Association of hepatic steatosis with subclinical cardiac dysfunction in asymptomatic people with type 2 diabetes

Introduction

Non-alcoholic fatty liver disease is highly prevalent among people with type 2 diabetes (T2D) and is an emerging risk factor for heart failure with preserved ejection fraction (HFpEF). Whether excess liver adiposity is simply a marker of the coexisting adverse cardiometabolic risk profile or independently contributes to the development of HFpEF is unclear.

Purpose

To assess the association between liver fat fraction and subclinical cardiac dysfunction in adults with T2D.

Methods

Prospective cross-sectional study. Two-hundred and thirty-eight adults with T2D (mean age 63±7 years, 62% males, HbA1c 7.2±1.5%, diabetes duration 10±8 years) with no signs, symptoms, or evidence of cardiovascular disease and 40 age-, sex-, and ethnicity-matched non-diabetic controls (mean age 61±8 years, 63% males, HbA1c 5.2±1.2%) underwent comprehensive phenotyping with echocardiography and multiparametric cardiac MRI including adenosine stress and rest perfusion. Volumetric liver fat fraction (VLFF) was measured using a histologically validated, proprietary MRI technique blinded to all participant details. Inter-study reproducibility was assessed in participants (n=28) who underwent a repeat MRI within two weeks. Linear regression analysis was performed to assess any independent associations between VLFF and identified markers of subclinical cardiac dysfunction in subjects with T2D.

Results

People with T2D had evidence of concentric left ventricular (LV) remodelling (higher LV mass/volume), extracellular matrix expansion (higher ECV fraction), both systolic and diastolic dysfunction (lower global longitudinal systolic strain and E/A ratio, respectively), and coronary microvascular dysfunction (lower myocardial perfusion reserve) (Table 1). VLFF demonstrated excellent inter-study reproducibility with an intra-class correlation coefficient (ICC) of 0.988 (0.974–0.994). T2Ds had higher VLFF compared to controls [7.5 (3.8–13.7)% vs 2.9 (1.7–4.7)%, p<0.001]. In multivariable regression analysis adjusting for age, sex, ethnicity, body mass index, ambulatory systolic blood pressure, HbA1c, and low-density lipoprotein, VLFF (β=−0.161, p=0.027) was independently associated with E/A, but not other imaging measures of subclinical cardiac dysfunction.

Conclusion

Liver fat fraction is elevated in people with T2D and is independently associated with early LV diastolic dysfunction. These results add to the growing evidence that ectopic fat plays an important role in the pathogenesis of HFpEF and may be a potential target for intervention.

Funding Acknowledgement

Type of funding sources: Public Institution(s). Main funding source(s): National Institute for Health Research (NIHR) United Kingdom through a Research Professorship award (RP-2017-08-ST2-007).British Heart Foundation through a Clinical Research Training Fellowship (FS/16/47/32190).

Co-regulation of survival of motor neuron and Bcl-xL expression: implications for neuroprotection in spinal muscular atrophy

Spinal muscular atrophy (SMA), a fatal genetic motor disorder of infants, is caused by diminished full-length survival of motor neuron (SMN) protein levels. Normally involved in small nuclear ribonucleoprotein (snRNP) assembly and pre-mRNA splicing, recent studies suggest that SMN plays a critical role in regulating apoptosis. Interestingly, the anti-apoptotic Bcl-x isoform, Bcl-xL, is reduced in SMA. In a related finding, Sam68, an RNA-binding protein, was found to modulate splicing of SMN and Bcl-xL transcripts, promoting SMNΔ7 and pro-apoptotic Bcl-xS transcripts. Here we demonstrate that Bcl-xL expression increases SMN protein by ∼2-fold in SH-SY5Y cells. Conversely, SMN expression increases Bcl-xL protein levels by ∼6-fold in SH-SY5Y cells, and ∼2.5-fold in the brains of transgenic mice over-expressing SMN (PrP-SMN). Moreover, Sam68 protein levels were markedly reduced following SMN and Bcl-xL expression in SH-SY5Y cells, suggesting a feedback mechanism co-regulating levels of both proteins. We also found that exogenous SMN expression increased full-length SMN transcripts, possibly by promoting exon 7 inclusion. Finally, co-expression of SMN and Bcl-xL produced an additive anti-apoptotic effect following PI3-kinase inhibition in SH-SY5Y cells. Our findings implicate Bcl-xL as another potential target in SMA therapeutics, and indicate that therapeutic increases in SMN may arise from modest increases in total SMN.

Survival of motor neuron protein over-expression prevents calpain-mediated cleavage and activation of procaspase-3 in differentiated human SH-SY5Y cells

Spinal muscular atrophy (SMA), a neurodegenerative disorder primarily affecting motor neurons, is the most common genetic cause of infant death. This incurable disease is caused by the absence of a functional SMN1 gene and a reduction in full length survival of motor neuron (SMN) protein. In this study, a neuroprotective function of SMN was investigated in differentiated human SH-SY5Y cells using an adenoviral vector to over-express SMN protein. The pro-survival capacity of SMN was assessed in an Akt/PI3-kinase inhibition (LY294002) model, as well as an oxidative stress (hydrogen peroxide) and excitotoxic (glutamate) model. SMN over-expression in SH-SY5Y cells protected against Akt/phosphatidylinositol 3-kinase (PI3-kinase) inhibition, but not oxidative stress, nor against excitotoxicity in rat cortical neurons. Western analysis of cell homogenates from SH-SY5Y cultures over-expressing SMN harvested pre- and post-Akt/PI3-kinase inhibition indicated that SMN protein inhibited caspase-3 activation via blockade of calpain-mediated procaspase-3 cleavage. This study has revealed a novel anti-apoptotic function for the SMN protein in differentiated SH-SY5Y cells. Finally, the cell death model described herein will allow the assessment of future therapeutic agents or strategies aimed at increasing SMN protein levels.

Breast screening in the emerging world: High prevalence of breast cancer in Cairo

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