Pathological alteration and caspase-dependent activity of feline kidneys in natural infection of feline morbillivirus

Abstract

Background: Feline morbillivirus (FeMV) has been associated with renal pathology in cats; however, the specific pathological alterations caused by FeMV infection remain controversial. This study aimed to investigate histopathological changes, viral localization, and apoptotic activity in the kidneys of FeMV-infected cats.

Methods: Kidney tissues from 150 deceased cats with suspected or confirmed chronic kidney disease (CKD) were screened for FeMV using conventional reverse-transcription PCR (cRT-PCR). Positive cases were genotyped and quantified for viral load using reverse-transcription digital PCR (RT-dPCR). A control group of nine FeMV-negative kidneys with CKD was included for comparison. Histological evaluation was conducted using hematoxylin and eosin (H&E), periodic acid-Schiff (PAS), and Masson's trichrome staining. Immunohistochemistry (IHC) and in situ hybridization (ISH) were employed to localize viral antigens and assess expression of apoptotic markers, including cleaved caspase-3 (cCasp3), B-cell lymphoma 2 (BCL-2), and BCL-2-associated X protein (BAX).

Results: FeMV RNA was detected in 6% (9/150) of kidneys, all classified as genotype 1. Histological findings in FeMV-positive cases included eosinophilic intracytoplasmic inclusion bodies, lymphoplasmacytic tubulointerstitial nephritis (TIN) and varying degrees of fibrosis. FeMV antigens were localized in the renal tubular epithelial cells. Statistically, cCasp3 expression (P = 0.005) and interstitial fibrosis (P = 0.040) were significantly higher in FeMV-positive cases than in FeMV-negative controls. No significant differences were observed for TIN, BAX, or BCL-2 expression (P > 0.05). Among FeMV-positive cases, viral load was significantly associated with cCasp3 expression (P = 0.049), but not with TIN, fibrosis, BAX, or BCL-2 expression. Spearman's correlation revealed a strong positive correlation between viral load and cCasp3 expression (ρ = 0.8222, P = 0.007).

Conclusions: FeMV infection in cats was associated with increased caspase-3-mediated apoptotic activity and interstitial fibrosis in kidney tissue, particularly in cases with higher viral loads. While these findings suggest a possible role for FeMV in renal injury, the absence of consistent associations with other apoptotic markers and inflammatory parameters indicates that additional factors may contribute to disease progression. Further studies, including longitudinal and experimental investigations, are needed to clarify the pathogenic mechanisms and the clinical relevance of FeMV in feline kidney disease.

Keywords: Apoptosis; Caspase-3; Chronic kidney disease; Feline morbillivirus; Kidney pathology.

Fig. 1

Feline morbillivirus (FeMV) infection. Kidney. Case 7. Hematoxylin and eosin (HE) (a-c), in situ hybridization (ISH) (d-f), immunohistochemistry (IHC) (g-i). Insets indicate an overview of kidney section of each investigation panel, and white squares indicate areas where examined. Black squares indicate a higher magnification where presented in a subsequent figure. (a) Multifocal renal tubular necrosis. (b) Focal lymphoplasmacytic interstitial nephritis (white arrow). (c) Renal tubular necrosis with eosinophilic intracytoplasmic inclusion bodies (ICIBs). (d) Multifocal labelling (purple chromogens) of FeMV probe in renal tubules. (e) ISH signals label ICIBs of renal tubular epithelial cells. (f) No hybridization signal presents in the slide incubation with an unrelated probe. (g) FeMV matrix antigens (brown chromogen) are identified in the cytoplasm of renal tubules. (h) The IHC-against FeMV labels the ICIBs. (i) There is no reaction presented in the slide incubation with normal rabbit IgG antibody

Fig. 2

Feline morbillivirus (FeMV) infection. Kidney. Cats. (a) Tubular integrity represented by intact tubular basement membrane. Inset: the presence of membranoproliferative glomerulonephritis (MPGN). Case 5. Periodic acid-Schiff (PAS). (b) Renal interstitial fibrosis. Fibrous tissue infiltrating renal parenchyma with minimal tubular atrophy. Case 4. Masson’s Trichrome (MT)

Fig. 3

Feline morbillivirus (FeMV) infection. Kidney. Cat. (a) Nuclei of tubular epithelial cells exhibiting immunostaining signals against FeMV-M protein (arrows). Immunostaining is also present in the ICIBs of tubular epithelial cells. Case 5. Immunohistochemistry (IHC). (b) Intense in situ hybridization (ISH) signals observed in the nuclei of tubular epithelial cells. Case 5. ISH. (c) Immunostaining signal for cleaved caspase-3 (cCasp3) observed in the nuclei of epithelial cells. Case 5. IHC. (d) No immunostaining signal for cCasp3 detected in FeMV-negative kidney (control group) obtained from chronic kidney disease (CKD)-cat. Case 13. IHC. (e) Intense brown chromogen labelled BAX expression observed in the cytoplasm of tubular epithelial cells within intact tubules. Case 5. IHC. (f) Few chromogen deposits marking weak BCL-2 expression in a FeMV-positive case. Case 5. IHC

Fig. 4

Feline morbillivirus (FeMV) infection. Kidney. Case 8. Dual labelling. (a) Co-labelling of apoptotic activities markers (cCasp3, purple chromogen) and FeMV-M protein (brown chromogen). The nucleus of renal epithelial cells displayed cCasp3 expression generating dark purple color, with slight cytoplasmic immunoreaction against the FeMV-M protein (inset). (b) Co-labelling of apoptotic activities markers (BAX, purple chromogen) and FeMV-M protein (brown chromogen). The cytoplasm of renal epithelial cells co-expressed BAX and FeMV-M protein, generating reddish-purple color in some tubules. Bars indicate 100 μm