Canine cutaneous and renal glomerular vasculopathy (CRGV) is a disease of unknown aetiology, which carries a mortality rate of 94.2%. Since the first reported case of CRGV in the UK in 2012, 324 dogs have died from clinical complications associated with CRGV. To date, studies have focused on clinical pathology and disease incidence, with only a single publication describing an experimental treatment regimen. The lack of knowledge on CRGV has contributed to the limited development of effective treatments. Thus, the studies presented in this thesis aimed to investigate the pathobiology of CRGV by characterising both the gut microbiota and metabolomic profiles and detecting anti-neutrophilic cytoplasmic antibody (ANCA) serotypes and endothelial cells associated with vascular dysfunction in CRGV-affected dogs compared to medically healthy and non-CRGV-associated acute kidney injury (AKI) dogs.

The gut microbiota of CRGV-affected (n = 104) and medically healthy (n = 96) samples were profiled using 16S rRNA amplicon sequencing on faeces, which revealed distinct microbial shifts in the taxonomic profile family during disease. CRGV-affected samples had statistically significantly (p = 0.05) more Enterobacteriaceae, Enterococcaceae, Anaeroplasmataceae and less Veillonellaceae, compared to medically healthy samples. Proton nuclear magnetic resonance was used to profile the gut metabolome of CRGV-affected samples (n = 75) compared to medically healthy samples (n = 97), which revealed that CRGV faecal samples contained significantly (p = 0.01) higher levels of choline and some amino acids (e.g., lysine, valine, leucine), accompanied by a decrease in the short-chain fatty acid propionic acid, compared to healthy control samples. A comparison between the bacterial families and metabolites significantly associated with CRGV revealed no clear microbiota-metabolite associations, however, a clear metabolite-metabolite association between amino acids (e.g., lysine, alanine, valine, leucine) was observed. The findings demonstrate that CRGV-affected dogs have altered gut bacterial abundance and diversity, and an altered metabolome indicative of early onset and/ or prolonged starvation.

Two studies were carried out to measure the percentages of circulating and progenitor endothelial cells (CECs, EPCs) and the concentration of ANCA serotypes associated with vascular dysfunction in CRGV- affected blood samples, compared to medically healthy and non-CRGV-associated AKI samples. Multicolour flow cytometry was utilised to detect the percentage of CECs and EPCs in CRGV-affected (n = 4), medically healthy (n = 56), and non-CRGV-associated AKI (n = 12) samples; and a sandwich enzyme linked immunosorbent assay was used to detect myeloperoxidase and proteinase 3 ANCA in the three respective cohorts (n = 55; n = 10; n = 15, respectively). The results demonstrated no clear associations with the percentage of CECs and EPCs nor ANCA concentrations across the three cohorts, possibly due to low sample sizes.

The studies presented in this thesis provide novel information regarding the pathobiology of CRGV, and the potential for early onset and/ or prolonged starvation to impact the glomerular filtration rate of the kidneys, which are already documented to be reduced due to AKI. These findings can be used to improve the treatment options for CRGV in an attempt to reduce disease mortality.