Changes in Renal Peritubular Capillaries in Canine and Feline Chronic Kidney Disease

Apoptosis in kidney tissue of senior and geriatric cats with chronic kidney disease

Apoptosis, an important pathological event associated with kidney disease progression, is expected to be a therapeutic target in chronic kidney disease (CKD). However, its role in naturally occurring CKD in aged cats remains unclear. Therefore, here, we investigated kidney tissues from aged cats (≥10 years) with or without azotemic CKD to evaluate apoptotic events using a terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL) assay. The positive TUNEL signals of the renal cells were quantified and statistically analyzed for correlation with the severity of plasma creatinine (pCre) concentration, renal lesions (glomerulosclerosis, interstitial cell infiltration, peritubular capillaries, and interstitial fibrosis), and oxidative damage of the kidney tissue. Oxidative damage was evaluated using immunohistochemistry for 8-hydroxy-2'-deoxyguanosine (OHdG) and 4-hydroxynonenal (HNE). In the TUNEL assay, regardless of azotemia, positive nuclear signals were observed in the tubular epithelial and intraluminal cells, interstitial infiltrating cells, and glomerular cells. Quantitative TUNEL scores showed no significant differences between the azotemic and non-azotemic groups in any compartment of the kidney tissues. In the azotemic group, TUNEL scores did not correlate with pCre or renal lesion severity. However, the scores showed a significant positive correlation with the scores of 8-OHdG and 4-HNE. These findings suggest that apoptosis associated with oxidative damage in renal tissue is an initial pathological event that leads to CKD, rather than a change following CKD progression, in aged cats. Inhibiting apoptosis by antioxidant treatment may be a key strategy to prevent the development of CKD.

Feline hypertrophic cardiomyopathy: reduced microvascular density and involvement of CD34+ interstitial cells

The sequence of pathological events in feline hypertrophic cardiomyopathy (fHCM) is still largely unknown, although we know that fHCM is characterized by interstitial remodeling in a macrophage-driven pro-inflammatory environment and that myocardial ischemia might contribute to its progression. This study aimed to gain further insights into the structural changes associated with interstitial remodeling in fHCM with special focus on the myocardial microvasculature and the phenotype of the interstitial cells. Twenty-eight hearts (16 hearts with fHCM and 12 without cardiac disease) were evaluated in the current study, with immunohistochemistry, RNA-in situ hybridization, and transmission electron microscopy. Morphometrical evaluations revealed a statistically significant lower microvascular density in fHCM. This was associated with structural alterations in capillaries that go along with a widening of the interstitium due to the accumulation of edema fluid, collagen fibers, and mononuclear cells that also proliferated locally. The interstitial cells were mainly of fibroblastic or vascular phenotype, with a substantial contribution of predominantly resident macrophages. A large proportion expressed CD34 mRNA, which suggests a progenitor cell potential. Our results indicate that microvascular alterations are key events in the pathogenesis of fHCM and that myocardial interstitial cell populations with CD34+ phenotype play a role in the pathogenesis of the disease.

Hypoxia and chronic kidney disease: Possible mechanisms, therapeutic targets, and relevance to cats

There is mounting evidence that kidney ischaemia/hypoxia plays an important role in feline chronic kidney disease (CKD) development and progression, as well as in human disease and laboratory animal models. Ischaemic acute kidney injury is widely accepted as a cause of CKD in people and data from laboratory species has identified some of the pathways underlying this continuum. Experimental kidney ischaemia in cats results in morphological changes, namely chronic tubulointerstitial inflammation, tubulointerstitial fibrosis, and tubular atrophy, akin to those observed in naturally-occurring CKD. Multiple situations are envisaged that could result in acute or chronic episodes of kidney hypoxia in cats, while risk factors identified in epidemiological studies provide further support that kidney hypoxia contributes to spontaneously occurring feline CKD. This review evaluates the evidence for the role of kidney ischaemia/hypoxia in feline CKD and the proposed mechanisms and consequences of kidney hypoxia. As no effective treatments exist that substantially slow or prevent feline CKD progression, there is a need for novel therapeutic strategies. Targeting kidney hypoxia is one such promising approach, with therapies including those that attenuate the hypoxia-inducible factor (HIF) pathway already being utilised in human CKD.

Renal Infiltration of Macrophages in Canine and Feline Chronic Kidney Disease

During the progression of chronic kidney disease (CKD), macrophage infiltration is a crucial event leading to tubulointerstitial fibrosis. In the present study, macrophages infiltrating renal tissue in dogs and cats with CKD were analysed immunohistochemically. Iba-1 was used as a pan-macrophage marker, CD204 was used as a marker of M2 macrophages and tumour necrosis factor (TNF)-α was used as a marker of M1 macrophages. Signals for Iba1 and CD204 were observed in the interstitium of all tested kidney samples. In dogs, the signals were diffusely scattered. In cats, both diffuse and focal signals were observed. Cells that were positive for Iba1 and CD204 were also observed in the tubular lumina in cats. Co-expression of Iba1 and CD204 was also observed in the infiltrating cells by immunofluorescence labelling, and these cells were negative for TNF-α. By quantitative analysis, the indices for Iba1- and CD204-positive cells were significantly correlated with the concentrations of plasma creatinine and/or urea and the extent of interstitial fibrosis in both dogs and cats. These results demonstrated that renal infiltration of M2 macrophages plays an important role in the progression of CKD in dogs and cats. The distribution pattern of the kidney-infiltrating macrophages was unique in cats and may be associated with a cat-specific renal fibrotic process.