Fredrick Pavalko, Ph.D.
Department of Cellular & Integrative Physiology
Indiana University School of Medicine
635 Barnhill Drive, Office: MS 334; Lab: MS 374
Indianapolis, Indiana 46202-5122
E-mail: fpavalko @ iupui.edu
Education / Training
- 1982, B.S. in Biology, Guilford College, Greensboro, North Carolina
- 1987, Ph.D. in Cell Biology, Florida State University, Tallahassee, Florida
- 1987-1991, Postdoctoral Fellowship, Cell Biology and Anatomy, University of North Carolina at Chapel Hill, NC
Research Biography Summary
The primary focus of my laboratory’s research is in understanding the cellular mechanisms of mechanotransduction through integrins in osteoblasts, osteocytes and endothelial cells. Understanding fundamental biology of signal transduction in bone and vascular tissues in response to mechanical cues from the microenvironment is important to a more complete understanding of how best to treat disease. We have developed the novel concept of the “mechanosome” to experimentally test how cells detect and respond appropriately to the mechanical loading environment that exists in the skeleton. My laboratory has over 15 years of experience using in vitro application of mechanical stimuli to cells to evaluating the cellular mechanisms of mechanotransduction. Typically studies on mechanotransduction have focused primarily on understanding the signaling pathways that stimulate cellular responses to load. Recently we have taken a different approach by also trying to understand and alter the structural, signaling and transcriptional molecules that suppress the stimulatory effects of loading. Manipulating these “off switches” might be of much greater therapeutic utility than intensifying the “on switches.” We propose that distinct types of mechanical loading such as fluid shear stress or substrate strain can be manipulated, so that modest mechanical loading can have sustained and/or enhanced anabolic effects via suppressing the MTD “off switches.” We have studied the roles of integrin-associated tyrosine kinases including FAK, Pyk2 and Src which are hot spots for mechanical sensing in focal adhesions. We are working to test the role of Src kinase in osteocytes during mechanotransduction in bone. We are using in vivo and in vitro models to test the novel hypothesis that Src functions in osteocytes to suppress load-induced bone formation. We predict that targeting osteocytes for deletion of Src kinase with remove a negative regulator of bone formation resulting in increased basal and load-induced bone density and that it accomplishes this, in part, by epigenetic regulation of critical bone genes including SOST, RANKL and OPG.
Contribution to Science
1) My research has focused on understanding how communication occurs across cell membranes at sites where the cell adheres to the extracellular matrix and to other cells. As a graduate student (1982-87) I identified and characterized the function of cytoplasmic and membrane proteins that facilitated the motility of ameboid sperm in Caenorhabditis elegans. Sperm from nematodes including C. elegans have a novel motility apparatus that does not involve actin and my doctoral dissertation work shed light on how this sperm was able to crawl rapidly without actin and is unique to nematodes.
Roberts, T.M., Pavalko, F.M. and Ward, S. (1986) Membrane and cytoplasmic proteins are transported in the same organelle complex during nematode spermatogenesis. Journal of Cell Biology 102: 1787 1796. PMID:3517007
Pavalko, F.M. and Roberts, T.M. (1987) Caenorhabditis elegans spermatozoa assemble membrane proteins onto the surface at the tips of pseudopodial projections. Cell Motility and the Cytoskeleton 7:169 177. PMID:3555849
Pavalko, F.M., Holliday, L.S. and Roberts, T.M. (1988) Relationship between plasma membrane mobility and substrate attachment in the crawling movement of spermatozoa from Caenorhabditis elegans. Cell Motility and the Cytoskeleton 11:16 23. PMID:3208296
Pavalko, F.M. and Roberts, T.M. (1989) Posttranslational insertion of a membrane protein on Caenorhabditis elegans sperm occurs without de novo protein synthesis. Journal of Cellular Biochemistry 41:57 70. PMID:2613747
2) As a postdoctoral fellow I worked to identify molecules that interact with the cytoplasmic domains of the integrin family of cell adhesion molecules. Integrins are the most ubiquitous adhesion molecules in human and animal cells and are clustered in the cell membrane at sites where cells interact with the extracellular matrix. I was the first to identify the actin binding protein alpha-actinin as a protein that could also bind directly to integrin beta subunit cytoplasmic domains. This was a significant discovery at the time (early 1990’s) as there were only three proteins known at that time that could link integrins to the actin cytoskeleton and potentially facilitate transmembrane signaling events.
Pavalko, F.M., Otey, C.A. and Burridge, K. (1989) Identification of a filamin isoform enriched at the ends of stress fibers in chick embryo fibroblasts. Journal of Cell Science 94:109 118. PMID:2693470
Otey, C.A., Pavalko, F.M. and Burridge, K. (1990) An interaction between alpha-actinin and the ß1 integrin subunit in vitro. Journal of Cell Biology 111:721 730. PMID:2116421
Pavalko, F.M. and Burridge, K. (1991) Disruption of the actin cytoskeleton by microinjection of proteolytic fragments of alpha-actinin. Journal of Cell Biology 114:481-491. PMID:1907287
Pavalko, F.M., Otey, C.A., Simon, K.O. and Burridge, K. (1991) alpha-Actinin: a direct link between actin and integrins. Biochemical Society Transactions 19:1065-1069. PMID:1794463
3) As part of establishing my own independent research program as an Assistant Professor (1991) I extending my postdoctoral studies to examine how interactions between the actin cytoskeleton and integrins are mediated in leukocytes during activation and crawling. This successful work led us to expand the project to investigate how the actin cytoskeleton interacts with another family of cell adhesion molecules – selectins. This led to the identification of cytoplasmic proteins including alpha-actinin that could interact with multiple cell adhesion molecule families to physically link actin to the cell membrane during cell adhesion, spreading and locomotion.
Pavalko, F.M. and LaRoche, S.M. (1993) Activation of human neutrophils induces an interaction between the integrin ß2 subunit (CD18) and the actin-binding protein alpha-actinin. Journal of Immunology 151:3795-3807. PMID:8104223.
Pavalko, F.M., Walker, D.M., Graham, L., Goheen, M., Doerschuk, C., and Kansas, G.S. (1995) The cytoplasmic domain of L-selectin interacts with cytoskeletal proteins via alpha-actinin: receptor positioning in microvilli does not require cytoskeletal associations. Journal of Cell Biology 129:115-1164. PMID:7538138
Kansas, G.S. and Pavalko, F.M. (1996) The cytoplasmic domains of E- and P-selectin do not constitutively interact with alpha-actinin and are not essential for leukocyte adhesion. Journal of Immunology 157:321-325. PMID:8683133
Sampath, R., Gallagher, P.J. and Pavalko, F.M. (1998) Cytoskeletal interactions with the leukocyte integrin ?2 cytoplasmic tail: activation-dependent regulation of associations with talin and alpha-actinin. Journal of Biological Chemistry 273: 33588-33594. PMID:9837942
4) I expanded this line of research to study the process of cellular mechanotransduction through integrins in bone cells beginning around 1998. This work became the focus of the laboratory and we have helped define the role of cytoplasmic proteins in mechanotransduction induced by fluid shear stress. This work has evolved and continues to the present as we use experimental strategies to determine the molecular mechanisms through which fluid shear stress affects gene expression and bone cell function.
Pavalko, F.M., Chen, N.X., Turner, C.H., Burr, D.B., Atkinson, S., Hsieh, Y.-F., Qiu, J. and Duncan, R.L. (1998) Fluid shear-induced mechanical signaling in MC3T3-E1 osteoblasts requires cytoskeleton-integrin interactions. American Journal of Physiology: Cell Physiology 275:C1591-C1601. PMID:9843721
Pavalko, F.M., Gerard, R.L., Ponik, S.M., Gallagher, P.J., Jin, Y., and Norvell, S.M. (2002) Fluid shear stress inhibits TNF-alpha-induced apoptosis in osteoblasts: a role for shear stress-induced activation of PI3-kinase and inhibition of caspase-3. Journal of Cellular Physiology 194: 194-205. PMID:12494458
Norvell, S.M. Ponik, S.M., Bowen, D.K., Gerard, R. and Pavalko, F.M. (2004) Fluid shear stress induction of Cox-2 protein and prostaglandin release in cultured MC3T3-E1 osteoblasts does not require intact microfilaments or microtubules. Journal of Applied Physiology, 96:957-966. PMID:14617531
Ponik, S.M. and Pavalko, F.M. (2004) Formation of focal adhesions on fibronectin promotes fluid shear stress induction of COX-2 and PGE2 release in MC3T3-E1 osteoblasts. Journal of Applied Physiology, 97:135-142. PMID:15004000
5) In collaboration with my long-time colleague Dr. Joe Bidwell we have developed the “mechanosome” model for experimentally testing molecular mechanisms that regulate the processes of cellular mechanotransduction. This working model has served a valuable function as a hypothesis that is testable in vitro and in vivo to better understand how mechanical stimuli (such as fluid shear stress) that are detected at the cell membrane where cells interact with the extracellular matrix (integrins) affect gene expression and bone cell function.
Pavalko, F.M., Norvell, S.M., Burr, D.B., Turner, C.H., Duncan, R.L. and Bidwell, J.P. (2003) A Model for Mechanotransduction in Bone Cells: The Load-Bearing Mechanosomes. Journal of Cellular Biochemistry 88:104-112. PMID:12461779
Bidwell, J.P. and Pavalko, F.M. (2010) The load-bearing mechanosome revisited. Clinical Reviews in Bone and Mineral Metabolism, 8:213-223. PMID:21479153
Hum J.M., Day R.N., Bidwell J.P., Wang Y., Pavalko F.M. (2014) Mechanical Loading in Osteocytes Induces Formation of a Src/Pyk2/MBD2 Complex That Suppresses Anabolic Gene Expression. PLoS ONE 9(5): e97942. PMID:24841674
Hum, J.M., Siegel, A.P., Pavalko, F.M., and Day, R.N. (2012) Monitoring biosensor activity in living cells with fluorescence lifetime imaging microscopy. International Journal of Molecular Sciences, 13:14385-400. PMID:23203070
Maintenance of optimal skeletal health requires continual remodeling of bone via resorption of old bone followed by deposition of healthy new bone. Our research seeks to understand the molecular mechanisms that direct bone formation and resorption in response to mechanical loading of the skeleton. This general area of research aimed at exploring how mechanical stimuli affect physiologic systems is often referred to as biomechanical signal transduction, or “mechanotransduction”. An important fundamental goal of this type of research is to discover ways in which we might manipulate specific mechanotransduction pathways at the molecular level so that even modest levels of exercise can have outsized anabolic effects. For example, if mechanisms or signaling pathways that inhibit load-induced bone formation are pharmacologically suppressed, it might be possible to get the skeletal benefits of vigorous exercise through more modest physical activity. This would be especially important in the elderly or physically challenged individuals not capable of high impact physical activities that build healthy bone.
Current projects are focused on the role of osteocytes (OCY), the most abundant cell type in bone, in coordinating the response of bone to mechanical load. We propose that the tyrosine kinase Src functions in OCY as a novel suppressor of load-induced bone formation. Global Src null mice have high bone mass (HBM). This is due in part to Src-dependent defects in osteoclast-mediated bone resorption. However, we risk missing an important role that tyrosine kinases may play in the anabolic arm of skeletal mechanotransduction if we attribute the HBM phenotype of Src KO mice entirely to an osteoclast defect in bone resorption. We suggest there is an additional underappreciated role for Src in the osteoblast/osteocyte (OB/OCY) population that inhibits mechanically-induced anabolic signals. Specifically, we propose that upon activation by mechanical stimuli, Src dissociates from integrins (membrane mechanosensors) and translocates to the nucleus as part of a multi-protein complex with Proline-rich Kinase-2 (Pyk2) and the methylated DNA binding protein Methyl-CpG Binding Domain Protein-2 (MBD2), to regulate epigenetics of key bone genes. Thus, OCY may utilize a SrcPyk2-MBD2 “mechanosome” to promote or suppress anabolic or anti-catabolic bone genes by altering promoter associated CpG islands. We are working to experimentally dissect the molecular mechanisms through which Src inhibits bone formation using in vivo and in vitro approaches with the long term goal of better understanding the clinical and translational potential of Src inhibitors to enhance bone density and fracture susceptibility.
Our research using in vitro (cell culture) and in vivo (mouse models) to determine the effect of targeted Src deletion from osteocytes on basal and load-induced bone formation and on disuse-induced bone loss in mice. We are using epigenetic approaches to determine the role of Src in regulation of mechanically sensitive bone genes via changes in promoter methylation. We also use innovative live cell imaging approaches to determine the molecular interactions of Src in the cytoplasm and nucleus of osteoblasts and osteocytes subjected to fluid shear stress in vitro using the technique of FRET-FLIM microscopy in collaboration with the laboratory of Dr. Richard Day.