Donor and recipient contribution to transplant vasculopathy in chronic renal transplant dysfunction

PLX3397, a CSF1 receptor inhibitor, limits allotransplantation-induced vascular remodelling

AIMS

Graft vascular disease (GVD), a clinically important and highly complex vascular occlusive disease, arises from the interplay of multiple cellular and molecular pathways. While occlusive intimal lesions are composed predominantly of smooth-muscle-like cells (SMLCs), the origin of these cells and the stimuli leading to their accumulation in GVD are uncertain. Macrophages have recently been identified as both potential drivers of intimal hyperplasia and precursors that undergo transdifferentiation to become SMLCs in non-transplant settings. Colony-stimulating factor-1 (CSF1) is a well-known regulator of macrophage development and differentiation, and prior preclinical studies have shown that lack of CSF1 limits GVD. We sought to identify the origins of SMLCs and of cells expressing the CSF1 receptor (CSF1R) in GVD, and to test the hypothesis that pharmacologic inhibition of CSF1 signalling would curtail both macrophage and SMLC activities and decrease vascular occlusion.

METHODS AND RESULTS

We used genetically modified mice and a vascular transplant model with minor antigen mismatch to assess cell origins. We found that neointimal SMLCs derive from both donor and recipient, and that transdifferentiation of macrophages to SMLC phenotype is minimal in this model. Cells expressing CSF1R in grafts were identified as recipient-derived myeloid cells of Cx3cr1 lineage, and these cells rarely expressed smooth muscle marker proteins. Blockade of CSF1R activity using the tyrosine kinase inhibitor PLX3397 limited the expression of genes associated with innate immunity and decreased levels of circulating monocytes and intimal macrophages. Importantly, PLX3397 attenuated the development of GVD in arterial allografts.

CONCLUSION

These studies provide proof of concept for pharmacologic inhibition of the CSF1/CSF1R signalling pathway as a therapeutic strategy in GVD. Further preclinical testing of this pathway in GVD is warranted.

The Framingham Risk Score Is Associated with Chronic Graft Failure in Renal Transplant Recipients

Predicting chronic graft failure in renal transplant recipients (RTR) is an unmet clinical need. Chronic graft failure is often accompanied by transplant vasculopathy, the formation of de novo atherosclerosis in the transplanted kidney. Therefore, we determined whether the 10-year Framingham risk score (FRS), an established atherosclerotic cardiovascular disease prediction module, is associated with chronic graft failure in RTR. In this prospective longitudinal study, 600 well-characterised RTR were followed for 10 years. The association with death-censored chronic graft failure (n = 81, 13.5%) was computed. An extended Cox model showed that each one percent increase of the FRS significantly increased the risk of chronic graft failure by 4% (HR: 1.04, p < 0.001). This association remained significant after adjustment for potential confounders, including eGFR (HR: 1.03, p = 0.014). Adding the FRS to eGFR resulted in a higher AUC in a receiver operating curve (AUC = 0.79, p < 0.001) than eGFR alone (AUC = 0.75, p < 0.001), and an improvement in the model likelihood ratio statistic (67.60 to 88.39, p < 0.001). These results suggest that a combination of the FRS and eGFR improves risk prediction. The easy to determine and widely available FRS has clinical potential to predict chronic graft failure in RTR.

Evidence for Recipient-Derived Cells in Peribiliary Glands and Biliary Epithelium of the Large Donor Bile Ducts After Liver Transplantation

Introduction

Chimerism after orthotopic liver transplantation (OLT) has largely been investigated in intrahepatic cellular constituents. However, little is known about chimerism in the extrahepatic and large intrahepatic bile ducts. Our aim was to evaluate the presence and extent of chimerism after OLT in the peribiliary glands (PBG) and the luminal epithelium of the large donor bile ducts.

Methods

For this study, we examined six extrahepatic and large intrahepatic bile ducts from livers that were re-transplanted. In all cases there was a sex-mismatch between donor and recipient (female donor organ and male recipient), which allowed to discriminate between donor- and recipient-derived cells. Specimens from female to female transplants were used as negative controls and male to male transplants as positive controls. Fluorescence in situ hybridization (FISH) for Y and X chromosomes was performed and the percentage of XY positive cells was determined among biliary epithelial cells. Immunohistochemistry was used to correlate chimerism with histological features.

Results

Cholangiocellular chimerism in all studied specimens ranged from 14 to 52%. The degree of chimerism was not associated with biliary damage. Marked chimerism was present at 5 days post-OLT. Ki-67-positivity was detected in 1–8% of the epithelial cells at the time of liver re-transplantation, and this correlated inversely with the degree of chimerism.

Conclusion

Recipient-derived cholangiocytes are present in the large bile ducts of the donor liver after OLT. The presence of chimerism in the large bile ducts suggests that recipient-derived cells may play a role in biliary regeneration following ischemia-induced injury during OLT.

Thalidomide ameliorate graft chronic rejection in an allogenic kidney transplant model

Chronic T cell mediated rejection (TCMR), which is characterized by infiltration of the interstitium by T cells and macrophages, still remains a major barrier to the long-term survival of kidney transplantation. Our recent report indicated that thalidomide can attenuate graft arteriosclerosis in an aortic transplant model. In this study, we investigated the effect of thalidomide on chronic TCMR in a rat model of kidney transplantation. Fischer or Lewis kidney allografts were transplanted into Lewis recipient rats. After kidney transplantation, recipient rats were divided into 3 groups: the isograft (Iso) group, allograft (Allo) group, and thalidomide (Tha) group. Rats were sacrificed at 8 weeks after kidney transplantation, and blood and kidney samples were collected. Serum concentrations of creatinine (SCr),interleukin (IL)-2, IL-6, IL-17, and TNF-α in recipients were determined, and flow cytometry was used to detect the percentages of CD4⁺CD25⁺, CD4⁺ Foxp3⁺and CD4⁺Th17⁺ cell subsets in the peripheral blood. Grafts were procured for histopathological examination, and the expressions of α-SMA, transforming growth-β1 (TGF-β1), and VEGF in kidney grafts were investigated using Western blot. Thalidomide treatment significantly ameliorated chronic rejection, reduced renal allograft tissue damage, and decreased serum creatinine levels. Attenuation of chronic TCMR was due to the prohibited production of inflammatory cytokines, altered distribution of the CD4⁺ CD25⁺ FoxP3⁺ regulatory T (Treg) and CD4⁺ Th17⁺ cells in the peripheral blood, and decreased expression of TGF-β1, α-SMA, and VEGF in the kidney graft. These results demonstrated that thalidomide could effectively ameliorate chronic TCMR in a rat kidney transplant model.

Association of MYH9 rs3752462 and rs5756168 Polymorphisms With Transplanted Kidney Artery Stenosis

Allelic variants of the MYH9 gene, encoding myosin nonmuscle heavy chain type IIA, have been shown to correlate with diminished glomerular filtration rates and end-stage kidney disease in individuals of Caucasian ancestry. Myosin nonmuscle heavy chain type IIA is expressed during development as well as in injured vessels and kidney structures. We hypothesized that MYH9 risk variants may correlate with kidney artery injury and dysfunctional healing, such as transplant renal artery stenosis (TRAS). Our study aimed at evaluating the association of MYH9 risk allelic variants (rs4821480, rs4821481, rs3752462, rs11089788, rs136211, rs5756168, rs2032487, and rs2239784) with TRAS, defined as >50% renal artery lumen reduction. Genotyping was performed with the use of custom Taqman genotyping assays on DNA samples (n = 295) from white deceased-donor kidney transplant recipients and genomic DNA from the corresponding donors. Statistical analysis was performed with the use of Kaplan-Meier estimates, log-rank tests, and proportional hazard Cox models. Recipients carrying TT in rs5756168 experienced diminished risk of TRAS (hazard ratio [HR], 0.31; P < .009), whereas organs carrying CC in rs3752462 were exposed to excessive TRAS risk (HR, 2.54; P < .047). In multivariate stepwise analysis TRAS was 10.9-fold increased in kidneys originating from rs3752462 CC, whereas the risk was decreased 3.45-fold (adjusted HR, 0.29) in recipients carrying rs5756168 TT (P < .007 and P < .033, respectively). Intracranial bleeding or trauma compared with other mechanisms of donor death diminished TRAS risk by 87% and 91%, respectively (P < .030 and P < .017). Our study is the first to identify genetic predisposition to transplant renal artery stenosis.

Distinct Differences on Neointima Formation in Immunodeficient and Humanized Mice after Carotid or Femoral Arterial Injury

Percutaneous coronary intervention is widely adopted to treat patients with coronary artery disease. However, restenosis remains an unsolved clinical problem after vascular interventions. The role of the systemic and local immune response in the development of restenosis is not fully understood. Hence, the aim of the current study was to investigate the role of the human immune system on subsequent neointima formation elicited by vascular injury in a humanized mouse model. Immunodeficient NOD.Cg-Prkdc^scidIL2rg^tm1Wjl(NSG) mice were reconstituted with human (h)PBMCs immediately after both carotid wire and femoral cuff injury were induced in order to identify how differences in the severity of injury influenced endothelial regeneration, neointima formation, and homing of human inflammatory and progenitor cells. In contrast to non-reconstituted mice, hPBMC reconstitution reduced neointima formation after femoral cuff injury whereas hPBMCs promoted neointima formation after carotid wire injury 4 weeks after induction of injury. Neointimal endothelium and smooth muscle cells in the injured arteries were of mouse origin. Our results indicate that the immune system may differentially respond to arterial injury depending on the severity of injury, which may also be influenced by the intrinsic properties of the arteries themselves, resulting in either minimal or aggravated neointima formation.

Chronic Renal Transplant Rejection and Possible Anti-Proliferative Drug Targets

The global prevalence of renal transplants is increasing with time, and renal transplantation is the only definite treatment for end-stage renal disease. We have limited the acute and late acute rejection of kidney allografts, but the long-term survival of renal tissues still remains a difficult and unanswered question as most of the renal transplants undergo failure within a decade of their transplantation. Among various histopathological changes that signify chronic allograft nephropathy (CAN), tubular atrophy, fibrous thickening of the arteries, fibrosis of the kidney interstitium, and glomerulosclerosis are the most important. Moreover, these structural changes are followed by a decline in the kidney function as well. The underlying mechanism that triggers the long-term rejection of renal transplants involves both humoral and cell-mediated immunity. T cells, with their related cytokines, cause tissue damage. In addition, CD 20+ B cells and their antibodies play an important role in the long-term graft rejection. Other risk factors that predispose a recipient to long-term graft rejection include HLA-mismatching, acute episodes of graft rejection, mismatch in donor-recipient age, and smoking. The purpose of this review article is the analyze current literature and find different anti-proliferative agents that can suppress the immune system and can thus contribute to the long-term survival of renal transplants. The findings of this review paper can be helpful in understanding the long-term survival of renal transplants and various ways to improve it.

Immunosuppressive nano-therapeutic micelles downregulate endothelial cell inflammation and immunogenicity

In this study, we developed a stable, nontoxic novel micelle nanoparticle to attenuate responses of endothelial cell (EC) inflammation when subjected to oxidative stress, such as observed in organ transplantation. Targeted Rapamycin Micelles (TRaM) were synthesized using PEG-PE-amine and N-palmitoyl homocysteine (PHC) with further tailoring of the micelle using targeting peptides (cRGD) and labeling with far-red fluorescent dye for tracking during cellular uptake studies. Our results revealed that the TRaM was approximately 10 nm in diameter and underwent successful internalization in Human Umbilical Vein EC (HUVEC) lines. Uptake efficiency of TRaM nanoparticles was improved with the addition of a targeting moiety. In addition, our TRaM therapy was able to downregulate both mouse cardiac endothelial cell (MCEC) and HUVEC production and release of the pro-inflammatory cytokines, IL-6 and IL-8 in normal oxygen tension and hypoxic conditions. We were also able to demonstrate a dose-dependent uptake of TRaM therapy into biologic tissues ex vivo. Taken together, these data demonstrate the feasibility of targeted drug delivery in transplantation, which has the potential for conferring local immunosuppressive effects without systemic consequences while also dampening endothelial cell injury responses.

Macrophage phenotypes in the collagen-induced foreign body reaction in rats

Implantation of biomaterials into the body elicits a material-dependent inflammatory response called the foreign body reaction (FBR). Macrophages play a pivotal role in the FBR by orchestrating the pro-inflammatory microenvironment around the biomaterials by secreting cytokines, chemokines and growth factors. When the biomaterial is porous or degradable, macrophages can migrate into the material and continue the generation of a pro-inflammatory microenvironment inside the materials. They also regulate the degradation of biomaterials by secreting proteolytic enzymes and by phagocytosis. We hypothesize that macrophages present in the different microenvironments of the FBR have different phenotypes. Fundamental knowledge of the phenotypes of macrophages and their dynamics during the FBR will contribute to our overall understanding of the mechanisms involved in the FBR, and may provide us with additional tools to modulate the FBR. To investigate the phenotype of macrophages in the FBR, we validated phenotype-specific markers for rat macrophages in vitro by stimulating them with IFNγ/LPS, IL4/IL13 or IL4/dexamethasone to induce classically activated macrophages (M1φ) or alternatively activated macrophages (M2φ). Gene expression analysis, Western blot and immunohistochemistry revealed that iNOS and CD206 are specifically expressed by M1φ and M2φ, respectively. Using these markers, we investigated the distribution of M1φ and M2φ in the FBR induced by subcutaneously implanted hexamethylenediisocyanate cross-linked dermal sheep collagen (HDSC) disks in AO rats. We found that part of the macrophages display an M2 phenotype, whereas the M1phenotype was not detected. Our data suggest that many macrophages in the FBR induced by HDSC do not fit into the classical M1 or M2 dichotomy.

Sirolimus reduces vasculopathy but exacerbates proteinuria in association with inhibition of VEGF and VEGFR in a rat kidney model of chronic allograft dysfunction

BACKGROUND

Use of the mTOR inhibitor (mTORi) sirolimus to replace calcineurin inhibitors in kidney transplantation has been associated with improved renal function but, in a proportion of cases, also with de novo or exacerbated proteinuria. Experimental deficiency of vascular endothelial growth factor (VEGF) induces proteinuria and mTOR is required for VEGF production and signalling. We therefore explored the impact of sirolimus on the development of chronic allograft dysfunction (CAD) in the rat, with a focus on VEGF biology.

METHODS

Lewis rats received F344 kidney allografts and were treated with 24 weeks of cyclosporine or sirolimus. Controls included allografts treated with cyclosporine for 10 days only and isografts treated with cyclosporine or sirolimus for 24 weeks. Kidney injury (proteinuria and histology) and expression of VEGF and VEGF-receptor (VEGFR; immunohistochemistry, laser capture micro-dissection and quantitative RT-PCR) were assessed.

RESULTS

Allograft controls developed proteinuria, tubulointerstitial fibrosis and atrophy, glomerulosclerosis, vasculopathy and leucocyte accumulation. Proteinuria was significantly reduced in both treatment groups but significantly more in cyclosporine treated animals. Tubulointerstitial damage, glomerulosclerosis and leucocyte accumulation were significantly attenuated in both treatment groups; however, vasculopathy was reduced only by sirolimus. Significantly diminished expression of VEGF and VEGFR mRNA and protein was evident in the sirolimus group. In vitro, sirolimus reduced VEGF production by podocytes (P < 0.05) and inhibited VEGF-induced proliferation of podocytes, endothelial and mesangial cells.

CONCLUSIONS

Cyclosporine and sirolimus retard development of CAD in this rat model. Sirolimus exhibits greater protection against vasculopathy but induces proteinuria; effects are likely to be related to inhibition of VEGF signalling.

31P-magnetic resonance spectroscopy (31P-MRS) detects early changes in kidney high-energy phosphate metabolism during a 6-month Valsartan treatment in diabetic and non-diabetic kidney-transplanted patients

(31)P-magnetic resonance spectroscopy ((31)P-MRS) is a non-invasive tool to study high-energy phosphate (HEP) metabolism. We evaluate whether 31P-MRS can detect early changes in kidney HEP metabolism during a 6-month trial with Valsartan. Twenty consecutive stable and normotensive kidney-transplanted patients were enrolled. Nine of them received short-term low-dose Valsartan treatment (80 mg/day) for 6 months, while 11 controls received no medication. Kidney HEP metabolism was evaluated both at baseline and after treatment by (31)P-MRS with a 1.5 T system (Gyroscan Intera Master 1.5 MR System; Philips Medical Systems, Best, The Netherlands). Valsartan-treated patients (n = 9) showed a significant increase in β-ATP/Pi ratio, a marker of kidney HEP metabolism (baseline = 1.03 ± 0.08 vs. 6 months = 1.26 ± 0.07, p = 0.03). In contrast, the b-ATP/Pi ratio in the control group (n = 11) did not change (baseline = 0.85 ± 0.10 vs. 6 months = 0.89 ± 0.08, ns). The improvement in the β-ATP/Pi ratio was not associated with a reduction in arterial blood pressure or in urinary albumin excretion. Kidney-localized (31)P-MRS can detect early changes in kidney HEP metabolism during a short-term low-dose Valsartan treatment in stable normotensive kidney-transplanted patients.

Local medial microenvironment directs phenotypic modulation of smooth muscle cells after experimental renal transplantation

Smooth muscle cells (SMCs) play a key role in the pathogenesis of occlusive vascular diseases, including transplant vasculopathy. Neointimal SMCs in experimental renal transplant vasculopathy are graft-derived. We propose that neointimal SMCs in renal allografts are derived from the vascular media resulting from a transplantation-induced phenotypic switch. We examined the molecular changes in the medial microenvironment that lead to phenotypic modulation of SMCs in rat renal allograft arteries with neointimal lesions. Dark Agouti donor kidneys were transplanted into Wistar Furth recipients and recovered at day 56. Neointimal and medial layers were isolated using laser microdissection. Gene expression was analyzed using low-density arrays and confirmed by immunostaining. In allografts, neointimal SMCs expressed increased levels of Tgf β1 and Pdgfb. In medial allograft SMCs, gene expression of Ctgf, Tgf β1 and Pdgfrb was upregulated. Gene expression of Klf4 was upregulated as well, while expression of Sm22α was downregulated. Finally, PDGF-BB-stimulated phenotypically modulated SMCs, as evidenced by reduced contractile function in vitro which was accompanied by increased Klf4 and Col1α1, and reduced α-Sma and Sm22α expression. In transplant vasculopathy, neointimal PDGF-BB induces phenotypic modulation of medial SMCs, through upregulation of KLF4 in the media to contribute to (further) expansion of the neointima.

The interstitial expression of alpha-smooth muscle actin in glomerulonephritis is associated with renal function

BACKGROUND

In a healthy kidney, contractile protein alpha-smooth muscle actin (ASMA) is immunohistochemically strongly expressed only in the blood vessels, while in pathological conditions it can be visualized in glomerular mesangial cells and interstitial myofibroblasts. The aim of this study was to explore the possible correlation between expression of ASMA in glomerulonephritis (GN) and indicators of renal function.

MATERIAL/METHODS

We analyzed expression of ASMA in percutaneous renal biopsy of 142 adult and pediatric patients with GN and its correlation with blood pressure, serum creatinine, creatinine clearance and 24-hour urine protein at the time of biopsy. Immunoexpression of ASMA was analyzed quantitatively using computer-assisted morphometric analysis. Relative surface of ASMA expression in all glomeruli and interstitium was calculated for each patient.

RESULTS

In adults and children, greater expression of ASMA in interstitium was associated with higher serum creatinine and reduced creatinine clearance. Conversely, greater ASMA expression in glomeruli was associated with normal or decreased serum creatinine in adults and increased creatinine clearance in children. In children, correlation was found between high blood pressure and ASMA expression in interstitium.

CONCLUSIONS

We confirmed that interstitial expression of ASMA is associated with reduced renal function at time of biopsy. The connection of ASMA expression in glomeruli with lower serum creatinine and normal or increased creatinine clearance suggests a favorable role of this phenotypic change in glomerular filtration rate; further investigation is needed.

The perlecan fragment LG3 is a novel regulator of obliterative remodeling associated with allograft vascular rejection

RATIONALE

Endothelial apoptosis is increased in association with acute and chronic vascular rejection (VR) of solid allografts. Apoptotic endothelial cells (EC) release LG3, a C-terminal fragment of perlecan of potential importance in vascular remodeling and neointima formation.

OBJECTIVE

Our 2 goals were to determine whether circulating levels of LG3 are increased in association with acute VR of renal allografts and to evaluate the impact of LG3 on vascular remodeling.

METHODS AND RESULTS

We conducted a case-control study to compare serum LG3 levels in human renal transplant patients with acute VR, tubulo-interstitial rejection (ATIR) and normal graft function. Aorta transplantation between fully MHC-mismatched mice in association with intravenous LG3 injection was used to characterize the impact of LG3 on vascular remodeling. Scratch assays evaluated the promigratory activity of LG3 on vascular smooth muscle cells (VSMC) in vitro. Serum LG3 levels were significantly elevated in human renal transplant patients with acute VR (n = 16) compared to ATIR (n = 16) and normal graft function (n = 32, P = 0.004). In patients with acute VR, graft loss was associated with elevated LG3 levels. Increasing LG3 serum levels in aortic allograft recipients significantly increased neointima formation. LG3 injection fostered accumulation of α-smooth muscle actin-positive cells and decreased the number of CD31 positive EC. LG3 increased the migration of VSMC through extracellular signal-regulated kinases 1/2-dependent pathways.

CONCLUSION

These results indicate that LG3 is a novel regulator of obliterative vascular remodeling during rejection.