Disease Severity-Associated Gene Expression in Canine Myxomatous Mitral Valve Disease Is Dominated by TGFβ Signaling

Abstract

Myxomatous mitral valve disease (MMVD) is the most common acquired canine cardiovascular disease and shares many similarities with human mitral valvulopathies. While transcriptomic datasets are available for the end-stage disease in both species, there is no information on how gene expression changes as the disease progresses, such that it cannot be stated with certainty if the changes seen in end-stage disease are casual or consequential. In contrast to humans, the disease in dogs can be more readily examined as it progresses, and this allows an opportunity for insight into disease pathogenesis relevant to both species. The aim of this study was to identify changes in valve gene expression as canine MMVD advances over an entire lifetime , from normal (grade 0) to severely affected (grade 4), and differences in gene expression comparing normal and disease areas of the same valve. Transcriptomic profiling identified 1002 differentially expressed genes (DEGs) across all four disease grades when compared with normal valves with the greatest number of DEGs in grade 3 (673) and grade 4 (507). DEGs were associated with a large number of gene families, including genes encoding cytoskeletal filaments, peptidases, extra-cellular matrix (ECM) proteins, chemokines and integrins. Gene enrichment analysis identified significant grade-dependent changes in gene clustering, with clusters trending both up and down as disease progressed. Significant grade-dependent changes in hallmark disease gene expression intensity were identified, including ACTA2, HTR2B, MMP12, and CDKN2A. Gene Ontology terms were dominated by terms for ECM and inflammation with TGFβ1, TNF, IFGN identified as the top upstream regulators in both whole and dissected diseased valve samples. These data show that while disease progression in MMVD is associated with increasing numbers of DEGs, TGFβ appears to be the dominant signaling pathway controlling pathogenesis irrespective of disease severity.

Comparative transcriptomic profiling of myxomatous mitral valve disease in the Cavalier King Charles Spaniel

“…We have recently shown that the transcriptome of the mitral valve changes as MMVD advances from the normal valve to the severely diseased Whitney grade 4 valve [21]. We found that TGFβ was the dominant signalling pathway controlling pathogenesis, consistent with ndings in cultured valve interstitial cells [22].…”

“…There were clear similarities in gene enrichment analysis and GO terms comparing both diseased groups to normal, including genes recognised as hallmarks of canine MMVD, such as ACTA2 (encoding α-SMA) and HTR2B (encoding 5HT2B receptor) [18,27]. This likely re ects the global gene signature typical of MMVD where there is aberrant extra-cellular matrix remodelling as a consequence of changes in TGFβ signalling [18,19,21,36]. The other shared DEGs, in particular those coding for the myosin heavy chains and growth factors, suggest the involvement of TGFβ non-canonical signalling pathways affecting downstream signals including MEK, ERK1/2, IP3 and RhoGTPase [37].…”

“…Furthermore, there is evidence of enhanced 5HT signalling in both human and canine MMVD valve tissue and valve interstitial cells (VIC) exposed to tensile strain, and genetic variation in the exons of the 5HT transporter gene (SLC6A4, also known as SERT) may be associated with MMVD development in the Maltese terrier [16,17]. Changes in expression of the 5HT receptor gene are reported for the canine mitral valve transcriptome, and in the dog HTR2B expression is associated with disease progression [18][19][20][21]. However, 5HT does not induce disease phenotype in cultured VICs and expression of 5HT receptor genes is controlled by TGFβ1 [22].…”

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

“…Furthermore, there is evidence of enhanced 5HT signalling in both human and canine MMVD valve tissue and valve interstitial cells (VIC) exposed to tensile strain, and genetic variation in the exons of the 5HT transporter gene ( SLC6A4 , also known as SERT ) may be associated with MMVD development in the Maltese terrier [ 16 , 17 ]. Changes in expression of the 5HT receptor gene are reported for the canine mitral valve transcriptome, and in the dog HTR2B expression is associated with disease progression [ 18 – 21 ]. However, 5HT does not induce disease phenotype in cultured VICs and expression of 5HT receptor genes is controlled by TGFβ1 [ 22 ].…”

Isolated Flailed P3 Scallop of the Mitral Valve Leaflet in the Setting of Newly Diagnosed Heart Failure With Preserved Ejection Fraction

“…Most patients with MVP have a risk of cardiovascular morbidity and mortality similar to that of the general population, though moderate to severe MR and left ventricular ejection fraction less than 50% have been postulated to increase the risk of adverse cardiac events. Other risk factors for cardiovascular morbidity include flail mitral leaflet, left atrium size greater than 40 mm, atrial fibrillation, and age above 50 years [ 7 , 8 ].…”