Rethinking chronic allograft nephropathy: the concept of accelerated senescence

Pre-transplant CDKN2A expression in kidney biopsies predicts renal function and is a future component of donor scoring criteria

CDKN2A is a proven and validated biomarker of ageing which acts as an off switch for cell proliferation. We have demonstrated previously that CDKN2A is the most robust and the strongest pre-transplant predictor of post- transplant serum creatinine when compared to “Gold Standard” clinical factors, such as cold ischaemic time and donor chronological age. This report shows that CDKN2A is better than telomere length, the most celebrated biomarker of ageing, as a predictor of post-transplant renal function. It also shows that CDKN2A is as strong a determinant of post-transplant organ function when compared to extended criteria (ECD) kidneys. A multivariate analysis model was able to predict up to 27.1% of eGFR at one year post-transplant (p = 0.008). Significantly, CDKN2A was also able to strongly predict delayed graft function. A pre-transplant donor risk classification system based on CDKN2A and ECD criteria is shown to be feasible and commendable for implementation in the near future.

Immunosenescence and organ transplantation

Increasing numbers of elderly transplant recipients and a growing demand for organs from older donors impose pressing challenges on transplantation medicine. Continuous and complex modifications of the immune system in parallel to aging have a major impact on transplant outcome and organ quality. Both, altered alloimmune responses and increased immunogenicity of organs present risk factors for inferior patient and graft survival. Moreover, a growing body of knowledge on age-dependent modifications of allorecognition and alloimmune responses may require age-adapted immunosuppression and organ allocation. Here, we summarize relevant aspects of immunosenescence and their possible clinical impact on organ transplantation.

Masked hypertension in renal transplant recipients

PURPOSE

Arterial hypertension is a risk factor affecting graft function in renal transplant recipients (RTRs). In pediatric RTRs, high prevalence of masked and nocturnal hypertension was reported. Most of the RTRs had a history of hypertension and some of them were normotensive at outpatient visits whereas home blood pressure (BP) levels were higher. Masked hypertension (MHT) is defined as a normal office BP but an elevated ambulatory BP. Previous reports have demonstrated the detrimental role of MHT in clinical outcomes in hypertensive patients. However, the true prevalence of MHT in RTRs is yet to be defined.

METHODS

A total of 113 RTRs (mean age 44 ± 16 years, 72 males, 41 females) with normal office BP (< 140/90 mmHg) were enrolled to the study from the outpatient renal transplantation clinic. Ambulatory BP monitoring (ABPM) was performed in all participants for a 24-h period. Average daytime BP values above 135 mmHg systolic and 85 mmHg diastolic were defined as MHT.

RESULTS

The prevalence of MHT in our cohort was 39% (n = 45). Fasting glucose and C-reactive protein levels were higher in patients with MHT compared with normal BP group (p = 0.02 and p = 0.04, respectively). RTRs with deceased donor type had higher prevalence of MHT than RTRs with living donor (40% vs 19%, p = 0.003). In multivariate analysis, deceased donor type could predict the MHT independent of age, gender, office systolic BP level, diabetes mellitus, serum creatinine, C-reactive protein, and glucose levels (OR = 3.62, 95% CI 1.16-11.31, p = 0.03).

CONCLUSION

We demonstrated an increased prevalence of MHT in a typical renal transplant cohort. In addition, transplantation from a deceased donor may be a predictor of MHT. The prevalence of MHT may help to explain high rate of cardiovascular events in RTRs. Therefore, routine application of ABPM in RTRs may be plausible, particularly in RTRs with deceased donor type.

Systemic varicella zoster virus reactive effector memory T-cells impaired in the elderly and in kidney transplant recipients

Varicella zoster virus (VZV) infections cause varicella and subsequently herpes zoster upon reactivation. Immune-compromised individuals and the elderly are at high risk of developing herpes zoster due to waning of VZV-specific T-cell immunity. In the present study, a novel functional T-cell assay was developed to test the correlation between age and VZV-specific T-cell responses in peripheral blood from healthy individuals. Secondly, VZV-specific T-cell responses from renal transplant recipients were compared with healthy individuals. Monocytes were differentiated into mature monocyte-derived dendritic cells (moDCs) and were infected with VZV. T-cells were co-cultured with autologous moDCs infected with VZV and subjected to flowcytometric analysis to identify the phenotype (i.e., naïve [NA: CCR7(+) CD45RO(-) ], central [CM: CCR7(+) CD45RO(+) ] and effector memory [EM: CCR7(-) CD45RO(+) ] T-cells) and the frequency of VZV-reactive T-cell subsets by intra-cellular IFN-γ flowcytometry. In contrast to NA and CM T-cells, the frequency of VZV-reactive CD4 and CD8 EM T-cells was inversely correlated with age (P = 0.0007 and P = 0.01). No difference was found in the percentage of VZV-reactive CD4 NA, CM and EM T-cells between transplant recipients and controls. However, the percentage of VZV-reactive CD8 EM T-cells was significantly lower in transplant recipients compared to controls (P = 0.02). In conclusion, moDCs infected with VZV are efficient antigen presenting cells applicable to enumerate and characterize the phenotype and differentiation status of the systemic VZV-specific T-cell response ex-vivo. The data suggest that VZV-reactive EM T-cells are impaired in the elderly and renal transplant recipients.

Posttransplant hypertension: multipathogenic disease process

Arterial hypertension is prevalent among kidney transplant recipients. The multifactorial pathogenesis involves the interaction of the donor and the recipient's genetic backgrounds with several environmental parameters that may precede or follow the transplant procedure (eg, the nature of the renal disease, the duration of the chronic kidney disease phase and maintenance dialytic therapy, the commonly associated cardiovascular disease with atherosclerosis and arteriosclerosis, the renal mass at implantation, the immunosuppressive regimen used, life of the graft, and de novo medical and surgical complications that may occur after a transplant). Among calcineurin inhibitors, tacrolimus seems to have a better cardiovascular profile. Steroid-free protocols and calcineurin inhibitor-free regimens seem to be associated with better blood pressure control. Posttransplant hypertension is a major amplifier of the chronic kidney disease-cardiovascular disease continuum. Despite the adverse effects of hypertension on graft and patient survival, blood pressure control remains poor because of the high cardiovascular risk profile of the donor-recipient pair. Although the optimal blood pressure level remains unknown, it is recommended to maintain the blood pressure at < 130/80 mm Hg and < 125/75 mm Hg in the absence or presence of proteinuria.

Donor age and ABCB1 1199G>A genetic polymorphism are independent factors affecting long-term renal function after kidney transplantation

BACKGROUND

In renal tubular cells, cytochrome P4503A enzyme and adenosine triphosphate-binding cassette transporter activities result in intracellular drug or metabolite exposure variability, depending on genetic polymorphisms. Our aim was to establish whether long-term renal function is affected by genetic polymorphisms in biotransformation enzymes and drug transporters of the donor after kidney transplantation.

MATERIALS AND METHODS

The study was conducted in a selected cohort of 97 kidney recipients. Genotyping of donors was performed on renal biopsy samples obtained before transplantation. Serum creatinine levels and Cockcroft-Gault estimated glomerular filtration rate were considered 1 y after transplantation and at the last follow-up.

RESULTS

Long-term function was significantly better in recipients of an organ from donors carrying the ABCB1 1199A mutated allele (median and range creatinine values were 1.1 mg/dL [0.8-1.5mg/dL] in case of at least one ABCB1 1199A allele versus 1.5 mg/dL [0.7-3.7 mg/dL] for homozygous carriers of wild-type allele, P < 0.01). ABCB1 1199G>A polymorphism and donor age had an independent impact on both serum creatinine and estimated glomerular filtration rate. Unlike donor age, the mutated ABCB1 1199A allele was found to have a protective effect on renal function.

CONCLUSIONS

Donor age and ABCB1 1199G>A polymorphism affect long-term renal function after transplantation. Analysis of genetic factors offers a promising approach to calcineurin inhibitor toxicity risk assessment.

Cellular senescence limits regenerative capacity and allograft survival

Long-term graft survival after kidney transplantation remains unsatisfactory and unpredictable. Interstitial fibrosis and tubular atrophy are major contributors to late graft loss; features of tubular cell senescence, such as increased p16(INK4a) expression, associate with these tubulointerstitial changes, but it is unknown whether the relationship is causal. Here, loss of the INK4a locus in mice, which allows escape from p16(INK4a)-dependent senescence, significantly reduced interstitial fibrosis and tubular atrophy and associated with improved renal function, conservation of nephron mass, and transplant survival. Compared with wild-type controls, kidneys from INK4a(-/-) mice developed significantly less interstitial fibrosis and tubular atrophy after ischemia-reperfusion injury. Consistently, mice that received kidney transplants from INK4a/ARF(-/-) donors had significantly better survival 21 days after life-supporting kidney transplantation and developed less tubulointerstitial changes. This correlated with higher proliferative rates of tubular cells and significantly fewer senescent cells. Taken together, these data suggest a pathogenic role of renal cellular senescence in the development of interstitial fibrosis and tubular atrophy and kidney graft deterioration by preventing the recovery from injury. Inhibiting premature senescence could have therapeutic benefit in kidney transplantation but has to be balanced against the risks of suspending antitumor defenses.

Donor age-specific injury and immune responses

Utilization rates of organs from elderly donors have shown the highest proportional increase during the last decade. Clinical reports support the concept of transplanting older organs. However, the engraftment of such organs has been linked to accelerated immune responses based on ageing changes per se and a proinflammatory environment subsequent to compromised injury and repair mechanism. We analyzed the clinical consequences of transplanting older donor organs and present mechanistic aspects correlating age, injury repair and effects on host immunoresponsiveness.

Is cellular senescence important in pediatric kidney disease?

Somatic cellular senescence (SCS) describes the limited ability of cells to divide. Normally, SCS is associated with physiological aging, but evidence suggests that it may play a role in disease progression, even in young patients. Stressors such as acute injury or chronic inflammation may induce SCS, which in turn exhausts organ regenerative potential. This review summarizes what is known about SCS in the kidney with aging and disease. As most patients with chronic kidney disease (CKD) also develop cardiovascular complications, a second focus of this review deals with the role of SCS in cardiovascular disease. Also, as SCS seems to accelerate CKD and cardiovascular disease progression, developing strategies for new treatment options that overcome SCS or protect a patient from it represents an exciting challenge.

Living donor age and kidney transplant outcomes

We assessed the relationship between living donor (LD) age and kidney survival in 1063 adults transplanted between 1980 and 2007. Increasing LD age was associated with lower kidney function (GFR) before and after transplantation and loss of GFR beyond 1 year. Increasing LD age was also associated with low-moderate proteinuria posttransplant (151-1500 mg/day, p < 0.0001). By univariate analysis, reduced graft survival related to lower GFR at 1 year [HR = 0.925 (0.906-0.944), p < 0.0001], proteinuria [HR = 1.481 (1.333-1.646), p < 0.0001] and increasing LD age [HR = 1.271 (1.219-1.326), p = 0.001]. The impact of LD age on graft survival was noted particularly >4 years posttransplant and was modified by recipient age. Thus, compared to a kidney graft that was within 5 years of the recipient age, younger kidneys had a survival advantage [HR = 0.600 (0.380-0.949), p = 0.029] while older kidneys had a survival disadvantage [HR = 2.217 (1.507-3.261), p < 0.0001]. However, this effect was seen only in recipients <50 years old. By multivariate analysis, the relationship between LD age and graft survival was independent of GFR but related to proteinuria. In conclusion, LD age is an important determinant of long-term graft survival, particularly in younger recipients. Older kidneys with reduced survival are identifiable by the development of proteinuria posttransplant.

Inflammation-associated graft loss in renal transplant recipients

BACKGROUND

Although short-term graft survival has improved substantially in renal transplant recipients, long-term graft survival has not improved over the last decades. The lack of knowledge of specific causes and risk factors has hampered improvements in long-term allograft survival. There is an uncertainty if inflammation is associated with late graft loss.

METHODS

We examined, in a large prospective trial, the inflammation markers high-sensitivity C-reactive protein (hsCRP) and interleukin-6 (IL-6) and their association with chronic graft dysfunction. We collected data from the Assessment of Lescol in Renal Transplant trial, which recruited 2102 maintenance renal transplant recipients.

RESULTS

Baseline values were hsCRP 3.8 ± 6.7 mg/L and IL-6 2.9 ± 1.9 pg/mL. Adjusted for traditional risk factors, hsCRP and IL-6 were independently associated with death-censored graft loss, the composite end points graft loss or death and doubling of serum creatinine, graft loss or death.

CONCLUSION

The inflammation markers hsCRP and IL-6 are associated with long-term graft outcomes in renal transplant recipients.

Consequences of transplant quality on chronic allograft nephropathy

Using kidneys from expanded-criteria donors to alleviate organ shortage has raised concern on reduced transplant outcomes. In this paper, we review how critical donor-related factors such as donor age, brain death, and consequences of ischemia-reperfusion injury (IRI) determine graft quality and impact chronic allograft nephropathy. We propose that combinatorial effects of organ-intrinsic features associated with increasing age and unspecific injuries related to brain death and IRI will impact innate and adaptive immune responses. Future research will need to explore avenues to optimize donor management, organ preservation, adapted immunosuppressive strategies, as well as modifications of the allocation of suboptimal allografts.

Deficiency or inhibition of CD73 protects in mild kidney ischemia-reperfusion injury

BACKGROUND

Adenosine agonists are protective in numerous models of ischemia-reperfusion injury (IRI). Pericellular adenosine is generated by the hydrolysis of extracellular adenosine triphosphate and adenosine diphosphate by the ectonucleotidase CD39 and the subsequent hydrolysis of adenosine monophosphate (AMP) by the ectonucleotidase CD73. CD39 activity is protective in kidney IRI, whereas the role of CD73 remains unclear.

METHODS

Wild-type (WT), CD73-deficient (CD73KO), CD39-transgenic (CD39tg), and hybrid CD39tg.CD73KO mice underwent right nephrectomy and unilateral renal ischemia (18-min ischemia by microvascular pedicle clamp). Renal function (serum creatinine [SCr], micromolar per liter) and histologic renal injury (score 0-9) were assessed after 24-hr reperfusion. Treatments included a CD73 inhibitor and soluble CD73.

RESULTS

Compared with WT mice (n=33, SCr 81.0, score 4.1), (1) CD73KO mice were protected (n=17, SCr 48.9, score 2.0, P<0.05), (2) CD39tg mice were protected (n=11, SCr 45.6, score 1.3, P<0.05), (3) WT mice treated with CD73 inhibitor were protected (n=9, SCr 43.3, score 1.2, P<0.05), (4) CD73KO mice reconstituted with soluble CD73 lost their protection (n=10, SCr 63.8, score 3.1, P=ns), (5) WT mice treated with soluble CD73 were not protected (n=7, SCr 78.0, score 4.1), and (6) CD39tg.CD73KO mice were protected (n=8, SCr 55.5, score 0.7, P<0.05).

CONCLUSIONS

Deficiency or inhibition of CD73 protects in kidney IRI, and CD39-mediated protection does not seem to be dependent on adenosine generation. These findings suggest that AMP may play a direct protective role in kidney IRI, which could be used in therapeutic development and organ preservation. Investigating the mechanisms by which AMP mediates protection may lead to new targets for research in kidney IRI.

Predonation quality of life and early postdonation safety of older living renal donors in China

BACKGROUND

Studies on the safety of older living renal donors are lacking in China.

METHODS

We observed 142 consecutive living renal donors before and early after (7 days) the operation. There were no prisoners used as donors or recipients. Subjects were divided into 2 groups: older than 50 years of age (n = 40) or younger age (n = 102). We compared differences in early safety between the 2 groups.

RESULTS

There were no significant differences in 8 aspects of the predonation quality of life using the SF-36 questionnaire, except for physical function (P < .001). Zero hour biopsies performed on 52 kidneys showed 15 to display abnormal renal tissues (28.85%), which was significantly greater among the older age group (P = .034). The perioperative indexes were similar between the 2 groups; however, the hospital stay was longer in the older group (P = .034). Compared with the younger group, the older group generally showed a lower creatinine clearance (CCr; P < .001), higher cystatin c (P = .006), and similar serum creatinine (Scr) preoperatively, conditions that persisted at 7 days postoperatively. Although the increased Scr and reduced CCr were present in all donors, the changes in Scr and CCr were similar between the 2 groups. Differences in urinary micro-albumin and proteinuria before and after operation were not significantly different for both groups.

CONCLUSIONS

Increased use of older living kidney donors in China may be a safe strategy to meet the demand for transplantation. However, long-term outcomes need further follow-up.

Hand transplantation and vascularized composite tissue allografts in orthopaedics and traumatology

Composite tissue allograft (CTA) is defined as heterologous transplantation of a complex comprising skin and subcutaneous, neurovascular and mesenchymal tissue. Such techniques allow complex reconstruction using matched tissue, without donor site morbidity. The potential indications in orthopaedics-traumatology could in the future be more frequent than the present indications of heart, lung, liver, kidney and pancreas transplantation. International clinical experience clearly demonstrates the feasibility of CTA, both surgically and immunologically. However, immunosuppression remains indispensable, exposing the patient to risks that are not acceptable for purely functional surgery, except in very particular indications. The main hope for the future lies in induction of graft-specific tolerance.

Immunological risk in recipients of kidney transplants from extended criteria donors

BACKGROUND

Determining if a kidney from a marginal donor is likely to elicit a strong and specific immune response, leading to an increased risk of acute rejection, is of importance in renal transplantation.

METHODS

In this study, we analysed the effect of extended criteria donor (ECD) on the incidence of biopsy-proven acute rejection (BPAR) and the effect of immunological risk factors on graft outcome in a large cohort of kidney transplant recipients (n = 2121 patients) grafted with ECD (n = 656 patients) or optimal donor (OD) (n = 1465 patients).

RESULTS

The incidence of BPAR was not statistically different between the ECD group recipients (105/656, 16%) and the OD group recipients (251/1465, 17%) (P = 0.52). These values remained similar after adjustment for immunological risk [defined as retransplantation and/or panel-reactive antibody (PRA) level >20%] (P = 0.92 for patients with immunological risk and P = 0.47 for patients without immunological risk). We next analysed the death-censored graft survival data for OD and ECD groups, as a function of immunological status, and found that the immunological risk factor did not affect graft survival in ECD transplant recipients (P = 0.64).

CONCLUSION

Although our groups were not homogenous, our study did not reveal an increased risk of acute rejection in recipients of ECD allograft.

Conversion from cyclosporin A to sirolimus retards the progression of chronic allograft nephropathy in the long term in a rat kidney transplantation model

In a rat renal allograft model, the long-term effect of conversion from cyclosporin A (CsA) to sirolimus on recipient kidneys and growth factor expression were compared with continuous use or withdrawal of CsA. Kidneys from Fisher 344 rats were orthotopically transplanted into Lewis rats. Four Fisher 344 to Lewis allograft groups were treated post-transplant as follows: (i) CsA (transplant to week 8) then sirolimus (weeks 8 - 24); (ii) CsA (transplant to week 24); (iii) CsA (transplant to week 8) then vehicle (weeks 8 - 24); (iv) control vehicle (transplant to week 24). A fifth group underwent syngeneic isograft (Lewis to Lewis) with no drug treatment. Proteinuria was measured every 4 weeks and grafts harvested at 24 weeks for morphological and immunohistochemical analysis. Conversion from CsA to sirolimus resulted in a significant decrease in proteinuria at 24 weeks, a lower Banff sum score and lower expression of transforming growth factor mRNA compared with continuous use or withdrawal of CsA. In conclusion, conversion from CsA to sirolimus retarded progression of chronic allograft nephropathy in the rat model.

Donor age and renal P-glycoprotein expression associate with chronic histological damage in renal allografts

The contributions of donor kidney quality (partially determined by donor age), allograft rejection, and calcineurin inhibitor nephrotoxicity on the progression of histologic damage of renal allografts are not completely defined. Moreover, the determinants of individual susceptibility to calcineurin inhibitor nephrotoxicity are not known but may include variability in drug transport and metabolism. In a prospective cohort of 252 adult renal allograft recipients treated with a combination of tacrolimus, mycophenolate mofetil, and corticosteroids, we studied 744 renal allograft biopsies obtained regularly from time of transplantation for 3 yr. We assessed determinants of histologic evolution, including tacrolimus exposure, renal P-glycoprotein (ABCB1) expression, and polymorphisms in the CYP3A4, CYP3A5, and ABCB1 genes. Within the first 3 yr after transplantation, we noted a progressive increase in interstitial fibrosis, tubular atrophy, glomerulosclerosis, and vascular intimal thickening. Older donor age, absence of P-glycoprotein expression at the apical membrane of tubular epithelial cells, and combined donor-recipient homozygosity for the C3435T variant in ABCB1 significantly associated with increased susceptibility to chronic allograft damage independent of graft quality at implantation. Changes in graft function over time reflected these associations with donor age and ABCB1 polymorphisms, but it was acute T cell-mediated and antibody-mediated rejection that determined early graft survival. In conclusion, the effects of older donor age reach beyond the quality of the allograft at implantation and continue to be important for histologic evolution in the posttransplantation period. In addition, ABCB1 genotype and expression of P-glycoprotein in renal tubular epithelial cells determine susceptibility to chronic tubulointerstitial damage of transplanted kidneys.

The pathogenesis and treatment of chronic allograft nephropathy

Despite improvements in immunosuppressive therapy, long-term allograft survival after kidney transplantation remains as low as 50%. Chronic allograft nephropathy (CAN) is a major cause of late graft loss in renal transplant recipients. The histopathologic signs of CAN-interstitial fibrosis, tubular atrophy, glomerulopathy and vasculopathy-are nonspecific; therefore, the 2007 Banff classification dispensed with the term CAN in favor of 'interstitial fibrosis and tubular atrophy without evidence of any specific etiology'. In this Review, however, the term CAN is used to describe a clinical syndrome that is characterized by progressive decline in renal function from 3 months after transplantation, accompanied by the development of proteinuria and hypertension. The pathogenesis of CAN is complex and incompletely understood, and involves several immunological and non-immunological factors. We discuss the contributory roles of acute rejection, donor age, anti-human-leukocyte-antigen antibodies, calcineurin inhibitor nephrotoxic effects, viral infection, hypertension and hyperlipidemia. The prevention and treatment of CAN needs multidisciplinary strategies. Early detection by means of protocol biopsy and calculation of glomerular filtration rate is the first step, followed by management of modifiable risk factors.

Calcineurin inhibitor nephrotoxicity

The use of the calcineurin inhibitors cyclosporine and tacrolimus led to major advances in the field of transplantation, with excellent short-term outcome. However, the chronic nephrotoxicity of these drugs is the Achilles' heel of current immunosuppressive regimens. In this review, the authors summarize the clinical features and histologic appearance of both acute and chronic calcineurin inhibitor nephrotoxicity in renal and nonrenal transplantation, together with the pitfalls in its diagnosis. The authors also review the available literature on the physiologic and molecular mechanisms underlying acute and chronic calcineurin inhibitor nephrotoxicity, and demonstrate that its development is related to both reversible alterations and irreversible damage to all compartments of the kidneys, including glomeruli, arterioles, and tubulo-interstitium. The main question--whether nephrotoxicity is secondary to the actions of cyclosporine and tacrolimus on the calcineurin-NFAT pathway--remains largely unanswered. The authors critically review the current evidence relating systemic blood levels of cyclosporine and tacrolimus to calcineurin inhibitor nephrotoxicity, and summarize the data suggesting that local exposure to cyclosporine or tacrolimus could be more important than systemic exposure. Finally, other local susceptibility factors for calcineurin inhibitor nephrotoxicity are reviewed, including variability in P-glycoprotein and CYP3A4/5 expression or activity, older kidney age, salt depletion, the use of nonsteroidal anti-inflammatory drugs, and genetic polymorphisms in genes like TGF-beta and ACE. Better insight into the mechanisms underlying calcineurin inhibitor nephrotoxicity might pave the way toward more targeted therapy or prevention of calcineurin inhibitor nephrotoxicity.

Hypertension in dialysis and kidney transplant patients

For the first time, the Canadian Hypertension Education Program has studied the evidence supporting blood pressure control in people requiring renal replacement therapy for end-stage kidney disease, including those on dialysis and with renal transplants. According to the Canadian Organ Replacement Registry's 2008 annual report, there were an estimated 33,832 people with end-stage renal disease in Canada at the end of 2006, an increase of 69.7% since 1997. Of these, 20,465 were on dialysis and 13,367 were living with a functioning kidney transplant. Thus, it is becoming more likely that primary care practitioners will be helping to care for these complex patients. With the lack of large controlled clinical trials, the consensus recommendation based on interpretation of the existing literature is that blood pressure should be lowered to below 140/90 mmHg in hypertensive patients on renal replacement therapy and to below 130/80 mmHg for renal transplant patients with diabetes or chronic kidney disease.

Renal allografts with IF/TA display distinct expression profiles of metzincins and related genes

Chronic renal allograft injury is often reflected by interstitial fibrosis (IF) and tubular atrophy (TA) without evidence of specific etiology. In most instances, IF/TA remains an irreversible disorder, representing a major cause of long-term allograft loss. As members of the protease family metzincins and functionally related genes are involved in fibrotic and sclerotic processes of the extracellular matrix (ECM), we hypothesized their deregulation in IF/TA. Gene expression and protein level analyses using allograft biopsies with and without Banff'05 classified IF/TA illustrated their deregulation. Expression profiles of these genes differentiated IF/TA from Banff'05 classified Normal biopsies in three independent microarray studies and demonstrated histological progression of IF/TA I to III. Significant upregulation of matrix metalloprotease-7 (MMP-7) and thrombospondin-2 (THBS-2) in IF/TA biopsies and sera was revealed in two independent patient sets. Furthermore, elevated THBS-2, osteopontin (SPP1) and beta-catenin may play regulatory roles on MMP. Our findings further suggest that deregulated ECM remodeling and possibly epithelial to mesenchymal transition (EMT) are implicated in IF/TA of kidney transplants, and that metzincins and related genes play an important role in these processes. Profiling of these genes may be used to complement IF/TA diagnosis and to disclose IF/TA progression in kidney transplant recipients.

Identifying specific causes of kidney allograft loss

The causes of kidney allograft loss remain unclear. Herein we investigated these causes in 1317 conventional kidney recipients. The cause of graft loss was determined by reviewing clinical and histologic information the latter available in 98% of cases. During 50.3 +/- 32.6 months of follow-up, 330 grafts were lost (25.0%), 138 (10.4%) due to death with function, 39 (2.9%) due to primary nonfunction and 153 (11.6%) due to graft failure censored for death. The latter group was subdivided by cause into: glomerular diseases (n = 56, 36.6%); fibrosis/atrophy (n = 47, 30.7%); medical/surgical conditions (n = 25, 16.3%); acute rejection (n = 18, 11.8%); and unclassifiable (n = 7, 4.6%). Glomerular pathologies leading to failure included recurrent disease (n = 23), transplant glomerulopathy (n = 23) and presumed nonrecurrent disease (n = 10). In cases with fibrosis/atrophy a specific cause(s) was identified in 81% and it was rarely attributable to calcineurin inhibitor (CNI) toxicity alone (n = 1, 0.7%). Contrary to current concepts, most cases of kidney graft loss have an identifiable cause that is not idiopathic fibrosis/atrophy or CNI toxicity. Glomerular pathologies cause the largest proportion of graft loss and alloinmunity remains the most common mechanism leading to failure. This study identifies targets for investigation and intervention that may result in improved kidney transplantation outcomes.

Chronic allograft dysfunction: can we use mammalian target of rapamycin inhibitors to replace calcineurin inhibitors to preserve graft function?

PURPOSE OF REVIEW

Graft loss after first year of transplantation can be due to composite of factors that may include immunological and nonimmunological factors. Among the nonimmunological factors, toxicity of immunosuppression drugs, especially calcineurin inhibitor (CNI) toxicity is perhaps the leading cause of graft dysfunction. The most common phenotype associated with progressive graft dysfunction is the development of interstitial fibrosis and tubular atrophy not otherwise specified, a hallmark finding of chronic allograft nephropathy as well as CNI toxicity. Protocol biopsies have demonstrated that histological lesions of CNI toxicity can develop as early as 3 months posttransplantation.

RECENT FINDINGS

Early detection of interstitial fibrosis and tubular atrophy offers the opportunity for replacement of the CNI with mammalian target of rapamycin inhibitors. Early detection of CNI-associated graft damage even before the onset of graft dysfunction is critical to prevent progressive nephron loss. Furthermore, the conversion to sirolimus in patients with advanced graft dysfunction may not be beneficial.

SUMMARY

Until the day transcriptomic assays and high-density microarrays are available routinely to detect the incipient graft injury, early allograft biopsy, preferably during the first 3-6 months of transplantation can detect the presence of interstitial fibrosis and tubular atrophy not otherwise specified before the onset of graft dysfunction and replacement of CNI with sirolimus could prevent the progressive nephron loss.

Cellular senescence in pretransplant renal biopsies predicts postoperative organ function

Older and marginal donors have been used to meet the shortfall in available organs for renal transplantation. Post-transplant renal function and outcome from these donors are often poorer than chronologically younger donors. Some organs, however, function adequately for many years. We have hypothesized that such organs are biologically younger than poorer performing counterparts. We have tested this hypothesis in a cohort of preimplantation human renal allograft biopsies ( n = 75) that have been assayed by real-time polymerase chain reaction for the expression of known markers of cellular damage and biological aging, including CDKN2A, CDKN1A, SIRT2 and POT1. These have been investigated for any associations with traditional factors affecting transplant outcome (donor age, cold ischaemic time) and organ function posttransplant (serum creatinine levels). Linear regression analyses indicated a strong association for serum creatinine with pre-transplant CDKN2A levels ( p = 0.001) and donor age ( p = 0.004) at 6 months post-transplant. Both these markers correlated significantly with urinary protein to creatinine ratios ( p = 0.002 and p = 0.005 respectively), an informative marker for subsequent graft dysfunction. POT1 expression also showed a significant association with this parameter ( p = 0.05). Multiple linear regression analyses for CDKN2A and donor age accounted for 24.6% ( p = 0.001) of observed variability in serum creatinine levels at 6 months and 23.7% ( p = 0.001) at 1 year posttransplant. Thus, these data indicate that allograft biological age is an important novel prognostic determinant for renal transplant outcome.

Effects of donor age and cell senescence on kidney allograft survival

The biological processes responsible for somatic cell senescence contribute to organ aging and progression of chronic diseases, and this may contribute to kidney transplant outcomes. We examined the effect of pre-existing donor aging on the performance of kidney transplants, comparing mouse kidney isografts and allografts from old versus young donors. Before transplantation, old kidneys were histologically normal, but displayed an increased expression of senescence marker p16(INK4a). Old allografts at day 7 showed a more rapid emergence of epithelial changes and a further increase in the expression of p16(INK4a). Similar but much milder changes occurred in old isografts. These changes were absent in young allografts at day 7, but emerged by day 21. The expression of p16(INK4a) remained low in young kidney allografts at day 7, but increased with severe rejection at day 21. Isografts from young donors showed no epithelial changes and no increase in p16(INK4a). The measurements of the alloimmune response-infiltrate, cytology, expression of perforin, granzyme B, IFN-gamma and MHC-were not increased in old allografts. Thus, old donor kidneys display abnormal parenchymal susceptibility to transplant stresses and enhanced induction of senescence marker p16(INK4a), but were not more immunogenic. These data are compatible with a key role of somatic cell senescence mechanisms in kidney transplant outcomes by contributing to donor aging, being accelerated by transplant stresses, and imposing limits on the capacity of the tissue to proliferate.

Nox-2 is a modulator of fibrogenesis in kidney allografts

We studied the role of classical phagocytic NADPH oxidase (Nox) in the pathogenesis of kidney allograft tubulointerstitial fibrosis. Immunofluorescence studies showed that Nox-2 and p22phox (electron transfer subunits of Nox) colocalized in the tubulointerstitium of human kidney allografts. Tubular Nox-2 also colocalized with alpha-SMA in areas of injury, suggestive of epithelial-to-mesenchymal transition (EMT). Interstitial macrophages (CD68(+)) and myofibroblasts (alpha-SMA(+)) expressed Nox-2 while graft infiltrating T cells (CD3(+)) and mature fibroblasts (S100A4(+)) were Nox-2(-). These results were confirmed in the Fisher-to-Lewis rat kidney transplant model. Areas of tubulitis were associated with Nox-2 and alpha-SMA, suggestive of EMT. Immunoblot analyses showed that Nox-2 upregulation was associated with oxidative stress (nitrotyrosine) and fibrogenesis (alpha-SMA and phospho-Smad2) at 3 weeks and 6 months. Allografts treated with Nox inhibitors (DPI or apocynin) for 1 week showed reduced fibronectin and phospho-Smad2 and increased E-cadherin levels. Cyclosporine A, TGF-beta1 and angiotensin II increased Nox-2 mRNA levels 2- to 7-fold in vitro (NRK52E cells). Treatment with specific Nox inhibitors (DPI or apocynin) prevented the downregulation of E-cadherin and upregulation of fibronectin transcripts. In aggregate, these studies suggest that Nox-2 is involved in the pathogenesis of allograft tubulointerstitial fibrosis via activation transcription factor Smad2, EMT and myofibroblasts.

Expression of transforming growth factor-beta1 and hypoxia-inducible factor-1alpha in renal transplantation

Chronic allograft nephropathy (CAN) includes pathologic changes of interstitial fibrosis, tubular atrophy, and fibrous intimal thickening. Transforming growth factor (TGF)-beta1 is a fibrogenic cytokine involved in renal allograft fibrosis. Hypoxia-inducible factor (HIF)-1alpha is induced as an adaptive response to hypoxia triggering the production of fibrogenic cytokines such as TGF-beta1. Between January 1995 and February 2005, we performed 71 renal allograft biopsies in 61 recipients. Immunohistochemical studies were performed with an immunoperoxidase technique using as the primary antibody either a rabbit anti-human TGF-beta1 polyclonal or a mouse anti-human HIF-1alpha monoclonal reagent. The glomerular TGF-beta1 expression in recipients diagnosed with glomerulonephritis was significantly greater than other pathologic groups (P < .05), and the glomerular TGF-beta1 expression in the heavy proteinuria group (> or =2.5 g/d) was significantly greater than the low proteinuria group (<1.0 g/d; P < .05). The tubular and interstitial TGF-beta1 and HIF-1alpha expressions in CAN were greater than in other groups (P < .05). The tubular TGF-beta1 expression among the graft loss group was significantly greater than the graft function group (P < .05).

Renal transplantation in the elderly

Elderly patients are increasingly being considered for kidney transplantation due to a global explosion of the aging population with end-stage renal disease (ESRD). However, mounting scarcity of available organs for transplant has led to a wider disparity between organ supply and demand. Consequently, the criteria for accepting kidneys for transplantation have been extended in an attempt to allow the use of organs from elderly donors or those with significant co-morbidities, so-called "expanded criteria donor" (ECD) kidneys. Excellent outcomes have been achieved from ECD kidneys with appropriate donor and recipient profiling and selection. With increasing recovery efforts directed at older donors, the concept of age-matching is becoming more accepted as a method of optimizing utilization of organs in elderly donors and recipients. Utilization of pulsatile perfusion has further improved ECD outcomes and helped the decision-making process for the UNOS (United Network for Organ Sharing) offer. However, age-related immune dysfunction and associated co-morbidities make the elderly transplant recipients ever more susceptible to complications associated with immunosuppressive agents. Consequently, the elderly population is at a higher risk to develop infections and malignancy in the post-transplant period notwithstanding improved transplant outcomes. Appropriate immunosuppressive agents and dosages should be selected to minimize adverse events while reducing the risk of acute rejections and maximizing patient and renal allograft survival.