| dc.description.abstracteng | Heart failure (HF) is the most potent epidemic of the 21st century. Based on ejection fraction (EF), HF has been classified into two distinct entities; heart failure with reduced EF (HFrEF) and heart failure with preserved EF (HFpEF). At present, HFpEF accounts for about half of all HF cases worldwide but owing to the rising incidence of comorbid diseases and an aging population, its prevalence is expected to rise in the coming years. While the medical community has a good arsenal of therapeutics to deal with HFrEF, there exists no dedicated treatment for HFpEF as of now. An important limitation in this context is the lack of animal models to capture the multifactorial and multi-organ pathological profile of HFpEF. This dearth of reliable animal models often translates into a lack of our collective understanding of the disease. This dissertation aims to create tailor-made models of ‘’HFpEF like’’ states based on different comorbid etiologies and seeks to stratify them based on clinically relevant end-points to gather insights about their pathomechanisms. To this end, two models were created using the most common factors associated with HFpEF. The first model was made by combining dyslipidemia induced by high fat diet (HFD) and low grade pressure overload (PO) using transverse aortic constriction (TAC) to realistically reflect the metabolic syndrome in HFpEF. The other model was based on natural aging and looked at the advanced age of 18-20 months in mice in terms of HF.
After 10 weeks of HFD and 2 weeks post TAC the models were assessed. For the first model we observed that the combination of HFD+PO resulted in a selective shift in EF towards a preserved state (≥50%) while control mice on normal diet (ND) + PO presented with a reduction in EF (≤40%) which reflects HFrEF. This prompted us to hypothesize that metabolic deregulation led by HFD induced dyslipidemia in presence of low grade PO was important in the differential presentation of HF. An in-depth structural characterization of the myocardium revealed a hypertrophic, apoptotic and a highly fibrotic phenotype which presented with evidence of atrial remodeling. There was significant accumulation of neutral lipid deposits in the myocardial tissue indicating global dyslipidemic effects. The model showed an overall preserved systolic function in HFD- TAC (in contrast to ND-TAC controls) as evidenced by unchanged echocardiographic parameters like EF and reverse longitudinal strain rate (r-LSR) and pressure volume (PV) loop parameters like ESPVR, dp/dtmax and PRSW when compared to HFD-Sham group. Moreover, an impairment in diastolic function was confirmed by significant changes in EDPVR, EDP and Tau. On the aspect of remodeling, the dyslipidemic HFpEF state presented with concentric hypertrophy as evidenced by higher relative wall thickness (RWT) as compared to dyslipidemic shams. Fetal gene reprogramming was highly active in both dietary groups but differed in terms of Serca-2α downregulation seen only in the HFrEF group. Perivascular fibrosis was uniquely enhanced in HFpEF state. The inflammatory cytokine profile within the two states also revealed a differential signature with more upregulation in the dyslipidemic group. VCAM-1 and PECAM-1 also presented with enhanced expression only in HFpEF group suggestive of distinct dynamics of endothelial dysfunction(ED). IL-1 showed enhanced expression in HFpEF only, while IL-6 showed no change in either groups. Endothelin-1 was exclusively upregulated in HFpEF state. Nox2 was upregulated in both HF states. In terms of cardiac kinases and calcium handling, phosphorylation levels of HDAC-4, Akt, Erk, RyR(2814) and Plb(Thr17) were only exclusively enhanced in HFpEF and cardiac troponin phosphorylation was preserved to basal levels in the HFpEF group indicating yet another differential aspect. Transcriptomic analysis of the two HF states identified several key genes involved mainly in actin-myosin structural and functional dynamics. Pathway analysis revealed an enrichment of gene-set involved in adrenergic signaling indicating that adrenergic deficits play a differentiating role between the two HF states.
The second model of cardiac aging was characterized on similar levels. In contrast to dyslipidemic HFpEF, it presented with an overall non-hypertrophic, non-remodeled, highly fibrotic, highly apoptotic and non-steatotic phenotype. There was no evidence for LA remodeling and concentric hypertrophy of the LV. Systolic parameters discussed above were preserved and all studied diastolic parameters were significantly perturbed. Fetal gene reprogramming was evident but, Acta-1 showed no change in contrast to dyslipidemic HFpEF. BNP was upregulated in both HFpEF states but ANP was preserved in aging. Perivascular fibrosis as the previous HFpEF group was remarkably enhanced. Inflammatory cytokine analysis showed no changes in IFN-γ levels which was in contrast to dyslipidemic HFpEF. PECAM-1 upregulation was not observed here as well (just like dyslipidemic HFpEF) suggesting an exclusive role. IL-6 expression unlike the previous HFpEF group, was upregulated here. Endothelin-1 expression was again upregulated in this HFpEF state too. Notably, higher accumulation of CD45+ cells was seen in LV myocardium of the aging HFpEF state only. Nox2 expression was not enhanced here unlike the previous dyslipidemia induced HFpEF cohort and HFrEF. Akt phosphorylation was not upregulated while Erk, p-38 and Jnk were. The latter two are in contrast with dyslipidemic HFpEF. In terms of calcium handling, phosphorylation of CAMKII, RyR(2814) , RyR(2808), Plb (Thr17) and Plb (Ser 16) were all enhanced showing a more potent deregulation than the dyslipidemic HFpEF group. Only HDAC-4 phosphorylation which was present in the previous group, could not be seen here. Assessment of the coding transcriptome of the two HFpEF states revealed an over representation of genes involved in response to chemokine and extracellular matrix (ECM) organization and the resulting KEGG pathway showed an enrichment in ECM-receptor pathway interaction genes. It suggests that these two HFpEF states differ strongly in the context of ECM based signaling.
PCA plot revealed a clustering of both HFpEF groups together despite their divergent etiologies. This further stresses on the multifactorial nature of HFpEF. The differences and similarities between the two ‘’HFpEF like’’ states and between HFpEF vs HFrEF reveal a distinct mechanistic profile. This study provides first such cross-comparative insight which ultimately may contribute to our collective understanding of different HFpEF pheno-groups and help in identifying mechanistically intuitive therapeutic targets for this elusive entity. | de |