Richard Egleton, Ph.D.

Richard-Egleton-2012Associate Professor
Department: Pharmacology, Physiology and Toxicology
Research Clusters: Cardiovascular Disease, Obesity, and Diabetes; Neuroscience and Developmental Biology (Cluster Coordinator)
Office: BBSC 435H | Laboratory: BBSC 411
Phone: (304) 696-3523 | Fax: (304) 696-7391
E-mail: egleton@marshall.edu

 

Research Gate: https://www.researchgate.net/profile/Richard_Egleton?ev=hdr_xprf
Pubmed: http://www.ncbi.nlm.nih.gov/pubmed/?term=Egleton+RD%2C

Research Interests

Research projects in Dr. Egleton’s laboratory focus on two primary areas, the regulation of CNS barrier function during disease, and substance abuse regulation of vascular function.

Area 1, CNS barriers:

The brain is protected from the fluctuations of substances in the peripheral circulation via the presence of a range of CNS barriers. The two major barriers are the blood-cerebrospinal fluid barrier, located in the choroid plexuses of the lateral IIIrd and IVth ventricles of the brain, and the blood brain barrier (BBB) found in the microvasculature of the brain. My studies focus primarily on the BBB and how this is regulated during disease states and also what the consequences are for the brain due to altered BBB function. The BBB protects the brain by utilizing three different layers of protection a physical barrier, a transport barrier and an enzymatic barrier (Figure 1.).

Fig 1. Click for larger imageFigure 1. A cartoon representation of the BBB The physical basis of the BBB is the presence of tight junctions that prevents para cellular diffusion of substances into the brain. In conjunction with this the transport barrier acts to ensure that specific nutrients can enter the brain and metabolites / toxins are restricted from entry. Finally the BBB has a metabolic barrier with a range of enzymes including those involved in stage 1 and 2 metabolism as well as a number of peptidases.

Unlike microvascular beds in the periphery, endothelial cells of the CNS microvasculature are connected via tight junctions, which prevent the diffusion of substances between the cells. This physical barrier is maintained via a complex interaction of cell-to-cell contacts regulated by transmembrane proteins at the tight junction (Figure 2.). My research has focused on the regulation of tight junction proteins and how this can affect physical barrier function in a number of disease models including diabetes and pain. During diabetes it has been shown that the para cellular permeability of the BBB to low molecular weight markers is increased, indicating that there has been a loss of tight junction integrity. In an animal model of diabetes we have shown a similar increase to low molecular weight markers (sucrose and lanthanum) but not high molecular weight marker (Evans blue albumin) see figure 3 a-b. Subsequent studies showed this was via an opening of tight junctions due to loss of tight junction proteins (figure 3 c-d). Thus during diabetes there is a change in molecular properties of the cerebral vasculature (Hawkins et al., 2007 a). The regulation of the BBB during diabetes appears to be highly regulated and coordinated. During the opening of the physical barrier, there is a simultaneous up regulation of efflux transporters that can help remove substances in the brain. We have shown that there is an increase in the levels and activity of MRP-2, an efflux transporter responsible for limiting drug entry to the brain (Hawkins et al., 2007 b). We believe that these changes in both the physical and transport barrier are coordinated in response to the diabetic insult. Currently my research focuses on what the mechanism is that regulates this process, and how this may be a factor in neurological disorders for which diabetes is a risk factor.

Fig 2. Click for larger imageFigure 2. BBB tight junction The tight junction (TJ) connects adjoining endothelial cells and forms the physical basis of the BBB. TJs consist of a complex interaction of 3 core protein components (1) transmembrane proteins (occludin, claudins and junctional adhesion molecules) (2) Accessory proteins (Zonulae occludins 1-3), and cytoskeletal proteins (actin etc.). Changes in the expression and location of these proteins can lead to significant changes in the BBB barrier function (see Daneman, 2012 for in depth review).

Fig 3a-b. Click for larger imageFig 3c-d. Click for larger image

Figures 3a-b and 3c-d. BBB regulation in rat model of diabetes The effects of streptozotocin (STZ) induced diabetes at 14 days post induction on the BBB in the cortex. (A) Electron microscopy shows an accumulation of the electron dense low molecular weight permeability marker lanthanum (La) in TJ between cells in STZ treated animals. In contrast no La accumulation is seen in control. Further there are indications of edema in the STZ slices. (B) Using in situ perfusion studies sucrose was also shown to be increased while the high molecular weight marker Evans blue albumin was not. These changes are indicative of a loss of TJ function. Molecular studies indicate a significant reduction in the expression of both ZO-1 and Occludin (C & D) and thus a loss of TJ integrity.

Prime candidates for regulating this process are growth factors and receptors in the VEGF cascade. VEGF is a pro angiogenic growth factor that has been linked to the pathogens is of diabetes and is a known regulator of tight junctions and efflux transporters. My studies focus on investigating the role of growth factor regulation on barrier function during diabetes.

Area 2, Substance Abuse Regulation of Vascular Function

West Virginia has a high rate of substance abuse in all demographics including pregnant women. Prescription opioids are one of the more common substances abused amongst pregnant women in WV. There is considerable information known about the effect of cocaine and alcohol on fetal development, but very little is known about how opioid use during pregnancy effects development. We do however know that there is a very high rate of neonatal abstinence syndrome (NAS, withdrawal) in neonates born to opioid abusing mothers, in fact at Cabell Huntington hospital the rate of NAS is almost 10 times the national average, indicating a high rate of abuse (Figure 4). Our studies focus on three main areas of research. The first area is investigating how opioids affect placental blood vessels. The placenta is highly vascularized and is an excellent source for harvesting neonatal blood vessels. In this study we harvest the vessels and investigate how they are altered in drug abuse. We also investigate how cord blood from neonates exposed to substances of abuse can regulate commercially available human endothelial cell lines.

For the second set of studies, we investigate how substances of abuse regulate the Neurovascular Unit (NVU). The NVU is a relatively new concept in the field which integrates the complex interactions of the brain and blood and how these regulate brain barrier function (see figure 4). This is of primary importance when we consider substances of abuse that that can regulate numerous systems within both the brain and periphery (See Egleton, 2014 for Review). My research has focused on two primary abusive substances, tobacco and opioids. For tobacco, we have observed that the primary addictive component nicotine not only regulates various neuronal pathways but also alters brain barrier function via an α-7 nicotinic receptor mediated mechanism leading to an opening of BBB TJ to low molecular weight markers such as sucrose (Hawkins, 2004; Hawkins, 2005). Interestingly in collaboration with Dr. Dasgupta we have seen that nicotine regulation of angiogenesis in several vascular beds is via a regulation of VEGF signaling (Brown 2012; Dom, 2011), a system that has been also linked to tight junction regulation as mentioned above.

Fig. 4. Click for larger imageFigure 4. The cells and interactions of the neurovascular unit (NVU) The NVU composes of a complex interaction between the cells of the brain and the cells and components of the blood. The endothelial cells carry out the major barrier functions of the NVU and are regulated via interactions with the basement membrane, astrocytes, pericytes, microglia and neurons. Further each of the other cellular components of the NVU can also interact and thus coordinate their regulation of barrier function. The interaction of the cells of the NVU can have a regional variation dependent on different receptor and neurotransmitter expression levels on the cellular components. The major interactions that can regulate localized NVU function include endothelial-pericyte (1), endothelial-astrocyte (2), endothelial-microglia (3), endothelial-local neuron (4), astrocyte-microglia (5), astrocyte-local neuron (6), microglia-local neuron (7). There is also considerable evidence for regulation of the NVU on a more global scale by several brain regions that have efferent connections throughout the brain (8). This includes the locus coeruleus and the raphe nuclei. (9) the blood and its various components including white blood cells platelets plasma proteins, hormones and various therapeutics and substances of abuse. The role of the above interactions (1-9) on regulating NVU function during substance abuse is a major focus of my field.

My primary focus in this area, however, is currently the role of opioids in regulating the NVU. Recently, we have observed that rat brain endothelial cells express functional opioid receptors, which can regulate the expression and activity of several key elements of barrier function. These studies are currently in their infancy, but have already produced some interesting data that we are hoping to turn into a grant application in the near future.

References

Brown, K.C., J.K. Lau, A.M. Dom, T.R. Witte, Luo H, C.M. Crabtree, Y.H. Shah, B.S. Shiflett, A.J. Marcelo, N.A. Proper, W.E. Hardman, R.D. Egleton, Y.C. Chen, E.I. Mangiarua, P. Dasgupta. MG624, an α7-nAChR antagonist, inhibits angiogenesis via the Egr-1/FGF2 pathway. Angiogenesis 15(1):99-114, 2012.

Dom, A.M., A.W. Buckley, K.C. Brown, R.D. Egleton, A.J. Marcelo, N.A. Proper, D.E. Weller, Y.H. Shah, J.K. Lau, and P. Dasgupta. The {alpha}7-nicotinic acetylcholine receptor and MMP-2/9 pathway mediate the pro-angiogenic effect of nicotine in human retinal endothelial cells. Invest Ophthalmol Vis Sci. 52(7):4428-4438, 2011

Egleton, R.D. and Abbruscato, T.J. Neurovascular Unit and Drug Abuse. Advances in Pharmacology, in Press, 2014.

Hawkins, B.T., T.F. Lundeen, K.M. Norwood, H.L. Brooks and R.D. Egleton. Increased blood-brain barrier permeability and altered tight junctions in experimental diabetes in the rat: contribution of hyperglycemia and matrix metalloproteinases. Diabetalogia, 50(1):202-211, 2007.

Hawkins B.T., S.M. Ocheltree, K.M. Norwood and R.D. Egleton. Decreased blood-brain barrier permeability to fluorescein in streptozotocin-treated rats. Neuroscience Letters, 411(1):1-5, 2007.

Hawkins, B.T., Egleton, R.D. and Davis, T.P. Modulation of cerebral microvascular permeability by endothelial nicotinic acetylcholine receptors. Am J Physiol Heart Circ Physiol. 289(1): H212-219, 2005.

Hawkins, B.T., T.J. Abbruscato, R.D. Egleton, R.C. Brown, J.D. Huber, C.R. Campos and T.P. Davis. Nicotine increases in vivo blood–brain barrier permeability and alters cerebral microvascular tight junction protein distribution. Brain Res. 1027 (1-2): 48-58, 2004.

Selected Publications

For a full listing of publications, please visit:
Research Gate: https://www.researchgate.net/profile/Richard_Egleton?ev=hdr_xprf
Pubmed: http://www.ncbi.nlm.nih.gov/pubmed/?term=Egleton+RD%2C

A paradigm shift for evaluating pharmacotherapy for Alzheimer’s disease: the 10-patient screening protocol. Weinstein JD, Gonzalez ER, Egleton RD, Hunt DA. Consult Pharm. 2013 Jul;28(7):443-54. doi: 10.4140/TCP.n.2013.443. Review. PMID:23835462 [PubMed – indexed for MEDLINE]

MG624, an α7-nAChR antagonist, inhibits angiogenesis via the Egr-1/FGF2 pathway. Brown KC, Lau JK, Dom AM, Witte TR, Luo H, Crabtree CM, Shah YH, Shiflett BS, Marcelo AJ, Proper NA, Hardman WE, Egleton RD, Chen YC, Mangiarua EI, Dasgupta P. Angiogenesis. 2012 Mar;15(1):99-114. doi: 10.1007/s10456-011-9246-9. Epub 2011 Dec 25. Erratum in: Angiogenesis. 2012 Jun;15(2):331. Dosage error in article text. PMID: 22198237 [PubMed – indexed for MEDLINE]

The α7-nicotinic acetylcholine receptor and MMP-2/-9 pathway mediate the proangiogenic effect of nicotine in human retinal endothelial cells. Dom AM, Buckley AW, Brown KC, Egleton RD, Marcelo AJ, Proper NA, Weller DE, Shah YH, Lau JK, Dasgupta P. Invest Ophthalmol Vis Sci. 2011 Jun 22;52(7):4428-38. doi: 10.1167/iovs.10-5461. PMID: 20554619 [PubMed – indexed for MEDLINE] Free PMC Article