors' and recipients' NADPH oxidase p22(phox) C242T polymorphism and acute rejection, delayed graft function and blood pressure in renal allograft recipients

BACKGROUND

Production of reactive oxygen species (ROS) and thereby induction of oxidative stress seem to be one of the major mediators of inflammatory adverse outcomes after renal transplantation. p22(phox) is a polymorphic subunit of NAD(P)H-oxidase that is critical for activation and stabilization of the enzyme. This enzyme is involved in the production of superoxide that triggers inflammatory injuries to the kidney. So in this study, the association between donors and recipients' C242T polymorphism of p22(phox) and acute rejection (AR), delayed graft function (DGF), creatinine clearance (CrCl), and blood pressure in renal-allograft recipients was studied.

METHODS

One hundred ninety six donor-recipient pairs were studied. The C242T polymorphism of p22(phox) was determined using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). According to p22 genotype, the subjects were divided in wild-type (CC) and T allele carriers (CT+TT). Transplantation outcomes were determined using acute rejection and delayed graft function criteria. The mean arterial pressure was also measured monthly after transplantation.

RESULTS

There was a significant association between the recipients' p22(phox) polymorphism and DGF occurrence (OR=2.5, CI: 1.2-4.9, p=0.0009). No significant association was detected between donors' p22(phox) polymorphism and AR and DGF events. CrCl during the six months follow-up after transplantation was lower in the patients who received allograft from donors carrying 242T allele (B=-12.8, CI: -22.9-12.8 (-22.9 to -2.6)). Changes in the blood pressure were not different among the patients having different genotypes of p22(phox).

CONCLUSION

These results suggest that the recipients' p22(phox) C242T polymorphism may be a major risk factor for DGF in renal transplantation. Moreover, the donors' 242T allele seems to affect the rate of CrCl in the renal allograft recipients.

The mechanisms of up-regulation of dendritic cell activity by oxidative stress

Whereas DC have increasingly been recognized for their role in activating the inflammatory cascades during IRIs, the mechanisms by which oxidative stress enhances DC activation remain to be explored. We examined the role of oxidative stress on two important features of DC: T cell activation and trafficking. Bone marrow-derived OS-DC were compared with untreated DC. DC exposed to oxidative stress augmented allogeneic T cell proliferation and showed increased migration in a chemotaxis chamber. These results were confirmed by using hypoxanthine and xanthine oxidase as another inducer of oxidative stress. We used OT-II and OT-I mice to assess the effect of oxidative stress on DC activation of OVA-specific CD4(+) and CD8(+) T cells, respectively. Oxidative stress increased DC capacity to promote OVA-specific CD4(+) T cell activity, demonstrated by an increase in their proliferation and production of IFN-γ, IL-6, and IL-2 proinflammatory cytokines. Whereas oxidative stress increased the DC ability to stimulate IFN-γ production by OVA-specific CD8(+) T cells, cellular proliferation and cytotoxicity were not affected. Compared with untreated DC, oxidative stress significantly reduced the capacity of DC to generate T(regs), which were restored by using anti-IL-6. With regard to DC trafficking, whereas oxidative stress increased DC expression of p-Akt and p-NF-κB, targeting PI3Kγ and NF-κB pathways abrogated the observed increase in DC migration. Our data propose novel insights on the activation of DC by oxidative stress and provide rationales for targeted therapies, which can potentially attenuate IRI.

Dendritic cell sphingosine 1-phosphate receptor-3 regulates Th1-Th2 polarity in kidney ischemia-reperfusion injury

Dendritic cells (DCs) are central to innate and adaptive immunity of early kidney ischemia-reperfusion injury (IRI), and strategies to alter DC function may provide new therapeutic opportunities. Sphingosine 1-phosphate (S1P) modulates immunity through binding to its receptors (S1P1-5), and protection from kidney IRI occurs in S1P3-deficient mice. Through a series of experiments we determined that this protective effect was owing in part to differences between S1P3-sufficient and -deficient DCs. Mice lacking S1P3 on bone marrow cells were protected from IRI, and S1P3-deficient DCs displayed an immature phenotype. Wild-type (WT) but not S1P3-deficient DCs injected into mice depleted of DCs prior to kidney IR reconstituted injury. Adoptive transfer (i.e., i.v. injection) of glycolipid (Ag)-loaded WT but not S1P3-deficient DCs into WT mice exacerbated IRI, suggesting that WT but not S1P3-deficient DCs activated NKT cells. Whereas WT DC transfers activated the Th1/IFN-γ pathway, S1P3-deficient DCs activated the Th2/IL-4 pathway, and an IL-4-blocking Ab reversed protection from IRI, supporting the concept that IL-4 mediates the protective effect of S1P3-deficient DCs. Administration of S1P3-deficient DCs 7 d prior to or 3 h after IRI protected mice from IRI and suggests their potential use in cell-based therapy. We conclude that absence of DC S1P3 prevents DC maturation and promotes a Th2/IL-4 response. These findings highlight the importance of DC S1P3 in modulating NKT cell function and IRI and support development of selective S1P3 antagonists for tolerizing DCs for cell-based therapy or for systemic administration for the prevention and treatment of IRI and autoimmune diseases.

Depletion of macrophages and dendritic cells in ischemic acute kidney injury

BACKGROUND

Inflammation is thought to play a role in ischemic acute kidney injury (AKI). We have demonstrated that macrophage and dendritic cell depletion, using liposome-encapsulated clodronate (LEC), is protective against ischemic AKI.

METHODS

To determine whether macrophages or dendritic cells or both play a role in ischemic AKI, we performed ischemic AKI in CD11b-DTR mice that have a diphtheria toxin (DT)-induced depletion of CD11b cells (macrophages) and CD11c-DTR mice that have a DT-induced depletion of CD11c cells (dendritic cells).

RESULTS

While LEC-treated animals had a significant functional protection from AKI, CD11b-DTR and CD11c-DTR mice were not protected against AKI despite a similar degree of renal macrophage and dendritic cell depletion. Proinflammatory cytokines are known to play a role in ischemic AKI. To determine the possible reasons for the lack of protection in CD11b-DTR and CD11c-DTR mice compared to LEC-treated mice, 32 cytokines/chemokines were measured in these mice. Of the cytokines/chemokines measured, IL-6, MCP-1, GMCSF, IL-1β and CXCL1 (also known as IL-8 in humans or KC in mice) showed significant differences in the LEC-treated, CD11b-DTR and CD11c-DTR mice. MCP-1 and CXCL1 (known mediators of AKI), and also GMCSF and IL-1β were increased in AKI and decreased in LEC-treated AKI but not AKI in CD11b-DTR or CD11c-DTR mice.

CONCLUSIONS

These findings suggest that LEC-mediated protection from AKI is not simply mediated by depletion of renal macrophage or dendritic cell subpopulations. Protection against AKI in LEC-treated compared to CD11b-DTR or CD11c-DTR mice may be partially explained by differences in proinflammatory cytokine profiles.

Dendritic cells in experimental renal inflammation--Part I

Dendritic cells (DCs) are bone marrow-derived professional antigen-presenting cells that act as master regulators of acquired and innate immune responses. While descriptions of cells with dendritic morphology in rodent kidneys date back to the early 1970s, a network of DCs in the mouse kidney has only recently been described. DCs acquire distinct phenotypic and functional characteristics depending on the microenvironment and the disease stages. Concomitantly, their communication with cells of the adaptive immunity might have tissue-protective or tissue-deleterious consequences. This review summarizes results from recent studies on the role of DCs in experimental renal inflammation.

Increased influx of myeloid dendritic cells during acute rejection is associated with interstitial fibrosis and tubular atrophy and predicts poor outcome

Dendritic cells are key players in renal allograft rejection and have been identified as an intrinsic part of the kidney. Here we quantified and phenotyped the dendritic cell populations in well-defined biopsies of 102 patients with acute renal allograft rejection in comparison with 78 available pretransplant biopsies. There was a strong increase in BDCA-1(+) and DC-SIGN(+) myeloid, BDCA-2(+) plasmacytoid, and DC-LAMP(+) mature dendritic cells in rejection biopsies compared with the corresponding pretransplant tissue. Mature dendritic cells were mostly found in clusters of lymphoid infiltrate and showed a strong correlation with the Banff infiltrate score. The presence of both myeloid and plasmacytoid dendritic cell subsets in the kidney during acute rejection correlated with interstitial fibrosis and tubular atrophy. Importantly, the myeloid dendritic cell density at the time of acute rejection was an independent risk factor for loss of renal function after the first year. Thus, acute renal allograft rejection is characterized by an influx of myeloid and plasmacytoid dendritic cells, strongly associated with local damage in the graft. Hence, the density of myeloid dendritic cells during acute rejection could be an important risk factor for the long-term development of chronic changes and loss of graft function.

Ischemia reperfusion induces IFN regulatory factor 4 in renal dendritic cells, which suppresses postischemic inflammation and prevents acute renal failure

Ischemia reperfusion (IR) activates TLRs causing subsequent sterile inflammation, for example in postischemic acute renal failure. Unexpectedly, TLR signaling predominates in intrinsic renal cells and not in intrarenal APCs in the postischemic kidney. We hypothesized that certain factors suppress APC activation and thereby limit sterile renal inflammation, for example, IFN regulatory factor 4 (IRF-4), an inducible inhibitor of LPS signaling. Oxidative stress was a trigger for IRF4 induction in myeloid cells in vitro as well as in CD45(+)/CD11c+ cells in the postischemic kidney. Lack of IRF4 aggravated acute renal failure 24 h after renal artery clamping together with increased intrarenal expression of TNF-alpha, IL-6, CXCL2, and CCL2 as well as excessive tubular necrosis and peritubular neutrophil influx as compared with wild-type IR kidneys. This effect almost entirely depended on the role of IRF4 to suppress TNF-alpha release by intrarenal APCs because either clodronate liposome depletion of these cells or TNF-alpha blockade with etanercept entirely abrogated the aggravation of cytokine expression and acute renal failure in Irf4-deficient mice. Thus, loss-of-function mutations in the IRF4 gene predispose to IR injury because the postischemic induction of IRF4 in resident APCs like CD11c(+) dendritic cells, suppresses them to secrete TNF-alpha, and thereby limits inappropriate immunopathology.

Resident dendritic cells prevent postischemic acute renal failure by help of single Ig IL-1 receptor-related protein

Ischemia-reperfusion (IR) triggers tissue injury by activating innate immunity, for example, via TLR2 and TLR4. Surprisingly, TLR signaling in intrinsic renal cells predominates in comparison to intrarenal myeloid cells in the postischemic kidney. We hypothesized that immune cell activation is specifically suppressed in the postischemic kidney, for example, by single Ig IL-1-related receptor (SIGIRR). SIGIRR deficiency aggravated postischemic acute renal failure in association with increased renal CXCL2/MIP2, CCL2/MCP-1, and IL-6 mRNA expression 24 h after IR. Consistent with this finding interstitial neutrophil and macrophage counts were increased and tubular cell necrosis was aggravated in Sigirr-deficient vs wild-type IR kidneys. In vivo microscopy revealed increased leukocyte transmigration in the postischemic microvasculature of Sigirr-deficient mice. IL-6 and CXCL2/MIP2 release was much higher in Sigirr-deficient renal myeloid cells but not in Sigirr-deficient tubular epithelial cells after transient hypoxic culture conditions. Renal IR studies with chimeric mice confirmed this finding, as lack of SIGIRR in myeloid cells largely reproduced the phenotype of renal IR injury seen in Sigirr(-/-) mice. Additionally, clodronate depletion of dendritic cells prevented the aggravated renal failure in Sigirr(-/-) mice. Thus, loss of function mutations in the SIGIRR gene predispose to acute renal failure because SIGIRR prevents overshooting tissue injury by suppressing the postischemic activation of intrarenal myeloid cells.

Dendritic cells contribute to autoimmune kidney injury in MRL-Faslpr mice

OBJECTIVE

Dendritic cells (DC) contribute to autoimmune disease progression and pathogenesis. Mature DC have been reported to secrete high mobility group box protein (HMGB-1), a novel inflammatory cytokine, via p38 mitogen-activated protein kinase (MAPK) activation. We investigated whether DC are involved in progression of autoimmune diseases followed by secretion of HMGB-1 via p38 MAPK activation in a lupus-prone mouse model.

METHODS

FR167653, a specific inhibitor of p38 MAPK, was given orally from 3 months of age in MRL-Fas(lpr) mice. Cultured DC, treated with or without FR167653, were stimulated with tumor necrosis factor-alpha.

RESULTS

Inhibition of p38 MAPK led to a reduction in the number of CD11c-positive cells, including those with the mature phenotype, in the diseased kidney and spleen, which resulted in improvement of kidney pathology in MRL-Fas(lpr) mice. The number of CD11c-positive cells in circulation was also reduced. HMGB-1 protein and transcripts detected in the diseased kidney, and the number of cells dual-positive for HMGB-1 and CD11c, were reduced by inhibition of p38 MAPK. Maturation of cultured DC and increased cytokines, including HMGB-1, in the supernatant were inhibited by FR167653 treatment. These results suggest that DC are involved in the progression of autoimmune kidney diseases in MRL-Fas(lpr) mice followed by HMGB-1 secretion via p38 MAPK activation.

CONCLUSION

Our results indicated that DC secrete HMGB-1 via p38 MAPK activation to participate in autoimmunity in MRL-Fas(lpr) mice.

The identity and regulation of the mitochondrial permeability transition pore: where the known meets the unknown

The mitochondrial permeability transition (MPT) pore complex is a key participant in the machinery that controls mitochondrial fate and, consequently, cell fate. The quest for the pore identity has been ongoing for several decades and yet the main structure remains unknown. Established "dogma" proposes that the core of the MPT pore is composed of an association of voltage-dependent anion channel (VDAC) and adenine nucleotide translocase (ANT). Recent genetic knockout experiments contradict this commonly accepted interpretation and provide a basis for substantial revision of the MPT pore identity. There is now sufficient evidence to exclude VDAC and ANT as the main pore structural components. Regarding MPT pore regulation, the role of cyclophilin D is confirmed and ANT may still serve some regulatory function, although the involvement of hexokinase II and creatine kinase remains unresolved. When cell protection signaling pathways are activated, we have found that the Bcl-2 family members relay the signal from glycogen synthase kinase-3 beta onto a target at or in close proximity to the pore. Our experimental findings in intact cardiac myocytes and neurons indicate that the current "dogma" related to the role of Ca2+ in MPT induction requires reevaluation. Emerging evidence suggests that after injury-producing stresses, reactive oxygen species (but not Ca2+) are largely responsible for the pore induction. In this article we discuss the current state of knowledge and provide new data related to the MPT pore structure and regulation.

Novel pharmacological approaches to the treatment of renal ischemia-reperfusion injury: a comprehensive review

Renal ischemia-reperfusion (I-R) contributes to the development of ischemic acute renal failure (ARF). Multi-factorial processes are involved in the development and progression of renal I-R injury with the generation of reactive oxygen species, nitric oxide and peroxynitrite, and the decline of antioxidant protection playing major roles, leading to dysfunction, injury, and death of the cells of the kidney. Renal inflammation, involving cytokine/adhesion molecule cascades with recruitment, activation, and diapedesis of circulating leukocytes is also implicated. Clinically, renal I-R occurs in a variety of medical and surgical settings and is responsible for the development of acute tubular necrosis (a characteristic feature of ischemic ARF), e.g., in renal transplantation where I-R of the kidney directly influences graft and patient survival. The cellular mechanisms involved in the development of renal I-R injury have been targeted by several pharmacological interventions. However, although showing promise in experimental models of renal I-R injury and ischemic ARF, they have not proved successful in the clinical setting (e.g., atrial natriuretic peptide, low-dose dopamine). This review highlights recent pharmacological developments, which have shown particular promise against experimental renal I-R injury and ischemic ARF, including novel antioxidants and antioxidant enzyme mimetics, nitric oxide and nitric oxide synthase inhibitors, erythropoietin, peroxisome-proliferator-activated receptor agonists, inhibitors of poly(ADP-ribose) polymerase, carbon monoxide-releasing molecules, statins, and adenosine. Novel approaches such as recent research involving combination therapies and the potential of non-pharmacological strategies are also considered.