Renal a-klotho functions as a co-receptor for fibroblast growth factor 23 (FGF-23) and therefore plays an important role in phosphate homeostasis. The transmembrane protein is primarily found in the renal tubules and its expression is reduced in patients with chronic kidney disease (CKD). In human studies and animal models, a-klotho deficiency has been associated with hyperphosphataemia, renal fibrosis, and increased mortality. Chronic kidney disease is a common disorder in ageing cats, with hyperphosphataemia and FGF-23 excess as important prognostic indicators, but the role of a-klotho has not been assessed in cats to date. Therefore, we aimed to localize renal a-klotho protein in feline kidney tissue.

Formalin-fixed paraffin-embedded sections of post-mortem kidney tissue from cats with varying kidney function were immunohistochemically stained using a rabbit polyclonal anti-a-klotho antibody (1:2000 dilution, anti-klotho antibody, ab203576, Abcam, Cambridge, UK) and visualized with an immunoenzymatic antigen detection system (rabbit specific HRP/DAB detection kit, ab64261, Abcam, Cambridge, UK). Mouse kidney sections were used as a positive control, and feline kidney sections incubated with isotype-specific immunoglobulins as a substitute for the primary antibody served as a negative control for staining specificity. Sections were counterstained with hematoxylin. Western blot analysis was performed on feline renal tubular cell lysate to assess molecular size of the antibody-bound protein.

Western blot analysis showed the primary antibody bound a single antigen of 120–130 kDa in size, which is the appropriate molecular size for a-klotho. No positive staining was detected in the negative isotype control sections, confirming the specificity of the staining for a-klotho. Alpha-klotho protein expression was identified immunohistochemically both in the proximal and distal tubules of murine and feline kidney tissue, with more intense staining of the distal tubules compared to the proximal tubules.

Renal a-klotho protein expression in cats shows similarities to its expression reported in other species. Further work is necessary to investigate if loss of a-klotho expression occurs in feline CKD and how this relates to renal fibrosis and mineral and bone disorder in cats with CKD.

Disclosures

Disclosures to report:

D.H.N. van den Broek, J.S. Lawson and Y.-M. Chang have no conflicts of interest to declare. J. Elliott received funding from Consultancies: Elanco Ltd, CEVA Animal Health Ltd, Boehringer Ingelheim Ltd, Bayer Animal Health, Orion Incorp, Idexx Ltd, Nextvet Ltd, Waltham Centre for Pet Nutrition; grant funding from Elanco Ltd, Waltham Centre for Pet Nutrition, Royal Canin Ltd, Zoetis Ltd, CEVA Animal Health, Member of the International Renal Interest Society which receives a grant from Elanco Ltd. R. Jepson received funding from PetPlan, Feline Foundation for Renal Research, RVC Internal Grant, PetSavers, and consultancy agreements: Boehringer Ingelheim, Merial. Speaking honoraria: Boehringer Ingelheim, Hills Pet Nutrition.