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. 2007 Mar;170(3):921-9.
doi: 10.2353/ajpath.2007.060664.

Evidence of a role for lactadherin in Alzheimer's disease

Jacques Boddaert  1 , Kiyoka Kinugawa, Jean-Charles Lambert, Fatiha Boukhtouche, Joffrey Zoll, Régine Merval, Olivier Blanc-Brude, David Mann, Claudine Berr, José Vilar, Béatrice Garabedian, Nathalie Journiac, Dominique Charue, Jean-Sébastien Silvestre, Charles Duyckaerts, Philippe Amouyel, Jean Mariani, Alain Tedgui, Ziad Mallat
Affiliations

Evidence of a role for lactadherin in Alzheimer's disease

Jacques Boddaert et al. Am J Pathol. 2007 Mar.

Abstract

Lactadherin is a secreted extracellular matrix protein expressed in phagocytes and contributes to the removal of apoptotic cells. We examined lactadherin expression in brain sections of patients with or without Alzheimer's disease and studied its role in the phagocytosis of amyloid beta-peptide (Abeta). Cells involved in Alzheimer's disease, including vascular smooth muscle cells, astrocytes, and microglia, showed a time-related increase in lactadherin production in culture. Quantitative analysis of the level of lactadherin showed a 35% reduction in lactadherin mRNA expression in the brains of patients with Alzheimer's disease (n = 52) compared with age-matched controls (n = 58; P = 0.003). Interestingly, lactadherin protein was detected in the brains of patients with Alzheimer's disease and controls, with low expression in areas rich in senile plaques and marked expression in areas without Abeta deposition. Using surface plasmon resonance, we observed a direct protein-protein interaction between recombinant lactadherin and Abeta 1-42 peptide in vitro. Lactadherin deficiency or its neutralization using specific antibodies significantly prevented Abeta 1-42 phagocytosis by murine and human macrophages. In conclusion, lactadherin plays an important role in the phagocytosis of Abeta 1-42 peptide, and its expression is reduced in Alzheimer's disease. Alterations in lactadherin production/function may contribute to the initiation and/or progression of Alzheimer's disease.

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Figures

Figure 1
Figure 1
Lactadherin expression in cultured cells. Shown are the results of Western blot analyses. In each panel, equal amounts of proteins were loaded. A: Western blot analysis was performed on protein extracts of confluent human aortic smooth muscle cells (SMCs) obtained at different time points (d indicates day) after the beginning of culture. SMCs were from either newborn (N; <2 years old) or adult (A; >18 years old) humans. Lactadherin expression is higher in adult SMCs and increases as a function of time in culture in both newborn and adult SMCs. B: Lactadherin is enriched in supernatant membrane fractions presenting the characteristics of exosomes, ie, membrane fractions rich in Lamp-2, MHC-I, and tsg101 (pellet 3). Pellets 1, 2, and 3 were obtained after serial centrifugation of cell supernatants at 2,500 × g for 20 minutes (pellet 1; cell debris), then 10,000 × g for 45 minutes (pellet 2, cell microparticles), then 100,000 × g for 90 minutes (pellet 3, exosomes). C: Lactadherin expression in confluent adult human astrocytes. D: Lactadherin expression in confluent murine neonatal astrocytes. Cell-associated lactadherin expression increases with time in culture.
Figure 2
Figure 2
Lactadherin expression in normal and AD brains. A: Representative immunohistochemical staining of lactadherin protein expression (green) in brains of patients with AD or controls. B: Brain mRNA levels of lactadherin/GAPDH ratio (expressed as percentage of controls), determined using quantitative RT-PCR. Results are expressed as mean ± SD (n = 52 AD brains and 58 control brains).
Figure 3
Figure 3
Lactadherin expression in brain temporal sections of patients with or without AD. A–E: Representative immunohistochemical staining of lactadherin protein expression in brain specimens of patients with AD (B–E) or controls (A). A: Staining for lactadherin (green) showing expression in cells with astrocyte morphology. B: Lactadherin appears in green and GFAP staining in red. C–E: Lactadherin appears in brown (arrows) and Aβ staining in pink/red (arrowheads). Note that lactadherin-expressing cells are negative for Aβ staining. F: Relation between lactadherin expression and the occurrence of senile plaques. Brain temporal sections of patients with AD were double-stained with lactadherin and Aβ (n = 6 patients). Three Aβ-positive and three Aβ-negative areas were identified in each patient, in which the mean intensity of lactadherin staining was estimated using a semiquantitative immunohistochemical score (0, no staining; 1, weak staining; 2, moderate; 3, strong). The histograms show the mean ± SD scores from six patients. Clearly, lactadherin expression occurred preferentially in Aβ-free areas.
Figure 4
Figure 4
Direct protein-protein interaction between recombinant human lactadherin and Aβ 1-42 peptide using surface plasmon resonance. Top: Recombinant human lactadherin or an RGE lactadherin mutant was injected at 25°C at a flow rate of 10 μl/minute over the active CM5 surface on which the Aβ 1-42 peptide had been immobilized. The RGE mutant of lactadherin does not bind Aβ 1-42 peptide. Bottom: Increased lactadherin-Aβ interaction with increasing amounts of lactadherin. The figure also shows partial but significant inhibition of lactadherin-Aβ interaction using anti-human lactadherin antibody (anti-lac, 45 μg/ml) directed against the RGD sequence of human lactadherin.
Figure 5
Figure 5
Lactadherin and phagocytosis of Aβ microaggregates. A: Representative example of uptake of FITC-conjugated Aβ 1-42 peptide by cultured bone marrow-derived murine macrophages obtained from lactadherin wild-type mice with (+anti-lac) or without (+IgG) in vitro pretreatment with a neutralizing anti-mouse lactadherin antibody (n = 3 to 5 per condition). B: Representative example of uptake of FITC-conjugated Aβ 1-42 peptide by primary murine microglial cells from C57BL/6 mice with (+anti-lac) or without (+IgG) in vitro pretreatment with a neutralizing anti-mouse lactadherin antibody (n = 3 per condition).
Figure 6
Figure 6
Lactadherin and phagocytosis of Aβ microaggregates. A: Example of uptake of FITC-conjugated Aβ 1-42 peptide by cultured bone marrow-derived murine macrophages obtained from either lactadherin-deficient mice (lac KO) or wild-type (lac WT) littermate controls. B: Quantitative analysis (Histolab software; Microvision) of the percentage of FITC-positive cells (percent positive cells) and the mean fluorescence intensity (expressed in arbitrary units, AU) in the murine macrophage cultures from lactadherin-deficient mice or from wild-type mice with or without in vitro pretreatment with a neutralizing anti-mouse lactadherin antibody (anti-lac) (n = 3 to 5 per condition). Control IgG antibody was added in lac WT and lac KO conditions.
Figure 7
Figure 7
Lactadherin and phagocytosis of Aβ microaggregates by blood-derived human macrophages in vitro. A: Two examples of uptake of FITC-conjugated Aβ 1-42 peptide by cultured blood-derived human macrophages in the presence (+anti-Lac) or absence (+IgG) of a neutralizing anti-human lactadherin antibody. B: Quantitative analysis (Histolab software; Microvision) of the percentage of FITC-positive cells (percent positive cells) and the mean fluorescence intensity (expressed in arbitrary units, AU) in the above-mentioned cultures (n = 3 per condition). Values are means ± SD. P values are versus IgG.
Figure 8
Figure 8
Lactadherin and phagocytosis of Aβ microaggregates by murine peritoneal macrophages in vivo. Quantification using flow cytometry of the uptake of FITC-conjugated Aβ 1-42 peptide by peritoneal macrophages in vivo. Macrophages of lactadherin-deficient mice (lac KO, n = 10) showed reduced Aβ uptake compared with littermate controls (lac WT, n = 11; P = 0.0009).
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