Release of cytokines by brain endothelial cells: A polarized response to lipopolysaccharide
Introduction
Brain endothelial cells (BECs) constitute an important part of the neuroimmune axis. They are able to both transport and secrete neuroimmune substances, including cytokines. BECs are exposed to endogenous and exogenous neuromodulatory substances, immune cells, neurotransmitters and hormones, environmental stresses and cues, and potentially toxic compounds at both their brain (abluminal) and blood (luminal) sides. Many of these substances, including lipopolysaccharide (LPS) and the endogenous peptide β-amyloid, have been shown or postulated to alter BBB functions (Banks and Morley, 2003, Blanc et al., 1997, Dorheim et al., 1994, Fiala et al., 1998, Jancso et al., 1998, Persidsky et al., 1997, Reyes et al., 1999, Xaio et al., 2001). Systemically, LPS activates macrophages and monocytes through binding to CD14 and toll-like receptor-4 (TLR4) and leads to release of nitric oxide, prostaglandins, and a repertoire of cytokines such as IL-1, TNF-α, and IL-6 (Cao et al., 1997, Chow et al., 1999, Wright et al., 1991). LPS can evidently have similar effects on BECs, inducing the release of IL-6 (Reyes et al., 1999). Other factors also induce the release from BECs of endothelin, IL-8, IL-6, MCP-1, TNF, RANTES, nitric oxide, and prostaglandins (Didier et al., 2002, Dorheim et al., 1994, Hofman et al., 1999, Lee et al., 2001, MCGuire et al., 2003, Simpson et al., 1998, Vadeboncoeur et al., 2003).
BECs are specially modified and positioned to perform BBB functions such as preventing harmful substances from entering the brain and rigorously controlling the passage of constituents in the blood-to-brain or brain-to-blood direction. Collectively, these functions of BBB are aided by a polarization of BBB properties; that is, lipid composition and transporter and receptor protein populations are distributed unevenly and, in some cases, uniquely between the luminal or abluminal membranes of the BEC (Banks and Broadwell, 1994, Betz and Goldstein, 1978, Davson and Segal, 1996, Taylor, 2002, Vorbrodt, 1994, Zambenedetti et al., 1996). Thus, BECs have the potential to receive signals from one compartment (e.g., blood) and to secrete into the other (e.g., brain). For example, BEC cultured as monolayers (MBEC) and exposed to luminal gp120, the viral coat of HIV-1, secrete the cytokine endothelin-1 into the abluminal chamber (Didier et al., 2002).
The MBEC model has been used for over 20 years to study BBB functions (see Fig. 1 schematic). Cells polarize with luminal (blood-side) and abluminal (brain-side) properties reminiscent of in vivo conditions, including the presence and function of tight junctions and polarized transporters (Deli et al., 2005, Joo, 1993, Minokoshi et al., 2002). Anatomical studies of the in vivo BBB show that BECs are very closely associated with neighboring cells such as astrocytes, pericytes, and microglia. These cells help to induce and maintain the BBB by secreting soluble factors capable of acting on the BEC, thus providing the local conditions required for the proper induction, maintenance, and functioning of the BBB. For this particular reason, many BMEC models co-culture BEC with astrocytes, macrophages, or glial cells. However, these models would fail to shed light on the specific abilities of BECs to release cytokines. Keeping that in mind, we used an MBEC model culturing BECs alone to (i) inventory which of 10 common cytokines BECs spontaneously secrete, (ii) determine whether the spontaneous secretion was polarized, (iii) determine the effect of LPS on BEC cytokine secretion, and (iv) determine whether the effect of LPS itself was polarized.
Section snippets
Reagents
Mouse β-amyloid 1–42 and 1–40 were obtained from American Peptide. Dnase I, LPS, fibroblast growth factor, and fibronectin were obtained from Sigma (St. Louis, MO). ProteoPlex murine cytokine array kits detecting 10 cytokines (IL-1α, IL-1β, IL-2, IL-4, IL-6, IL-10, IL-12, GM-CSF, IFN-γ, and TNF-α) were provided by EMD Biosciences (St. Louis, MO).
Isolation and culture of brain endothelial cells
The protocol for isolating mouse BECs and growing them into monolayers (MBEC) was modified as previously reported by our laboratory (Banks et al., 2004
Spontaneous polarized secretion of cytokines by MBEC
We first examined the baseline level of cytokine secretion by MBEC. Since MBEC presents a luminal (facing blood) and an abluminal (facing brain) side, we measured the levels of cytokines in the luminal and abluminal chambers (n = 2/group). Under our experimental conditions, IL-6, GM-CSF, and TNF-α were detected in the fluids from both the luminal and abluminal chambers, while IL-1α and IL-10 were detected in the luminal fluid only (Fig. 2). The concentrations for the other cytokines (IL-1β, IL-2,
Discussion
BECs constitute a distinct category of endothelial cells because of their separation of the CNS and blood and the polarized nature of the luminal and abluminal membranes. BECs have been added to the list of cells which secrete neuroimmune substances into the brain and blood (Didier et al., 2002, Dorheim et al., 1994, Hofman et al., 1999, Lee et al., 2001, MCGuire et al., 2003, Simpson et al., 1998, Vadeboncoeur et al., 2003). Here, we took advantage of a well-established in vitro monolayer
References (37)
- et al.
Lipid peroxidation and protein oxidation in Alzheimer’s disease brain: potential causes and consequences involving amyloid beta-peptide-associated free radical oxidative stress
Free Radic. Biol. Med.
(2002) - et al.
Endothelin-1 and monocyte chemoattractant protein-1 modulation in ischemia and human brain-derived endothelial cell cultures
J. Neuroimmunol.
(2001) - et al.
Nitric oxide synthase activity is elevated in brain microvessels in Alzheimer’s disease
Biochem. Biophys. Res. Commun.
(1994) - et al.
HIV-tat protein induces the production of interleukin-8 by human brain-derived endothelial cells
J. Neuroimmunol.
(1999) - et al.
Beta-amyloid (1–42) peptide impairs blood–brain barrier function after intracarotid infusion in rats
Neurosci. Lett.
(1998) The blood–brain barrier in vitro: the second decade
Neurochem. Int.
(1993)- et al.
Mechanisms of sickness-induced decreases in food-motivated behavior
Neurosci. Biobehav. Rev.
(1996) - et al.
Behavioral effects of cytokines
Brain Behav. Immun.
(2001) - et al.
Cocaine activates redox-regulated transcription factors and induces TNF-alpha expression in human brain endothelial cells
Brain Res.
(2001) - et al.
In vitro demonstration of a saturable transport system for leptin across the blood–brain barrier
Life Sci.
(2001)
Release of prostaglandin E-2 in bovine brain endothelial cells after exposure to three unique forms of the antifungal drug amphotericin-B: role of COX-2 in amphotericin-B induced fever
Life Sci.
Alzheimer’s disease through the eye of a mouse: Acceptance lecture for the 2001 Gayle A. Olson and Richard D. Olson prize
Peptides
Brain endothelial cell production of a neuroprotective cytokine, interleukin-6, in response to noxious stimuli
Brain Res.
Expression of monocyte chemoattractant protein-1 and other beta-chemokines by resident glia and inflammatory cells in multiple sclerosis
J. Neuroimmunol.
How does peripheral lipopolysaccharide induce gene expression in the brain of rats?
Toxicology
Proinflammatory cytokine and chemokine release by human brain microvascular endothelial cells stimulated by Streptococcus suis serotype 2
FEMS Immunol. Med. Microbiol.
Review: Alzheimer’s amyloid beta-peptide-associated free radical oxidative stress and neurotoxicity
J. Struct. Biol.
Effect of LPS on the permeability of the blood–brain barrier to insulin
Brain Res.
Cited by (218)
Melatonin ameliorates lipopolysaccharide induced brain inflammation through modulation of oxidative status and diminution of cytokine rush in Danio rerio
2022, Environmental Toxicology and PharmacologyTissue resident cell processes determine organ damage in systemic lupus erythematosus
2022, Clinical ImmunologyCitation Excerpt :Infection and systemic inflammation are potent activators of ECs and upregulate cytokine and chemokine production which potentiate local immune responses [61]. IL-1, TNF, and LPS signals increase E-selectin, ICAM-1, and VCAM-1 expression in microvascular ECs in vitro [61,62]. Complement activation which occurs invariably in patients and further contributes to inflammation.
A Gut-Brain Axis-on-a-Chip for studying transport across epithelial and endothelial barriers
2021, Journal of Industrial and Engineering Chemistry