Paul D. Killen

Accelerated Macrophage Apoptosis Induces Autoantibody Formation and Organ Damage in Systemic Lupus Erythematosus

Increased monocyte/macrophage (Mφ) apoptosis occurs in patients with systemic lupus erythematosus (SLE) and is mediated, at least in part, by an autoreactive CD4+ T cell subset. Furthermore, autoreactive murine CD4+ T cells that kill syngeneic Mφ in vitro induce a lupus-like disease in vivo. However, it is unclear whether increased Mφ apoptosis in SLE per se is sufficient to accelerate/promote autoimmunity. We have investigated whether increased Mφ apoptosis in vivo, induced by the administration of clodronate liposomes, can exacerbate the autoimmune phenotype in NZB × SWR (SNF1) lupus-prone mice, and induce autoantibody production in haplotype-matched BALB/c × DBA1 (DBF1) non-lupus-prone mice. Lupus-prone mice SNF1 mice that were treated with clodronate liposomes, but not mice treated with vehicle, developed significant increases in autoantibodies to dsDNA, nucleosomes, and the idiotypically related family of nephritic Abs IdLNF1, when compared with untreated SNF1 mice. Furthermore, clodronate treatment hastened the onset of proteinuria and worsened SNF1 lupus nephritis. When compared with vehicle-treated controls, clodronate-treated non-lupus-prone DBF1 mice developed significantly higher levels of anti-nucleosome and IdLNF1 Abs but did not develop lupus nephritis. We propose that Mφ apoptosis contributes to the pathogenesis of autoantibody formation and organ damage through both an increase in the apoptotic load and impairment in the clearance of apoptotic material. This study suggests that mechanisms that induce scavenger cell apoptosis, such as death induced by autoreactive cytotoxic T cells observed in SLE, could play a pathogenic role and contribute to the severity of the disease.

Extrarenal ETB Plays a Significant Role in Controlling Cardiovascular Responses to High Dietary Sodium in Rats

Endothelin-B receptor (ETB)-deficient rats have low-renin, salt-sensitive hypertension. We hypothesized this was caused by an absence of renal ETB signaling and performed a series of experiments to examine the effect of dietary sodium (Na) on endothelin-1 (ET1) expression and renal function in wild-type (WT) and ETB-deficient rats. We found that ETB deficiency, but not dietary Na, increases circulating and tissue (kidney and aorta) ET1 levels. Quantitative reverse-transcription polymerase chain reaction reveals that aortic and renal ET1 and endothelin-A receptor (ETA) mRNA, however, are similarly increased by dietary Na in ETB-WT and ETB-deficient rats. We then determined the effect of chronic ETA blockade on blood pressure (direct conscious measurements), urinary protein excretion, and creatinine clearance (Crcl). On a Na-deficient diet, ETB-deficient rats have mild proteinuria and impaired Crcl. On a high-Na diet, severe hypertension and renal dysfunction develop in ETB-deficient rats. Chronic ETA blockade prevents hypertension and renal injury. To determine the role of the renal versus the extrarenal endothelin system, we performed renal cross-transplantation. We found that ETB deficiency in the body is associated with renal injury and an impaired ability to excrete an Na load. We also found that ETB deficiency in the body affects blood pressure response to dietary Na. Expression of ET1 and ETA are regulated by dietary Na. ETB receptors outside of the kidney, likely by functioning as a clearance receptor for ET1, limit salt-sensitivity in rats.

The role of aldosterone blockade in murine lupus nephritis

BackgroundThe purpose of this study was to examine the effect of aldosterone receptor blockade on the immunopathogenesis and progression of nephritis in the (NZB × NZW) F1 murine lupus model.MethodsFemale NZB/W F1 mice (11 weeks old) were treated daily with 25 or 50 mg/kg oral spironolactone or vehicle. Proteinuria, renal function, and serum autoantibody levels were monitored. Renal histopathology, immune complex deposition, and immunohistochemistry were analyzed at various time points. Targeted microarray analysis was performed on renal tissue, with subsequent real-time PCR analysis of several differentially expressed genes.ResultsTreatment with spironolactone was well tolerated by the mice throughout the course of their disease progression, with no significant differences in azotemia or serum potassium levels between vehicle-treated and spironolactone-treated animals. By 36 weeks of age, fewer spironolactone-treated mice developed nephrotic range proteinuria as compared with the control mice (control 70.8%, 25 mg/kg spironolactone 51.3%, and 50 mg/kg spironolactone 48.6%). Compared with control mice, mice treated with 25 mg/kg spironolactone had significantly lower serum anti-single-stranded DNA levels (2,042 μg/ml versus 1,036 μg/ml; P = 0.03) and anti-double-stranded DNA levels (3,433 μg/ml versus 614 μg/ml; P = 0.05). Spironolactone-treated mice exhibited decreased histopathologic evidence of inflammation and tissue damage, as compared with control mice. Additionally, spironolactone treatment resulted in decreased expression in the kidney of several inflammatory and proapoptotic genes, including those encoding interferon-γ, B lymphocyte stimulator (BlyS), tumor necrosis factor related apoptosis inducing ligand (TRAIL), tumor necrosis factor related weak inducer of apoptosis (TWEAK), and Fas ligand.ConclusionAldosterone receptor blockade is safe and well tolerated in progressive murine lupus nephritis, and it results in decreased levels of clinical proteinuria, lower serum levels of autoantibodies, and decreased kidney damage. It appears to modulate inflammatory changes during the progression of glomerulonephritis and may also have a previously undescribed role in attenuating apoptosis.

Differential expression of collagen IV isoforms in experimental glomerulosclerosis

Expansion of the glomerular mesangial matrix (MM), thickening of the glomerular basement membrane (GBM), and eventually the development of glomerulosclerosis are often seen in immunologically mediated kidney diseases. In addition to quantitative changes in the extracellular matrix (ECM), qualitative changes in ECM molecules may contribute to alterations in the composition of the glomerular matrix. The expression of collagen IV, α1–5(IV) mRNA, and polypeptides was therefore investigated during the development of chronic graft‐versus‐host disease (GvHD) in mice, a model for lupus nephritis, and in chronic serum sickness (CSS) in rats, a model for membranous nephropathy. Immunohistochemical studies showed increased mesangial expression of α1 and α2 early in the disease, but only late in the GBM. In contrast, α3 and α4 increased in the GBM during disease, but not in the MM. The mRNA levels for all collagen IV chains were increased in isolated glomeruli before morphological alterations were detectable. The mRNA increase was earlier and more profound for α3, α4 and α5 than for α1 and α2. Expression of α3(IV) was greatest in GvHD, whereas expression of α4 was greatest in CSS. As determined by in situ hybridization (ISH), α1 mRNA was observed dispersed in the glomerulus, but α3, α4, and α5 mRNAs were mainly located in cells at the periphery of the glomerular tuft. The changes in the relative abundance of collagen IV mRNA in disease states may perturb the collagen IV network, altering glomerular structure and function, and may thereby play a central role in the development of glomerulonephritis and glomerulosclerosis.

Time course of stimulation of renal renin messenger RNA by furosemide.

Renin secretion responds rapidly to a variety of stimuli; however, reported changes in renal renin messenger RNA (mRNA) levels in vivo have been observed only after prolonged stimulation. Studies were designed to test whether rapid changes in renin mRNA levels can be produced in vivo. In the first series, Sprague-Dawley rats received furosemide (10 mg/kg) intraperitoneally and a low sodium diet (0.05% sodium); renin secretion was significantly stimulated at 8 or 16 hours after treatment, but renin mRNA levels did not change. In a second series, rats were pretreated with deoxycorticosterone acetate (200 mg/kg) and saline drinking water for 3 days and then killed 0, 2, 4, 8, or 48 hours after furosemide administration. The renin mRNA level was unchanged at 2 hours but was stimulated twofold at 4 and 8 hours and threefold at 48 hours. In additional animals, the response of renin mRNA 4 hours after furosemide was found not to be potentiated by the converting enzyme inhibitor quinapril (5 mg/kg). The results demonstrate that with acute stimulation, renin mRNA levels lag 2-4 hours behind the change in plasma renin levels.

Human Na+-myo-inositol cotransporter gene: alternate splicing generates diverse transcripts

Na+- myo-inositol cotransport activity generally maintains millimolar intracellular concentrations of myo-inositol and specifically promotes transepithelial myo-inositol transport in kidney, intestine, retina, and choroid plexus. Glucose-induced, tissue-specific myo-inositol depletion and impaired Na+- myo-inositol cotransport activity are implicated in the pathogenesis of diabetic complications, a process modeled in vitro in cultured human retinal pigment epithelium (RPE) cells. To explore this process at the molecular level, a human RPE cDNA library was screened with a canine Na+-dependent myo-inositol cotransporter (SMIT) cDNA. Overlapping cDNAs spanning 3569 nt were cloned. The resulting cDNA sequence contained a 2154-nt open reading frame, 97% identical to the canine SMIT amino acid sequence. Genomic clones containing SMIT exons suggested that the cDNA is derived from at least five exons. Hypertonic stress induced a time-dependent increase, initially in a 16-kb transcript and subsequently in 11.5-, 9.8-, 8.5-, 3.8-, and ∼1.2-kb SMIT transcripts, that was ascribed to alternate exon splicing using exon-specific probes and direct cDNA sequencing. The human SMIT gene is a complex multiexon transcriptional unit that by alternate exon splicing generates multiple SMIT transcripts that accumulate differentially in response to hypertonic stress.

CLONING OF THE MOUSE FIBRONECTIN V‐REGION AND VARIATION OF ITS SPLICING PATTERN IN EXPERIMENTAL IMMUNE COMPLEX GLOMERULONEPHRITIS

Increased mRNA and protein expression of extracellular matrix (ECM) components, including fibronectin, occurs during the development of glomerulonephritis and glomerulosclerosis in immunologically mediated kidney diseases. However, in addition to these quantitative changes in ECM expression, qualitative changes in these molecules may contribute to malformations in the composition of the glomerular matrix. These qualitative changes may include alterations in the splicing pattern of the V‐region of fibronectin, since this region plays a role in its accumulation. The splicing patterns of this region have been studied in chronic graft‐versus‐host disease (GvHD) in mice, a model of lupus nephritis, and in chronic serum sickness (CSS) in rats, a model of immune complex nephritis. Cloning of the mouse fibronectin V‐region from kidney tissue revealed 96·1 per cent homology with the corresponding domain in rat fibronectin. PCR (polymerase chain reaction) analysis of RNA from isolated glomeruli revealed three isoforms of this region in both mouse and rat fibronectin, namely inclusion or exclusion of the whole region, or exclusion of only the CS1 domain. In both models, increased exclusion of the V‐region was observed early in the disease. However, in GvHD the splicing pattern returned to normal, whereas in CSS the shift persisted during the course of the experiment. Differentiated expression of fibronectin isoforms may exert an important effect on the structure and biological function of the glomerulus and may thus play a role in the development of glomerulonephritis and glomerulosclerosis.

Differential expression of collagen type IV alpha-chains in the tubulointerstitial compartment in experimental chronic serum sickness nephritis

The expression of collagen type IV chains in the renal tubulointerstitium was investigated during the development of chronic serum sickness (CSS) in rats, a model for immune complex‐mediated renal disease. Immunohistochemical studies showed increased expression of α4(IV) collagen early during disease development, followed by an increase in α1(IV) through α3(IV) collagen subchain expression, especially in the tubular basement membrane. Dot‐blot and in situ hybridization analysis showed a transient increase in steady‐state mRNA levels for all collagen IV subchains during the development of CSS, which was most abundant for α1(IV), α2(IV), and α4(IV). Statistical correlations were found between the mRNA levels of α1(IV) and α2(IV) collagen and between α3(IV) and α4(IV), in line with the results of others which showed that these chains are co‐distributed as heterotrimer collagen type IV molecules. However, additional correlations were found between the mRNA levels coding for α1(IV) and α3(IV) collagen, and between α1(IV) and α4(IV) mRNAs in the course of CSS. These abnormal correlations support the hypothesis that changes occur in the co‐expression of the collagen IV subchains during the development of CSS. In addition, a strong correlation was found between the presence in the tubulointerstitium of α1(IV) and α2(IV) collagen chains, on the one hand, and the tubulointerstitial influx of R73+ and ED1+ cells, on the other, suggesting the involvement of inflammatory cells in the observed alterations in matrix production. Changes in the relative abundance of collagen IV chains in disease states may perturb the collagen IV network in the tubulointerstitial compartment and thereby play a role in the development of renal failure. Copyright

Focal segmental glomerulosclerosis in association with neurofibromatosis type 1: a case report and proposed molecular pathways.

A 42-year-old Caucasian female with history of neurofibromatosis type 1 presented with nephrotic range proteinuria and focal segmental glomerulosclerosis (FSGS). On final dose of lisinopril 20 mg/day, protein–creatinine ratio declined to 0.33 within 10 months. We propose the hypothesis that development of FSGS in NF1 may be mediated by activation of mitogen-activated protein kinase (MAPK) and mammalian target of rapamycin (mTOR) signaling pathways secondary to up-regulation of ras proteins due to deficient neurofibromin. Since mTOR signaling pathway is partially mediated through angiotensin-II activation, angiotensin-converting enzyme (ACE) inhibition may serve as an effective initial treatment beyond anti-proteinuric properties of ACE-inhibitors.

An unusual case of membranous nephropathy associated with an ovarian tumor

Secondary membranous nephropathy (MN) associated with malignancy is not uncommon in adults, but it is rare in children. We report a 6-year-old girl who developed nephrotic-range proteinuria following diagnosis of a Sertoli–Leydig ovarian tumor. A renal biopsy was performed, which led to the diagnosis of MN. The patient maintained normal renal function and gradually showed improvement in proteinuria over several months without the use of corticosteroids or angiotensin-converting enzyme inhibitors. Our case highlights the importance of performing screening urinalyses in children with tumors to recognize the presence of clinically significant, but potentially asymptomatic kidney disease.