Functional analysis of melanocortin 2 receptor variants and dimer formation

PhDThe adrenocorticotropic hormone (ACTH) receptor, also known as the melanocortin 2 receptor (MC2R) is primarily expressed in the adrenal gland and binds to ACTH to activate a signalling cascade that leads to steroidogenesis. The characterisation of the melanocortin 2 receptor has previously been hindered by the failure of cell surface expression in heterologous cells. Unlike other melanocortin receptors, MC2R surface expression requires an accessory protein called melanocortin 2 receptor accessory protein (MRAP). MRAP has been shown to facilitate trafficking of MC2R from the endoplasmic reticulum to the plasma membrane and it also has a role in MC2R signalling. Naturally occurring MC2R mutations occur in Familial Glucocorticoid Deficiency (FGD) type 1. The functional defect remains uncertain for the majority, mainly due to the difficulties in characterisation which has been limited in Y6 cells (mouse derived adrenal cells which are free of MCRs) because of poor transfection efficiency. The first two results chapter of this thesis focus on the molecular biology of FGD mutations and the genotype-phenotype relationship of the disease. The functional defects of these mutations have been analysed in transfectable heterologuous cells stably expressing MRAP. The majority of the missense mutations are trafficking-defective, and yet all appear to interact with MRAP, but some mutations are trafficking-competent and fail to signal. Clinical details including the age of presentation; presenting plasma ACTH and cortisol; height and weight were examined in FGD type 1 and 2 (mutation of MC2R or MRAP respectively) to determine whether there is a genotype-phenotype correlation. Within FGD type 1, there was no clear clinical distinction between the functional defects in vitro and in vivo data. However, there were phenotypic differences between 3 FGD type 1 and 2, with FGD 2 appearing to be more severe with a younger age and a lower height SDS at presentation. The final part of this thesis focuses on MC2R dimerisation and signalling of the receptor. Co-immunoprecipitation studies showed that MC2R homodimerisation is constitutive. This interaction was not enhanced in the presence of MRAP or ACTH. No effect on signalling was observed. When a signalling mutant (R128C) and a ligand binding mutant (D103N) were co-transfected with MRAP and stimulated with ACTH, signalling was not restored, suggesting no cross talk between the two receptors. In the final discussion the implication of these findings are considered with respect to their relevance to disease and novel therapeutic strategies

Left atrial structure and function in heart failure with reduced (HFrEF) versus preserved ejection fraction (HFpEF):systematic review and meta-analysis

Left atrial (LA) structure and function in heart failure with reduced (HFrEF) versus preserved ejection fraction (HFpEF) is only established in small studies. Therefore, we conducted a systematic review of LA structure and function in order to find differences between patients with HFrEF and HFpEF. English literature on LA structure and function using echocardiography was reviewed to calculate pooled prevalence and weighted mean differences (WMD). A total of 61 studies, comprising 8806 patients with HFrEF and 9928 patients with HFpEF, were included. The pooled prevalence of atrial fibrillation (AF) was 34.4% versus 42.8% in the acute inpatient setting, and 20.1% versus 33.1% in the chronic outpatient setting when comparing between HFrEF and HFpEF. LA volume index (LAVi), LA reservoir global longitudinal strain (LAGLS(R)), and E/e' was 59.7 versus 52.7 ml/m(2), 9.0% versus 18.9%, and 18.5 versus 14.0 in the acute inpatient setting, and 48.3 versus 38.2 ml/m(2), 12.8% versus 23.4%, and 16.9 versus 13.5 in the chronic outpatient setting when comparing HFrEF versus HFpEF, respectively. The relationship between LAVi and LAGLS(R) was significant in HFpEF, but not in HFrEF. Also, in those studies that directly compared patients with HFrEF versus HFpEF, those with HFrEF had worse LAGLS(R) [WMD = 16.3% (22.05,8.61); p < 0.001], and higher E/e' [WMD = -0.40 (-0.56, -0.24); p < 0.05], while LAVi was comparable. When focusing on acute hospitalized patients, E/e' was comparable between patients with HFrEF and HFpEF. Despite the higher burden of AF in HFpEF, patients with HFrEF had worse LA global function. Left atrial myopathy is not specifically related to HFpEF

Readmissions, death and its associated predictors in heart failure with preserved versus reduced ejection fraction

BACKGROUND: Data on rehospitalizations for heart failure (HF) in Asia are scarce. We sought to determine the burden and predictors of HF (first and recurrent) rehospitalizations and all‐cause mortality in patients with HF and preserved versus reduced ejection fraction (preserved EF, ≥50%; reduced EF, <40%), in the multinational ASIAN‐HF (Asian Sudden Cardiac Death in Heart Failure) registry. METHODS AND RESULTS: Patients with symptomatic (stage C) chronic HF were followed up for death and recurrent HF hospitalizations for 1 year. Predictors of HF hospitalizations or all‐cause mortality were examined with Cox regression for time to first event and other methods for recurrent events analyses. Among 1666 patients with HF with preserved EF (mean age, 68±12 years; 50% women), and 4479 with HF with reduced EF (mean age, 61±13 years; 22% women), there were 642 and 2302 readmissions, with 28% and 45% attributed to HF, respectively. The 1‐year composite event rate for first HF hospitalization or all‐cause death was 11% and 21%, and for total HF hospitalization and all‐cause death was 17.7 and 38.7 per 100 patient‐years in HF with preserved EF and HF with reduced EF, respectively. In HF with preserved EF, consistent independent predictors of these clinical end points included enrollment as an inpatient, Southeast Asian location, and comorbid chronic kidney disease or atrial fibrillation. The same variables were predictive of outcomes in HF with reduced EF except atrial fibrillation, and also included Northeast Asian location, older age, elevated heart rate, decreased systolic blood pressure, diabetes, smoking, and non‐usage of beta blockers. CONCLUSIONS: One‐year HF rehospitalization and mortality rates were high among Asian patients with HF. Predictors of outcomes identified in this study could aid in risk stratification and timely interventions. REGISTRATION: URL: https://www.clinicaltrials.gov; Unique identifier: NCT01633398

Prevalence and Prognostic Significance of Frailty in Asian Patients With Heart Failure:Insights From ASIAN-HF

Background: Frailty is common in patients with heart failure (HF) and can adversely impact outcomes. Objectives: This study examined the prevalence of frailty among Asian patients with HF, its association with 1-year outcomes, and if race-ethnicity, HF subtypes, and sex modify this relationship. Methods: In the multinational ASIAN-HF (Asian Sudden Cardiac Death in Heart Failure) registry, a baseline frailty index (FI) was constructed using a cumulative deficits approach with 48 baseline variables, and patients were followed for the 1-year primary outcome of all-cause death or HF hospitalization. Results: Among 3,881 participants (age 61 ± 13 years, 27% female), the mean FI was 0.28 ± 0.11, and 69% were frail (FI &gt;0.21). Higher FI was associated with older age, Malay ethnicity, and Southeast Asian residency. While comorbidities were more frequent in frail patients (by definition), body mass index was not different across frailty classes. Compared with FI class 1 (&lt;0.21, nonfrail), FI class 2 (0.21-0.31) and FI class 3 (&gt;0.31) had increased risk of the 1-year composite outcome (hazard ratios of 1.84 [95% confidence interval (CI): 1.42-2.38] and 4.51 [95% CI: 3.59-5.67], respectively), even after multivariable adjustment (adjusted hazard ratios of 1.49 [95% CI: 1.13-1.97] and 2.69 [95% CI: 2.06-3.50], respectively). Race-ethnicity modified the association of frailty with the composite outcome (Pinteraction = 0.0097), wherein the impact of frailty was strongest among Chinese patients. The association between frailty and outcomes did not differ between men and women (Pinteraction = 0.186) or for HF with reduced ejection fraction versus HF with preserved ejection fraction (Pinteraction = 0.094). Conclusions: Most Asian patients with HF are frail despite relatively young age. Our results reveal specific ethnic (Malay) and regional (Southeast Asia) predisposition to frailty and highlight its prognostic importance, especially in Chinese individuals.</p

Prevalence and Prognostic Significance of Frailty in Asian Patients With Heart Failure:Insights From ASIAN-HF

Background: Frailty is common in patients with heart failure (HF) and can adversely impact outcomes. Objectives: This study examined the prevalence of frailty among Asian patients with HF, its association with 1-year outcomes, and if race-ethnicity, HF subtypes, and sex modify this relationship. Methods: In the multinational ASIAN-HF (Asian Sudden Cardiac Death in Heart Failure) registry, a baseline frailty index (FI) was constructed using a cumulative deficits approach with 48 baseline variables, and patients were followed for the 1-year primary outcome of all-cause death or HF hospitalization. Results: Among 3,881 participants (age 61 ± 13 years, 27% female), the mean FI was 0.28 ± 0.11, and 69% were frail (FI &gt;0.21). Higher FI was associated with older age, Malay ethnicity, and Southeast Asian residency. While comorbidities were more frequent in frail patients (by definition), body mass index was not different across frailty classes. Compared with FI class 1 (&lt;0.21, nonfrail), FI class 2 (0.21-0.31) and FI class 3 (&gt;0.31) had increased risk of the 1-year composite outcome (hazard ratios of 1.84 [95% confidence interval (CI): 1.42-2.38] and 4.51 [95% CI: 3.59-5.67], respectively), even after multivariable adjustment (adjusted hazard ratios of 1.49 [95% CI: 1.13-1.97] and 2.69 [95% CI: 2.06-3.50], respectively). Race-ethnicity modified the association of frailty with the composite outcome (Pinteraction = 0.0097), wherein the impact of frailty was strongest among Chinese patients. The association between frailty and outcomes did not differ between men and women (Pinteraction = 0.186) or for HF with reduced ejection fraction versus HF with preserved ejection fraction (Pinteraction = 0.094). Conclusions: Most Asian patients with HF are frail despite relatively young age. Our results reveal specific ethnic (Malay) and regional (Southeast Asia) predisposition to frailty and highlight its prognostic importance, especially in Chinese individuals.</p

Association Between Diabetes, Chronic Kidney Disease, and Outcomes in People With Heart Failure From Asia

Background: Diabetes mellitus (DM), chronic kidney disease (CKD), and heart failure (HF) are pathophysiologically linked and increasing in prevalence in Asian populations, but little is known about the interplay of DM and CKD on outcomes in HF. Objectives: This study sought to investigate outcomes in patients with heart failure with preserved ejection fraction (HFpEF) vs heart failure with reduced ejection fraction (HFrEF) in relation to the presence of DM and CKD. Methods: Using the multinational ASIAN-HF registry, we investigated associations between DM only, CKD only, and DM+CKD with: 1) composite of 1-year mortality or HF hospitalization; and 2) Kansas City Cardiomyopathy Questionnaire scores, according to HF subtype. Results: In 5,239 patients with HF (74.6% HFrEF, 25.4% HFpEF; mean age 63 years; 29.1% female), 1,107 (21.1%) had DM only, 1,087 (20.7%) had CKD only, and 1,400 (26.7%) had DM+CKD. Compared with patients without DM nor CKD, DM+CKD was associated with 1-year all-cause mortality or HF hospitalization in HFrEF (adjusted HR: 2.07; 95% CI: 1.68-2.55) and HFpEF (HR: 2.37; 95% CI: 1.40-4.02). In HFrEF, DM only and CKD only were associated with 1-year all-cause mortality or HF hospitalization (both HRs: 1.43; 95% CI: 1.14-1.80), while in HFpEF, CKD only (HR: 2.54; 95% CI: 1.46-4.41) but not DM only (HR: 1.01; 95% CI: 0.52-1.95) was associated with increased risk (interaction P &lt; 0.01). Adjusted Kansas City Cardiomyopathy Questionnaire scores were lower in patients with DM+CKD (HFrEF: mean 60.50, SEM 0.77, HFpEF: mean 70.10, SEM 1.06; P &lt; 0.001) than with no DM or CKD (HFrEF: mean 66.00, SEM 0.65; and HFpEF: mean 75.80, SEM 0.99). Conclusions: Combined DM and CKD adversely effected outcomes independently of HF subtype, with CKD a consistent predictor of worse outcomes. Strategies to prevent and treat DM and CKD in HF are urgently required.</p