Glomerular hyperfiltration, intrarenal hemodynamics, and chronic allograft nephropathy: physiopathology of chronic allograft nephropathy

Diminished met signaling in podocytes contributes to the development of podocytopenia in transplant glomerulopathy

Transplant glomerulopathy (TxG) can show secondary focal and segmental glomerulosclerosis (FSGS). FSGS in native kidneys is caused by podocytopenia. This study examines podocytopenia and the role of decreased paracrine Met activation on podocytes by decreased glomerular hepatocyte growth factor (HGF) levels in the development of podocytopenia in TxG. Podocytes were counted in 10 zero-hour biopsies and 10 specimens each with and without TxG. HGF/Met was examined with immunostains and quantitative RT-PCR in a set of three consecutive biopsies from 10 patients with TxG, including the diagnostic biopsy (DiagnBx) and the two previous biopsies (1stPrevBx and 2ndPrevBx). Antiapoptotic effects of HGF on podocytes were examined in vitro. Mean podocyte numbers per glomerulus were lower and glomerular volume higher in TxG. Fewer of the two preceding biopsies of the patients than of the controls contained phospho-Met(Tyr1349)-positive podocytes (2 of 8 versus 7 of 7, P = 0.0070; 4 of 9 versus 9 of 9, P = 0.0294). Glomerular HGF mRNA levels were lower in the 1stPrevBx of the patients (0.049 ± 0.083 versus 0.284 ± 0.331; P = 0.0155). In vitro, HGF stimulation of podocytes resulted in antiapoptotic phosphorylation of AKT and extracellular signal-regulated kinase (ERK) and induction of X-linked inhibitor of apoptosis protein (XIAP). Decreased antiapoptotic Met signaling in podocytes, probably due to decreased HGF secretion by glomerular epithelial cells, could contribute to podocyte loss and FSGS in TxG.

Induction of chronic renal allograft dysfunction in a rat model with complete and exclusive MHC incompatibility

Chronic allograft dysfunction is one of the most important reasons for late graft loss after renal transplantation. Its etiology is multifactorial and combines immunological as well as non-immunological mechanisms. It is known from large registry data that MHC mismatches are inversely correlated to long term allograft survival. Although this is a well known aspect, the mechanisms of MHC-driven graft damage and the impact of other immunological factors leading to chronic rejection are poorly understood. In patients it is impossible to study MHC mismatches without considering non-MHC differences. Further more common animal models for chronic rejection are all characterized by non-MHC as well as MHC disparities. To exclusively study MHC mediated immunoresponses we established a rat model of renal transplantation using congenic rat strains differing in their entire MHC class I and class II, but sharing the genetic background of the LEW rat. After an initial short term of immunosuppression all animals developed renal impairment with severe albuminuria. Half of the animals died of renal failure in week 7 to 14 and showed pathological characteristics of chronic allograft damage including IF/TA and severe glomerulopathy. The majority of these recipients developed circulating donor-specific MHC alloantibodies. Allografts were significantly infiltrated with T-cells, macrophages and NK-cells. We established a MHC congenic rat model to investigate immunological mechanisms of chronic renal allograft rejection exclusively induced by a complete MHC mismatch. We demonstrated humoral as well as cellular immunoresponses leading to chronic allograft loss in 50% of animals.

Histopathologic Evaluation of Pretransplant Biopsy as a Factor Influencing Graft Function After Kidney Transplantation: A 1-Year Observation

INTRODUCTION

Many factors affect long-term results in kidney transplantation including histologic damage as a independent predictor, such as chronic allograft/nephropathy in protocol biopsies and age-dependent lesions. Histopathologic findings correlate with the incidence of delayed graft function, renal function, and allograft survival, allowing a rather precise prediction of graft outcome.

MATERIALS AND METHODS

We analyzed 92 renal thick needle preimplantation and 29 postexplantation biopsies. Biopsies were preserved in 4% formalin and immersed in paraffin. Optimal biopsies contained at least 10 glomeruli and at least 2 cross-sections of arteries. We analyzed tubulitis, intensity of acute tubular necrosis, inflammatory infiltration, glomerulonephritis, arterial hyalinization, arteritis, fibrosis, tubular atrophy, arterial intimal fibrosis, increase of mesangial matrix, and percentage of glomerulosclerosis. During the postoperative course we analyzed patients condition, exigency of postoperative dialysis, urine output, as well as serum concentrations of creatinine, urea, uric acid, and ions. During a 1-year observation period, we analyzed living recipients, graft loss, death with a functioning graft, incidence of nephropathy (CAN), and acute rejection episodes (ARE).

RESULTS

We observed a significant correlation between immediate graft function (IGF) and lack of ATN in the pre-0 biopsy. We observed no correlation between renal function and arterial hyalinization and fibrosis, inflammatory infiltration, tubular atrophy. In the postoperative period, we observed a significant correlation between IGF and lack of interstitial fibrosis with significantly lower levels of creatinine, urea, and potassium and higher urine output early after transplantation. IGF and better function of the right kidney was correlated with shorter time to reach a creatinine level of 2 mg%. In the postoperative periods, we also observed a difference between renal function depending on gender. The presence of acute tubular necrosis, arterial fibrosis, lack of inflammatory infiltration in the pre-0 biopsy correlated with worse late renal function. Among explantation biopsies 65.5% showed signs of CAN, and 37.93%, histologic marks of ARE.

Classification of Tc-99m DTPA Renograms Based on the Relationship Between Uptake and Perfusion Pattern

INTRODUCTION

Various parameters can be derived from a renogram, but the relationship between uptake and perfusion pattern on Tc-99m DTPA time-activity curves has not been evaluated to date. A previous report documented sequential changes in the relationship between perfusion and uptake in renal transplant donors. The current study looked at serial changes in renogram patterns in kidneys exhibiting hyperfiltration. The aim was to reveal the pathophysiological significance of different perfusion-uptake patterns observed on Tc-99m DTPA renal scintigraphy.

METHODS

Serial changes in two patient groups were evaluated: (A) renal transplant donors before, early after, and late after donor nephrectomy; and (B) renal transplant recipients at the initial and later stages of chronic allograft nephropathy (CAN). Quantitative scintigraphic parameters included: the ratio of peak perfusion counts to plateau counts (P:PL); the ratio of counts at peak perfusion to counts at peak uptake (P:U); and the glomerular filtration rate. The effect of background selection on the parameters, P:PL and P:U, was evaluated using three different background regions of interest.

RESULTS

Each group in the study exhibited a different renogram pattern. Based on these results, renograms were classified into six patterns. Compared to the preoperative findings, P:U and P:PL increased significantly early after the operation. Late after the operation, P:U decreased significantly compared to both pre- and early postoperative values. In patients at the early stages of CAN, both P:PL and P:U were lower than normal. During the later stages of CAN, perfusion and uptake peaks were absent.

CONCLUSION

Our results identified several different renogram patterns that were thought to correspond with hyperperfusion, hyperfiltration, increased intraglomerular pressure, and glomerulosclerosis. The ratios of P:PL and P:U underwent significant change under conditions that affected kidney hemodynamics and function.

The morphological compensatory change of peritubular capillary network in chronic allograft rejection

To clarify the compensatory hemodynamic alterations in the interstitium of renal allograft biopsies with chronic rejection, we evaluated the morphological changes in the peritubular capillary (PTC) network. Seven renal biopsy specimens from recipients with chronic rejection presenting with elevation of serum creatinine of 1.9 +/- 0.5 mg/dL were examined. Renal biopsy specimens from their counterpart donors were used as normal controls. In each specimen, non-pathological interstitial areas without fibrosis, tubular atrophy or cell infiltration were compared with pathological areas (PA) showing fibrosis and/or tubular atrophy using a computer image analysis. Morphological measurements revealed that the mean cut surface area of the PTC in the non-pathological and pathological interstitial areas in the recipient biopsies were significantly larger than that of the normal controls (p < 0.001 and 0.001, respectively). In the recipient biopsies, both of the mean cut surface areas of the tubules and PTC in the non-pathological areas were significantly higher than those in the PA (p < 0.001). The mean glomerular diameter in the recipient biopsies was also significantly higher than that of the donors (p < 0.01). In this study, we provided pathological evidence for the compensatory interstitial and glomerular hemodynamic alterations in kidney graft with chronic rejection and the condition as single kidney.

Focal segmental sclerotic lesions of the glomerulus in transplanted kidneys assessed using computerized image analysis

Mechanisms responsible for the development of focal segmental sclerotic lesions of the glomerulus (FSGS lesions) in transplanted kidneys were investigated by morphometric analysis. The mean glomerular area and the interstitial area were measured using computerized image analysis to compare implantation biopsies (so-called 1-h biopsies; 1Bx) with later biopsies (episode Bx; EBx) that had been taken for diagnostic purposes to identify the cause of deteriorating renal function. Groups of patients with (group A, n = 15) or without (group B, n = 10) FSGS lesions were compared. Twelve of 15 in group A and all in group B had lost graft function due to chronic allograft nephropathy. It was found that neither the mean glomerular area nor the interstitial area differed significantly between the two groups in either 1Bx or EBx. The interstitial area was significantly increased (P = 0.007) and the mean glomerular area tended to be increased (P = 0.085) in EBx compared with 1Bx in group A but not in group B. The serum creatinine level at the time of EBx in group A correlated with the interstitial area (P = 0.031) but not the mean glomerular area. However, there was no similar correlation in group B. In conclusion, factors for the development of FSGS lesions in transplanted kidneys may be the increase in interstitial area and possible glomerular hypertrophy following transplantation, rather than pre-existing reduced renal mass of the donor kidneys.