Kidney endothelial cell heterogeneity, angiocrine activity and paracrine regulatory mechanisms

The blood microvascular endothelium consists of a heterogeneous population of cells with regionally distinct morphologies and transcriptional signatures in different tissues and organs. In addition to providing an anti-thrombogenic surface for blood flow, endothelial cells perform a multitude of additional regulatory tasks involving organogenesis, metabolism, angiogenesis, inflammation, repair and organ homeostasis. To communicate with surrounding cells and accomplish their many functions, endothelial cells secrete angiocrine factors including growth factors, chemokines, cytokines, extracellular matrix components, and proteolytic enzymes. Nonendothelial parenchymal and stromal cells in turn regulate endothelial growth, differentiation and survival during embryonal development and in the adult by paracrine mechanisms. Driven by advances in molecular biology, animal genetics, single cell transcriptomics and microscopic imaging, knowledge of organotypic vasculatures has expanded rapidly in recent years. The kidney vasculature, in particular, has been the focus of intensive investigation and represents a primary example of how endothelial heterogeneity and crosstalk with nonendothelial cells contribute to the development and function of a vital organ. In this paper, we review the morphology, function, and development of the kidney vasculature, with an emphasis on blood microvascular endothelial heterogeneity, and provide examples of endothelial and nonendothelial-derived factors that are critically involved in kidney development, growth, response to injury, and homeostasis.

Single Cell Transcriptomics of Fibrotic Lungs Unveils Aging-associated Alterations in Endothelial and Epithelial Cell Regeneration

Lung regeneration deteriorates with aging leading to increased susceptibility to pathologic conditions, including fibrosis. Here, we investigated bleomycin-induced lung injury responses in young and aged mice at single-cell resolution to gain insights into the cellular and molecular contributions of aging to fibrosis. Analysis of 52,542 cells in young (8 weeks) and aged (72 weeks) mice identified 15 cellular clusters, many of which exhibited distinct injury responses that associated with age. We identified Pdgfra + alveolar fibroblasts as a major source of collagen expression following bleomycin challenge, with those from aged lungs exhibiting a more persistent activation compared to young ones. We also observed age-associated transcriptional abnormalities affecting lung progenitor cells, including ATII pneumocytes and general capillary (gCap) endothelial cells (ECs). Transcriptional analysis combined with lineage tracing identified a sub-population of gCap ECs marked by the expression of Tropomyosin Receptor Kinase B (TrkB) that appeared in bleomycin-injured lungs and accumulated with aging. This newly emerged TrkB + EC population expressed common gCap EC markers but also exhibited a distinct gene expression signature associated with aberrant YAP/TAZ signaling, mitochondrial dysfunction, and hypoxia. Finally, we defined ACKR1 + venous ECs that exclusively emerged in injured lungs of aged animals and were closely associated with areas of collagen deposition and inflammation. Immunostaining and FACS analysis of human IPF lungs demonstrated that ACKR1 + venous ECs were dominant cells within the fibrotic regions and accumulated in areas of myofibroblast aggregation. Together, these data provide high-resolution insights into the impact of aging on lung cell adaptability to injury responses.

Kidney Disease and Viral Infection in COVID-19: Why Are Kidney Organoid and Biopsy Studies Not in Agreement?

CONTEXT

The clinical course of coronavirus disease-19 (COVID-19) can be complicated by acute kidney injury and proteinuria. Kidney cells express receptors for SARS-CoV-2, the virus responsible for COVID-19. Direct infection of the kidney parenchyma by SARS-CoV-2 has been proposed as the cause of renal dysfunction in COVID-19. Subject of Review: Kidney organoids derived from human embryonic stem cells or induced pluripotent cells can be reproducibly infected by SARS-CoV-2 in vitro and used to study therapeutics. However, kidney biopsy studies of COVID-19 patients with renal dysfunction have shown no evidence of viral infection. Second Opinion: Kidney organoids are susceptible to SARS-CoV-2 infection, which is probably facilitated by their limited architectural complexity and maturation compared to the intact organ and by the in vitro culture conditions. Conversely, kidneys in COVID-19 patients appear resistant to infection and may be injured through indirect mechanisms mediated by the host response to the respiratory viral infection, genetic susceptibility to the immune response, physiological disturbances, and therapies. More studies are needed to better understand why kidney organoids are more susceptible than mature kidneys to SARS-CoV-2 infection and further characterize the mechanisms of kidney injury in COVID-19.

Dysfunctional ERG signaling drives pulmonary vascular aging and persistent fibrosis

Vascular dysfunction is a hallmark of chronic diseases in elderly. The contribution of the vasculature to lung repair and fibrosis is not fully understood. Here, we performed an epigenetic and transcriptional analysis of lung endothelial cells (ECs) from young and aged mice during the resolution or progression of bleomycin-induced lung fibrosis. We identified the transcription factor ETS-related gene (ERG) as putative orchestrator of lung capillary homeostasis and repair, and whose function is dysregulated in aging. ERG dysregulation is associated with reduced chromatin accessibility and maladaptive transcriptional responses to injury. Loss of endothelial ERG enhances paracrine fibroblast activation in vitro, and impairs lung fibrosis resolution in young mice in vivo. scRNA-seq of ERG deficient mouse lungs reveales transcriptional and fibrogenic abnormalities resembling those associated with aging and human lung fibrosis, including reduced number of general capillary (gCap) ECs. Our findings demonstrate that lung endothelial chromatin remodeling deteriorates with aging leading to abnormal transcription, vascular dysrepair, and persistent fibrosis following injury.

COVID-19 Vasculopathy: Mounting Evidence for an Indirect Mechanism of Endothelial Injury

Patients with coronavirus disease 2019 (COVID-19) who are critically ill develop vascular complications characterized by thrombosis of small, medium, and large vessels. Dysfunction of the vascular endothelium due to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has been implicated in the pathogenesis of the COVID-19 vasculopathy. Although initial reports suggested that endothelial injury was caused directly by the virus, recent studies indicate that endothelial cells do not express angiotensin-converting enzyme 2, the receptor that SARS-CoV-2 uses to gain entry into cells, or express it at low levels and are resistant to the infection. These new findings, together with the observation that COVID-19 triggers a cytokine storm capable of injuring the endothelium and disrupting its antithrombogenic properties, favor an indirect mechanism of endothelial injury mediated locally by an augmented inflammatory reaction to infected nonendothelial cells, such as the bronchial and alveolar epithelium, and systemically by the excessive immune response to infection. Herein we review the vascular pathology of COVID-19 and critically discuss the potential mechanisms of endothelial injury in this disease.

Early Transplant Arteriopathy in Kidney Transplantation

BACKGROUND

Early dysfunction of renal allografts may be associated with vascular injury, which raises the specter of active rejection processes that require medical intervention. In our practice, we have encountered patients who present with delayed graft function and demonstrate a unique pattern of endothelial cell injury that raises concern for rejection in their biopsy. Therefore, we sought to systematically determine the biopsy characteristics and outcome of these patients.

METHODS

During a 17-year period at the University of Washington in Seattle, United States, we identified 24 cases of a distinct arterial vasculopathy presenting in the first year posttransplantation. This early transplant arteriopathy (ETA) is characterized by endothelial cell swelling and intimal edema but without the intimal arteritis that defines vascular rejection.

RESULTS

Approximately 1% of transplant biopsies during the study period showed ETA, almost all of which were in deceased donor organs (96%), and most presented with delayed graft function (54%) or increased serum creatinine (38%) soon after transplantation (median 13 days; range, 5-139). In this study, 77% of patients were managed expectantly, with only 2 patients (7.6%) subsequently developing acute vascular rejection. Except for 1 patient who died, all patients had functioning allografts at 1 year follow-up.

CONCLUSION

Recognizing ETA and distinguishing it from vascular rejection is important to prevent over-treatment because most patients appear to recover allograft function rapidly with expectant management.

Multicenter Clinicopathologic Correlation of Kidney Biopsies Performed in COVID-19 Patients Presenting With Acute Kidney Injury or Proteinuria

RATIONALE & OBJECTIVE

Kidney biopsy data inform us about pathologic processes associated with infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We conducted a multicenter evaluation of kidney biopsy findings in living patients to identify various kidney disease pathology findings in patients with coronavirus disease 2019 (COVID-19) and their association with SARS-CoV-2 infection.

STUDY DESIGN

Case series.

SETTING & PARTICIPANTS

We identified 14 native and 3 transplant kidney biopsies performed for cause in patients with documented recent or concurrent SARS-CoV-2 infection treated at 7 large hospital systems in the United States.

OBSERVATIONS

Men and women were equally represented in this case series, with a higher proportion of Black (n=8) and Hispanic (n=5) patients. All 17 patients had SARS-CoV-2 infection confirmed by reverse transcriptase-polymerase chain reaction, but only 3 presented with severe COVID-19 symptoms. Acute kidney injury (n=15) and proteinuria (n=11) were the most common indications for biopsy and these symptoms developed concurrently or within 1 week of COVID-19 symptoms in all patients. Acute tubular injury (n=14), collapsing glomerulopathy (n=7), and endothelial injury/thrombotic microangiopathy (n=6) were the most common histologic findings. 2 of the 3 transplant recipients developed active antibody-mediated rejection weeks after COVID-19. 8 patients required dialysis, but others improved with conservative management.

LIMITATIONS

Small study size and short clinical follow-up.

CONCLUSIONS

Cases of even symptomatically mild COVID-19 were accompanied by acute kidney injury and/or heavy proteinuria that prompted a diagnostic kidney biopsy. Although acute tubular injury was seen among most of them, uncommon pathology such as collapsing glomerulopathy and acute endothelial injury were detected, and most of these patients progressed to irreversible kidney injury and dialysis.

Characterizing Viral Infection by Electron Microscopy: Lessons from the Coronavirus Disease 2019 Pandemic

The severe acute respiratory syndrome coronavirus 2 pandemic has infected millions of individuals in the United States and caused hundreds of thousands of deaths. Direct infection of extrapulmonary tissues has been postulated, and using sensitive techniques, viral RNA has been detected in multiple organs in the body, including the kidney. However, direct infection of tissues outside of the lung has been more challenging to demonstrate. This has been in part due to misinterpretation of electron microscopy studies. In this perspective, we will discuss what is known about coronavirus infection, some of the basic ultrastructural cell biology that has been confused for coronavirus infection of cells, and rigorous criteria that should be used when identifying pathogens by electron microscopy.

Parallel Murine and Human Plaque Proteomics Reveals Pathways of Plaque Rupture

RATIONALE

Plaque rupture is the proximate cause of most myocardial infarctions and many strokes. However, the molecular mechanisms that precipitate plaque rupture are unknown.

OBJECTIVE

By applying proteomic and bioinformatic approaches in mouse models of protease-induced plaque rupture and in ruptured human plaques, we aimed to illuminate biochemical pathways through which proteolysis causes plaque rupture and identify substrates that are cleaved in ruptured plaques.

METHODS AND RESULTS

We performed shotgun proteomics analyses of aortas of transgenic mice with macrophage-specific overexpression of urokinase (SR-uPA^+/0 mice) and of SR-uPA^+/0 bone marrow transplant recipients, and we used bioinformatic tools to evaluate protein abundance and functional category enrichment in these aortas. In parallel, we performed shotgun proteomics and bioinformatics studies on extracts of ruptured and stable areas of freshly harvested human carotid plaques. We also applied a separate protein-analysis method (protein topography and migration analysis platform) to attempt to identify substrates and proteolytic fragments in mouse and human plaque extracts. Approximately 10% of extracted aortic proteins were reproducibly altered in SR-uPA^+/0 aortas. Proteases, inflammatory signaling molecules, as well as proteins involved with cell adhesion, the cytoskeleton, and apoptosis, were increased. ECM (Extracellular matrix) proteins, including basement-membrane proteins, were decreased. Approximately 40% of proteins were altered in ruptured versus stable areas of human carotid plaques, including many of the same functional categories that were altered in SR-uPA^+/0 aortas. Collagens were minimally altered in SR-uPA^+/0 aortas and ruptured human plaques; however, several basement-membrane proteins were reduced in both SR-uPA^+/0 aortas and ruptured human plaques. Protein topography and migration analysis platform did not detect robust increases in proteolytic fragments of ECM proteins in either setting.

CONCLUSIONS

Parallel studies of SR-uPA^+/0 mouse aortas and human plaques identify mechanisms that connect proteolysis with plaque rupture, including inflammation, basement-membrane protein loss, and apoptosis. Basement-membrane protein loss is a prominent feature of ruptured human plaques, suggesting a major role for basement-membrane proteins in maintaining plaque stability.

Fibrillary Glomerulonephritis: Clinicopathologic Features and Atypical Cases from a Multi-Institutional Cohort

BACKGROUND AND OBJECTIVES

Fibrillary GN has been defined as an immune complex-mediated GN with amyloid-like fibrils larger than amyloid which are IgG positive and Congo red negative. With discovery of DNAJB9 as a highly sensitive and specific marker for fibrillary GN, the specificity of the morphologic criteria for establishing the diagnosis of fibrillary GN has come into question.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We sought to (1) determine anatomic characteristics that best define fibrillary GN and (2) identify clinical and pathologic features that predict outcomes.

RESULTS

We retrospectively reviewed kidney biopsies from patients diagnosed with fibrillary GN or suspected fibrillary GN between 1997 and 2017 (n=266, 65% female, median age 61). Approximately 11% of kidney biopsies had one or more unusual feature including monotypic deposits, Congo red positivity, or unusual fibril diameter. Fibrillary GN as a possible monoclonal gammopathy of renal significance represented <1% of cases. Immunostaining for DNAJB9 confirmed fibrillary GN in 100% of cases diagnosed as fibrillary GN and 79% of atypical cases diagnosed as possible fibrillary GN. At a median time of 24 months (interquartile range, 8-46 months) after biopsy (n=100), 53% of patients reached the combined primary outcome of ESKD or death, 18% had CKD, and 18% had partial remission. On multivariable analysis, male sex (adjusted hazard ratio [aHR], 3.82; 95% confidence interval [95% CI], 1.97 to 7.37) and eGFR were the most significant predictors of primary outcome (aHR of 8.02 if eGFR <30 ml/min per 1.73 m2 [95% CI, 1.85 to 34.75]; aHR of 6.44 if eGFR 30 to <45 ml/min per 1.73 m2 [95% CI, 1.38 to 29.99]). Immunosuppressive therapy with rituximab was significantly associated with stabilization of disease progression.

CONCLUSIONS

Detection of DNAJB9 is a useful diagnostic tool for diagnosing atypical forms of fibrillary GN. The outcomes for fibrillary GN are poor and progression to ESKD is influenced predominantly by the degree of kidney insufficiency at the time of diagnosis and male sex. Rituximab may help preserve kidney function for select patients with fibrillary GN.

PODCAST

This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2019_11_04_CJN03870319.mp3.

Consensus guidelines for the use and interpretation of angiogenesis assays

The formation of new blood vessels, or angiogenesis, is a complex process that plays important roles in growth and development, tissue and organ regeneration, as well as numerous pathological conditions. Angiogenesis undergoes multiple discrete steps that can be individually evaluated and quantified by a large number of bioassays. These independent assessments hold advantages but also have limitations. This article describes in vivo, ex vivo, and in vitro bioassays that are available for the evaluation of angiogenesis and highlights critical aspects that are relevant for their execution and proper interpretation. As such, this collaborative work is the first edition of consensus guidelines on angiogenesis bioassays to serve for current and future reference.

Hyperactive FOXO1 results in lack of tip stalk identity and deficient microvascular regeneration during kidney injury

Loss of the microvascular (MV) network results in tissue ischemia, loss of tissue function, and is a hallmark of chronic diseases. The incorporation of a functional vascular network with that of the host remains a challenge to utilizing engineered tissues in clinically relevant therapies. We showed that vascular-bed-specific endothelial cells (ECs) exhibit differing angiogenic capacities, with kidney microvascular endothelial cells (MVECs) being the most deficient, and sought to explore the underlying mechanism. Constitutive activation of the phosphatase PTEN in kidney MVECs resulted in impaired PI3K/AKT activity in response to vascular endothelial growth factor (VEGF). Suppression of PTEN in vivo resulted in microvascular regeneration, but was insufficient to improve tissue function. Promoter analysis of the differentially regulated genes in KMVECs suggests that the transcription factor FOXO1 is highly active and RNAseq analysis revealed that hyperactive FOXO1 inhibits VEGF-Notch-dependent tip-cell formation by direct and indirect inhibition of DLL4 expression in response to VEGF. Inhibition of FOXO1 enhanced angiogenesis in human bio-engineered capillaries, and resulted in microvascular regeneration and improved function in mouse models of injury-repair.

Hypoxia paradoxically inhibits the angiogenic response of isolated vessel explants while inducing overexpression of vascular endothelial growth factor

This study was designed to investigate how changes in O2 levels affected angiogenesis in vascular organ culture. Although hypoxia is a potent inducer of angiogenesis, aortic rings cultured in collagen paradoxically failed to produce an angiogenic response in 1-4 % O2. Additionally, aortic neovessels preformed in atmospheric O2 lost pericytes and regressed at a faster rate than control when exposed to hypoxia. Aortic explants remained viable in hypoxia and produced an angiogenic response when returned to atmospheric O2. Hypoxic aortic rings were unresponsive to VEGF, while increased oxygenation of the system dose-dependently enhanced VEGF-induced angiogenesis. Hypoxia-induced refractoriness to angiogenic stimulation was not restricted to the aorta because similar results were obtained with vena cava explants or isolated endothelial cells. Unlike endothelial cells, aorta-derived mural cells were unaffected by hypoxia. Hypoxia downregulated expression in aortic explants of key signaling molecules including VEGFR2, NRP1 and Prkc-beta while upregulating expression of VEGFR1. Medium conditioned by hypoxic cultures exhibited angiostatic and anti-VEGF activities likely mediated by sVEGFr1. Hypoxia reduced expression of VEGFR1 and VEGFR2 in endothelial cells while upregulating VEGFR1 in macrophages and VEGF in both macrophages and mural cells. Thus, changes in O2 levels profoundly affect the endothelial response to angiogenic stimuli. These results suggest that hypoxia-induced angiogenesis is fine-tuned by complex regulatory mechanisms involving not only production of angiogenic factors including VEGF but also differential regulation of VEGFR expression in different cell types and production of inhibitors of VEGF function such as sVEGFR1.

The rat aortic ring model of angiogenesis

Protocols outlined in this chapter illustrate how to prepare and analyze angiogenic cultures of rat aorta. Aortic rings embedded in gels of extracellular matrix generate vascular outgrowths that can easily be monitored over time with inverted microscopy. The angiogenic response can be measured by counting vessels or with image analysis. Aortic ring cultures can be used to investigate molecular mechanisms of angiogenesis and test the efficacy of stimulators and inhibitors of the angiogenic process. As such this assay is an invaluable tool for both basic and applied angiogenesis research.

Interstitial eosinophilic aggregates in diabetic nephropathy: allergy or not?

BACKGROUND

Interstitial eosinophilic aggregates (IEA) in renal biopsies often suggest allergic tubulointerstitial nephritis, yet clear associations with drug reactions are often difficult to establish. IEA are also encountered in diabetic nephropathy (DN) and thought to be attributed to medication exposure.

METHODS

Native medical kidney biopsies performed at the University of Washington Medical Center were reviewed, including DN (n = 64), IgA nephropathy (IgAN, n = 28), membranous nephropathy (MN, n = 14), focal and segmental glomerulosclerosis (FSGS, n = 27) and membranoproliferative glomerulonephritis (MPGN, n = 28). IEA were defined as ≥5 eosinophils per high power field. The severity of interstitial fibrosis and tubular atrophy (IFTA) was scored semi-quantitatively as minimal, mild, moderate or severe.

RESULTS

IEA were remarkably more prevalent in DN (41%), when compared with IgAN (7%, P = 0.001), MN (8%, P = 0.017) or MPGN (14%, P = 0.013), but not FSGS (26%, P = 0.18). In DN cases, univariate analysis revealed that IEA were associated with greater IFTA severity, but not with the percentage of glomerulosclerosis, mesangial expansion, history of drug allergy, number of prescribed medications or particular class of medications (antibiotics, NSAIDs, aspirin, thiazide, loop diuretics, angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, calcium channel blockers, beta blockers, insulin, sulfonylurea, metformin or allopurinol). Multivariate analysis showed that the severity of IFTA was the only significant predictor for IEA (P < 0.01) after stepwise adjustment for age, number of medications, drug allergy, diabetes type, % global glomerulosclerosis and mesangial expansion.

CONCLUSIONS

Our study shows that IEA are more common in DN, when compared with other types of glomerulopathy. In DN, IEA are associated with the severity of IFTA but not with prescribed medications or clinical history of allergy. This suggests that in DN IEA are often associated with chronic tubulointerstitial injury and are not diagnostic of an allergic interstitial nephritis.

Renal ApoA-1 amyloidosis with Glu34Lys mutation and intra-amyloid lipid accumulation

Apolipoprotein A-1 (ApoA-1) amyloidosis occurs as a nonhereditary condition in atherosclerotic plaques, but it can also manifest as a hereditary disorder caused by mutations of the APOA1 gene. Hereditary ApoA-1 amyloidosis presents with diverse organ involvement based on the position of the mutation. We describe a case of ApoA-1 amyloidosis with a Glu34Lys mutation; testicular, conjunctival, and renal involvement; and the notable finding of lipid deposition within the amyloid deposits.

Combined crystalline podocytopathy and tubulopathy associated with multiple myeloma

Lymphoplasmacytic neoplasms cause a wide range of injuries to the kidney exemplified by light chain cast nephropathy and amyloidosis. Filtered paraproteins can also accumulate within kidney cells and cause direct cytotoxic injury. Rarely, paraproteins that are resistant to proteolysis can crystallize within proximal tubules and cause acute tubular injury. In contrast, accumulation of crystallized paraproteins in other kidney cells, especially podocytes, is exceptional. Here, we report the finding of crystalline inclusions within podocytes and proximal tubules in a patient who presented with a combined nephrotic syndrome and Fanconi syndrome. Further workup revealed previously unsuspected multiple myeloma and elevated serum free light chains, highlighting the protean presentation of paraprotein-mediated injuries to the kidney.

Regulation of angiogenesis, mural cell recruitment and adventitial macrophage behavior by Toll-like receptors

The angiogenic response to injury can be studied by culturing rat or mouse aortic explants in collagen gels. Gene expression studies show that aortic angiogenesis is preceded by an immune reaction with overexpression of Toll-like receptors (TLRs) and TLR-inducible genes. TLR1, 3, and 6 are transiently upregulated at 24 h whereas TLR2, 4, and 8 expression peaks at 24 h but remains elevated during angiogenesis and vascular regression. Expression of TLR5, 7 and 9 steadily increases over time and is highest during vascular regression. Studies with isolated cells show that TLRs are expressed at higher levels in aortic macrophages compared to endothelial or mural cells with the exception of TLR2 and TLR9 which are more abundant in the aortic endothelium. LPS and other TLR ligands dose dependently stimulate angiogenesis and vascular endothelial growth factor production. TLR9 ligands also influence the behavior of nonendothelial cell types by blocking mural cell recruitment and inducing formation of multinucleated giant cells by macrophages. TLR9-induced mural cell depletion is associated with reduced expression of the mural cell recruiting factor PDGFB. The spontaneous angiogenic response of the aortic rings to injury is reduced in cultures from mice deficient in myeloid differentiation primary response 88 (MyD88), a key adapter molecule of TLRs, and following treatment with an inhibitor of the NFκB pathway. These results suggest that the TLR system participates in the angiogenic response of the vessel wall to injury and may play an important role in the regulation of inflammatory angiogenesis in reactive and pathologic processes.

SCNH2 is a novel apelinergic family member acting as a potent mitogenic and chemotactic factor for both endothelial and epithelial cells

The gut hormone apelin is a major therapeutic focus for several diseases involving inflammation and aberrant cell growth. We investigated whether apelin-36 contained alternative bioactive peptides associated with normal physiology or disease. Amino acid sequence analysis of apelin-36 identified an amidation motif consistent with the formation of a secondary bioactive peptide (SCNH2). SCNH2 is proven to be mitogenic and chemotactic in normal/malignant cells and augments angiogenesis via a PTX-resistant/CT-X-sensitive G protein-coupled receptor (GPCR). Notably, SCNH2 is substantially more potent and sensitive than apelin-13 and vascular endothelial growth factor-A. Endogenous SCNH2 is highly expressed in human tumors and placenta and in mouse embryonic tissues. Our findings demonstrate that SCNH2 is a new apelinergic member with critical pluripotent roles in angiogenesis related diseases and embryogenesis via a non-APJ GPCR.

Intraglomerular micrometastasis of squamous cell carcinoma

Intraglomerular metastasis is a rare manifestation of disseminated malignancies. We present here a case of intraglomerular metastatic carcinoma diagnosed as an incidental finding on a kidney biopsy in a 62-year-old male presenting with acute renal failure and metastatic penile squamous cell carcinoma. A proliferative lesion composed of highly atypical epithelial cells was found within a capillary loop and adjacent urinary space of an isolated glomerulus, which was immunoreactive for markers of squamous cell carcinoma. This case is a reminder that circulating cancer cells can occasionally lodge in glomeruli and appear as micrometastasis in kidney biopsies performed for the evaluation of renal dysfunction.

Paracrine regulation of angiogenesis by different cell types in the aorta ring model

The development of blood vessels during angiogenesis is the result of paracrine interactions between tube-forming endothelial cells and angiogenic factor-producing nonendothelial cells. This process can be reproduced and studied under chemically defined culture conditions by culturing vascular explants in three-dimensional gels of extracellular matrix. Rings of rat or mouse aorta cultured in collagen, fibrin or basement membrane gels produce angiogenic outgrowths composed of a mixed population of endothelial cells and nonendothelial cells. Aortic angiogenesis is regulated by endogenous angiogenic factors, inflammatory cytokines, chemokines, extracellular matrix molecules, and proteolytic enzymes produced by cells of the vessel wall in response to the injury of the dissection procedure. In this paper, we review how macrophages, mural cells and fibroblasts regulate different stages of the angiogenic process, from the formation of immature endothelial sprouts to the reabsorption of the neovessels. We also describe how aortic cultures can be used to study interactions between angiogenic outgrowths and nonvascular cell types such as bone marrow macrophages, platelets or cancer cells. Morphologic, genetic and functional studies of this model have provided invaluable information on how vessels form, mature, interact with nonvascular cell types, and are eventually reabsorbed. Further analysis of the paracrine cross-talk between aortic endothelial and nonendothelial cells is likely to provide new insights into the angiogenic process and its key mechanisms.

Three-dimensional self-organizing neural architectures: a neural stem cells reservoir and a system for neurodevelopmental studies

Complex microenvironmental stimuli influence neural cell properties. To study this, we developed a three-dimensional (3-D) neural culture system, composed of different populations including neurons, astrocytes, and neural stem cells (NSCs). In particular, these last-mentioned cells represent a source potentially exploitable to test drugs, to study neurodevelopment and cell-therapies for neuroregenerations. On seeding on matrigel in a medium supplemented with serum and mitogens, cells obtained from human fetal brain tissue formed 3-D self-organizing neural architectures. Immunocytochemical analysis demonstrated the presence of undifferentiated nestin+ and CD133+ cells, surrounded by β-tub-III+ and GFAP+ cells, suggesting the formation of niches containing potential human NSCs (hNSCs). The presence of hNSCs was confirmed by both neurosphere assay and RT-PCR, and their multipotentiality was demonstrated by both immunofluorescent staining and RT-PCR. Flow cytometry analysis revealed that neurosphere forming cells originating from at least two different subsets expressing, respectively, CD133 and CD146 markers were endowed with different proliferative and differentiation potential. Our data implicate that the complexity of environment within niches and aggregates of heterogeneous neural cell subsets may represent an innovative platform for neurobiological and neurodevelopmental investigations and a reservoir for a rapid expansion of hNSCs.

Macrophage-derived tumor necrosis factor-alpha is an early component of the molecular cascade leading to angiogenesis in response to aortic injury

OBJECTIVE

The goal of this study was to define the role of tumor necrosis factor-α (TNFα) in the cascade of gene activation that regulates aortic angiogenesis in response to injury.

METHODS AND RESULTS

Angiogenesis was studied by culturing rat or mouse aortic rings in collagen gels. Gene expression was evaluated by quantitative reverse transcription-polymerase chain reaction, microarray analysis, immunocytochemistry, and ELISA. TNFα gene disruption and recombinant TNFα or blocking antibodies against vascular endothelial growth factor (VEGF) or TNF receptors were used to investigate TNFα-mediated angiogenic mechanisms. Resident aortic macrophages were depleted with liposomal clodronate. Angiogenesis was preceded by overexpression of TNFα and TNFα-inducible genes. Studies with isolated cells showed that macrophages were the main source of TNFα. Angiogenesis, VEGF production, and macrophage outgrowth were impaired by TNFα gene disruption and promoted by exogenous TNFα. Antibody-mediated inhibition of TNF receptor 1 significantly inhibited angiogenesis. The proangiogenic effect of TNFα was suppressed by blocking VEGF or by ablating aortic macrophages. Exogenous TNFα, however, maintained a limited proangiogenic capacity in the absence of macrophages and macrophage-mediated VEGF production.

CONCLUSIONS

Overexpression of TNFα is required for optimal VEGF production and angiogenesis in response to injury. This TNFα/VEGF-mediated angiogenic pathway requires macrophages. The residual capacity of TNFα to stimulate angiogenesis in macrophage-depleted aortic cultures implies the existence of a VEGF-independent alternate pathway of TNFα-induced angiogenesis.

Technical Advance: The rat aorta contains resident mononuclear phagocytes with proliferative capacity and proangiogenic properties

Angiogenesis in the aortic ring model is preceded by activation of the immune system and impaired by ablation of adventitial macrophages. Treatment of aortic cultures with M-CSF induced extensive periaortic outgrowth of CD45(+) CD68(+) mononuclear cells with ultrastructural features of macrophages and DCs. Periaortic lysis of collagen caused many CD45(+) CD68(+) cells to attach to the bottom of the culture dish. Lifting the collagen gels left behind patches of CD45(+) CD68(+) cells, which focally organized into branching cords. These cells also expressed CD14, CD169, F4/80, and α-SMA but not CD31, vWF, desmin, or CD163. DNA synthesis studies showed that M-CSF-stimulated cells were actively proliferating. Aortic patch cells showed phagocytic properties and responded to IL-4 and GM-CSF by expressing MHC II, differentiating into DCs, and forming multinucleated giant cells. They also stimulated angiogenesis and VEGF production in aortic ring cultures. This study demonstrates that the rat aorta contains a distinct subset of immature immunocytes capable of proliferating, differentiating into macrophages and DCs, and stimulating angiogenesis. Isolation of these cells in patches from M-CSF-stimulated aortic rings provides a reproducible system to study the biology and angiogenic role of the resident immune system of the aortic wall.

MCP-1 promotes mural cell recruitment during angiogenesis in the aortic ring model

Rings of rat or mouse aorta embedded in collagen gels produce angiogenic outgrowths in response to the injury of the dissection procedure. Aortic outgrowths are composed of branching endothelial tubes and surrounding mural cells. Mural cells emerge following endothelial sprouting and gradually increase during the maturation of the neovessels. Treatment of aortic cultures with angiopoietin-1 (Ang-1), an angiogenic factor implicated in vascular maturation and remodeling, stimulates the mural cell recruitment process. Ang-1 induces expression of many cytokines and chemokines including monocyte chemotactic protein-1 (MCP-1). Inhibition of p38 MAP kinase, a signaling molecule required for mural cell recruitment, blocks Ang1-induced MCP-1 expression. Recombinant MCP-1 dose-dependently increases mural cell number while an anti-MCP-1 blocking antibody reduces it. In addition, antibody mediated neutralization of MCP-1 abrogates the stimulatory effect of Ang-1 on mural cell recruitment. Aortic rings from genetically modified mice deficient in MCP-1 or its receptor CCR2 have fewer mural cells than controls. MCP-1 deficiency also impairs the mural cell recruitment activity of Ang-1. Our studies indicate that spontaneous and Ang1-induced mural cell recruitment in the aortic ring of model of angiogenesis are in part mediated by MCP-1. These results implicate MCP-1 as one of the mediators of mural cell recruitment in the aortic ring model, and suggest that chemokine pathways may contribute to the assembly of the vessel wall during the angiogenesis response to injury.

The aortic ring model of angiogenesis: a quarter century of search and discovery

The aortic ring model has become one of the most widely used methods to study angiogenesis and its mechanisms. Many factors have contributed to its popularity including reproducibility, cost effectiveness, ease of use and good correlation with in vivo studies. In this system aortic rings embedded in biomatrix gels and cultured under chemically defined conditions generate arborizing vascular outgrowths which can be stimulated or inhibited with angiogenic regulators. Originally based on the rat aorta, the aortic ring model was later adapted to the mouse for the evaluation of specific molecular alterations in genetically modified animals. Viral transduction of the aortic rings has enabled investigators to overexpress genes of interest in the aortic cultures. Experiments on angiogenic mechanisms have demonstrated that formation of neovessels in aortic cultures is regulated by macrophages, pericytes and fibroblasts through a complex molecular cascade involving growth factors, inflammatory cytokines, axonal guidance cues, extracellular matrix (ECM) molecules and matrix-degrading proteolytic enzymes. These studies have shown that endothelial sprouting can be effectively blocked by depleting the aortic explants of macrophages or by interfering with the angiogenic cascade at multiple levels including growth factor signalling, cell adhesion and proteolytic degradation of the ECM. In this paper, we review the literature in this field and retrace the journey from our first morphological descriptions of the aortic outgrowths to the latest breakthroughs in the cellular and molecular regulation of aortic vessel growth and regression.

Combination of peritubular c4d and transplant glomerulopathy predicts late renal allograft failure

The histologic associations and clinical implications of peritubular capillary C4d staining from long-term renal allografts are unknown. We identified 99 renal transplant patients who underwent an allograft biopsy for renal dysfunction at least 10 yr after transplantation, 25 of whom were C4d-positive and 74 of whom were C4d-negative. The average time of the index biopsy from transplantation was 14 yr in both groups. Compared with C4d-negative patients, C4d-positive patients were younger at transplantation (29 +/- 13 versus 38 +/- 12 yr; P < 0.05) and were more likely to have received an allograft from a living donor (65 versus 35%; P < 0.001). C4d-positive patients had more inflammation, were more likely to have transplant glomerulopathy, and had worse graft outcome. The combined presence of C4d positivity, transplant glomerulopathy, and serum creatinine of >2.3 mg/dl at biopsy were very strong predictors of rapid graft loss. C4d alone did not independently predict graft loss. Retrospective staining of historical samples from C4d-positive patients demonstrated C4d deposition in the majority of cases. In summary, these data show that in long-term renal allografts, peritubular capillary staining for C4d occurs in approximately 25% of biopsies, can persist for many years after transplantation, and strongly predicts graft loss when combined with transplant glomerulopathy.

Vascular regression and survival are differentially regulated by MT1-MMP and TIMPs in the aortic ring model of angiogenesis

This study was designed to investigate the role of matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs) in the reabsorption of neovessels in collagen gel cultures of rat and mouse aortic rings. Aortic angiogenesis was associated with collagen lysis and production of the matrix-degrading enzymes MMP-2, MMP-9, and membrane-type MMP (MT1-MMP, or MMP-14). Vascular growth and regression were not affected by disruption of MMP-2 or MMP-9. In addition, no effect on vascular regression was observed by blocking plasmin, a protease implicated in the activation of MMPs, with epsilon-aminocaproic acid or by adding plasminogen, which caused a modest increase in vascular proliferation. Conversely, angiogenesis was blocked and vessels stabilized by inhibiting MT1-MMP with neutralizing antibodies, TIMP-2, TIMP-3, or TIMP-4. TIMP-1, which blocks MMP-2 and MMP-9 but is a poor inhibitor of MT1-MMP, had no antiangiogenic effect. However, TIMP-1 prolonged the survival of neovessels following angiogenesis. Vascular regression was accelerated in aortic cultures from TIMP-1- and TIMP-2-deficient mice. The vascular survival effect of anti-MT1-MMP antibodies and TIMPs with MT1-MMP inhibitory activity was associated with complete inhibition of collagen lysis. In contrast, TIMP-1 had no anticollagenolytic effect. These results indicate that MT1-MMP plays a critical role not only in angiogenesis but also in vascular regression and demonstrate that TIMPs with anti-MT1-MMP activity have opposite effects on angiogenic outcomes depending on the stage of the angiogenic process. This study also suggests the existence of a TIMP-1-mediated alternate pathway of vascular survival that is unrelated to MT1-MMP inhibitory activity.

Regulation of angiogenesis by macrophages, dendritic cells, and circulating myelomonocytic cells

Angiogenesis during reactive and pathologic processes is characteristically associated with inflammation. Macrophages and dendritic cells present in the inflammatory infiltrate contribute to the angiogenic process by multiple mechanisms. Macrophages produce a broad array of angiogenic growth factors and cytokines, generate conduits for blood flow through proteolytic mechanisms, and promote the remodeling of arterioles into arteries. They can also inhibit angiogenesis and cause reabsorption of neovessels by inducing endothelial cell death. Dendritic cells can stimulate or inhibit angiogenesis depending on their activation status and subset specificity. Dendritic cells stimulate angiogenesis by secreting angiogenic factors and cytokines, promoting the proangiogenic activity of T lymphocytes, and trans-differentiating into endothelial cells. Inflammatory infiltrates associated with angiogenesis also contain Tie2+, VEGFR2+, and GR1+ myelomonocytic cells which actively regulate the angiogenic process through paracrine mechanisms. In this paper we review our current knowledge of this field and discuss how recent advances have provided the rationale for novel therapeutic approaches against cancer.

Parstatin, the cleaved peptide on proteinase-activated receptor 1 activation, is a potent inhibitor of angiogenesis

The proteolytic activation by thrombin of the proteinase-activated receptor 1 unveils the tethered peptide ligand and cleaves a 41-amino acid peptide. In this report, we show that this peptide, which we have designated as "parstatin," is a potent inhibitor of angiogenesis. Synthesized parstatin suppressed both the basic angiogenesis and that stimulated by basic fibroblast growth factor and vascular endothelial growth factor in the chick embryo model in vivo and in the rat aortic ring assay. Parstatin also abrogated endothelial cell migration and capillary-like network formation on the Matrigel and fibrin angiogenesis models in vitro. Treatment of endothelial cells with parstatin resulted in inhibition of cell growth by inhibiting the phosphorylation of extracellular signal-regulated kinases in a specific and reversible fashion and by promoting cell cycle arrest and apoptosis through a mechanism involving activation of caspases. We have shown that parstatin acts as a cell-penetrating peptide, exerting its biological effects intracellularly. The uptake into cells and the inhibitory activity were dependent on parstatin hydrophobic region. These results support the notion that parstatin may represent an important negative regulator of angiogenesis with possible therapeutic applications.

The angiogenic response of the aorta to injury and inflammatory cytokines requires macrophages

The purpose of this study was to define early events during the angiogenic response of the aortic wall to injury. Rat aortic rings produced neovessels in collagen culture but lost this capacity over time. These quiescent rings responded to vascular endothelial growth factor but not to a mixture of macrophage-stimulatory cytokines and chemokines that was angiogenically active on fresh rings. Analysis of cytokine receptor expression revealed selective loss in quiescent rings of the proangiogenic chemokine receptor CXCR2, which was expressed predominantly in aortic macrophages. Pharmacologic inhibition of CXCR2 impaired angiogenesis from fresh rings but had no effect on vascular endothelial growth factor-induced angiogenesis from quiescent explants. Angiogenesis was also impaired in cultures of aortic rings from CXCR2-deficient mice. Reduced CXCR2 expression in quiescent rat aortic rings correlated with marked macrophage depletion. Pharmacologic ablation of macrophages from aortic explants blocked formation of neovessels in vitro and reduced aortic ring-induced angiogenesis in vivo. The angiogenic response of macrophage-depleted rings was completely restored by adding exogenous macrophages. Moreover, angiogenesis from fresh rings was promoted by macrophage CSF (CSF-1) and inhibited with anti-CSF-1 Ab. Thus, aortic angiogenic sprouting following injury is strongly influenced by conditions that modulate resident macrophage numbers and function.

Aortic rings stimulate inflammatory angiogenesis in a subcutaneous implant in vivo model

Rat or mouse aortic rings produce angiogenic outgrowths in vitro through endogenous production of growth factors and inflammatory cytokines. To further investigate this process in vivo, collagen-Gelfoam constructs containing aortic rings were implanted subcutaneously in syngeneic animals. Aortic rings stimulated a prominent angiogenic response characterized by peri- and intra-aortic accumulation of florid granulation tissue. Conversely, implants without rings elicited a non-specific inflammatory reaction without significant angiogenesis. The angiogenic response to the rings peaked at day 14 and was followed by regression of neovessels, which were mostly reabsorbed by day 28. Gene expression studies showed upregulated expression of angiogenic growth factors and cytokines in implants with rings. Tracking experiments with LacZ expressing ROSA26 transgenic mice demonstrated that both the aorta and the host contributed to the angiogenic response. These studies show that the angiogenic properties of the rodent aorta can be studied in the live animal under conditions that can be monitored and quantified. This in vivo assay can be used to study the molecular mechanisms by which the arterial wall and its proangiogenic cytokines regulate formation of granulation tissue during wound healing.

Spectrum of renal pathology in hematopoietic cell transplantation: a series of 20 patients and review of the literature

BACKGROUND AND OBJECTIVES

Hematopoietic cell transplantation is a common treatment option for a variety of hematopoietic malignancies. As a result of the use of total body irradiation and/or chemotherapeutic agents, renal dysfunction often ensues. Many pharmacologic agents, such as cyclosporine and high-intensity conditioning regimens, have been linked with thrombotic microangiopathy. In addition, an association between membranous nephropathy and graft-versus-host disease has been reported in this clinical setting.

DESIGN, SETTING, PARTICIPANTS, AND MEASUREMENTS

A study of autologous and allogeneic hematopoietic cell transplantation patients with renal dysfunction was conducted to document the spectrum of renal manifestations. The pathology files at the University of Washington and University of Chicago Medical Centers were reviewed, and 20 patients with a kidney biopsy after hematopoietic cell transplantation were identified. The histologic findings were correlated with relevant clinical information.

RESULTS

A wide spectrum of renal diseases could be classified into four categories: (1) Complications related to hematopoietic cell transplantation (conditioning regimen, immunosuppression, or posttransplantation complications), (2) podocytopathy, (3) membranous nephropathy, or (4) recurrence or persistence of original hematologic disease. Pathologic diagnoses included thrombotic microangiopathy, polyoma virus nephropathy, acute kidney injury/acute tubular necrosis, acute and chronic interstitial nephritis, minimal-change disease, "tip" variant of focal segmental glomerulosclerosis, membranous nephropathy, amyloidosis, and myeloma cast nephropathy. Membranous nephropathy, minimal-change disease, and amyloidosis were common causes of severe proteinuria. Because of the conditioning regimens, posttransplantation complications, and potential nephrotoxic agents used during hematopoietic cell transplantation, it was difficult to attribute the subsequent renal dysfunction to specific factors.

CONCLUSIONS

The renal biopsy remains essential for diagnosing the underlying injury that can affect one or more compartments of the kidney in this unique clinical setting.

Tubular basement membrane immune deposits in association with BK polyomavirus nephropathy

Tubular basement membrane immune deposits (TBMID) are rare in renal allografts and usually have been found in association with immune complex mediated glomerular injury. We report an association between TBMID and BK polyomavirus nephropathy (BKN). We reviewed clinical data and results of allograft biopsies of 30 patients with BKN (16 with and 14 without TBMID). TBMID were detected by immunofluorescence or electron microscopy. Initial and follow-up biopsies were assessed for degree of interstitial inflammation and fibrosis and severity of viral infection, and were correlated with patients' clinical data. Biopsies initially diagnostic for BKN with TBMID, compared to BKN biopsies without deposits, demonstrated more severe interstitial inflammation and fibrosis, and greater numbers of virally infected cells. Similar findings were present in follow-up biopsies. Utilizing three different antibodies directed against viral epitopes, viral antigens could not be detected within TBMID. Thirty percent of patients with TBMID and 70% without deposits had follow-up biopsies, in which virus could not be detected immunohistochemically. Treatment for all included decreasing immunosuppression, cidofovir and/or leflunomide. Clinical data correlated well with histological findings. We conclude that a significant proportion of patients with BKN show TBMID on kidney biopsy. The prognostic significance of this finding remains to be elucidated.

A clinicopathologic study of thrombotic microangiopathy in the setting of IgA nephropathy

BACKGROUND

IgA nephropathy is the most common glomerulonephritis in the world. Thrombotic microangiopathy occurs in a number of clinical settings, including but not limited to thrombotic thrombocytopenic purpura/hemolytic uremic syndrome, malignant hypertension, anti-phospholipid antibody syndrome and radiation nephropathy. Renovascular complications, such as thrombotic microangiopathy, in the setting of IgA nephropathy may be overlooked and their significance as a concomitant histologic finding is unclear.

METHODS

We conducted a clinicopathologic study to understand the possible relationship between IgA nephropathy and a concurrent thrombotic microangiopathy injury process. We identified 10 patients with an established diagnosis of IgA nephropathy and concurrent findings of thrombotic microangiopathy based on their renal biopsies.

RESULTS

Six patients presented with malignant hypertension, while three others had severe hypertension (> or = 100 mmHg, diastolic). Five patients had nephrotic-range proteinuria. Seven patients had occasional arteriolar thrombi identified by light microscopy and prominent glomerular subendothelial space widening by electron microscopy, while three patients demonstrated only ultrastructural features of thrombotic microangiopathy. Other possible etiologic causes of thrombotic microangiopathy were not identified with the available clinical information.

CONCLUSION

Our study suggests that a thrombotic microangiopathy injury, when present, is usually found in advanced stages of IgA nephropathy and can be associated with severe proteinuria. Although other possible causes of thrombotic microangiopathy, such as anti-phospholipid antibody syndrome, were excluded in only two patients, the thrombotic microangiopathy injury process may be a cause or a consequence of the severe hypertension encountered in most of the patients which, in turn, may be a consequence of the disease progression of IgA nephropathy.

Regulation of Postangiogenic Neovessel Survival by β1 and β3 Integrins in Collagen and Fibrin Matrices

We used the aortic ring model of angiogenesis to investigate the role of beta(1) and beta(3) integrins in postangiogenic vascular survival in collagen and fibrin matrices. Confocal microscopy studies showed that both beta(1) and beta(3) integrins were expressed in endothelial cells and pericytes of sprouting neovessels. Antibody blocking experiments demonstrated that beta(1) integrins but not beta(3) integrins were required for angiogenic sprouting in collagen. Conversely, in fibrin, blockade of both integrins was needed to inhibit angiogenesis whereas treatment with either antibody alone was ineffective. Antibody-mediated blockade of beta(1) but not beta(3) integrins accelerated vascular regression in collagen. In contrast, both anti-beta(1) and -beta(3) integrin antibodies were required to promote neovessel breakdown in fibrin. These results demonstrate that angiogenic sprouting and postangiogenic neovessel survival in collagen are critically dependent on beta(1) integrins. They also indicate that these processes involve a redundant repertoire of beta(1) and beta(3) integrins when angiogenesis occurs in fibrin. Thus, pharmacologic targeting of integrin receptors aimed at blocking neovessel formation and survival must be tailored to the specific extracellular matrix environment in which angiogenesis takes place.

Angiopoietin-1 and vascular endothelial growth factor induce expression of inflammatory cytokines before angiogenesis

The purpose of this study was to identify novel transcriptional events occurring in the aortic wall before angiogenesis. We used a defined tissue culture system that takes advantage of the capacity of rat aortic rings to generate neovessels ex vivo in response to angiogenic factor stimulation. Total RNA isolated from aortic rings 18 h posttreatment with angiopoietin (Ang)-1 or vascular endothelial growth factor (VEGF) was used to probe oligonucleotide microarrays. Many genes were up- or downregulated by either Ang-1 or VEGF, with a subset being affected by treatment with both growth factors. Grouping of genes by biological function revealed that Ang-1 and VEGF both upregulated a host of immune-related genes including many inflammatory cytokines. A mixture of the Ang-1- and VEGF-induced cytokines stimulated the spontaneous angiogenic response of aortic rings and was synergistic with a low dose of recombinant VEGF. This effect was associated with enhanced recruitment of adventitial macrophages and dendritic cells in the angiogenic outgrowths. Thus Ang-1 and VEGF activate the innate immune system of the vessel wall, stimulating the production of proangiogenic inflammatory cytokines before the emergence of neovessels. This hitherto unreported feature of the angiogenic response might represent an important early component of the cellular and molecular cascade responsible for the angiogenic response of the aortic wall.

An anti-major histocompatibility complex class I intrabody protects endothelial cells from an attack by immune mediators

OBJECTIVE

In vitro endothelialization has significantly improved the overall outcome of artificial prostheses in cardiovascular bypass surgery. A drawback of this tissue-engineering method remains the limited availability of suitable autologous endothelial cells (EC), especially in aged patients. Allogeneic EC with high proliferative capacity represent a potentially valuable alternative to a patient-specific vascular transplant. However, such cells carry the risk of being rejected due to Major Histocompatibility Complex (MHC) mismatches.

METHODS

We investigated the effects of a very potent, intracellularly expressed antibody directed against MHC class I molecules, referred to as alpha-rat MHC I single chain variable fragment (sFv) intrabody. The intrabody was stably expressed in rat aortic EC (RAEC) following lentiviral vector-mediated gene transfer. The functional consequence of the MHC I down-regulation was tested in an allogeneic setting in two different in vitro assays.

RESULTS

Stable expression of the alpha-rat MHC I sFv intrabody resulted in a highly efficient depletion of surface MHC I. Thereby those RAEC which displayed low MHC I levels over extended periods of time were protected against killing by allo-specific, cytotoxic T cells (CTL) and by allo-antibody/complement-mediated lysis.

CONCLUSIONS

These results demonstrate that intrabody-mediated down-regulation of MHC I reduces the immunogenicity of RAEC which may provide a suitable alternative supply for the lining of vascular prostheses.

Membranous glomerulopathy with spherules: an uncommon variant with obscure pathogenesis

BACKGROUND

Occasional case reports of membranous glomerulopathy described unique subepithelial accumulations of an unusual type of immune deposit composed of spherular structures. The identity of such structures as nuclear pores has been suggested, but not established.

METHODS

We identified a cohort of patients (n = 14, including 1 patient with disease recurrence in an allograft) who presented with nephrotic syndrome and had renal biopsy specimens with light and immunofluorescence microscopic findings characteristic of membranous glomerulopathy. These patients were distinguished by ultrastructural studies that showed glomerular capillary wall accumulations of subepithelial immune deposits composed of uniform spherular structures, while lacking the typical granular electron-dense deposits seen in membranous glomerulopathy. The molecular identity of these spherular structures as nuclear pores was tested by using immunofluorescence microscopy and immunohistochemistry with mouse monoclonal antinuclear pore antibodies (Covance, Princeton, NJ) and anti-Nuclear Pore-O-Linked Glycoprotein (Affinity BioReagents Inc, Golden, CO) antibodies.

RESULTS

Measurement of spherular structures by using high-magnification electron microscopy showed an average diameter of 84.5 nm, which correlated well with accepted diameters of nuclear pores (80 to 120 nm). Immunofluorescence microscopy and immunoperoxidase staining with both antibodies showed characteristic beaded staining of nuclear membranes of multiple cell types within normal control kidney, but no staining of immune-type deposits within glomerular basement membranes.

CONCLUSION

These cases form a rare, but distinctive, morphological subclass of membranous glomerulopathy. The antigenic specificity of immune deposits in these cases remains elusive.

IgA nephropathy with crescents in kidney transplant recipients

BACKGROUND

Crescentic glomerulonephritis is an uncommon finding in renal allografts. Recurrence or de novo mesangial deposition of immunoglobulin A (IgA) in renal allografts most often is clinically benign, but some case reports have shown that IgA nephropathy in renal allografts can present as crescentic glomerulonephritis and may lead to rapid deterioration of graft function and/or graft loss.

METHODS

We reviewed diagnoses of all allograft biopsies at University of Washington Medical Center (Seattle, WA) from 1989 to 2003 and found 33 cases of glomerulonephritis with crescents. Eight of these cases were the result of recurrent or de novo IgA nephropathy. Clinical and pathological features of these patients were reviewed.

RESULTS

Six of 8 cases with crescents were the result of recurrent IgA nephropathy, and 2 cases were presumptive de novo IgA nephropathy. Of the 8 patients with IgA nephropathy with crescents, 6 patients presented clinically with increasing serum creatinine levels; 4 patients, with proteinuria; and 4 patients, with hematuria. In 6 patients, there was 10% to 30% involvement of glomeruli, with crescents partially or completely filling urinary spaces. The other patients showed lesser (approximately 7% of sampled glomeruli) involvement. Four patients with IgA nephropathy with crescents developed renal failure and returned to hemodialysis therapy. Three patients had a benign clinical course, with stabilization of renal function. One patient was lost to follow-up.

CONCLUSION

We identified a cohort of patients with glomerulonephritis with crescents in renal allografts with IgA nephropathy as the cause. In half the affected patients, this led to early progressive renal insufficiency and return to hemodialysis therapy.