In vivo diffusion of lactoferrin in brain extracellular space is regulated by interactions with heparan sulfate Academic Article uri icon

Overview

MeSH Major

  • Extracellular Matrix
  • Heparan Sulfate Proteoglycans
  • Lactoferrin
  • Somatosensory Cortex

abstract

  • The intercellular spaces between neurons and glia contain an amorphous, negatively charged extracellular matrix (ECM) with the potential to shape and regulate the distribution of many diffusing ions, proteins and drugs. However, little evidence exists for direct regulation of extracellular diffusion by the ECM in living tissue. Here, we demonstrate macromolecule sequestration by an ECM component in vivo, using quantitative diffusion measurements from integrative optical imaging. Diffusion measurements in free solution, supported by confocal imaging and binding assays with cultured cells, were used to characterize the properties of a fluorescently labeled protein, lactoferrin (Lf), and its association with heparin and heparan sulfate in vitro. In vivo diffusion measurements were then performed through an open cranial window over rat somatosensory cortex to measure effective diffusion coefficients (D*) under different conditions, revealing that D* for Lf was reduced approximately 60% by binding to heparan sulfate proteoglycans, a prominent component of the ECM and cell surfaces in brain. Finally, we describe a method for quantifying heparan sulfate binding site density from data for Lf and the structurally similar protein transferrin, allowing us to predict a low micromolar concentration of these binding sites in neocortex, the first estimate in living tissue. Our results have significance for many tissues, because heparan sulfate is synthesized by almost every type of cell in the body. Quantifying ECM effects on diffusion will also aid in the modeling and design of drug delivery strategies for growth factors and viral vectors, some of which are likely to interact with heparan sulfate.

publication date

  • June 17, 2008

Research

keywords

  • Academic Article

Identity

Language

  • eng

PubMed Central ID

  • PMC2448851

Digital Object Identifier (DOI)

  • 10.1073/pnas.0711345105

PubMed ID

  • 18541909

Additional Document Info

start page

  • 8416

end page

  • 21

volume

  • 105

number

  • 24