Grant Abstracts: Dr. Melkani's Lab Home Page


Title: Molecular basis of circadian rhythms disruptions linked cardiometabolic disorders and their mitigation using dietary intervention

Funding Source: R01 NIH/NIA 2019-2024

Abstract:
Genetic and lifestyle perturbation of the circadian clock trigger cardiovascular diseases. The proposed study will examine how aging, obesity and circadian rhythm disruptions linked with cardiometabolic disorders, and how time-restricted feeding (TRF) mitigates these defects. The leading risk factors for cardiometabolic diseases are age, shift work, energy dense diet and aberrant eating/sleeping patterns. Each of these factors disrupts circadian rhythms, and it has been shown in model organisms that genetic perturbation of the circadian clock increases the incidence and severity of cardiac diseases. For example, an aberrant eating pattern in human, increases the risk of developing cardiovascular diseases by as much as 55%, after controlling for diet and lifestyle, possibly by disruption of circadian clock. Also, mutations of circadian clock genes prone to cardiac diseases and light-induced circadian disruptions further deteriorates cardiac abnormalities. Conversely, TRF paradigm without reducing caloric intake has been shown to prevent various metabolic disorders and attenuates age-linked cardiac dysfunction. However, pathogenic linkage of circadian clock disruptions with cardiometabolic diseases, or the potential benefit of TRF intervention has not been assessed at the molecular or genetic level. Thus, our scientific premise is that factors that affect circadian rhythms offer new avenues to understand the etiology and attenuation of cardiometabolic disorders.

To address the mechanistic basis of this alarming public health issue, we have developed novel Drosophila melanogaster (fruit fly) models to mitigate age, obesity and circadian disruption-induced cardiac disorders by imposing feeding/fasting rhythms with TRF. Drosophila will serve as an excellent model system for basic discoveries in circadian rhythms, energy metabolism and cardiac muscle physiology. Aim 1 of the proposed study is to determine the molecular basis of the effectiveness of TRF in delaying age-, obesogenic challenges, and circadian disruption-induced deterioration of cardiac physiology in Drosophila. Aim 2's goals are to monitor the effect of dietary intervention on the diurnal and long-term reprogramming of cardiac gene expression under aging, obesogenic challenges and circadian rhythms disruption. Aim 3 will employ genetic validation of circadian clock with other identified genes/pathways mediating the effect of eating pattern on cardiac health.

Our study will use hypothesis-driven experiments to address the molecular basis of the alarming public health problem of age and obesity-induced cardiac dysfunction associated with circadian dysregulation. Successful completion of this proposal will dramatically accelerate our understanding of the impact of daily rhythms on cardiac muscle physiology. The TRF paradigm may prove applicable to human health through application of community-based approaches to ameliorating obesity-induced comorbidities and thereby improving cardiovascular and metabolic health.

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Title: Genetic analysis and regulation of laminopathy induced cardiac defects

Funding Source: NIH/NIA 2015-2017

Abstract:
Laminopathies are a group of genetic disorders caused by dominant mutations in the human LMNA gene encoding A-type lamins, intermediate filaments that line the inner nuclear membrane. Patients with laminopathies exhibit phenotypes of aging, including cardiac and skeletal muscle dysfunction, dysplasia, diabetes, and premature aging. Lamins are nearly ubiquitously expressed, however many laminopathies are associated with cardiomyopathy, which is frequently fatal; yet, the underlying molecular mechanisms are not well understood. Given that many of the laminopathy patients die from cardiomyopathy, it is vital to understand the functions of lamins in the heart. The majority of mutations in LMNA that cause heart disease result in single amino acid substitutions within the rod and Ig-fold domains, which interact with different partner proteins. How mutant lamins cause disease is unknown and there is a lack of efficient genetic models to functionally dissect the physiological and pathological role(s) of lamins in heart function.

To determine the function of mutant lamins within the rod and Ig-fold domains, we have established a novel Drosophila melanogaster model. Using tissue-specific expression tools, mutant lamins are expressed specifically in the heart. Expression of wild-type lamin causes no obvious phenotypes. In contrast, expression of mutant lamins results in cardiac dysfunction accompanied by cytoplasmic aggregation and impairment of cellular redox homeostasis. Based on our preliminary findings, we hypothesize that expression of mutant lamins results in cytoplasmic aggregates, which leads to an impairment of cellular redox homeostasis and defective clearance pathways thus affecting cardiac defects. Furthermore, to mimic human disease condition and to identify nonautonomous or cardiac restricted dyfunctions linked with lamin mutations, we will use a complementary CRISPR/Cas9 expression approach. Specific Aim 1 will define the progressive dysfunction, at the physiological, functional, biochemical and ultrastructural levels, caused by the mutant lmains. Specific Aim 2 will identify genetic and pharmacological suppressors of the cardiac phenotypes caused by mutant lamins to generate insight into the primary cause of cardiac-based laminopathies and to identify potential avenues for therapies. Our suppression approach will involve protein interactions between Lamin and other nuclear envelope and aggregation clearance pathways in cardiac tissue will help us to identify heart-specific features of laminopathy-associated mechanisms that may provide new and potentially therapeutic targets.

Identifying genetic factors and pathways that modulate or mediate cardiac laminopathies is expected to uncover molecular pathways that define how cardiac laminopathies develop. The outcome of our studies will then allow the design of strategies to identify therapeutic targets. Furthermore, this study will likely provide insight into how laminopathy is linked with cardiac failure. Future directions in research will include validation of the findings in mouse models of laminopathies and human biospy tissue.

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Title: Genetic analysis and regulation of amyloids flux in the Drosophila heart

Funding Source: NIH/NCRR (No cost extension 08/2014) 1R21 RR032100-01A1 (Melkani, G.C., P.I.) 09/01/2011 - 08/31/2013

Abstract:
The specific aims of the project are to: 1) Expression and detection of HD- and AD-causing amyloids in the Drosophila heart to explore their impact on cardiac physiology. 2) Ameliorate cardiac amyloidosis by over-expression of chaperones and superoxide dismutase (SOD) or by using pharmacological agents.

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Title: Tau-induced cardiomyopathy in a Drosophila heart model

Funding Source: AHA, WSA-Beginning Grant in Aid 13BGIA17260057 (Melkani, G.C., P.I.) 07/01/13 - 08/31/15

Abstract:
The aims of the project are to: 1) Establish a Drosophila cardiac model to investigate structural and functional defects in heart caused by hyperphosphorylation of Tau; and, 2) identification of genetic and pharmacological suppressors of Tau-mediated cardiomyopathy.

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Title: Mechanism of Myosin Chaperone UNC-45: Structural, Functional & Genetic Approaches

Funding Source: NIH/NIAMS 1 R01 AR055958 (Bernstein, S.I., PI) 04/01/13 - 03/31/18

Abstract:
The aims of the project are to: 1) Investigate the dimerization of UNC-45 at a structural level and determine the importance of dimerization in UNC-45 function, 2) perform a structure-function analysis of a conserved surface cleft of UNC-45 that we identified by crystallography and phylogenetic sequence comparisons and 3) use combined genetic and biochemical approaches to identify additional partners and targets of UNC-45.

Role on project: Collaborator

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