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. 2013;3:2582.
doi: 10.1038/srep02582.

Paravascular microcirculation facilitates rapid lipid transport and astrocyte signaling in the brain

Vinita Rangroo Thrane  1 , Alexander S Thrane, Benjamin A Plog, Meenakshisundaram Thiyagarajan, Jeffrey J Iliff, Rashid Deane, Erlend A Nagelhus, Maiken Nedergaard
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Paravascular microcirculation facilitates rapid lipid transport and astrocyte signaling in the brain

Vinita Rangroo Thrane et al. Sci Rep. .
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Abstract

In the brain, a paravascular space exists between vascular cells and astroglial end-foot processes, creating a continuous sheath surrounding blood vessels. Using in vivo two-photon imaging we demonstrate that the paravascular circulation facilitates selective transport of small lipophilic molecules, rapid interstitial fluid movement and widespread glial calcium signaling. Depressurizing the paravascular system leads to unselective lipid diffusion, intracellular lipid accumulation and pathological signaling in astrocytes. As the central nervous system is devoid of lymphatic vessels, the paravascular space may serve as a lymphatic equivalent that represents a separate highway for the transport of lipids and signaling molecules.

Figures

Figure 1. Rapid paravascular movement of lipophilic tracers.
(a) Experimental design for studying tracer (red) movement in paravascular space via cisterna magna. Inset: electron micrograph of penetrating arteriole (PA) with surrounding paravascular space (PVS). Scale bar represents 2.5 μm. (b) Epifluorescence montages illustrate distribution of Texas red hydrazide (TXR), fluorescein isothiocyanate dextran (FITC) and tetramethylrhodamine dextran (TMR). Top insets display auto-thresholded images. Scale bar represents 200 μm. (c) Quantification of brain parenchymal penetration. **P < 0.01, n = 6 animals for all groups, Mann-Whitney U. Data are shown as mean ± SEM.
Figure 2
Figure 2. Lipophilic tracers selectively enter and exit brain via paravascular space surrounding arterioles and venules.
(a) Left: in vivo two-photon image of rhod-2 circulation via the paravascular space in Glt1-eGFP mouse. White circles indicate penetrating arterioles. Surface artery (SA). Scale bar represents 100 μm. Right: high magnification images of the paravascular space surrounding penetrating arteriole at serial depths. (b) Cross sectional intensity traces illustrating the paravascular space (rhod-2, red) and intravascular space (Texas red dextran) around a penetrating arteriole (PA). Endfoot (EF). Scale bar represents 7.5 (top) and 5 (bottom) μm. (c) Region of interest (left) and analysis of tracer intensity (right) in the paravascular space and surrounding parenchyma. Scale bar represents 10 μm. n = 24 arterioles from 7 animals, paired t test. (d) Ratio of lipophilic tracer fluorescence in paravascular space to surrounding parenchyma at 60 min. Sulforhodamine (SR101), Oregon green BAPTA (OGB). n = 11 (OGB), 15 (SR101), 24 (rhod-2) and 12 (Aqp4−/− rhod-2) arterioles from 16 animals (total), unpaired t test. (e) Immunofluorescence micrographs from NG2-DsRed mouse show entry of palmitic acid lipid along the paravascular space. Antibody against lectin outlines vascular endothelium. White arrows indicate arterioles. Scale bar represents 100 μm. (f, g) Representative images and quantification of rhod-2 tracer in the paravascular space surrounding an arteriole, a capillary and venule. Scale bars represent 7.5 μm. n = 24 (arterioles), 14 (capillaries) and 12 (venules) from 7 animals, paired t test. ***P < 0.001. Data are shown as mean ± SEM.
Figure 3. Depressurizing the paravascular space impairs lipid transport and astrocyte signaling.
(a) Cisterna magna puncture (CMP) temporarily depressurizes the paravascular space. Lipophilic tracer (rhod-2) was applied to cortical surface or injected into parenchyma to assess tissue influx. (b) Cisterna magna puncture (CMP) drains nearly all paravascular tracer (rhod-2). n = 7 arterioles from 2 animals, Wilcoxon signed ranks test. Scale bar represents 10 μm. (c, d) Two-photon images and quantification of lipid tracer labeling in eGFP expressing cortical astrocytes (circled) following sham control and cisterna magna puncture (CMP). Scale bars represent 75 μm. n = 45 cells from 5 animals for both groups, unpaired t test. (e) Normalized rhod-2 astrocyte labeling intensity. n = 45 (Ctrl), 32 (Aqp4−/−) and 45 (CMP) cells from 14 animals (total), one-way ANOVA. (f) Representative traces of spontaneous calcium activity from cortical astrocytes in awake mice. Synchronized (red) and individual (green) transients. (g, h) CMP increases frequency and reduces synchronization of astrocyte calcium signals. n = 60 (ctrl) and 52 (CMP) cells from 10 animals (total), unpaired t test. (i–k) ATP injection (visualized with FITC-dextran) into the paravascular space stimulates rapid and widespread astrocyte calcium wave spreading outwards from the blood vessel. n = 16 (intraparenchymal, IP) and 9 (paravascular space, PVS) slices from 11 animals (total), unpaired t test. Scale bar represents 40 μm. *P < 0.05, **P < 0.01, ***P < 0.001. Data are shown as mean ± SEM.
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References

    1. Abbott N. J. Evidence for bulk flow of brain interstitial fluid: significance for physiology and pathology. Neurochemistry international 45, 545–552 (2004). - PubMed
    1. Abbott N. J., Patabendige A. A., Dolman D. E., Yusof S. R. & Begley D. J. Structure and function of the blood-brain barrier. Neurobiology of disease 37, 13–25 (2010). - PubMed
    1. Sykova E. & Nicholson C. Diffusion in brain extracellular space. Physiological reviews 88, 1277–1340 (2008). - PMC - PubMed
    1. Iliff J. J. et al. A Paravascular Pathway Facilitates CSF Flow Through the Brain Parenchyma and the Clearance of Interstitial Solutes, Including Amyloid beta. Science translational medicine 4, 147ra111 (2012). - PMC - PubMed
    1. Iliff J. J. et al. Brain-wide pathway for waste clearance captured by contrast-enhanced MRI. The Journal of clinical investigation 123, 1299–1309 (2013). - PMC - PubMed

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