Comparative transcriptomic profiling of myxomatous mitral valve disease in the cavalier King Charles spaniel

Abstract

Background Almost all elderly dogs develop myxomatous mitral valve disease by the end of their life, but the cavalier King Charles spaniel (CKCS) has a heightened susceptibility, frequently resulting in death at a young age and suggesting that there is a genetic component to the condition in this breed. Transcriptional profiling can reveal the impact of genetic variation through differences in gene expression levels. The aim of this study was to determine whether expression patterns were different in mitral valves showing myxomatous degeneration from CKCS dogs compared to valves from non-CKCS dogs. Results Gene expression patterns in three groups of canine valves resulted in distinct separation of normal valves, diseased valves from CKCS and diseased valves from other breeds; the latter were more similar to the normal valves than were the valves from CKCS. Gene expression patterns in diseased valves from CKCS dogs were quite different from those in the valves from other dogs, both affected and normal. Patterns in all diseased valves (from CKCS and other breeds) were also somewhat different from normal non-diseased samples. Analysis of differentially expressed genes showed enrichment in GO terms relating to cardiac development and function and to calcium signalling canonical pathway in the genes down-regulated in the diseased valves from CKCS, compared to normal valves and to diseased valves from other breeds. F2 (prothrombin) (CKCS diseased valves compared to normal) and MEF2C pathway activation (CKCS diseased valves compared to non-CKCS diseased valves) had the strongest association with the gene changes. A large number of genes that were differentially expressed in the CKCS diseased valves compared with normal valves and diseased valves from other breeds were associated with cardiomyocytes including CASQ2, TNNI3 and RYR2. Conclusion Transcriptomic profiling identified gene expression changes in CKCS diseased valves that were not present in age and disease severity-matched non-CKCS valves. These genes are associated with cardiomyocytes, coagulation and extra-cellular matrix remodelling. Identification of genes that vary in the CKCS will allow exploration of genetic variation to understand the aetiology of the disease in this breed, and ultimately development of breeding strategies to eliminate this disease from the breed.

Clinical and Echocardiographic Findings in an Aged Population of Cavalier King Charles Spaniels

“…This study showed that despite the 100% prevalence of MMVD in this population of aged CKCSs, a relatively large proportion (44%) showed an absence of cardiac remodelling, indicating that a proportion of elderly CKCSs with confirmed MMVD do not undergo advanced stages of this pathology. This could be because the form of MMVD affecting CKCS at a young age, for which strong heritability has been demonstrated [42], is more aggressive and leads to death in young subjects, while a sub-cohort of dogs are affected by milder disease, more similar to that affecting all elderly dogs regardless of breed [43], which allows them to live longer. Identification of genetic and pathophysiologic mechanisms that lead to delayed progression of the disease may warrant future studies in order to reduce the clinical impact of the condition in this breed.…”

Genetic Variants at the Nebulette Locus Are Associated with Myxomatous Mitral Valve Disease Severity in Cavalier King Charles Spaniels

“…Array genotypes within 500 kb of candidate risk variants identified by Axelsson et al [ 10 ] ( Table 1 and Table 2 ) were extracted from the genome-wide array genotypes using PLINK [ 19 ]. Minor allele frequencies for individual variants (--freq) and genotype counts (--freqx) were reported, with no quality filtering.…”

“…Additionally, this study found that the genotype for one of the NEBL risk variants ( NEBL3 ) was a significant predictor of graded MMVD disease status in the dachshund. Considering the previous finding of the gene expression differences in NEBL in the CKCS [ 10 ], this is concerning for the breed. If NEBL risk alleles are fixed in the CKCS breed and proven as causative for MMVD risk and/or severity, cross-breeding would be required to breed out severe MMVD in the CKCS.…”

“…An increase in age in dogs also sees a significant increase in MMVD disease incidence in CKCSs, with a total 85% of dogs affected by 13 years of age [ 7 , 9 ]. Further, CKCSs have been observed to exhibit an unusually high prevalence of early-onset MMVD [ 8 , 10 ]. Expressivity of this condition is variable, with some dogs showing evidence of more severe disease at earlier ages than other dogs.…”

“…Following this, later research quantified heritability estimates for both the degree of a murmur (0.67 ± 0.07) and presence or absence of a murmur (0.33 ± 0.07) [ 7 ]. Transcriptomic studies have identified genes associated with cardiomyocytes that show gene fold changes and gene expression differences in the CKCS compared to other breeds, such as Nebulette (NEBL) [ 10 ]. This, however, does not definitively determine that these changes are involved in MMVD pathogenesis.…”