James D. Lechleiter, Ph.D.Professor
University of Arizona, 1984
Director, Core Optical Imaging Facility
Dr. Lechleiter joined the department in March, 2000. He served as a member of the National Science Foundation (NSF) Study Panels on Instrumentation Development for Biomedical Research and served on Signal Transduction and Regulation. He has also served as an adhoc member for multiple National Institutes of Health (NIH) Special Emphasis Panels and study sections including: "Radiation Study Section", "Cell Development and Function-5", "Cell Biology and Physiology" and "Membrane Biology and Protein Processing". Dr. Lechleiter has extensive experience with imaging technology, its application towards current problems in cell biology and is the director of the institutional Optical Imaging facility. He lectures in biophysics, cell biology and neurobiology as well as the fundamental principles of light microscopy. He also shares patents on a confocal microscope for simultaneous imaging with visible and ultraviolet light, a multi-photon laser scanning microscope using an acoustic optical detector and a provisional patent entitled "G-protein coupled receptor enhanced neuroprotection to treat brain injury" has been filed by the University of Texas Health Science Center at San Antonio on his behalf. Dr. Lechleiter is a member of both the Biophysical Society and the Society for Neuroscience.
Click here to view an Video Introduction to Dr. Lechleiter's Lab!
In general, our laboratory is interested in the molecular and cellular mechanisms of neuroprotection that occur in response to ischemic stress, acute brain injury and aging. Most strategies to reduce, slow and repair the severity of brain injuries have focused almost exclusively on neurons. We have focused our research on the potential of astrocytes as a novel theurapeutic avenue for brain treatment. Astrocytes are known to play a crucial role in supporting and protecting neuronal function and in modulating brain energy metabolism. A therapeutic strategy that increases energy production is inherently robust, since the number of potential neuroprotective processes that benefit are significantly higher than a single molecular target.
There are currently four distinct research projects in my laboratory:
First, we are investigating the impact of astrocyte mitochondrial metabolism on neuroprotection during brain injury. We have demonstrated that increased astrocyte energy production significantly decreases the size of brain infarcts induced by photothrombosis (Zheng et al, 2010). This work also highlights our expertise with in vivo optical imaging. In brief, we presented the first in vivo single cell images of cortical mouse astrocytes expressing green fluorescent protein (GFP) documenting the impact of single vessel photothrombosis on cytotoxic edema. The subsequent growth of cerebral infarcts was easily followed as the loss of GFP fluorescence as astrocytes lysed. Cytotoxic edema and the magnitude of ischemic lesions were significantly reduced by treatment with the P2Y1R ligand, 2-MeSADP. At 24 hours, cytotoxic edema in astrocytes was still apparent at the penumbra and preceded the cell lysis that defined the infarct. Delayed 2MeSADP treatment, 24 hours after the initial thrombosis, also significantly reduced cytotoxic edema and the continued growth of the brain infarction. Pharmacological and genetic evidence were presented indicating that 2MeSADP protection was mediated by enhanced astrocyte mitochondrial metabolism via increased IP3-dependent Ca2+ release. Our most recent work in stroke-injured mice indicate that stimulation of P2Y1Rs, 3 hours after the initial photothrombosis, reverses neuronal damage induced by ischemia, as observed in transgenic mice expressing yellow fluorescent protein in neurons (Thy1-YFP). We have also begun to investigate the impact of enhancing neural stem cell activity by stimulating their mitochondrial metabolism. The goal is to enhance the repair and recovery of neuronal tissue after injury. Additional goals in these experiments are to determine the impact of aging on P2Y1R-enhanced neuroprotection as well as investigate details of the underlying mechanism of action.
The second research project investigates a complimentary signaling pathway in astrocytes that also stimulates mitochondrial metabolism. Unlike neurons, astrocytes are capable of utilizing fatty acids as an energy source. At least 20% of astrocyte energy production can come from fatty acid oxidation (FAO). Consequently, increasing FAO in astrocytes is viable strategy to increase mitochondrial metabolism and hence, increase neuroprotection during ischemia when glucose is low. We have shown that a non-transcriptional regulation of Ca2+ signaling and mitochondrial metabolism by T3-bound mTRs (Saelim et al 2004, 2007). Our current work indicates that mTR-dependent stimulation of metabolism is mediated by the mitochondrial trifunctional protein (MTP), the enzyme responsible for long-chain FAO (LCFAO). T3 treatment appears to acutely stabilize the assembly of subunits within the MTP complex in an mTR dependent manner, which in turn, increases FAO and energy production. Our goal is to determine the effect of T3 treatment on MTP stabilization, mitochondrial metabolism, and survival of astrocytes and neurons during ischemia. We will also test the ability of chemical thyroid hormone analogs to affect astrocyte survival, FAO and MTP stabilization. Finally, we want to determine whether T3 or its chemical TH analogs reduce damage from stroke and trauma in vivo.
A third research project is focused on Parkinson's Disease (PD). Repetitive traumatic brain injury (rTBI), which is a major risk factor for developing PD and synuclein-related neurodegenerative diseases and MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) toxin, which targets dopaminergic neurons, are being used as model environmental stressors. Our goal in these experiments is to develop a combinatorial therapy of P2Y1R ligand and T3, alone which would have no side effects, but in concert would be neuroprotective. Our research plan is to first, determine the long-term neuroprotective impact of P2Y1R-enhanced astrocyte mitochondrial metabolism followed by the neuroprotective effects of mTR-enhanced mitochondrial metabolism on injured mouse brain. We then plan to determine the potential synergistic, long-term neuroprotective effects of P2Y1R and mTR stimulation on recovery and repair after brain injury. We note that T3-mTR increased FAO in the mitochondria generates acetyl CoA, which is a critical substrate of the tricarboxylic acid cycle (TCA). Since P2Y1Rs stimulate Ca2+ sensitive dehydrogenases in the TCA, we anticipate that astrocyte mitochondrial metabolism will be synergistically increased. Indeed, preliminary experiments indicated the combined treatment of cultured astrocytes with T3 and 2MeSADP significantly increases cell viability in response to glucose deprivation and oxidative stress, conditions that are likely exist in the early, causative stages of PD.
The final research project in our laboratory is an investigation of the role of Ca2+ signaling during the initiation and recovery of cells from the unfolded protein response (UPR). Our data indicate that the ubiquitous Ca2+ dependent phosphatase, calcineurin (CN), plays a central role in the early phase of the UPR. This classic phosphatase binds to PERK and surprisingly, increases its autophosphorylation. This new protective role of CN is opposite to its later function during stress when CN has been reported to enhance neuronal cell death after ischemia. Our data also indicate that a small stress-induced Ca2+ leak from the ER is critical to PERK-mediated phosphorylation of elF2α. The long-term goal of this work is to be able to turn the early UPR on or off as a new therapeutic tool. Our plan is to first determine the molecular mechanism by which CN binding to PERK increases autophosphorytion during the early UPR and subsequently, to determine how the interaction of CN with PERK is terminated when ER stress is removed. Second, we plan to define the impact of isoform specific CN binding to PERK on astrocyte-mediated neuroprotection in cells cultured from wildtype, CN-A deficient and PERK deficient mouse models during OGD. Third, we will delineate the in vivo impact of CN regulated UPR in the brain during the early phase of cell stress induced by stroke, prior to ischemia-induced cell death.
Recombinant DNA, single and two-photon imaging techniques are used in our laboratory.
The model systems that we work with include cell culture, whole animal mice, C. elegans and Xenopus oocytes.
Chocron ES, Sayre NL, Holstein D, Saelim N, Ibdah JA, Dong LQ, Zhu X, Cheng SY, Lechleiter JD. (2012) The Trifunctional Protein Mediates Thyroid Hormone Receptor Dependent Stimulation of Mitochondria Metabolism. Mol Endocrinol. 2012 May 8. Molecular Endocrinology Original Research.
Zheng W, Watts LT, Holstein DM, Prajapati SI, Keller C, Grass EH, Walter CA, Lechleiter JD. (2010) Purinergic Receptor Stimulation Reduces Cytotoxic Edema and Brain Infarcts in Mouse Induced by Photothrombosis by Energizing Glial Mitochondria. PLoS One. 2010 Dec 22;5(12):e14401. PLoS ONE Research Article.
Bollo M, Paredes RM, Holstein D, Zheleznova N, Camacho P, Lechleiter JD. (2010) Calcineurin interacts with PERK and dephosphorylates calnexin to relieve ER stress in mammals and frogs. PLoS One. 2010 Aug 5;5(8). pii: e11925. PLoS ONE Research Article.
Wu, J., Holstein, D., Upadhyay, G., Lin, D.T., Conway, S., Muller, E. and Lechleiter, J.D. (2007) Purinergic Receptor Stimulated IP3-Mediated Ca2+ Release Enhances Neuroprotection by Increasing Astrocyte Mitochondrial Metabolism During Aging. J. Neuroscience 2007 Jun 13;27(24):6510-20.
Saelim, N., John, L.M., Park, J.S., Wu, J., Bai, Y., Camacho, P. and Lechleiter, J.D. (2004) Non-Transcriptional Modulation Of Intracellular Ca2+ Signaling By Ligand Stimulated Thyroid Hormone Receptor. J. Cell Biol. Dec 6; 167(5):915-24.
Lin, D. and Lechleiter, J.D. (2002) Mitochondrial Targeted Cyclophilin D Protects Cells From Cell Death by Peptidyl Prolyl Isomerization. J. Biol. Chem. 277, 31134-31141.
Jouaville, L.S., Ichas, F., Holmuhamedov, E., Camacho, P. and Lechleiter, J.D. (1995) Synchronization of calcium waves by mitochondrial substrates in Xenopus laevis oocytes. Nature. Oct 5;377(6548):438-41 (with coverphoto).
Lechleiter, J.D., Girard, S., Peralta, E. and Clapham, D. (1991) Spiral calcium wave propagation and annihilation in Xenopus laevis oocytes. Science. Apr 5;252(5002):123-6 (with coverphoto).
Movie Title: Spiral Ca2+ waves in Xenopus oocyte.
Text Spiral Wave Movie
Intracellular Ca2+ is a ubiquitous second messenger that controls the activity of a multitude of enzymatic processes. Ca2+ cannot be metabolized in a manner that is analogous to the cycle of protein phosphorylation / de-phosphorylation. Rather, Ca2+ signals are mediated by changes in concentration of the ion. Studies in our laboratory revealed spiral waves of intracellular Ca2+ release induced by inositol 1,4,5 trisphosphate (IP3) (Figure 2). Spiral waves are the trademark pattern formations of excitable media and have been described in other systems such as the classic Belousov-Zhabotinsky chemical reaction, aggregating slime mold, and electrical activity in neuronal tissue. The active propagation of Ca2+ release in the form of Ca2+ waves provides an efficient mechanism to communicate hormonal signals over long distances.