CIMED has Awarded Two Pilot and Feasibility Grants for 2020
Tracey Hermanstyne, PhD
Instructor, Department of Developmental Biology
“Molecular Dissection of the Distinct Cellular Mechanisms in the SCN Driving Circadian Rhythms in Physiology and Behavior”
Circadian rhythms, which reflect the presence and functioning of endogenous pacemakers or clocks, have evolved to enable organisms to adapt to daily (24 hour), cyclical changes in the environment. In mammals, including humans, the suprachiasmatic nucleus (SCN) in the hypothalamus is the master circadian pacemaker driving daily rhythms in physiology and behavior. Inherited and acquired (i.e., environmentally-induced) disruptions in circadian rhythms have been associated with a range of pathologies, from cardiac arrhythmias to disturbances in metabolism, mood and sleep. It is well established that the (~20,000) neurons in the SCN utilize a transcription/ translation feedback loop between clock gene and protein expression and generate circadian changes in the repetitive firing rates (higher during the day and lower at night) of SCN neurons that regulate and synchronize the output of the clock to control daily rhythms in physiology and behavior. The cellular and molecular mechanisms linking the clock and the repetitive firing rates of SCN neurons, however, are not known. The studies outlined in this proposal will define these mechanisms directly in three functionally distinct subtypes of GABAergic, Neuromedin S- (NMS-) expressing neurons in the SCN: Vasoactive Intestinal Polypeptide- (VIP-) expressing NMS (VIP+/NMS+) cells; Arginine Vasopressin- (AVP-) expressing NMS (AVP+/NMS+) cells; and, non-VIP/non-AVP NMSexpressing (VIP-/AVP-/NMS+) cells. The proposed studies in this pilot grant will characterize firing properties of three major SCN cell-types, determine the ionic conductances that control cell-type specific differences in firing properties between these cell-types, and determine the ionic conductances that regulate the daily switch (i.e. daytime-to-nighttime and nighttime-to daytime repetitive firing rates) in these SCN cell-types. These studies will provide direct evidence for multiple conductance pathways that regulate
daily rhythms in SCN neuronal excitability and help elucidate how the ‘molecular clock’ drives daily rhythms in repetitive firing rates (the critical output signal that maintains circadian rhythmicity) in each SCN cell-type, helping to clarify the cellular basis of circadian rhythms in physiology and behavior.
********************************
Regina Clemens, MD PhD
Assistant Professor of Pediatrics
“Developmental Regulation of Neutrophil Calcium Signaling by KCa3.1”
Neutrophils are innate immune cells that are a central component of host defense against bacterial and fungal pathogens. Calcium signals initiated via store-operated calcium entry (SOCE) are critical for neutrophil activation however little is known about the mechanisms that modulate the intensity of these signals. We have made a novel observation that mouse neutrophils segregate into two populations characterized by distinct calcium signatures during SOCE. These populations are transcriptionally distinct, suggesting that these are indeed two discrete neutrophil subsets. Our preliminary data demonstrate that: 1) The magnitude of the calcium response in these populations is driven primarily by differential regulation of the cell membrane potential. 2) The cell membrane potential is maintained by expression of the calciumactivated potassium channel KCa3.1 (Kcnn4) in a subset of cells. 3) These populations are regulated during neutrophil development. The goal of this proposal is to test the hypothesis that KCa3.1 expression is a defining feature of a subset of neutrophils, regulated during homeostatic and emergency granulopoiesis, and a key modifier of calcium-dependent neutrophil function. Specific Aim 1 will assess KCa3.1 expression and role in SOCE during neutrophil development and Aim 2 will evaluate the contribution of KCa3.1 to calcium-dependent neutrophil function and use KCa3.1-deficient mice as a tool to probe the role of these neutrophil subsets in disease.
Together these studies will provide novel insight on the mechanisms of regulation of calcium signaling in mature and developing neutrophils, and on the functional role of neutrophil subsets in disease.