Min Zhou, MD, Ph.D - US grants

9984298
This research concerns on the computational and experimental characterization of microstructural toughening effects in advanced ceramics. Focusing on a new TiB2/Al2O3 ceramic composite system
with very promising properties, it will (1) yield a novel micromechanical approach for explicit fracture modeling over multiple size scales, (2) characterize the effects of microstructural morphologies,
phase length scales, constituent properties, and interphase bonding on fracture resistance, (3) elucidate the failure modes and develop failure models for ceramic composites with microstructures of multiple size scales, and (4) identify mechanisms for property enhancement through microstructural revisions.Combined modeling and experiments will focus on the full, time-dependent process of damage initiation, damage progression and failure using time-resolved diagnostics. Experiments will be used to allow direct correlation of applied loading, time-resolved response, and microscopic damage. The education component of this program consists of undergraduate curriculum development at Georgia Tech, outreach to local high school students and teachers for recruitment and engineering awareness, outreach to minority students for recruitment, and outreach to a local minority institution. The curriculum innovation recognizes the drawback of classroom instruction without hands-on experimentation in engineering mechanics education. This effort focuses on strengthening Georgia Tech's undergraduate curriculum in mechanical engineering through proper integration of classroom learning with laboratory experimentation. A novel feature of this effort is the use of an experimental technique developed in the proposed research to facilitate the development of an aptitude for comprehensive engineering analysis. The curriculum innovation and outreach will use the facilities also used for research, offering a natural synergy of graduate research, undergraduate participation, curriculum development, and outreach.

LAY SUMMARY; ION CHANNELS in HIPPOCAMPAL ASTROCYTES. Harold K. Kimelberg and Min Zhou

Voltage gated ion channels for the small cations sodium (Na+ ) and potassium (K+ ) are responsible for the wave of depolarization that travels down the neuronal axon and excites other neurons to which it is linked by synapses, where the depolarization releases neurotransmitters which rapidly diffuse across the synaptic cleft to stimulate the next neuron, and so on,. The formation of circuits by such connected neurons are thought to underlie how the brain works. The properties of the Na+ and K+ ion channels in neurons have been extensively studied. The other major type of brain cells are called glia and they are not excitable. Current studies have now shown that these cells can contain the same type of voltage sensitive sodium and potassium channels as are found in neurons, and also voltage dependant chloride channels. This is surprising as the function of these channels is thought to be to modulate neuronal excitability and the glia are unexcitable.
This project will use a freshly isolated preparation of one of the main kinds of glial cells the astroglia to identify what ion channels are present in these cells and to help understand their functions. Our work to date shows that this preparation can be divided into two different classes of astroglia based on a different repertoire of channels. Knowledge of the detailed properties of these channels will give us important clues as to their functions. We will test one hypothesis that one type of astrocyte but not the other has K+ channels and Cl- channels designed to allow it take up K+ plus Cl- when K+ is released via the outward rectifying K+ channel on neurons during impulse conduction. (293 words).

The Industry/University Cooperative Research Center for Computational Materials Design jointly proposed by Penn State and Georgia Tech, aims to substantially impact progress towards systems-based materials design by promoting research programs of interest to both industry and universities, to enhance the infrastructure of computational materials research in the nation, to explore and extend the interface between engineering systems design, information technology and physics-based simulation of process-structure and structure-property relations of materials, to improve the intellectual capacity of the workforce through industrial participation and conduct of high quality research projects, and to develop curriculum in computational and systems design aspects of materials. This will be achieved by developing long-term partnerships among industry, university and other organizations.

The Industry/University Cooperative Research Center for Computational Materials Design joins Penn State and Georgia Tech to substantially impact progress towards systems-based materials design by promoting research programs of interest to both industry and universities, to enhance the infrastructure of computational materials research in the nation, to explore and extend the interface between engineering systems design, information technology and physics-based simulation of process-structure and structure-property relations of materials, to improve the intellectual capacity of the workforce through industrial participation and conduct of high quality research projects, and to develop curriculum in computational and systems design aspects of materials.

Astrocytes are star-shaped cells that have long been functionally considered to provide structural, housekeeping and metabolic support to neurons in the central nervous system (CNS). This supposition has been based on the fact that astrocytes are not able to relay signals by means of electric impulses, as do neurons. However, astrocytes do exhibit membrane currents that are carried through poorly characterized potassium channels. Although these currents were discovered over 40 years ago, the nature of these channels remains largely unknown. This proposal is focused on determining whether astrocyte currents are carried through a a newly discovery potassium channel family, called two-pore domain potassium channels (2PKs). This project will further explore how changes in astrocyte 2PKs could modulate astrocyte homeostatic functions with consequent effect on neuronal function. Membrane ion channel currents from astrocytes will be measured in acute rat hippocampal slices measure. Potential astrocyte 2PKs will be further explored at the gene level by using single cell RT-PCR, and at the protein level by specific antibody labeling to post astrocytes using confocal immunocytochemistry. The functional impact of astrocytic 2PKs will be determined by silencing identified 2PKs using RNAi in the organotypic cultured hippocampus. These experiments will delineate the role of these channels and clarify the function of astrocytes in general. Since astrocytes play integral roles response of the nervous system to injury or disease, such knowledge has implications for human health as well as for the fundamental understanding of the nervous system.

The PI will provide opportunities for undergraduate, graduate, and postdoctoral students to participate in research on astrocytes. The broader impacts were judged as strong, particularly considering the PI is in an institute without ready access to undergraduate students.

Center for Computational Materials Design (CCMD)

IIP-1034965 Pennsylvania State University (PSU)
IIP-1034968 Georgia Tech (GT)

This is a proposal to renew the Center for Computational Materials Design (CCMD), an I/UCRC center that was created in 2005. The lead institution is Pennsylvania State University, and the research partner is Georgia Tech. The main research mission of the CCMD is to develop simulation tools and methods to support materials design decisions and novel methods for collaborative, decision-based systems robust design of materials.

The intellectual merit of CCMD is based on the integration of multiscale, interdisciplinary computational expertise at PSU and GT. CCMD provides leadership in articulating the importance of integrated design of materials and products to industry and the broad profession of materials engineering; and is developing new methods and algorithms for concurrent design of components and materials.

CCMD has operated successfully in Phase I, and has helped develop a partnership amongst academe, industry and national laboratories. Based on feedback received from the various members, CCMD has outlined in the renewal proposal research thrusts and initiatives for Phase II; and has also identified gaps that will be addressed as research opportunities in Phase II.

CCMD will have a large impact on how industry addresses material selection and development. The expanded university/industry interaction of this multi-university center offers all participants a broader view of material design activities in all sectors. CCMD contributes to US competitiveness in computational materials design by educating new generations of students who have valuable perspectives on fundamental modeling and simulation methods, as well as industry-relevant design integration and materials development. CCMD participates in programs at PSU and GT that support K-12 STEM issues, women and underrepresented groups, undergraduate students, and high school teachers. CCMD plans to disseminate research results via papers, conferences and the CCMD website.

DESCRIPTION (provided by applicant): Astrocytes are the most numerous cell types in the brain and are known to provide structural, metabolic and homeostatic support to the central nervous system (CNS). Although astrocytes can better survive than neurons in cerebral ischemia, the mechanisms accounting for such a different susceptibility among different brain cells are not clear. Predominant expression of a voltage-independent K+ channel conductance, or passive conductance, is a hallmark of mature astrocytes and essential for the homeostatic support of astrocytes to the CNS. Now we know that two members of the two-pore domain K+ channels (K2Ps) K+ channels, TWIK-1 and TREK-1, are among the long-sought for K+ channels accounting for astrocyte passive conductance. K2Ps can be dynamically modulated by a variety of physiochemical and pathological stimuli, including cerebral-ischemia-produced-neuronal-injury-factors (CIPNJFs), such as hypoxia, hypoglycemia, acidosis and pathological release of neurotransmitters. Pathological induction of K2P expression also contributes to the necrotic and apoptotic cell death and cell proliferation that are the two prominent pathological events occurring in the ischemic infarct and penumbra regions. To understand how the physiological expression of astrocyte K2Ps offers protection to astrocytes against early ischemic insults, and how the long-term ischemic conditions induce altered K2P expression in reactive astrocytes and its consequence on the post-stroke outcomes, we hypothesize that the activity of astrocytic K2Ps can be modulated by CIPNJFs in a manner protecting astrocytes against early ischemic insults, and the altered expression of K2P in reactive astrocytes contributes to the compromised homeostatic function in the peri- infarct penumbra region. Five specific aims are proposed to explore these completely unknown areas. 1) Modulation of astrocyte membrane potential and passive conductance by CIPNJFs. This will be done in rat hippocampal slices with gramicidin perforated patch recording to monitor K2Ps modulation without interfering with the CIPNJFs mediated intracellular energy failure and altered signal transduction; 2) Modulation of electrophysiological response of astrocytes to CIPNJFs by neuroprotectant and TREK-1 channel modulator riluzole and sipatrigine; 3) Identify specific K2P-CIPNJF interaction mechanisms by selective silencing of astrocytic K2Ps with siRNAs in organotypic hippocampal slice cultures; 4) Identify K2P expression in rat hippocampal reactive astrocytes in slices prepared from the penumbra region after reversible middle carotid artery occlusion (rMCAO) by confocal immunocytochemistry. 5) Identify functional K2P in reactive astrocytes in rat focal ischemia penumbra region using electrophysiology in acutely prepared hippocampal slices from the rat rMCAO penumbra region. The proposed studies should provide novel insights into the physiological roles and pathological involvement of astrocytic K2P in cerebral ischemia and whether these predominant astrocytic K+ channels could be potential targets for stroke therapeutic strategy.

While astrocytes establish the largest syncytium in the brain through gap junctions, the basic role of syncytial coupling in astrocyte function remains poorly understood. This project takes a novel approach by considering syncytial coupled astrocytes as a functional system based on a mechanism we?ve just discovered. We show that astrocytes are strongly electrically coupled to achieve syncytial isopotentiality, which enables astrocytes to be more efficient in potassium clearance. Based on this, our long-term goal is to understand the mechanisms by which an astrocyte syncytium functions as an integral part of neural circuitries. A central hypothesis of this proposal is that syncytial isopotentiality requires a developmentally mature anatomic structure in a syncytium and can be dynamically regulated by physiological neuronal activity. Because syncytial isopotentiality approaches maturity after the postnatal day 12, the first objective is to determine the anatomic basis underpinning syncytial isopotentiality. We will follow postnatal development to identify the anatomic features underpinning CA1 syncytial isopotentiality. The 3-D structure of CA1 syncytium will be resolved by CLARITY in ALDHIL1-eGFP transgenic mice using confocal microscopy. The ultra-structural details of process-to-process contacts and gap junctions between neighboring astrocytes will be resolved by blockface serial scanning EM. Mathematical models will be used to biophysically rationalize the resultant anatomic database that explains syncytial isopotentiality. The second objective is to identify mechanisms that coordinate dynamic neuronal activity, coupling strength, and isopotentiality. We hypothesize that, in order to maintain syncytial isopotentiality, intensive neuronal activity increases the gating probability of gap junctions through a Ca2+-dependent mechanism. Double patch recording from astrocytes in hippocampal slices and pairs of freshly dissociated astrocytes will be used in proposed studies. The third objective is to determine the pathological impact of epileptic neuronal discharge and structurally altered syncytia in disease models on syncytial isopotentiality. We hypothesize that syncytial isopotentiality can be acutely disrupted by epileptic neuronal firing and chronically disrupted by disease induced astrogliosis. Epileptic neuronal firings will be induced by picrotoxin/Mg2+-free bath solution applied to slices. Astrogliosis, induced by cuprizone in CA1 and by amyloid precursor protein (APP) overexpression in the dentate gyrus, will be used to create structurally altered syncytia over the course of astrogliosis progression. The expected outcomes from the proposed works are to establish a clear syncytial anatomy and isopotentiality relationship, to prove that under physiological conditions, the astrocyte syncytium and its associated neuronal circuitries are interactive components in the brain, and to corroborate above notions from disease model studies. Such results are expected to shed new lights for a novel research direction, in which the mysterious astrocyte function in the adult brain can be explored at a higher hierarchy, syncytial system level, in the normal brain as well as in neurological disorders.

Astrocytes are key players in regulating neuronal excitability and neurotransmission. We have recently shown that astrocytes participate in brain functions thrugh ?team-work?. Specifically, a strong gap junction coupling, astrocytes achieve a state of syncytial isopotentiality across the brain that is crucial for potassium homeostasis. Now our new studies further show that acute disruption of syncytial isopotentiality impairs neuronal excitability nad synaptic transmision. However, our understanding is still in its infancy with respect to how the syncytial isopotentiality is established and dynamically regulated through crosstalk with neuronal signals. To begin to gain insight into this system-wide electrical feature of the astrocyte network, the objective of this proposal will be mostly focused on how neuronal signalings regulate syncytial isopotentiality. Our new studies show that intracellular Ca2+ ([Ca2+]i) is a key regulator of the electrical coupling of astrocyte syncytium. Also through regulating [Ca2+]i, glutamate potentiates electrical coupling of astrocyte syncytial coupling. At the basal physiological level, norepinephrine signaling is indicated to bidirectionally regulate the set point strength of astrocyte coupling through Gq-coupled ?1-adrenergic receptors (?1-AR). Thus, we hypothesize that neuronal norepinephrine signaling establishes the set point of syncytial coupling, whereas glutamatergic signaling induces a novel form of glioplasity for potentiation of astrocyte syncytial coupling. Our first specific aim will establish the role of [Ca2+]i in bidirectionally regulating the electrical coupling of astrocyte syncytium. The electrophysiology and chemogentics with astrocytic expression of Gq-DREADD will be used in these studies. The second aim will determine the mechanism underlying a glutamatergic signaling- induced potentiation of syncytial coupling. Hippocampal CA3?CA1 glutamatergic transmission will be activated in wildtype and conditional Cx43 knockout (hGfap-Cre:Cx43flox/flox) mice to validate that this glial network plasticity is mediated through Cx43 in an [Ca2+]i-dependent fashion. The third aim will determine the role of norepinephrine signaling in establishing a set point strength of astrocyte syncytial coupling. This hypothesis will be examined through pharmacologial and genetic manipulation of astrocytic ?1-AR. The completion of this project is expected to validate the view that astrocyte syncytium indeed interacts as a functional system with neuronal signaling. We expect to uncover the molecular mechanisms underlying the regulation of the basic and plasticity of astrocyte syncytial coupling. Ultimately, these results are expected to shed light on a new research direction, in which the mysterious function of astrocytes can be explored at a biologically higher hierarchy, the level of the syncytial system. This work in healthy CNS lays the foundation for exploring how alteration of astrocyte syncytium etiologically contributes to diseased and injured brains.