Research
The Sanabria lab studies the intersection between stress and aging. How do organisms deal with stress and how does the aging process impact the capacity to deal with stress? On the cellular level, cells deal with stress by activating cellular stress responses – often transcriptional responses to activate genes required for restoring cellular homeostasis. These stress responses decline in function during aging, and we are interested in understanding the mechanisms that govern the activation of these stress responses, how and why they fail with age, and how this impacts organismal health.
1) More than just a loading control: actin cytoskeletal function in stress and aging
The actin cytoskeleton is one of the primary “organelles” or “protein complexes”, which we study in the lab. The cytoskeleton is made up of numerous actin monomers that are polymerized together into cables, branches, and other complex structures that play important roles in providing structural support to the cell, trafficking of intracellular components, and cell division. The cytoskeleton is similar to how a single brick can be linked together to make intricate structures such as the scaffold and walls for a house or roads and bridges to allow flow of traffic. Much like the structures of brick walls and roads deteriorate as they age, our lab studies how the actin cytoskeleton within the cell breaks down during the aging process, and how this breakdown can contribute to general loss of health as we age. Our lab aims to define actin cytoskeletal dysfunction as a new fundamental biological hallmark of aging.
A biological hallmark of aging follows three rules: 1) the dysfunction occurs during natural aging in all aging organisms, 2) experimentally causing the hallmark would result in premature aging, and 3) preventing the hallmark from happening can prolong longevity. Using the C. elegans model system, our lab has defined that the actin cytoskeleton shows marked deterioration in organization and function during natural aging, experimentally disrupting the cytoskeleton can cause premature aging, and protecting the cytoskeleton can promote longevity. We are currently translating these studies into other model systems, including drosophila, rodents, and non-human primates.
Our lab is also trying to understand the cell-type specific effects of altering cytoskeletal organization, function, and dynamics on aging. We use both genetic and chemical tools to alter cytoskeletal function and understand how this affects neuron, muscle, intestinal, and skin function. In addition, we aim to understand what machinery exists to preserve actin cytoskeletal health during stress. To accomplish this, we have performed large-scale screens to identify novel regulators of actin health. We have identified numerous critical components of actin regulation, which we define as the “Actin Cytoskeletal Stress Response” (ACSR), which promotes actin quality and function to drive organismal health under conditions of stress. We argue that fundamentally, actin cytoskeletal health dictates organismal health and longevity, and thus activation of the ACSR can have potentially “anti-aging” properties. Finally, we are investigating whether the actin cytoskeleton can be a feasible target for therapeutics both as an anti-cancer and senolytic (targeting senescent cells) agent.
2) Branching out from actin filaments: actin-organelle contacts during aging
Communication between stress responses and organelles has consistently been a growing field; however, the impact of actin health on other organelles is only just starting to be understood. While the impact of actin on mitochondrial fitness and health is well-studied, the direct impact of actin on other organelles, such as the ER, nucleus, and lysosome, are still heavily unexplored. The Sanabria lab hopes to fill this gap in knowledge by studying the impact of actin health and the actin cytoskeletal stress response on the function of other organelles, and also studying how previously identified compartment specific stress responses, such as the unfolded protein responses of the mitochondria (UPRMT) and ER (UPRER), can impact actin health. We are currently performing large-scale genetic screens to identify regulators of the actin cytoskeleton that have direct implications on the form and function of the ER and mitochondria.
The identification of a novel ACSR is a core driving factor for this project. Our preliminary data showed that ACSR components can drive increased resistance to both ER and mitochondrial stress. This data suggests that the ACSR and the actin cytoskeleton can have direct impact on ER and mitochondrial health under conditions of stress and potentially during aging. Thus, we aim to understand what direct or indirect impact the actin cytoskeleton and the ACSR have on organelle dynamics and organelle fitness during stress and aging. We hope to uncover the delicate and tailored regulation of the cytoskeleton and its intricate connections with the form and function of many organelles. Our primary goal is to build a roadmap of interorganelle contacts and how they change during aging, placing the cytoskeleton at the center.
In addition, we are highly interested in studying the function of nuclear actin, an elusive actin species that structurally resembles cytoplasmic actin, but has very little-known function. We are developing tools to both visualize and alter nuclear actin function and aim to uncover how nuclear actin can impact cellular health, cellular stress responses, DNA repair machinery, and transcriptional regulation. Importantly, we are dissecting the similarities and differences between cytoplasmic and nuclear actin to determine whether unique mechanisms drive the form and function of each.
3) Extreme lessons from extremophiles: Tardigrades as a novel organism for aging
“What doesn’t kill you makes you stronger”, the adage by Nietzsche and sung by Clarkson is a concept that is easy to understand. While extreme stress can be damaging, non-lethal stress can activate beneficial stress responses that can promote health and longevity (i.e., hormesis). In numerous model systems, the concept of hormesis is clear: hyperactive stress responses in C. elegans promote longevity, while exercise causes microtears in mammalian muscles that can strengthen them upon repair. Here, we propose to develop a new model system for studying the intersection of stress and aging: Tardigrada (AKA water bears).
Tardigrades are hydrophilous microinvertebrates with unmatched resistance to thermal stress, cold stress, and desiccation, among other stressors. Since they are easy to handle laboratory animals, they represent an ideal model system to uncover the important roles for stress resilience and numerous investigators harness the power of tardigrades to understand stress biology. The short lifespan of tardigrades of ~2-3 months makes them ideal for aging studies; however, their utility as an aging model organism has not yet been explored. This new model system can help determine the mechanistic pathways that provide extreme stress resilience that could potentially impact aging (in potentially extreme ways!) through novel hormesis mechanisms. Our lab is developing new techniques that would allow us to synchronize and age tardigrades, map out the transcriptional, biological, and physiological aging hallmarks of tardigrades, and develop novel stress resilience assays to determine how aging impacts tardigrade stress resilience. Through these studies, we aim to identify which tardigrade mechanisms grant them extreme stress resilience and determine whether these pathways can be harnessed by other organisms to provide both stress resilience and anti-aging benefits.
4) Hijacking cellular stress responses to combat Alzheimer’s Disease
Alzheimer’s disease (AD) is the most common form of dementia and a leading cause of death in the United States. Currently, two of the leading hypotheses for AD pathogenesis involve two proteins that exist in normal, healthy individuals: amyloid beta (Aβ) and Apolipoprotein E (ApoE). The amyloid hypothesis dictates that accumulation of toxic species of Aβ can cause disease due to dense plaques that cause cell death. In addition, the most universally accepted genetic factor associated with AD are ApoE variants. Specifically, three isoforms of ApoE exist in humans: ApoE2, E3, and E4, with ApoE4 exhibiting the highest risk. Considering the almost universal acceptance of ApoE4 risk in AD, ApoE-therapeutic strategies seemed to be a highly promising avenue of research. However, as a critical regulator of lipid transport and synaptic homeostasis, it is clearly becoming evident that targeting ApoE directly may come with its challenges. Thus, while AD research has made tremendous progress within the past several decades, additional work is required to better understand the molecular basis of the disease, maximize diagnosability, and offer the most effective and earliest possible interventions.
Therefore, our lab is investigating multiple methods to better understand disease pathology related to both Aβ and ApoE4. First, we are performing unbiased and agnostic approaches to fully characterize in depth the changes that happen within the human brain during AD in carriers of ApoE2, ApoE3, and ApoE4. We also aim to create new, physiologically relevant models for AD in both C. elegans and transdifferentiated neuron cell culture, which will allow us to directly translate our findings from post-mortem tissue into genetic and molecular model systems. We hope to apply our understanding of the ACSR and other stress responses to test the hypothesis that stress resilience can not only be a driving factor for prolonged longevity but can also have anti-neurodegenerative effects.
5) Beyond the protein factory: endoplasmic reticulum homeostasis
Another major organelle of interest in our lab is the endoplasmic reticulum (ER), which resembles a “factory” of the cell, as it serves as a major site of synthesis for proteins and lipids. Since the ER serves as the “factory,” it is unsurprising that many specific stress response machineries exist to protect the ER. As an analogy, we would want to have our factories that produce our food, clothing, etc. to have sufficient quality control checks and protocols to ensure product quality and safety; the ER must have the same quality control systems to ensure proper synthesis of lipids and proteins that impact the health of the entire cell. One of these quality control mechanisms is called the unfolded protein response of the ER (UPRER). The UPRER is important for maintaining numerous aspects of the ER including protein homeostasis, lipid metabolism, and even functions of other organelles, such as the lysosome.
When the ER is exposed to stress, an ER sensor called IRE-1 will cause splicing of xbp-1 mRNA, allowing synthesis of XBP-1s, which activates the transcription of genes required to restore the functional output of the ER, such as protein and lipid synthesis. UPRER can be hyperactivated by the overexpression of xbp-1s, which increases stress resistance. Importantly, UPRER can be communicated across tissues: overexpression of xbp-1s in neurons is sufficient to result in an organism-wide increase in stress resistance and lifespan extension. We found that there are different neuronal subtypes and their respective neurotransmitter signaling mechanisms that are involved in this neuron-to-body communication that promotes stress resilience and lifespan. Currently, we are studying all neuronal subtypes, their neurotransmitters, and how they can participate in neuron-to-body communication to impact whole organism stress resilience and lifespan.
In addition to these studies, we are interested in several additional projects involving ER homeostasis: 1) The extracellular matrix can communicate with the intracellular environment and affect the ER. Specifically, we find that breakdown of the extracellular sugar hyaluronan can increase ER stress resistance and extend lifespan. We propose to study how changes to the ECM are communicated to the intracellular environment, how these changes impact ER form and function, and how this impacts the aging process. 2) The lysosome, the cell’s primary recycling hub, serves as a counterpart to the ER and thus lysosome-ER communication is essential to balance the synthesis and breakdown of cellular components. We aim to understand this intricate balance between the lysosome and ER to maintain cellular homeostasis. 3) Studying how the actin cytoskeleton can impact ER homeostasis and vice versa (see project 2).