The Biological Mechanisms Core leadership continues to facilitate genetics research in the area of aging and frailty. To date, we have made substantial progress in meeting these aims and in providing services to numerous investigators interested in frailty research.
Our extensive genetics expertise, provided through collaborative efforts with the biostatistics core and the Research Career Development Core (RCDC), Pilot, and Leadership and Administrative Core (LAC), has resulted in the development and refinement of endophenotypes related to frailty, including skeletal muscle strength, inflammation, cognitive frailty and sleep apnea.
The development of these endophenotypes of frailty has facilitated the well rationalized choice of candidate genes, state-of the art selection of candidate SNPs within these genes, and ultimately the provision of the latest genetic technology available for high throughput genotyping. In addition, genetic analyses of complex traits for thousands of SNPs have become more streamlined and more available to those pursuing genetics studies in aging and frailty.
Recent data analyses from the initial developmental project have highlighted ten genes as potentially important in the development of frailty, based on association studies. These genes are mostly related to inflammation and apoptosis, and correlate closely with genes differentially expressed in a frail mouse model. In addition, the Biological Mechanisms Core functions as a key location for replication of genome-wide association studies, and has facilitated multiple collaborations with groups of investigators from across the country.
Now that much of that infrastructure is completed, and several ongoing genetics core projects led by investigators from multiple disciplines are in process, the leadership of the core has begun to develop the next generation of molecular studies that will need to take place in order to further understand the biology that contributes to the development of frailty.
The development project, "Development of a Frail Mouse Model," was deemed necessary in order to have access to biological samples necessary to test hypotheses generated as a result of genetics data obtained in the first years of the Hopkins Older Americans Independence Center (OAIC). This frail mouse is now being proposed for utilization by several investigators who work closely with the OAIC, and will be utilized to test hypotheses supported projects.
In addition to this mouse model, the Biological Mechanisms Core leadership has also planned to add more extensive epigenetic, mitochondrial and gene expression support services to our core in order to more comprehensively support biological discovery in frailty and aging research.
RC-2 Development Project, 2013-2015 (Years 11-12)
The IL10Tm/Tm mouse, like frail humans, develops age-related skeletal muscle weakness, endocrine abnormalities, inflammatory pathway activation, mitochondrial abnormalities, and early mortality. These findings support the further use of this mouse to dissect molecular pathways that may impact frailty. Rapid advances in molecular technology now allow for the comprehensive examination of molecular phenotypes using several powerful ‘omic’ approaches. We hypothesize that omic technologies supported in RC-2 can be utilized to identify a molecular signature in the frail mouse that will facilitate etiological understanding of frailty. To test this hypothesis, Dr. Arking will lead a 2 year developmental project that will comprehensively evaluate DNA methylation, gene expression, and proteomics in the skeletal muscle and metabolomics and proteomics in the serum of frail versus non-frail IL10 mice. Three female mice IL10Tm/Tm and age / gender- matched C57Bl/6 mice will be utilized for the primary screen (N=18: young - 3 mo., middle age - 1 yr., and old - 22 mo.).
Jiou Wang, PhD, Assistant Professor of Biochemistry and Molecular Biology. “Identifying Molecular Biomarkers and Genetic Modifiers of Frailty in Caenorhabditis elegans Models”
Project Overview / Specific Aims
Frailty is increasingly recognized as a clinical condition with a biological basis. The phenotypes of frailty are thought to represent combinations of the following symptoms: weakness, fatigue, weight loss, slow walking speed, low levels of physical activity, and mild cognitive changes. Frailty is highly prevalent in the elderly but the mechanisms through which aging might affect the frailty syndrome remain unknown. Dr. Jiou Wang and colleagues seek to understand the common molecular basis underlying degenerative diseases and aging-dependent frailty. Their hypothesis is that during the development of frailty there are predictable molecular events that can be monitored by specific biomarkers and that these molecular events partially overlap with molecular cascades that lead to the tissue decline in normal aging or degenerative diseases. If this hypothesis is true, they can apply what is learned from particular degenerative diseases to understand and treat conditions of the multisystemic decline in the frailty syndrome. Much of the current understanding of degenerative diseases, including neurodegeneration, comes from studies using animal models. One example is Amyotrophic Lateral Sclerosis (ALS), which is the major form of motor neuron degenerative disease. Discoveries of genetic mutations in a subset of ALS patients have opened doors for engineering genetically modified animals models and accelerated our understanding of the molecular mechanism of the disease. Recently, to overcome the limitation of the mouse model in its adaptability to largescale screening, Dr. Wang created an invertebrate model of ALS in C. elegans, a model organism that is also widely used for studying aging. The C. elegans model of ALS developed robust phenotypes mimicking the human disease, including pronounced movement defects and protein aggregation, and studies using this C. elegans model have revealed promising genetic modifiers of disease that we recently find operating similarly in mammalian systems. Here, Dr. Wang proposes to systematically study aging-related frailty using C. elegans as a model organism. The advantages of this model organism include its short lifespan, transparency, and powerful molecular tools. Furthermore, the studies of aging dependent degenerative diseases in C. elegans provided tools and candidate genes to explore genetic modifiers of the frailty phenotypes in normally aged C. elegans and the underlying age-dependent molecular basis. This exploration provides insight into conserved molecular underpinnings in human frailty. The specific aims are as follows: Specific Aim 1: To identify molecular markers for the frailty phenotypes in C. elegans, such as sarcopenia, by examining synaptic neurotransmission and mitochondrial integrity. Specific Aim 2: To identify genetic modifiers of the frailty phenotypes in C. elegans by examining candidate genes involved in aging and degenerative diseases.
Dr. Wang and colleagues have established of a new C. elegans model of age-depedend neurodegeneration that is linked to TAR DNA-binding protein 43 (TDP-43). TDP-43 plays a key role in the neurodegenerative diseases including amyotrophic lateral sclerosis and frontotemporal lobar degeneration. The C. elegans models developed severe locomotor defects associated with the aggregation of TDP-43 in neurons. Importantly, the TDP-43 C. elegans model exhibit age-dependent decline in its phenotype including a worsening locomotor defect. Towards the Specific Aim 1 of the OAIC project, they found that TDP-43 demonstrated an unusually high tendency to aggregate, a property intrinsic to the wild-type protein. Distinct disulfidelinked TDP-43 dimers and oligomers were detected. In C. elegans, the toxicity and protein aggregation of TDP-43 were regulated by environmental temperature and heat shock transcriptional factor 1, indicating that a deficiency in protein quality control is a risk factor for TDP-43 proteinopathy. Furthermore, they have found that synaptic defects at the neuromuscular junctions are underlying the locomotor defects in the TDP-43 C. elegans models. Towards the Specific Aim 2, the investigators found that the toxicity and protein aggregation of TDP-43 can be significantly attenuated by a deficiency in the insulin/ insulin-like growth factor 1 (IGF-1) signaling in C. elegans and mammalian cells. These results established a direct link between the aging program and the toxicity and aggregation of TDP-43.
The investigators have identified candidate genes that suppress protein aggregation and expand lifespan in C. elegans. They will focus our effects on validating and charactering the candidate genes in the remainder of the project. They will continue to meet regularly with the RC-2 and LAC leadership to identify ways to integrate these findings into human and/or animal models studies.
Publications Progress / Abstracts / Presentations /Grant Development
The progress summarized above has been published in the latest issue of Human Molecular Genetics. Zhang T, Mullane PC, Periz G, Wang J. TDP-43 Neurotoxicity and Protein Aggregation Modulated by Heat Shock Factor and Insulin/IGF-1 Signaling. Hum Mol Genet 2011;doi: 101093/hmg/ddr076. They have also presented this work as a poster entitled “Aging Pathways modulate TDP-43 Protein Aggregation and Neurotoxicity” at the 2011 Pepper OAIC Annual Meeting at Bethesda, Maryland.