Author Correction: RNA-seq of serial kidney biopsies obtained during progression of chronic kidney disease from dogs with X-linked hereditary nephropathy.

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Associations of patient characteristics, disease stage, and biopsy technique with the diagnostic quality of core needle renal biopsy specimens from dogs with suspected kidney disease.

OBJECTIVE To identify factors affecting the diagnostic quality of core needle renal biopsy specimens from dogs with suspected kidney disease. DESIGN Cross-sectional study. ANIMALS 522 client-owned dogs with suspected kidney disease for which core needle renal biopsy specimens (n = 1,089) were submitted to the International Veterinary Renal Pathology Service for evaluation and inclusion in their database. PROCEDURES Data regarding dog signalment, clinical variables, biopsy method, needle brand and gauge, biopsy results, and other variables were extracted from the database. Variables were tested for association with 3 outcomes of light microscopic evaluation of core specimens: number of glomeruli per core specimen, obtainment of < 10 glomeruli, and presence or absence of renal medullary tissue. RESULTS Number of glomeruli per core specimen was significantly associated with needle gauge, dog age, serum creatinine concentration, and degree of proteinuria, whereas biopsy method and submitting hospital were significantly associated with the presence of renal medullary tissue in specimens. Mean numbers of glomeruli per core specimen obtained with 14- or 16-gauge needles were similar, but both were significantly greater than the mean number obtained with 18-gauge needles. Needle gauge had a similar association with the likelihood of obtaining < 10 glomeruli in a core specimen. Specimens obtained via laparotomy or laparoscopic approaches more commonly contained medullary tissue than those obtained by ultrasound-guided approaches. CONCLUSIONS AND CLINICAL RELEVANCE Overall, findings suggested that ultrasound-guided biopsy with a 16-gauge needle should maximize the diagnostic quality of renal biopsy specimens from dogs with suspected kidney disease, while avoiding potential adverse effects caused by larger needles.

RNA-seq of serial kidney biopsies obtained during progression of chronic kidney disease from dogs with X-linked hereditary nephropathy.

Dogs with X-linked hereditary nephropathy (XLHN) have a glomerular basement membrane defect that leads to progressive juvenile-onset renal failure. Their disease is analogous to Alport syndrome in humans, and they also serve as a good model of progressive chronic kidney disease (CKD). However, the gene expression profile that affects progression in this disease has only been partially characterized. To help fill this gap, we used RNA sequencing to identify differentially expressed genes (DEGs), over-represented pathways, and upstream regulators that contribute to kidney disease progression. Total RNA from kidney biopsies was isolated at 3 clinical time points from 3 males with rapidly-progressing CKD, 3 males with slowly-progressing CKD, and 2 age-matched controls. We identified 70 DEGs by comparing rapid and slow groups at specific time points. Based on time course analysis, 1,947 DEGs were identified over the 3 time points revealing upregulation of inflammatory pathways: integrin signaling, T cell activation, and chemokine and cytokine signaling pathways. T cell infiltration was verified by immunohistochemistry. TGF-ß1 was identified as the primary upstream regulator. These results provide new insights into the underlying molecular mechanisms of disease progression in XLHN, and the identified DEGs can be potential biomarkers and therapeutic targets translatable to all CKDs.

Glomerular Lipidosis in Dogs.

Glomerular lipidosis (GL) is characterized by dilated glomerular capillary loops containing lipid-laden cells (foam cells). Previously, GL was considered to be an incidental finding because affected dogs were typically not azotemic. However, the International Renal Interest Society staging system for canine chronic kidney disease has increased the awareness of other clinical parameters (eg, proteinuria and hypertension) that should be included in the assessment of renal function. As such, the aim of this study was to determine clinical abnormalities and concurrent renal lesions in dogs with GL. GL was identified in renal biopsies from 46 dogs evaluated by the International Veterinary Renal Pathology Service. GL was the sole diagnosis in 5 of 46 cases (11%), all of which were proteinuric. All 5 dogs had at least 1 additional clinicopathologic abnormality consistent with renal disease, including hypertension (4), azotemia (3), and/or hypoalbuminemia (2). The remaining 41 dogs had GL in combination with other glomerular lesions, the most common being focal segmental glomerulosclerosis (16, 35%), lesions consistent with juvenile nephropathy (8, 17%), and glomerular amyloidosis (5, 11%). Overall, dogs with severe GL were younger than were those with mild GL ( P < .001). The percentage of glomeruli affected by GL differed by concurrent diagnoses ( P = .034), with the highest percentage of affected glomeruli in dogs with GL alone or those with concurrent juvenile nephropathy. These findings suggest that GL should be a recognized histologic phenotype of glomerular injury associated with clinical renal dysfunction and/or juvenile nephropathies.

Proliferative, necrotizing and crescentic immune complex-mediated glomerulonephritis in a cat.

CASE SUMMARY: A 5-year-old cat was examined for vomiting and anorexia of 2 days' duration. Azotemia, hyperphosphatemia and hypoalbuminemia were the main biochemical findings. Serial analyses of the urine revealed isosthenuria, proteinuria and eventual glucosuria. Hyperechoic perirenal fat was detected surrounding the right kidney by ultrasonography. Histopathologic evaluation of ante-mortem ultrasound-guided needle biopsies of the right kidney was consistent with proliferative, necrotizing and crescentic glomerulonephritis with fibrin thrombi, proteinaceous and red blood cell casts, and moderate multifocal chronic-active interstitial nephritis. Owing to a lack of clinical improvement, the cat was eventually euthanized. Post-mortem renal biopsies were processed for light microscopy, transmission electron microscopy and immunofluorescence. This revealed severe focal proliferative and necrotizing glomerulonephritis with cellular crescent formation, podocyte injury and secondary segmental sclerosis. Ultrastructural analysis revealed scattered electron-dense deposits in the mesangium, and immunofluorescence demonstrated positive granular staining for λ light chains, consistent with immune complex-mediated glomerulonephritis. Severe diffuse acute tubular epithelial injury and numerous red blood cell casts were also seen. RELEVANCE AND NOVEL INFORMATION: To our knowledge, this is the first report of naturally occurring proliferative, necrotizing and crescentic immune complex glomerulonephritis in a cat.

Kidney diseases caused by glomerular basement membrane type IV collagen defects in dogs.

OBJECTIVE: To review the pathogenesis, as well as the clinical and pathologic features of canine glomerular diseases caused by genetic type IV collagen defects. DATA SOURCES: Original studies and review articles from human and veterinary medical fields. HUMAN DATA SYNTHESIS: Presence in glomerular basement membranes (GBM) of a network composed of α3.α4.α5 heterotrimers of type IV collagen is required to maintain structure and function of glomerular capillary walls. VETERINARY DATA SYNTHESIS: Hereditary nephropathy (HN) is the most commonly used name for kidney diseases that occur in dogs due to genetic type IV collagen abnormalities. To date, 4 different collagen IV gene mutations have been identified in dogs with HN; 2 are COL4A5 mutations that cause X-linked HN (XL-HN), and 2 are COL4A4 mutations that cause autosomal recessive HN (AR-HN). Affected males with XL-HN and affected males and females with AR-HN develop juvenile-onset kidney disease manifested by proteinuria typically starting at 3-6 months of age and followed by progressive kidney disease leading to terminal failure usually at 6-24 months of age. Carrier female dogs with XL-HN also develop proteinuria starting at 3-6 months of age, but progressive disease causing kidney failure is uncommon until they are >5 years old. The distinctive pathologic lesions of HN are extensive multilaminar splitting and thickening of the GBM, as demonstrated by electron microscopy, and abnormal type IV collagen α-chain content of basement membranes, as demonstrated by immunolabeling. Identification of the underlying gene mutations has permitted genetic testing and selective breeding practices that currently are minimizing HN in breeds known to be at risk. CONCLUSIONS: Canine HN is a rare disease that should be considered whenever a dog exhibits a juvenile-onset kidney disease characterized partly by proteinuria, but highly specialized methods are required to pursue a definitive diagnosis.

Resolution of a proteinuric nephropathy associated with Babesia gibsoni infection in a dog.

A 4 yr old male castrated Labrador retriever was evaluated for a short history of inappetance, lethargy, small-bowel diarrhea, polyuria, and polydipsia. Clinicopathologic abnormalities were consistent with protein-losing nephropathy and renal azotemia. Expansive infectious disease testing implicated Babesia gibsoni via whole blood polymerase chain reaction. Renal histopathology results were consistent with membranoproliferative glomerulonephritis and immune complex deposition. The dog was treated with azithromycin, atovaquone, and one dose of corticosteroids/cyclophosphamide. Three months after therapy was completed, the dog was clinically healthy, and all clinicopathologic abnormalities (including Babesia species polymerase chain reaction) had resolved. Atypical presentations of Babesia gibsoni should be considered with proteinuric nephropathy.

Renal biopsy and pathologic evaluation of glomerular disease.

Presence of suspected primary glomerular disease is the most common and compelling reason to consider renal biopsy. Pathologic findings in samples from animals with nephritic or nephrotic glomerulopathies, as well as from animals with persistent subclinical glomerular proteinuria that is not associated with advanced chronic kidney disease, frequently guide treatment decisions and inform prognosis when suitable specimens are obtained and examined appropriately. Ultrasound-guided needle biopsy techniques generally are satisfactory; however, other methods of locating or approaching the kidney, such as manual palpation (e.g., in cats), laparoscopy, or open surgery, also can be used. Visual assessment of the tissue content of needle biopsy samples to verify that they are renal cortex (i.e., contain glomeruli) as they are obtained is a key step that minimizes the submission of uninformative samples for examination. Adequate planning for a renal biopsy also requires prior procurement of the fixatives and preservatives needed to process and submit samples that will be suitable for electron microscopic examination and immunostaining, as well as for light microscopic evaluation. Finally, to be optimally informative, renal biopsy specimens must be processed by laboratories that routinely perform the required specialized examinations and then be evaluated by experienced veterinary nephropathologists. The pathologic findings must be carefully integrated with one another and with information derived from the clinical investigation of the patient's illness to formulate the correct diagnosis and most informative guidance for therapeutic management of the animal's glomerular disease.

Proteomic analysis of urine from male dogs during early stages of tubulointerstitial injury in a canine model of progressive glomerular disease.

BACKGROUND: Sensitive and specific noninvasive biomarkers for tubulointerstitial injury are lacking, and proteomic techniques provide a powerful tool for biomarker discovery. OBJECTIVE: The aim of this study was to identify novel urinary biomarkers of early tubulointerstitial injury in canine progressive renal disease using both 2-dimensional differential in-gel electrophoresis (2-D DIGE), which identifies individual proteins, and surface-enhanced laser desorption ionization time-of-flight mass spectrometry (SELDI-TOF), which generates protein peak profiles. METHODS: Urine was collected from 6 male dogs with X-linked hereditary nephropathy (XLHN) at 2 time points (TP): 1) the onset of overt proteinuria (urine protein:creatinine ratio>2) and 2) the onset of azotemia (creatinine ≥ 1.2 mg/dL); corresponding renal biopsies were analyzed from 3 of the dogs. Urine samples from the 6 dogs were subjected to analysis by 2-D DIGE and SELDI-TOF. Urinary retinol-binding protein (RBP) was evaluated in 25 male dogs with XLHN and normal control dogs by Western blot analysis. RESULTS: Clinical data and histologic evaluation revealed reduced renal function and increased tubulointerstitial fibrosis at TP 2. A number of urine proteins and protein peaks were differentially present at the 2 time points, with several known biomarkers of renal disease identified in addition to several promising new biomarkers. RBP was first detected in urine approximately 2 months before onset of azotemia (TP 2), but after onset of overt proteinuria, and amounts increased with progression of disease. CONCLUSIONS: Proteomic techniques were successfully used to identify urinary biomarkers of renal disease in dogs with XLHN. Urinary RBP is a promising biomarker for early detection of tubulointerstitial damage and progression to end-stage renal disease.

Minimal change glomerulopathy in a cat.

A 6-year-old domestic shorthair male castrated cat was evaluated for sudden onset of vomiting and anorexia. A diagnosis of hypereosinophilic syndrome (HES) was made, and the cat was treated with imatinib mesylate. The cat had an initial clinical improvement with the normalization of the peripheral eosinophil count. After approximately 8 weeks of treatment, lethargy and anorexia recurred despite the normal eosinophil count and a significant proteinuric nephropathy was identified. Treatment with imatinib was discontinued. Ultrasound guided renal biopsies exhibited histologic, ultrastructural, and immunostaining changes indicative of a minimal change glomerulopathy (MCG) which has not previously been reported in the literature in a cat. The proteinuria and HES initially improved while the cat was treated with more traditional medications; however, both the problems persisted for 30 months that the cat was followed subsequently. Previous studies demonstrating the safety and efficacy of imatinib in cats do not report any glomerular injury or significant adverse drug reactions, and the exact cause of this cat's proteinuric nephropathy is uncertain. Nonetheless, the possibility of an adverse drug reaction causing proteinuria should be considered when initiating treatment with imatinib in a cat.

Renal failure associated with mucopolysaccharidosis type I in a cat from a MPS I research colony.

Renal failure was diagnosed in an 11-mo-old male domestic shorthair cat from a colony with mucopolysaccharidosis type I lysosomal storage disease. Grossly, the kidneys were enlarged and bulged on cut section. Histology revealed tubular necrosis and regeneration with severe interstitial macrophage accumulation. Tubular epithelial cells and interstitial macrophages were distended by abundant, large cytoplasmic vacuoles. Electron microscopy demonstrated severe tubular epithelial vacuolar degeneration with lysosomes distended by granular debris and mineral precipitates. Interstitial macrophages contained similarly distended lysosomes. Although the initial cause of the tubular injury was not identified, the presence of macrophages laden with storage product most likely exacerbated the disease. The macrophage infiltrate may have caused tubular ischemia by compressing peritubular capillaries and separating tubules from their blood supply. Because the kidney is not normally affected in MPS I, this case is an unusual presentation of a well-characterized disease. Furthermore, this report documents the diagnostic workflow used to investigate a single case of feline acute renal failure in the setting of numerous at-risk laboratory animals.

The effect of progressive glomerular disease on megalin-mediated endocytosis in the kidney.

BACKGROUND: A well-characterized dog model of the X-linked collagen disease Alport syndrome (XLAS) was used to study the effect of progressive glomerular disease on megalin-mediated endocytosis. In XLAS, altered structure and function of the glomerular basement membrane induces a progressive proteinuric nephropathy. METHODS: The investigation was performed in male XLAS dogs and age-matched normal male littermates. The urine profile and megalin-mediated endocytosis in the proximal tubule of six healthy and six XLAS dogs were examined at 2, 4, 6, 8 and 10 months of age using SDS-PAGE, immunoblotting and immunohistochemistry. RESULTS: Gradually increasing urinary excretion of proteins over time and a reduced content of the same proteins in proximal tubule cells were found. Besides the glomerular component of the proteinuria, a significant tubular component was seen, which is due to a progressive change in the uptake of low-molecular-weight (LMW) ligands by megalin. Furthermore, the protein overload present in the lumen of the proximal tubule exceeds the reabsorption capacity of megalin and the co-receptor cubilin and results in a combined low- and high-molecular-weight (HMW) proteinuria. Also, a shift in the distribution of lysosomes was seen in the XLAS dogs suggesting changes in the lysosomal degradation pattern in response to the altered endocytosis. CONCLUSIONS: The present study shows that the increased glomerular permeability and the subsequently altered megalin-mediated and megalin-dependent cubilin-mediated endocytosis lead to a partial LMW proteinuria and partial HMW proteinuria.

X-inactivation modifies disease severity in female carriers of murine X-linked Alport syndrome.

BACKGROUND: Female carriers of X-linked Alport syndrome (XLAS) demonstrate variability in clinical phenotype that, unlike males, cannot be correlated with genotype. X-inactivation, the method by which females (XX) silence transcription from one X chromosome in order to achieve gene dosage parity with males (XY), likely modifies the carrier phenotype, but this hypothesis has not been tested directly. METHODS: Using a genetically defined mouse model of XLAS, we generated two groups of Alport female (Col4a5(+/-)) carriers that differed only in the X-controlling element (Xce) allele regulating X-inactivation. We followed the groups as far as 6 months of age comparing survival and surrogate outcome measures of urine protein and plasma urea nitrogen. RESULTS: Preferential inactivation of the mutant Col4a5 gene improved survival and surrogate outcome measures of urine protein and plasma urea nitrogen. In studies of surviving mice, we found that X-inactivation in kidney, measured by allele-specific mRNA expression assays, correlated with surrogate outcomes. CONCLUSIONS: Our findings establish X-inactivation as a major modifier of the carrier phenotype in X-linked Alport syndrome. Thus, X-inactivation patterns may offer prognostic information and point to possible treatment strategies for symptomatic carriers.

Stability of canine pancreatic lipase immunoreactivity concentration in serum samples and effects of long-term administration of prednisone to dogs on serum canine pancreatic lipase immunoreactivity concentrations.

OBJECTIVE: To evaluate stability of canine pancreatic lipase immunoreactivity (cPLI) in serum samples and to determine the effect of long-term administration of prednisone on serum cPLI concentrations. SAMPLE POPULATION: 8 canine serum samples for the stability evaluation and serum samples obtained from 6 healthy young adult heterozygous (carrier) dogs with X-linked hereditary nephritis for determining the effect of prednisone administration. PROCEDURES: To evaluate stability of serum cPLI concentration, an aliquot of each serum sample was stored at each of 4 temperatures between -80 degrees and 24 degrees C; samples were analyzed on days 0, 3, 7, 14, and 21. To determine the effect of long-term prednisone administration, pretreatment serum samples were obtained (days 0 and 14) and prednisone was administered (2.2 mg/kg, q 24 h, PO) on days 15 through 42, with serum samples obtained on days 28 and 42. Additional serum samples were obtained on days 56 and 70. RESULTS: Mean serum cPLI concentrations did not change significantly from day 0 to day 21 regardless of storage temperature. Serum cPLI concentrations in dogs after prednisone administration were within the reference range for all dogs at all time points, and results of repeated-measures ANOVA revealed that serum cPLI concentrations did not change significantly over time. CONCLUSIONS AND CLINICAL RELEVANCE: Serum cPLI concentrations measured in canine serum samples stored at room temperature, in a refrigerator, or in a freezer at -20 degrees or -80 degrees C were stable for at least 21 days. Also, long-term prednisone administration to dogs did not significantly affect serum cPLI concentrations.

Evaluation of perinuclear anti-neutrophilic cytoplasmic autoantibodies as an early marker of protein-losing enteropathy and protein-losing nephropathy in Soft Coated Wheaten Terriers.

OBJECTIVE: To evaluate perinuclear anti-neutrophilic cytoplasmic autoantibody (pANCA) status in Soft Coated Wheaten Terriers (SCWTs) and SCWT-Beagle crossbred dogs and to correlate pANCA status of dogs with clinicopathologic variables of protein-losing enteropathy (PLE), protein-losing nephropathy (PLN), or both. ANIMALS: 13 SCWTs and 8 SCWT-Beagle crossbred dogs in a research colony and a control group comprising 7 dogs with X-linked hereditary nephropathy and 12 healthy SCWTs > 9 years old. PROCEDURES: Samples were obtained from dogs in the research colony every 6 months. At each sample-collection time point, serum concentrations of albumin, globulin, creatinine, and urea nitrogen; fecal concentration of alpha-proteinase inhibitor; and urinary protein-to-creatinine ratios were determined and correlated with pANCA status. RESULTS: 20 of 21 dogs in the research colony had positive results for pANCAs at a minimum of 2 time points, and 18 of 21 dogs had definitive evidence of disease. None of the control dogs had positive results for pANCAs. A positive result for pANCAs was significantly associated with hypoalbuminemia, and pANCAs preceded the onset of hypoalbuminemia on an average of 2.4 years. Sensitivity and specificity for use of pANCAs to predict development of PLE or PLN were 0.95 (95% confidence interval, 0.72 to 1.00) and 0.8 (95% confidence interval, 0.51 to 0.95), respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Most dogs in this study affected with PLE, PLN, or both had positive results for pANCAs before clinicopathologic evidence of disease was detected. Thus, pANCAs may be useful as an early noninvasive test of disease in SCWTs.

Isolation, culture, and characterization of canine Sertoli cells.

Primary Sertoli cell cultures have been established from several animals including the sheep and rhesus monkey; however, not for the domestic dog, Canis familiaris. Sertoli cells are the only readily accessible cell type in the body which expresses all six type IV collagens. These collagens play key roles in tissue structure, basement membrane formation, and filtration. The study of these genes is necessary to determine their exact roles and regulation in the aforementioned functions and to investigate diseases associated with mutations in these genes. For such studies, a cell culture system is a requisite tool. Therefore, Sertoli cells were targeted, and a culture was established from cells isolated from canine testes. Cultures maintained consistent morphology and steady growth for up to seven passages. Cultured cells were identified as Sertoli cells through positive Western blot results for SOX9 and Clusterin B proteins and transcript sequence verification of SOX9 as well as the presence of type IV collagen transcripts. Primary cultures of canine Sertoli cells will provide a useful tool for study of the function and regulation of collagen genes and will permit new research pertaining to canine health while also serving as a model for the study of human diseases.

Genetic cause of autosomal recessive hereditary nephropathy in the English Cocker Spaniel.

BACKGROUND: Autosomal recessive hereditary nephropathy (ARHN) in the English Cocker Spaniel is caused by a type IV collagen defect, but the underlying mutation is unknown. ANIMALS: One hundred thirty-four English Cocker Spaniels (12 with ARHN, 8 obligate carriers, and 114 others), 3 mixed breed dogs with X-linked hereditary nephropathy (XLHN), and 7 other dogs without hereditary nephropathy were included. METHODS: Diagnosis of ARHN was based on transmission electron microscopy and immunostaining of kidney. Quantitative real time reverse transcriptase polymerase chain reaction (qRT-PCR) was used to compare COL4A3, COL4A4, and COL4A5 mRNA concentrations in the renal cortex from ARHN-affected English Cocker Spaniels, XLHN-affected dogs, and dogs without hereditary nephropathy. The entire coding region of COL4A4 was sequenced in 2 ARHN-affected dogs, 2 obligate carriers, 2 English Cocker Spaniels of unknown status, and 2 healthy mixed breed dogs. The exon containing the mutation was sequenced for all 134 English Cocker Spaniels. RESULTS: Quantitative real time RT-PCR implicated COL4A4 as the gene harboring the mutation, and sequencing identified a single nucleotide substitution at base 115 as the cause of ARHN in English Cocker Spaniels. This mutation, which causes a premature stop codon in exon 3 of COL4A4, was segregated with clinical status in all affected dogs and obligate carriers. The mutation also was identified in 39 of 114 other English Cocker Spaniels with previously unknown status. CONCLUSIONS AND CLINICAL IMPORTANCE: The cause of this disease has been identified, and use of a test for the mutation will permit eradication of ARHN in the English Cocker Spaniel.

Day-to-Day variation of the urine protein: creatinine ratio in female dogs with stable glomerular proteinuria caused by X-linked hereditary nephropathy.

BACKGROUND: Interpretation of serial urine protein:creatinine (UPC) values is confounded by a lack of data regarding random biologic variation of UPC values in dogs with stable glomerular proteinuria. HYPOTHESIS: That there is minimal day-to-day variability in the UPC of dogs with unchanging proteinuria and the number of measurements needed to reliably estimate UPC varies with the magnitude of proteinuria. ANIMALS: Forty-eight heterozygous (carrier) female dogs with X-linked hereditary nephropathy (XLHN) causing stable proteinuria. METHODS: Urine samples were obtained daily by cystocentesis for 3 consecutive days on 183 occasions (549 samples). The UPC was measured for each sample with a single dry-film chemistry auto-analyzer. Data were analyzed retrospectively by a power of the mean model because the variance of UPC values within the 3-day evaluation periods increased as the magnitude of proteinuria increased. RESULTS: To demonstrate a significant difference (P < .05) between serial values in these proteinuric dogs, the UPC must change by at least 35% at high UPC values (near 12) and 80% at low UPC values (near 0.5). One measurement is adequate to reliably estimate the UPC when UPC <4, but 2-5 determinations are necessary at higher UPC values. CONCLUSIONS AND CLINICAL IMPORTANCE: These guidelines for interpretation of serial UPC values in female dogs with XLHN may also be helpful for interpretation of UPC values in dogs with other glomerulopathies.

Gene expression analysis in a canine model of X-linked Alport syndrome.

Chronic kidney disease (CKD) often culminates in renal failure as a consequence of progressive interstitial fibrosis and is an important cause of illness and death in dogs. Identification of disease biomarkers and gene expression changes will yield valuable information regarding the specific biological pathways involved in disease progression. Toward these goals, gene expression changes in the renal cortex of dogs with X-linked Alport syndrome (XLAS) were examined using microarray technology. Extensive changes in inflammatory, metabolic, immune, and extracellular matrix biology were revealed in affected dogs. Statistical analysis showed 133 genes that were robustly induced or repressed in affected animals relative to age-matched littermates. Altered expression of numerous major histocompatibility complex (MHC) molecules suggests that the immune system plays a significant role in XLAS. Increased expression of COL4A1 and TIMP-1 at the end stage of disease supports the suggestion that expression increases in association with progression of fibrosis and confirms an observation of increased COL4A1 protein expression. Clusterin may function as one of the primary defenses of the renal cortex against progressive injury in dogs with XLAS, as demonstrated here by increased CLU gene expression. Cellular mechanisms that function during excess oxidative stress might also act to deter renal damage, as evidenced by alterations in gene expression of SOD1, ACO1, FDXR, and GPX1. This investigation provides a better understanding of interstitial fibrosis pathogenesis, and potential biomarkers for early detection, factors that are essential to discovering more effective treatments thereby reducing clinical illness and death due to CKD.