Key words: Blood-brain barrier; Astrocytes; Endothelial cells; Neuroregeneration; Cytokines; Trafficking; Spinal cord injury; Neuroinflammation; Obesity

The BBB Group is composed of two laboratories that share resources and provide mutual support.

Blood-Brain Barrier Laboratory - I (Dr. Weihong Pan, Dr. Chuanhui Yu, Dr. Yan Zhang, Dr. Xiaojun Wu)

General Theme - To determine the role of the blood-brain barrier (BBB) in neuroinflammation and neuroregeneration.

Current Projects

• Transport of cytokines in spinal cord injury (SCI): We have shown that in mice after SCI, the transport system for the proinflammatory cytokines tumor necrosis factor alpha (TNF) and leukemia inhibitory factor (LIF) show time- and region-dependent upregulation. We also identified the respective receptors involved in the transport process. These findings lead to further questions: (1) How does transcytosis occur, so that a protein molecule can be directed from the blood side (apical surface of the endothelia of the BBB) to the brain side (basolateral surface), avoiding intracellular degradation so that it can be exocytosed to reach CNS targets? (2) What mechanisms after SCI drive the upregulation of the transport of these molecules? (3) Which are the key steps involved in the upregulation? Thus, we mainly focus on protein trafficking and turnover in the cerebral microvascular endothelial cells composing the BBB.
• Functional implications of the upregulated transport: Cytokines are dynamically involved in neuroinflammation, neuroendocrine changes, and regenerative processes. The specific changes of cytokine transport systems might just reflect an adaptive change of the BBB to CNS insults, or they may serve beneficial roles in promoting functional recovery. Thus, we address the specific consequences of cytokine transport by use of overexpression and knockdown approaches in combination with histological and behavioral parameters.
• Signal modification at the BBB: We have shown at the BBB level that one proinflammatory cytokine can affect the signal transduction and transport of another. This indicates that the BBB plays a crucial role in integrating peripheral stimuli and in relaying messages to the CNS after its “interpretation”. We know only very little from studies with LIF receptors, which are subject to modulation by TNF and lipopolysaccharide. Our ongoing studies mainly focus on the interleukin-15 system and the P-glycoprotein efflux transporter.

Figure from Pan et al., J Neuroimmunol 07: TNF signal across the mouse BBB after iv injection, shown by EM autoradiography.

Figure from Pan et al., Endocrinology 08: Astrocytes (green) express leptin receptor (red). The co-localization (orange) is shown by confocal microscopy.

Blood-Brain Barrier Laboratory - II (Dr. Abba Kastin, Dr. Hong Tu, Dr. Yi He, Mr. Hung Hsuchou)

Focus - To determine the role of the blood-brain barrier (BBB) in neuroendocrine control, particularly related to peptides/polypeptides involved in feeding behavior.

Current Projects

We pioneered the concept that peptides in the periphery have CNS effects several decades ago, and are still on the lead to illustrate the mechanisms of such actions. Our current focus is how these small proteins cross the blood-brain barrier (BBB) and elicit signaling transduction in the cerebral endothelial cells. The significance of these studies lies in the conceptual illustration that the BBB is a dynamic interface between the body and brain, actively engaged in regulatory functions while also protecting the brain from harmful substances.

Adipokines are peptides/protein molecules produced by the fat cells (adipocytes) as well as some other cells in the body. The production of individual adipokines changes over the course of obesity and its subsequent pathological changes; so is the BBB permeation to adipokines. The communication of apipokines and its CNS targets by way of the BBB in turn affects the neuroendocrine status. At the cellular level, our overall goal is to determine the driving force and sorting signals of the intracellular trafficking of adipokines across the cerebral endothelial cells. Peptide and protein ligands were usually thought to be degraded within cells, but the BBB cells may be an exception. Protein-protein interactions during transport across the BBB are being investigated by various techniques, including transport assays in vitro and in vivo involving overexpression, gene knockdown, fluorescent imaging, flow cytometry, fluorescent resonance energy transfer, electron microscopy, immunoprecipitation, gene and protein arrays, and routine quantification of mRNA and protein expression.

In the normal mouse, we continue to characterize transport systems for peptides and proteins. How does the transport of feeding-related peptides change in altered feeding and nutritional states? Do nesfatin and FGF21 enter the brain from the blood? How do different peptides and polypeptides, such as urocortin and leptin, interact at the BBB level? What isoforms of the leptin receptor are involved in transcytosis and also exocytosis? Are both CRH receptors involved in urocortin transport? What long-term effects do urocortin and leptin exert after injection during the neonatal period? Are there differences in expression of leptin receptors and leptin transport between neonatal and adult mice? Do Avy mice, which develop obesity later in life, transport ingestive peptides differently than their controls? And then, how can we use this information to assist in the treatment of pathological obesity?

The studies have been fruitful in the past year. We have published more than 10 papers on this subject this year, provided several didactic reviews, and advocated our research and our institution in a variety of international meetings. Dr. Kastin received an honorary doctorate from University of Uppsala in Sweden, an honorary professorship in Beijing University China, and two awards, in Brazil and in niversity of Florida, respectively. We also organized two international meetings and set up two regional branches of the International Neuropeptide Society (INPS), in Asia and South America. These, along with our publication of the 200-chapter book Biologically Active Peptides by Elsevier last year, and our continued success in editing the journal Peptides, indicated our continuous effort to move the field forward.