Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2011 Sep 14;31(37):13110-7.
doi: 10.1523/JNEUROSCI.2569-11.2011.

In vivo microdialysis reveals age-dependent decrease of brain interstitial fluid tau levels in P301S human tau transgenic mice

Affiliations
Free PMC article

In vivo microdialysis reveals age-dependent decrease of brain interstitial fluid tau levels in P301S human tau transgenic mice

Kaoru Yamada et al. J Neurosci. .
Free PMC article

Abstract

Although tau is a cytoplasmic protein, it is also found in brain extracellular fluids, e.g., CSF. Recent findings suggest that aggregated tau can be transferred between cells and extracellular tau aggregates might mediate spread of tau pathology. Despite these data, details of whether tau is normally released into the brain interstitial fluid (ISF), its concentration in ISF in relation to CSF, and whether ISF tau is influenced by its aggregation are unknown. To address these issues, we developed a microdialysis technique to analyze monomeric ISF tau levels within the hippocampus of awake, freely moving mice. We detected tau in ISF of wild-type mice, suggesting that tau is released in the absence of neurodegeneration. ISF tau was significantly higher than CSF tau and their concentrations were not significantly correlated. Using P301S human tau transgenic mice (P301S tg mice), we found that ISF tau is fivefold higher than endogenous murine tau, consistent with its elevated levels of expression. However, following the onset of tau aggregation, monomeric ISF tau decreased markedly. Biochemical analysis demonstrated that soluble tau in brain homogenates decreased along with the deposition of insoluble tau. Tau fibrils injected into the hippocampus decreased ISF tau, suggesting that extracellular tau is in equilibrium with extracellular or intracellular tau aggregates. This technique should facilitate further studies of tau secretion, spread of tau pathology, the effects of different disease states on ISF tau, and the efficacy of experimental treatments.

Figures

Figure 1.
e-tau in 3-month-old wild-type mice and P301S tau tg mice. A, Tau-5/BT-2 ELISA recognizes recombinant human tau and mouse tau equivalently. n = 4. B, At varying flow rates of the microdialysis perfusion buffer from 0.35 μl/min to 1.5 μl/min, e-tau was quantified by ELISA in the hippocampus in wild-type (WT, n = 12) and P301S tg (P301S tg, n = 7) mice. C, The mean e-tau levels were calculated by the zero flow method. ***p < 0.0001 by unpaired t test. D, ISF (n = 13) and CSF (n = 8) tau levels were measured in 3-month-old wild-type mice. **p < 0.01 by unpaired t test. E, e-tau levels was determined in 3-month-old wild-type mice (WT, n = 5) and tau knock-out mice (Tau KO, n = 5).
Figure 2.
Full-length tau is present in ISF of wild-type and P301S tg mice. A, Hippocampal lysates from Tau KO (KO), wild-type (WT), and P301S tg (P301S tg) mice were analyzed by immunoblot with the anti-tau antibody BT-2 or anti-actin antibody. Thirteen micrograms of protein were loaded per well. Four bands corresponding to endogenous murine tau and one band corresponding to human tau are indicated as white circles and a black circle, respectively. There is also a 39 kDa band representing a form of human tau in the P301S tg hippocampal lysate. This may represent a tau degradation product. ISF tau from wild-type (WT) and P301S tg (P301S tg) mice was immunoprecipitated by anti-tau monoclonal antibodies HJ9.3 (B) or HJ8.1 (C) and analyzed by immunoblot. The bands were visualized by biotinylated BT-2 antibody. The gray and black arrows indicate endogenous murine tau and human tau, respectively.
Figure 3.
e-tau in P301S tg mice and wild-type mice at different ages. A, Zero flow experiments were performed in 3- (3 mo, n = 12), 6- (6 mo, n = 12), and 12- (12 mo, n = 8) month-old P301S tg mice. Tau levels at each flow rate were quantified by ELISA. B, Zero flow experiments were performed in 3- (3mo, n = 12) and 12- to 15- (12–15 mo, n = 6) month-old wild-type mice. Tau levels at each flow rate were quantified by ELISA. C, The mean e-tau was assessed in 3- (3mo, n = 12), 6- (6mo, n = 8), and 12- (12 mo, n = 8) month-old P301S tg mice and 3- (3 mo, n = 12) and 12- to 15- (12–15 mo, n = 6) month-old wild-type mice by the zero flow method. *p < 0.05, **p < 0.01. D, The percentage recovery of tau from P301S tg mice was calculated and plotted against flow rates. There is no difference in the percentage recovery between groups.
Figure 4.
CSF tau concentration in P301S tg mice. A, CSF tau levels in 3- (3mo, n = 10), 6- (6mo, n = 5), and 12- (12mo, n = 8) month-old P301S tg mice were quantified by ELISA. *p < 0.05. B, Relationship between ISF tau and CSF tau in P301S tg mice. There is no significant correlation between ISF tau and CSF tau.
Figure 5.
Hippocampal soluble and insoluble tau levels in P301S tg mice. A, The hippocampus from P301S tg (P301S tg), wild-type (WT), and Tau KO (Tau KO) mice were sequentially extracted by RAB, RIPA, 70% FA, and extracted proteins were analyzed by immunoblot with BT-2 (anti-tau) or anti-actin antibody as a control. Black and gray arrows indicate human tau and endogenous murine tau, respectively. Tau levels in RAB fractions (B), RIPA fractions (C), and 70% formic acid fractions (D) were quantified by ELISA. n = 5–8, **p < 0.01, ***p < 0.001.
Figure 6.
Tau aggregates induce an acute decrease of ISF tau levels in 3-month-old P301S tg mice. A, Tau aggregates containing the MTBR. MTBR is not recognized by tau antibodies (BT-2, Tau-5) used in ELISA. B, Relative e-tau levels after injection of vehicle (n = 3) or MTBR aggregates (n = 4) in P301S tg mice were measured by ELISA. *p < 0.05.
Figure 7.
Proposed diagram of tau release in the presence or absence of tau aggregates. A, Tau is released from neurons under normal conditions. B, Once tau aggregates form inside (1) or potentially outside (2) of cells, they can sequester intracellular and extracellular soluble tau and lower the level of monomeric tau in the extracellular space.

Similar articles

See all similar articles

Cited by 125 articles

See all "Cited by" articles

Publication types

Feedback