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-β1 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.

Glomerular Lesions in Proteinuric Miniature Schnauzer Dogs

Miniature Schnauzer dogs are predisposed to idiopathic hypertriglyerceridemia, which increases risk for diseases such as pancreatitis and gallbladder mucocele. Recently, elevated triglyceride concentrations have been associated with proteinuria in this breed, although it is difficult to determine which abnormality is primary. Retrospective review of renal tissue from 27 proteinuric Miniature Schnauzers revealed that 20 dogs had ultrastructural evidence of osmophilic globules consistent with lipid in glomerular tufts. Seven of these dogs had lipid thromboemboli in glomerular capillary loops that distorted their shape and compressed circulating erythrocytes. Triglyceride concentrations were reported in 6 of these 7 dogs, and all were hypertriglyceridemic. In addition, glomerular lipidosis (defined as accumulation of foam cells within peripheral capillary loops) was identified in a single dog. The remaining 12 dogs had smaller amounts of lipid that could only be identified ultrastructurally. Neither signalment data nor clinicopathologic parameters (serum albumin, serum creatinine, urine protein-to-creatinine ratio, and blood pressure) differed among the various types of lipid lesions. During the time course of this study, all dogs diagnosed with glomerular lipid thromboemboli were Miniature Schnauzers, underscoring the importance of recognizing these clear spaces within capillary loops as lipid.

X-Linked Hereditary Nephropathy in Navasota Dogs: Clinical Pathology, Morphology, and Gene Expression During Disease Progression

X-linked hereditary nephropathy (XLHN) in Navasota dogs is a spontaneously occurring disease caused by a mutation resulting in defective production of type IV collagen and juvenile-onset renal failure. The study was aimed at examining the evolution of renal damage and the expression of selected molecules potentially involved in the pathogenesis of XLHN. Clinical data and renal samples were obtained in 10 XLHN male dogs and 5 controls at 4 (T0), 6 (T1), and 9 (T2) months of age. Glomerular and tubulointerstitial lesions were scored by light microscopy, and the expression of 21 molecules was investigated by quantitative real-time polymerase chain reaction with selected proteins evaluated by immunohistochemistry. No significant histologic lesions or clinicopathologic abnormalities were identified in controls at any time-point. XLHN dogs had progressive proteinuria starting at T0. At T1, XLHN dogs had a mesangioproliferative glomerulopathy with glomerular loss, tubular necrosis, and interstitial fibrosis. At T2, glomerular and tubulointerstitial lesions were more severe, particularly glomerular loss, interstitial fibrosis, and inflammation. At T0, transforming growth factor β, connective tissue growth factor, and platelet-derived growth factor α mRNA were overexpressed in XLHN dogs compared with controls. Clusterin and TIMP1 transcripts were upregulated in later stages of the disease. Transforming growth factor β, connective tissue growth factor, and platelet-derived growth factor α should be considered as key players in the initial events of XHLN. Clusterin and TIMP1 appear to be more associated with the progression rather than initiation of tubulointerstitial damage in chronic renal disease.

Correlation of Urine and Serum Biomarkers with Renal Damage and Survival in Dogs with Naturally Occurring Proteinuric Chronic Kidney Disease

Background

Urine protein loss is common in dogs with chronic kidney disease (CKD).

Hypothesis/Objectives

To evaluate new biomarkers of glomerular and tubulointerstitial (TI) damage compared with histology and as survival indicators in dogs with naturally occurring, proteinuric CKD.

Animals

One hunderd and eighty dogs with naturally occurring kidney disease.

Methods

Retrospective study using urine, serum, and renal biopsies from dogs with kidney disease, 91% of which had proteinuric CKD. Biomarkers were evaluated and correlated with pathologic renal damage, and significant associations, sensitivities, and specificities of biomarkers for renal disease type were determined.

Results

Fractional excretions of immunogloblin M (IgM_FE) and immunoglobulin G (IgG_FE) correlated most strongly with glomerular damage based on light microscopy (r = 0.58 and 0.56, respectively; P < .01). Serum creatinine (SCr) correlated most strongly with TI damage (r = 0.70, P < .01). Urine IgM/creatinine and urine NAG/creatinine had the highest sensitivity (75%) and specificity (78%) for detection of immune complex‐mediated glomerulonephritis. Although individually most biomarkers were significantly associated with decreased survival time (P < .05), in a multivariate analysis, SCr, IgM_FE, and glomerular damage based on transmission electron microscopy (TEM) were the only biomarkers significantly associated with survival time (SCr: P = .001; IgM_FE: P = .008; TEM: P = .017).

Conclusions and Clinical Importance

Novel urine biomarkers and FEs are useful for detection of glomerular and TI damage in dogs with proteinuric CKD and might predict specific disease types and survival.

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.

Symmetric Dimethylarginine Assay Validation, Stability, and Evaluation as a Marker for the Early Detection of Chronic Kidney Disease in Dogs

BACKGROUND

Symmetric dimethylarginine (SDMA) is a small molecule formed by methylation of arginine, and released into blood during protein degradation. SDMA is primarily eliminated by renal excretion and is a promising endogenous marker of glomerular filtration rate (GFR).

OBJECTIVES

To validate an assay for SDMA measurement, determine stability of SDMA in blood, and compare SDMA with serum creatinine concentration (sCr) and GFR for early detection of decreasing kidney function in dogs with chronic kidney disease (CKD).

ANIMALS

Eight male dogs affected with X-linked hereditary nephropathy and 4 unaffected male littermates.

METHODS

Prospective study validating SDMA measurement using liquid chromatography-mass spectrometry, assessing stability of SDMA in serum and plasma, and serially determining sCr, SDMA, and GFR (using iohexol clearance) in dogs during progression from preclinical disease to end-stage renal failure. Correlations were determined using linear regression. Timepoints at which sCr, SDMA, and GFR identified decreased renal function were compared using defined cutoffs, trending in an individual dog, and comparison with unaffected littermates.

RESULTS

Symmetric dimethylarginine was highly stable in serum and plasma, and the assay demonstrated excellent analytical performance. In unaffected dogs, SDMA remained unchanged whereas in affected dogs, SDMA increased during disease progression, correlating strongly with an increase in sCr (r = 0.95) and decrease in GFR (r = -0.95). Although trending improved sCr's sensitivity, SDMA identified, on average, <20% decrease in GFR, which was earlier than sCr using any comparison method.

CONCLUSIONS AND CLINICAL IMPORTANCE

Symmetric dimethylarginine is useful for both early identification and monitoring of decreased renal function in dogs with CKD.

World Small Animal Veterinary Association Renal Pathology Initiative: Classification of Glomerular Diseases in Dogs

Evaluation of canine renal biopsy tissue has generally relied on light microscopic (LM) evaluation of hematoxylin and eosin-stained sections ranging in thickness from 3 to 5 µm. Advanced modalities, such as transmission electron microscopy (TEM) and immunofluorescence (IF), have been used sporadically or retrospectively. Diagnostic algorithms of glomerular diseases have been extrapolated from the World Health Organization classification scheme for human glomerular disease. With the recent establishment of 2 veterinary nephropathology services that evaluate 3-µm sections with a panel of histochemical stains and routinely perform TEM and IF, a standardized objective species-specific approach for the diagnosis of canine glomerular disease was needed. Eight veterinary pathologists evaluated 114 parameters (lesions) in renal biopsy specimens from 89 dogs. Hierarchical cluster analysis of the data revealed 2 large categories of glomerular disease based on the presence or absence of immune complex deposition: The immune complex-mediated glomerulonephritis (ICGN) category included cases with histologic lesions of membranoproliferative or membranous patterns. The second category included control dogs and dogs with non-ICGN (glomerular amyloidosis or focal segmental glomerulosclerosis). Cluster analysis performed on only the LM parameters led to misdiagnosis of 22 of the 89 cases-that is, ICGN cases moved to the non-ICGN branch of the dendrogram or vice versa, thereby emphasizing the importance of advanced diagnostic modalities in the evaluation of canine glomerular disease. Salient LM, TEM, and IF features for each pattern of disease were identified, and a preliminary investigation of related clinicopathologic data was performed.

Consensus recommendations for the diagnostic investigation of dogs with suspected glomerular disease

BACKGROUND

The International Renal Interest Society (IRIS) offers guidelines for chronic kidney disease and acute kidney injury. As dogs with glomerular disease may present differently and require different treatment than those with whole nephron or tubular disease, the IRIS Canine Glomerulonephritis (GN) Study Group was convened to formulate guidelines for these cases. The Diagnosis Subgroup was asked to make recommendations for diagnostic evaluation of such cases.

OBJECTIVE

To seek consensus among renal specialists for the evaluation of dogs with proteinuria because of suspected glomerular disease.

METHODS

After reviewing the literature, subgroup members discussed and wrote the draft paper and recommendations, which members of the IRIS Canine GN Study Group voted upon by electronic secret ballot, with comments noted. Consensus was declared if votes showed strong or general agreement from 85% of the respondents.

RESULTS

Diagnostic tests were categorized as essential, recommended, or potentially helpful, with prioritization dependent on case characteristics, eg, for cases with uncomplicated proteinuria versus complicated with hypoalbuminemia, azotemia, or both. Consensus was reached with 86-100% agreement on all questions posed. All cases should have basic examinations including blood pressure measurement, blood, and urine testing, and a search for infectious diseases relevant to their environs. The majority ranked imaging (chest radiographs, abdominal ultrasonogram) and renal biopsy procured and interpreted by experienced personnel as essential evaluations in complicated cases, but a few respondents deemed these to be essential in uncomplicated cases as well.

CONCLUSIONS AND CLINICAL IMPORTANCE

Strong consensus about recommendations for diagnostic evaluation of dogs with suspected glomerular protein loss was attained. These guidelines help clinicians characterize disease processes for more informed therapeutic decision-making.

Epithelial mesenchymal transition in the progression of renal disease in dogs

Chronic kidney disease (CKD) in dogs is the final common pathway resulting from persistent renal injury and is characterized by progressive tubulointerstitial damage (TID). Pathogenesis of CKD is divided into an initial inflammatory phase with a predominantly mononuclear infiltrate followed by a fibrotic phase with increased numbers of fibroblasts and extracellular matrix deposition that causes a progressive reduction of functional parenchyma. Proteinuria is a common manifestation of renal diseases in dogs, and its role in the pathogenesis of CKD is still uncertain. Nevertheless, the degree of proteinuria in dogs correlates with TID progression. Increased protein filtration may have direct effects on tubular epithelial cells (TECs) that induce them to express the major histocompatibility complex type II, and thereby contribute to lymphocyte recruitment. Thus, an active pro-inflammatory role is proposed for TECs in TID progression. Moreover TECs are believed to actively participate in the mechanisms of renal fibrosis. Epithelial-Mesenchymal-Transition (EMT) of TECs in canine TID has been studied in the last decade. Down-regulation of adhesion molecules and loss of epithelial markers in TECs directly correlate with the severity of TID and with de novo expression of mesenchymal markers. Tubular basement membrane (TBM) disruption is an early EMT event. Increased activity of Matrix Metalloproteinase-2 and its co-localization with TBM splitting suggests an active role for the enzyme in inducing EMT. Processes occurring in canine CKD share many similarities with its human counterpart, making the dog a good model in which to examine the mechanisms of TID progression.

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.

Characterization of the genetic basis for autosomal recessive hereditary nephropathy in the English Springer Spaniel

BACKGROUND

Autosomal recessive hereditary nephropathy (ARHN) was diagnosed in 2 English Springer Spaniels (ESS), a breed not previously reported to be affected by hereditary nephropathy (HN).

OBJECTIVE

To identify and characterize the genetic cause of ARHN in ESS.

ANIMALS

Sixty-three ESS (2 with ARHN, 2 obligate carriers, and 59 others), 2 mixed-breed dogs with X-linked HN, and 2 English Cocker Spaniels (ECS) with ARHN were included.

METHODS

ARHN was diagnosed based on transmission electron microscopy and immunostaining of kidney. DNA from affected dogs was screened for the mutation known to cause ARHN in ECS. Quantities of COL4A3, COL4A4, and COL4A5 mRNA transcripts in renal cortex were determined using quantitative reverse transcription-polymerase chain reaction (qRT-PCR) for ARHN-affected dogs and 7 other dogs. The coding regions of COL4A3 and COL4A4 were sequenced for the 2 ARHN-affected ESS and an unaffected dog. Exon 30 of COL4A4 was sequenced for all 63 ESS.

RESULTS

qRT-PCR indicated a significant reduction in transcript levels of both COL4A3 and COL4A4 mRNA in the kidney of ARHN-affected ESS. Sequencing identified a single nucleotide substitution in COL4A4 at base 2806 resulting in a premature stop codon. Thirteen of 25 related dogs were identified as carriers.

CONCLUSIONS AND CLINICAL IMPORTANCE

A mutation highly likely to cause ARHN in ESS has been identified.

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.

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.

X chromosome inactivation patterns in normal and X-linked hereditary nephropathy carrier dogs

Alport syndrome (AS) and hereditary nephropathy (HN) are glomerular nephropathies caused by mutations in the genes encoding the type IV collagens. In a mixed breed of dog, termed Navasota (NAV) dogs, X-linked hereditary nephropathy (XLHN) is caused by a 10-bp deletion in exon 9 of COL4A5. Males harboring this mutation succumb to end-stage renal disease before 18 months of age. In contrast, female carriers of this disease survive much longer, most have a normal life-span, and vary in disease progression as compared with XLHN-affected males. X chromosome inactivation (XCI) patterns have been studied in human X-linked AS carriers and some have been shown to have a high degree of skewed XCI. However, similar studies have never been reported in an animal model of this disease. Therefore, patterns of XCI were examined in XLHN-carrier NAV dogs. The variation in XCI among the 26 XLHN-carrier and seven normal female NAV dogs studied was low and only three were found to preferentially inactivate one X chromosome, all of which were XLHN-carriers. The average skewedness among all dogs was 59% and 57% among the XLHN-carriers. No significant difference in XCI was found between the two groups (P = 0.477). It is clear from these data that genotype does not seem to have an effect on inactivation; the majority of these dogs have random patterns of XCI. Highly skewed X chromosome inactivation also appears to be random, given that no difference was observed between the XLHN-carriers and normal females. Because of the apparent rarity of skewed XCI, these dogs may not be a suitable model for studying a potential correlation between this phenomenon and disease progression.

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.

Renal biopsy: a retrospective study of methods and complications in 283 dogs and 65 cats

Renal biopsy often is required to establish a definitive diagnosis in dogs and cats with renal disease. In this retrospective study, we determined the complications of renal biopsy as well as factors that may be associated with development of complications and procurement of adequate renal biopsy specimens in 283 dogs and 65 cats. Data extracted from medical records at 4 institutions were evaluated using logistic regression. Proteinuria was the most common indication for renal biopsy in dogs. Complications were reported in 13.4 and 18.5% of dogs and cats, respectively. The most common complication was severe hemorrhage; hydronephrosis and death were uncommon. Dogs that developed complications after renal biopsy were more likely to have been 4 to < 7 years of age and > 9 years, to weigh < or = 5 kg, and to have serum creatinine concentrations > 5 mg/dL. The majority of biopsies from both dogs (87.6%) and cats (86.2%) were considered to be of satisfactory quality. Biopsies from dogs were more likely to be of high quality if they were obtained when the patient was under general anesthesia and more likely to contain only renal cortex if they were obtained by surgery. We concluded that renal biopsy is a relatively safe procedure, with a low frequency of severe complications. Hospital practices and patient variables have the potential to impact both the quality of the specimen obtained and the rate of complications.

EVALUATION OF 99MTC-DIETHYLENETRIAMINEPENTAACETIC ACID RENAL SCINTIGRAM CURVES IN NORMAL DOGS AFTER INDUCTION OF DIURESIS

The normal 99mTc-diethylenetriaminepentaacetic acid (DTPA) renal scintigram curve has 3 distinct phases; an arterial phase followed by progressive uptake and subsequent excretion from the kidney. In dogs with X-linked hereditary nephritis, a distinct flattening of the renal scintigram curve has been observed prior to any decline in glomerular filtration rate (GFR). The cause of this shape change is not known, however, it coincided with decreased urine-specific gravity and thus might be related to polyuria. To further evaluate this possibility, we assessed whether diuresis without concurrent renal disease could flatten the 99mTc-DTPA renal scintigram curve. GFR scintigraphy was performed in six healthy dogs once as a baseline, and again after induction of diuresis by each of four different methods. Scintigram curves were evaluated subjectively as well as quantitatively by calculation of GFR estimates, mean renal transit times, time to peak activity and half-time clearance. Complete flattening of the renal scintigram curve did not occur with diuresis alone, and therefore, flattening of the scintigram curve may serve as an early indicator of renal dysfunction. However, during diuresis after intravenous saline administration, alterations in time to peak activity and mean renal transit time may create inaccuracies in GFR estimates based on the conventional regression formula that cause a false lowering of the resultant global GFR value.

Dietary fatty acids alter plasma lipids and lipoprotein distributions in dogs during gestation, lactation, and the perinatal period

Alterations of plasma lipids and lipoproteins occur during mammalian pregnancy and reproduction. This study investigated the effects of dietary fatty acids on plasma lipid and lipoprotein alterations during canine gestation, lactation, and the neonatal period. Four diets containing varying amounts of alpha-linolenic acid relative to marine-based (n-3) long-chain fatty acids were studied and fed to dogs from the time of estrus, and throughout pregnancy and lactation. In addition, puppies born to these dams suckled and were weaned using the same diets their mothers had been fed. Plasma cholesterol (total, free, and esterified fractions) and triglycerides were determined at selected time points and lipoprotein fractions were characterized in both mothers and offspring. During gestation, plasma total cholesterol concentrations were depressed early on, then increased in the later stages independently of diet. Both beta- and alpha2-migrating lipoproteins also increased during these times. Lactation was also characterized by lower lipid and lipoprotein amounts compared with the nonpregnant state. In puppies, total plasma and beta-lipoprotein cholesterol were elevated at 4 and 10 d of age. Diet effects included cholesterol, triglyceride, and lipoprotein lowering with increased amounts of marine (n-3) fatty acids in all life stages investigated. The increase in beta-lipoprotein cholesterol in puppies during wk 1 of life is consistent with an earlier report of increased canine apoprotein B,E receptor activities in immature dogs compared with undetectable activities in mature animals in which the HDL fractions become even more predominant in this species.

Long-chain (n-3) polyunsaturated fatty acids are more efficient than alpha-linolenic acid in improving electroretinogram responses of puppies exposed during gestation, lactation, and weaning

Long-chain PUFAs (LCPUFAs) are essential for proper neural and retinal development in many mammalian species. We investigated puppies born to dogs fed diets containing varying amounts of vegetable and marine (n-3) fatty acids during gestation/lactation. The fatty acid compositions of dogs' milk and puppy plasma phospholipids were evaluated, and electroretinographic responses of the young dogs were determined after they were weaned to the same diets. Dogs' milk fatty acid composition reflected the diets fed during gestation/lactation. The milk of dogs fed a high alpha-linolenic acid (ALA) diet was enriched in ALA but not docosahexaenoic acid (DHA). Puppies fed this ALA-enriched milk accumulated more plasma phospholipid DHA than the low (n-3) fatty acid group. However, this accumulation was less than that obtained in puppies fed preformed DHA during development and suckling (P < 0.05). Electroretinograms (ERGs) of 12-wk-old puppies revealed significantly improved visual performance in dogs fed the highest amounts of (n-3) LCPUFAs (P < 0.05). These puppies demonstrated improved rod response (improved amplitude and implicit time of the a-wave, P < 0.05). Puppies from the low (n-3) fatty acid group exhibited the poorest ERG responses compared with the high-marine or high-vegetable (n-3) groups. A novel parameter devised in this study, the initial intensity at which the a-wave was detectable (i.e., threshold intensity), also demonstrated that retinal response of puppies consuming the (n-3) LCPUFA-containing diets occurred at lower light intensity, thereby exhibiting greater rod sensitivity, than the other diet groups. These findings indicate that preformed dietary (n-3) LCPUFA is more effective than ALA in enriching plasma DHA during perinatal development and results in improved visual performance in developing dogs.

Assessment and management of proteinuria in dogs and cats: 2004 ACVIM Forum Consensus Statement (small animal)

Emerging data indicate that more attention should be given to the detection, evaluation, monitoring, and treatment of dogs and cats with proteinuria. The purposes of this consensus statement are to describe an appropriate approach for accomplishing these tasks and to provide specific recommendations for assessing and managing dogs and cats with proteinuria based on data that are currently available. Because proteinuria and albuminuria have numerous possible causes, they must be assessed appropriately to determine their implications for the patient. This assessment involves localization of the origin of the proteinuria as well as determination of its persistence and magnitude. Because persistent renal proteinuria usually indicates presence of chronic kidney disease, which sometimes is a progressive disorder, its detection identifies dogs and cats that have increased risk for adverse health outcomes. Thus, urine testing that will detect proteinuria should be a component of the clinical evaluations of dogs and cats under all circumstances that prompt their veterinarians to also perform comprehensive hematologic and serum biochemical evaluations. At a minimum, this testing should consist of a complete urinalysis that includes a satisfactorily accurate semiquantitative test for protein, and positive reactions should be properly followed with further testing. The appropriate response to persistent renal proteinuria depends on the magnitude of proteinuria and the status of the patient. The recommended response generally involves continued monitoring, further investigation, and therapeutic intervention, which should be implemented as an escalating series of inclusive, stepwise responses.

Dysregulation of renal MMP-3 and MMP-7 in canine X-linked Alport syndrome

Matrix metalloproteinases (MMPs) play an important regulatory role in many biological and pathological processes and their specific role in Alport syndrome (AS) is not yet clearly defined. In this study, the naturally occurring canine X-linked AS was used to demonstrate a potential role for MMP-3 and MMP-7 in Alport renal pathogenesis. Recently, we demonstrated that the expression of MMP-2, MMP-9 and MMP-14 was upregulated in the renal cortex of dogs with a spontaneous form of XLAS. In the present study, we examined necropsy samples of renal cortex from normal and XLAS dogs for MMP-3 and MMP-7 as they have the potential to activate MMP-2 and MMP-9. Immunohistochemical analysis showed strong immunostaining for both MMP-3 and MMP-7 in the interstitial space of XLAS kidneys, while virtually no immunostaining was observed in similar fields from normal dogs. RT-PCR and casein zymography confirmed that both mRNA transcripts and activities of MMP-3 and MMP-7 are elevated in XLAS kidneys. The induction of these MMPs likely contributes to tissue destruction associated with the fibrogenic process, while augmenting the activation of MMP-2 and MMP-9 by MMP-3 and MMP-7 in XLAS. Thus, these data further implicate a role for the MMPs in progressive renal pathogenesis associated with AS.

Early diagnosis of renal disease and renal failure

The main goal of early diagnosis of renal disease and renal failure in dogs and cats is to enable timely application of therapeutic interventions that may slow or halt disease progression. Strategies for early diagnosis of renal disease use urine tests that detect proteinuria that is a manifestation of altered glomerular permselectivity or impaired urine-concentrating ability as well blood tests to evaluate plasma creatinine concentration. Animals with progressive renal disease should be carefully investigated and treated appropriately. Animals with mild, possibly nonprogressive, renal disease should be monitored adequately to detect any worsening trends,which should lead to further investigation and treatment even if the increments of change are small.

Diet modulates proteinuria in heterozygous female dogs with X-linked hereditary nephropathy

Young adult heterozygous (carrier) female dogs with X-linked hereditary nephropathy (XLHN) have glomerular proteinuria but are otherwise healthy. Because data regarding dietary influences on the magnitude of proteinuria in dogs with spontaneous glomerular disease are not available, 12 such dogs were studied in a double crossover experiment intended to determine effects of altering dietary protein intake for up to 6 weeks. Dogs were blocked by urine protein : creatinine ratio (UPC) and randomly assigned to receive 2 diets: high protein (34.6% dry matter [DM], HP) or low protein (14.1% DM, LP) fed in HP-LP-HP or LP-HP-LP sequence. Food intake was measured daily, body weight (BW) was measured twice weekly, and UPC, plasma creatinine, blood urea nitrogen, phosphorus, albumin, and protein concentrations were measured at 2-week intervals. Nutrient digestibility was measured during the third treatment period. Diet had a significant effect (P < .0001) on all measured variables except plasma phosphorus (P > .5), but unintended differences in digestibility of protein and energy (P < or = .01) prevented assignment of the diet effect exclusively to protein. Proteinuria was greater (UPC 4.7 +/- 2.2 versus 1.8 +/- 1.1, P < .0001) when the HP diet was fed, but the LP diet did not maintain starting BW or plasma albumin concentration within the normal reference range. Diet greatly affects the magnitude of proteinuria in XLHN carrier females. Dietary protein restriction can reduce proteinuria in dogs with glomerular disease, but BW and blood protein concentrations may not be maintained if the restriction is too severe.

Effects of serial ultrasound-guided renal biopsies on kidneys of healthy adolescent dogs

Ten healthy mixed-breed dogs were used to evaluate the functional and structural effects of serial ultrasound-guided renal biopsies obtained with an automated biopsy needle. In each dog, one lateral renal cortex was biopsied at 2, 4, and 6 months of age; the other kidney was the control. Five dogs had two tissue cores and five dogs had four tissue cores taken on each biopsy occasion, and one core was examined microscopically. One week before each biopsy and a month after the final biopsy, the glomerular filtration rate (GFR) was determined by renal scintigraphy. Dogs were then euthanized for evaluation of gross and microscopic lesions attributable to the biopsies. There was no difference between GFR values for biopsied kidneys and those of control kidneys (P > 0.05). Microscopic lesions were not identified in biopsies taken at 2 and 4 months, but focal lesions were found in three of 10 specimens taken at 6 months of age. At necropsy, six of 10 biopsied kidneys had small visible capsular scars, and linear tracts < 2 mm wide were observed on cut surfaces in six of 10 biopsied kidneys cut transversely into slices 5 mm thick. Discrete light microscopic lesions were observed in 25 of 452 (5.5%) of randomly selected 6-mm-diameter sections of renal cortex from biopsied kidneys. We conclude that serial renal cortical biopsies can be obtained by our method from healthy adolescent dogs with minimal risk of inducing changes that might be confused with those of a progressive renal disease.

Genetic cause of X-linked Alport syndrome in a family of domestic dogs

Alport syndrome is a hereditary disease of type IV (basement membrane) collagens that occurs spontaneously in humans and dogs. In the human, X-linked Alport syndrome (XLAS) is caused by mutations in COL4A5, resulting in absence of type IV collagen alpha5 chains from the glomerular basement membrane (GBM) of affected individuals. The consequence of this defect is progressive renal failure, for which the only available treatments are dialysis and transplantation. Recent studies support the prospect of gene transfer therapy for Alport syndrome, but further development of required technologies and demonstration of safety and efficacy must be accomplished in a suitable animal model. We previously identified and have propagated a family of mixed-breed dogs with an inherited nephropathy that exhibits the clinical, immunohistochemical, pathological, and ultrastructural features of human XLAS. To identify the causative mutation, COL4A5 cDNAs from normal and affected dogs were sequenced in their entirety. Sequence analyses revealed a 10-bp deletion in exon 9 of affected dogs. This deletion causes a frame-shift that results in a premature stop codon in exon 10. Characterization of the causative mutation was followed by development of an allele-specific test for identification of dogs in this kindred that are destined to develop XLAS.

Increased expression of MMP-2, MMP-9 (type IV collagenases/gelatinases), and MT1-MMP in canine X-linked Alport syndrome (XLAS)

BACKGROUND

Alport syndrome is a group of genetic disorders resulting from mutations in either the alpha3(IV), alpha4(IV) or alpha5(IV) collagen chains. The disease is characterized by a progressive glomerulonephritis, usually associated with a high-frequency specific sensorineural hearing loss, dot and fleck retinopathy, and lens abnormalities. Dogs with naturally occurring genetic disorders of basement membrane collagen (type IV) may serve as animal models of Alport syndrome. In this study, a well-characterized naturally occurring canine model was employed to demonstrate a potential role for matrix metalloproteinases (MMPs) in Alport renal disease pathogenesis.

METHODS

Adolescent male dogs that developed renal failure were euthanized and necropsied. Clinicopathologic features of the disease were characterized, and kidneys from normal and Alport dogs were analyzed by gelatin zymography, Western blotting, in situ zymography, immunohistology, and by reverse transcription polymerase chain reaction (RT-PCR) for expression of MMP-2, MMP-9, and membrane type 1-MMP (MT1-MMP).

RESULTS

Affected dogs developed proteinuria and rapidly progressive juvenile-onset chronic renal failure. The activities of MMP-2 and MMP-9 were significantly induced in Alport kidney. In situ zymography confirmed elevated active metalloproteinases in kidney cryosections of affected dogs. The mRNAs encoding MMP-2, MMP-9 and MT1-MMP were also increased in Alport dogs suggesting that elevated expression of MMPs reflects events in the progression of Alport syndrome in dogs.

CONCLUSION

Elevated expression of MMP-2, MMP-9, and MT1-MMP is observed in fibrotic renal cortex from X-linked Alport syndrome dogs. These findings suggest that MMPs may play an important role in matrix accumulation associated with progressive renal scarring in this model.