- Email: [email protected]
Glutamate but not interleukin-6 influences the phosphorylation of tau in primary rat hippocampal neurons
Neuroscience Letters 261 (1999) 33–36
Glutamate but not interleukin-6 influences the phosphorylation of tau in primary rat hippocampal neurons Michael Hu¨ll*, Ju¨rgen Eistetter, Bernd L. Fiebich, Joachim Bauer Department of Psychiatry and Psychotherapy, University of Freiburg, Medical School, Hauptstrasse 5, D-79104 Freiburg, Germany Received 26 October 1998; received in revised form 7 December 1998; accepted 9 December 1998
Abstract Alzheimer’s disease (AD) is characterized by amyloid plaques, neuritic degenerations, disturbed glutamatergic neurotransmission and a peculiar inflammatory response. Diffuse plaques develop into neuritic plaques when neurites undergo degeneration in the plaque area. Hyperphosphorylation of tau proteins is a major step in neuritic pathology. Interleukin-6 (IL-6) has been found in diffuse and neuritic amyloid plaques in AD. Therefore the question arises whether IL-6 is involved in the transformation of diffuse into neuritic plaques by affecting tau phosphorylation. We investigated the influence of glutamate and IL-6 on tau phosphorylation in cultured primary rat hippocampal neurons. Glutamate but not IL-6 induced a dephosphorylation of tau. Furthermore IL-6 did not influence the glutamate-induced dephoshorylation of tau. We conclude that the role of IL-6 in AD is not related to the phosphorylation of tau. 1999 Elsevier Science Ireland Ltd. All rights reserved.
Keywords: Alzheimer’s disease; Interleukin-6; Tau; Neuritic degeneration; Glutamate
Amyloid plaques and neuritic degenerations are hallmarks of Alzheimer’s disease (AD) [2]. During the pathogenesis of AD, early (diffuse) plaques without neuritic pathology develop into mature (neuritic) plaques exhibiting marked neuritic degeneration in the plaque area. [17]. The major component of neuritic degeneration in AD is hyperphosphorylated tau [8]. Activation of microglia and production of complement proteins and cytokines such as interleukin-6 (IL-6) have previously been demonstrated in amyloid plaques [10,15,16]. IL-6 has been found in early stages of plaque formation where neuritic degeneration is still not detectable [11]. In AD alterations of glutamatergic neurotransmission have been suggested with loss of the physiological ‘beneficial’ role and augmention of excitotoxicity [13]. In cultured primary hippocampal neurons tau is phosphorylated at serine 199 and 202 as is hyperphosphorylated tau in AD [5]. Glutamate has been shown to induce the dephosphorylation
* Corresponding author. Tel.: +49-761-2706501; fax: +49-7612706619; e-mail: [email protected]
0304-3940/99/$ - see front matter PII: S03 04-3940(98)010 03-9
of tau in cultured rat hippocampal neurons [4]. IL-6 can influence the effect of glutamate on neurons. IL-6 protects cultured primary hippocampal neurons against glutamate induce cell death [19]. However, after several days of treatment with IL-6, cultured cerebellar neurons respond to glutamate with an increased calcium influx [14]. Therefore the divergent effects of IL-6 depend on duration of treatment and neuronal cell type. The relationship between IL-6 and the transformation of early (diffuse) amyloid plaques into mature (neuritic) amyloid plaques is unclear. Here we investigated both the effects of IL-6 on tau phosphorylation, and the effects of IL-6 on glutamate-induced tau dephosphorylation in hippocampal neurons. Hippocampal neuronal cell culture were prepared as described (Mattson et al., 1995) without the use of enzymes for dissociation. Briefly, the hippocampi of rat embryos from embryonic day 18 were mechanically dissociated in Dulbecco’s modified essential medium (DMEM) with 10% horse serum. Cells were seeded onto poly-D-lysine coated tissue culture plastic at a density of 2000 cells/mm2. Two hours after plating, medium was replaced by serum-free
1999 Elsevier Science Ireland Ltd. All rights reserved.
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M. Hu¨ll et al. / Neuroscience Letters 261 (1999) 33–36
DMEM/Ham’s F12 without glutamate, with N2 supplement and 0.1% bovine serum albumin. Cultures were treated at various time points with recombinant IL-6 (TEBU) at a final concentration of 100 U/ml. After 8 days in culture, neurons were exposed to various concentrations of glutamate for 6 h. Neuronal proteins were harvested in preheated SDS sample buffer containing 100 mM orthovanadate. For western blotting 20 mg of cell lysates were subjected to SDS-PAGE electrophoresis using a 7.5% acrylamide gel. Blotting onto PVDF membrane (Millipore) was followed by blocking of unspecific binding sites with Rotiblock (Roth, Germany) for 1 h. Protein bands representing total tau (phosphorylated and dephosphorylated tau) were visualized with a polyclonal antibody against total tau (DAKO, Germany). Further, we used the phosphorylation specific monoclonal antibodies AT8, recognizing tau phosphorylated at serine 202 (Innogenetic, Belgium), and BT2, recognizing tau unphosphorylated at this epitope (Innogenetic, Belgium). The antibody AT8 recognizes phosphorylated tau in protein extracts and tissue sections of AD brains and in cultured rat hippocampal neurons [9]. Antibodies were diluted 1:5000. Bound antibodies were detected with horseradish peroxidase coupled secondary antibodies using chemiluminescence (ECL western blotting system from Amersham) according to the manufacturer’s instructions. In control hippocampal cultures, AT8 detects a phosphorylated band of tau proteins at approximately 58 kDa which is absent after stimulation with 200 mM glutamate (Fig. 1A, compare lanes 1 and 2). In parallel with the disappearance of the phosphorylated band after glutamate treatment, a band of dephosphorylated tau proteins is
newly detected by the BT-2 antibody at approximately 50 kDa in the same protein sample (Fig. 1B, compare lanes 1 and 2). The effect of glutamate on the dephosphorylation of tau depends on the concentration of glutamate with a half maximal effect at approximately 100 mM (Fig. 1, compare lanes 1, 2, 3 and 4). Stimulation of hippocampal neurons for 48 or 72 h with 100 U/ml IL-6 alone had no influence on tau phosphorylation (Fig. 1A,B, compare lanes 1, 5 and 6). Prestimulation with IL-6 for 42 or 66 h prior to a 6 h challenge with glutamate did neither enhance nor reduce the glutamateinduced dephosphorylation of tau (Fig. 1, compare lanes 2 with 6 and 10, lanes 3 with 7 and 11, lanes 4 with 8 and 12). We also investigated the ability of IL-6 to block the effect of glutamate after shorter periods of prestimulation (5 min, 18 h; Fig. 2). Interestingly IL-6 has been shown to protect hippocampal neurons against glutamate toxicity under these conditions [19]. However, neither a prestimulation for 5 min (Fig. 2, lane 3) nor 18 h (Fig. 2, lane 4) altered the glutamate-induced dephosphorylation of tau. The unaltered glutamate-induced dephosphorylation is again obvious in the disappearance of the AT8-positive (Fig. 2A) and the appearance of the BT-2-reactive band (Fig. 2B) after a 6 h challenge with glutamate. Again, prolonged stimulation with IL-6 (48 h, 72 h) showed no inhibiting effect (Fig. 2, lanes 5 and 6). In conclusion, our experiments did neither show any influence of IL-6 itself on the phosphorylation of tau nor on the glutamate-induced dephosphorylation of tau. The inability of IL-6 to prevent the glutamate-induced dephosphorylation is interesting, because IL-6 has previously
Fig. 1. The effects of IL-6 and glutamate on tau phosphorylation. Western blots were incubated with AT8 (A) or BT2 (B). Protein samples were loaded in the same order on both gels. 100 U/ml IL-6 was added 48 or 72 h before harvesting. Stimulation with various concentrations of glutamate started 6 h before harvesting. Treatments of primary hippocampal neurons were as follows: lane 1, untreated; lanes 2–4, 200, 100 or 50 mM glutamate; lane 5, IL-6 for 48 h; lanes 6–8, IL-6 for 48 h plus 200, 100 or 50 mM glutamate; lane 9, IL-6 for 72 h; lanes 10–12, IL-6 for 72 h plus 200, 100 or 50 mM glutamate. The arrow in (A) marks the AT8 immunoreactive band which is present in the control (lane 1) and after IL-6 treatment (lanes 5 and 9) but disappears dose dependently after glutamate stimulation. The arrow in (B) marks the band of dephosphorylated tau which appears after glutamate treatment.
M. Hu¨ll et al. / Neuroscience Letters 261 (1999) 33–36
35
mice expressing IL-6 in a brain specific manner [3,11,18]. However the molecular mechanisms that may mediate the pathogenic effects of IL-6 in AD remain to be resolved. The technical assistance of Sandra Hess and the helpful discussion with Alexander Craig are gratefully acknowledged. This work was supported in part by grants of the Deutsche Forschungsgemeinschaft (Fi 683/1-1 and SFB 505/B1).
Fig. 2. The effect of IL-6 on glutamate-induced tau dephosphorylation. Western blots were incubated with AT8 (A), BT2 (B) or a phosphorylation insensitive polyclonal antibody (C). Protein samples were loaded in the same order on all three gels. Lane 1, untreated control; lanes 2–6 after treatment for 6 h with 1 mM glutamate. IL-6 was added 5 min (lane 3), 18 h (lane 4), 42 h (lane 5) and 66 h (lane 6) prior to the treatment with glutamate. The arrow in (A) marks the AT8 positive band in the control (lane 1) which disappears after glutamate stimulation. The arrow in (B) marks the band of dephosphorylated tau which appears after glutamate treatment. The arrow in C marks a band of tau proteins with a lower apparent molecular weight after glutamate treatment. This amount of the total tau immunoreactivity is shifted from the tau immunoreactivity at approximately 58 kDa indicating a loss of phosphorylation.
been shown to protect hippocampal neurons against glutamate toxicity [19]. Thus, the role of IL-6 in AD is presumably not related to tau pathology. During recent years, a divergent role of IL-6 in the CNS has been emerging. IL-6 and its receptor have been found in the hippocampus which argues for a physiological role of IL-6 in neuronal metabolismus [7]. Furthermore neurotransmitters and prostaglandins have been shown to induce IL-6 in glial cells [6,12]. However, the effects of IL-6 on neurons have only partially been characterized. Cultured hippocampal neurons show no altered short time survival in the presence of IL-6, but seem to degenerate faster in long-time cultures [1]. A pathogenic role of IL-6 in AD is indicated by its presence in the brains of AD patients and by the marked neurodegeneration that has been observed in transgenic
[1] Araujo, D.M. and Cotman, C.W., Trophic effects of interleukin4, -7 and -8 on hippocampal neuronal cultures: potential involvement of glial derived factors, Brain Res., 600 (1993) 49–55. [2] Braak, H. and Braak, E., Frequency of stages of Alzheimerrelated lesions in different age categories, Neurobiol. Aging, 18 (1997) 351–357. [3] Campbell, I.L., Abraham, C.R., Masliah, E., Kemper, P., Inglis, J.D., Oldstone, M.B.A. and Mucke, L., Neurologic disease induced in transgenic mice by cerebral overexpression of interleukin 6, Proc. Natl. Acad. Sci. USA, 90 (1993) 10061–10065. [4] Davis, D.R., Brion, J.P., Couck, A.M., Gallo, J.M., Hanger, D.P., Ladhani, K., Lewis, C., Miller, C.C., Rupniak, T., Smith, C. and Anderton, B.H., The phosphorylation state of the microtubuleassociated protein tau as affected by glutamate, colchicine and beta-amyloid in primary rat cortical neuronal cultures, Biochem. J., 309 (1995) 941–949. [5] Ferreira, A., Lu, Q., Orecchio, L. and Kosik, K.S., Selective phosphorylation of adult tau isoforms in mature hippocampal neurons exposed to fibrillar A beta, Mol. Cell Neurosci., 9 (1997) 220–234. [6] Fiebich, B.L., Hu¨ll, M., Lieb, K., Gyufko, K., Berger, M. and Bauer, J., Prostaglandin E2 induces interleukin-6 synthesis in human astrocytoma cells, J. Neurochem., 68 (1997) 704–709. [7] Gadient, R.A. and Otten, U., Expression of interleukin-6 (IL-6) and interleukin-6 receptor (IL-6R) mRNAs in rat brain during postnatal development, Brain Res., 637 (1994) 10–14. [8] Goedert, M., Tau protein and the neurofibrillary pathology of Alzheimer’s disease, Ann. N.Y. Acad. Sci., 777 (1996) 121– 131. [9] Goedert, M., Jakes, R. and Vanmechelen, E., Monoclonal antibody AT8 recognises tau protein phosphorylated at both serine 202 and threonine 205, Neurosci. Lett., 189 (1995) 167–170. [10] Griffin, W.S.T., Stanley, L.C., Ling, C., White, L., MacLeod, V., Perrot, L.J., White, C.L. and Araoz, C., Brain interleukin 1 and S-100 immunoreactivity are elevated in Down syndrome and Alzheimer disease, Proc. Natl. Acad. Sci. USA, 86 (1989) 7611–7615. [11] Hu¨ll, M., Strauss, S., Volk, B., Berger, M. and Bauer, J., Interleukin-6 is present in early stages of plaque formation and is restricted to the brains of Alzheimer’s disease patients, Acta Neuropathol. (Berl.), 89 (1995) 544–551. [12] Maimone, D., Cioni, C., Rosa, S., Macchia, G., Aloisi, F. and Annunziata, P., Norepinephrine and vasoactive intestinal peptide induce IL-6 secretion by astrocytes: synergism with IL1beta and TNFalpha., J. Neuroimmunol., 47 (1993) 73–82. [13] Olney, J.W., Wozniak, D.F. and Farber, N.B., Excitotoxic neurodegeneration in Alzheimer disease: new hypothesis and new therapeutic strategies, Arch. Neurol., 54 (1997) 1234–1240. [14] Qiu, Z., Parsons, K.L. and Gruol, D.L., Interleukin-6 selectively enhances the intracellular calcium response to NMDA in developing CNS neurons, J. Neurosci., 15 (1995) 6688–6699. [15] Rogers, J., Webster, S., Lue, L.F., Brachova, L., Civin, W.H., Emmerling, M., Shivers, B., Walker, D. and McGeer, P., Inflammation and Alzheimer’s disease pathogenesis, Neurobiol. Aging, 17 (1996) 681–686.
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[16] Strauss, S., Bauer, J., Ganter, U., Jonas, U., Berger, M. and Volk, B., Detection of interleukin 6 and alpha-2-macroglobulin immunoreactivity in cortex and hippocampus of Alzheimer’s disease patients, Lab. Invest., 66 (1992) 223–230. [17] Wisniewski, H.M. and Terry, R.D., Reexamination of the pathogenesis of the senile plaque, Prog. Neuropathol., 2 (1973) 1– 26. [18] Wood, J.A., Wood, P.L., Ryan, R., Graff-Radford, N.R., Pilapil,
C., Robitaille, Y. and Quirion, R., Cytokine indices in Alzheimer’s temporal cortex: no changes in mature IL-1 beta or IL-1 RA but increases in the associated acute phase proteins IL-6, alpha-2-macroglobulin and C-reactive protein, Brain Res., 629 (1993) 245–252. [19] Yamada, M. and Hatanaka, H., Interleukin-6 protects cultured rat hippocampal neurons against glutamate-induced cell death, Brain Res., 643 (1994) 173–180.
Glutamate but not interleukin-6 influences the phosphorylation of tau in primary rat hippocampal neurons Michael Hu¨ll*, Ju¨rgen Eistetter, Bernd L. Fiebich, Joachim Bauer Department of Psychiatry and Psychotherapy, University of Freiburg, Medical School, Hauptstrasse 5, D-79104 Freiburg, Germany Received 26 October 1998; received in revised form 7 December 1998; accepted 9 December 1998
Abstract Alzheimer’s disease (AD) is characterized by amyloid plaques, neuritic degenerations, disturbed glutamatergic neurotransmission and a peculiar inflammatory response. Diffuse plaques develop into neuritic plaques when neurites undergo degeneration in the plaque area. Hyperphosphorylation of tau proteins is a major step in neuritic pathology. Interleukin-6 (IL-6) has been found in diffuse and neuritic amyloid plaques in AD. Therefore the question arises whether IL-6 is involved in the transformation of diffuse into neuritic plaques by affecting tau phosphorylation. We investigated the influence of glutamate and IL-6 on tau phosphorylation in cultured primary rat hippocampal neurons. Glutamate but not IL-6 induced a dephosphorylation of tau. Furthermore IL-6 did not influence the glutamate-induced dephoshorylation of tau. We conclude that the role of IL-6 in AD is not related to the phosphorylation of tau. 1999 Elsevier Science Ireland Ltd. All rights reserved.
Keywords: Alzheimer’s disease; Interleukin-6; Tau; Neuritic degeneration; Glutamate
Amyloid plaques and neuritic degenerations are hallmarks of Alzheimer’s disease (AD) [2]. During the pathogenesis of AD, early (diffuse) plaques without neuritic pathology develop into mature (neuritic) plaques exhibiting marked neuritic degeneration in the plaque area. [17]. The major component of neuritic degeneration in AD is hyperphosphorylated tau [8]. Activation of microglia and production of complement proteins and cytokines such as interleukin-6 (IL-6) have previously been demonstrated in amyloid plaques [10,15,16]. IL-6 has been found in early stages of plaque formation where neuritic degeneration is still not detectable [11]. In AD alterations of glutamatergic neurotransmission have been suggested with loss of the physiological ‘beneficial’ role and augmention of excitotoxicity [13]. In cultured primary hippocampal neurons tau is phosphorylated at serine 199 and 202 as is hyperphosphorylated tau in AD [5]. Glutamate has been shown to induce the dephosphorylation
* Corresponding author. Tel.: +49-761-2706501; fax: +49-7612706619; e-mail: [email protected]
0304-3940/99/$ - see front matter PII: S03 04-3940(98)010 03-9
of tau in cultured rat hippocampal neurons [4]. IL-6 can influence the effect of glutamate on neurons. IL-6 protects cultured primary hippocampal neurons against glutamate induce cell death [19]. However, after several days of treatment with IL-6, cultured cerebellar neurons respond to glutamate with an increased calcium influx [14]. Therefore the divergent effects of IL-6 depend on duration of treatment and neuronal cell type. The relationship between IL-6 and the transformation of early (diffuse) amyloid plaques into mature (neuritic) amyloid plaques is unclear. Here we investigated both the effects of IL-6 on tau phosphorylation, and the effects of IL-6 on glutamate-induced tau dephosphorylation in hippocampal neurons. Hippocampal neuronal cell culture were prepared as described (Mattson et al., 1995) without the use of enzymes for dissociation. Briefly, the hippocampi of rat embryos from embryonic day 18 were mechanically dissociated in Dulbecco’s modified essential medium (DMEM) with 10% horse serum. Cells were seeded onto poly-D-lysine coated tissue culture plastic at a density of 2000 cells/mm2. Two hours after plating, medium was replaced by serum-free
1999 Elsevier Science Ireland Ltd. All rights reserved.
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M. Hu¨ll et al. / Neuroscience Letters 261 (1999) 33–36
DMEM/Ham’s F12 without glutamate, with N2 supplement and 0.1% bovine serum albumin. Cultures were treated at various time points with recombinant IL-6 (TEBU) at a final concentration of 100 U/ml. After 8 days in culture, neurons were exposed to various concentrations of glutamate for 6 h. Neuronal proteins were harvested in preheated SDS sample buffer containing 100 mM orthovanadate. For western blotting 20 mg of cell lysates were subjected to SDS-PAGE electrophoresis using a 7.5% acrylamide gel. Blotting onto PVDF membrane (Millipore) was followed by blocking of unspecific binding sites with Rotiblock (Roth, Germany) for 1 h. Protein bands representing total tau (phosphorylated and dephosphorylated tau) were visualized with a polyclonal antibody against total tau (DAKO, Germany). Further, we used the phosphorylation specific monoclonal antibodies AT8, recognizing tau phosphorylated at serine 202 (Innogenetic, Belgium), and BT2, recognizing tau unphosphorylated at this epitope (Innogenetic, Belgium). The antibody AT8 recognizes phosphorylated tau in protein extracts and tissue sections of AD brains and in cultured rat hippocampal neurons [9]. Antibodies were diluted 1:5000. Bound antibodies were detected with horseradish peroxidase coupled secondary antibodies using chemiluminescence (ECL western blotting system from Amersham) according to the manufacturer’s instructions. In control hippocampal cultures, AT8 detects a phosphorylated band of tau proteins at approximately 58 kDa which is absent after stimulation with 200 mM glutamate (Fig. 1A, compare lanes 1 and 2). In parallel with the disappearance of the phosphorylated band after glutamate treatment, a band of dephosphorylated tau proteins is
newly detected by the BT-2 antibody at approximately 50 kDa in the same protein sample (Fig. 1B, compare lanes 1 and 2). The effect of glutamate on the dephosphorylation of tau depends on the concentration of glutamate with a half maximal effect at approximately 100 mM (Fig. 1, compare lanes 1, 2, 3 and 4). Stimulation of hippocampal neurons for 48 or 72 h with 100 U/ml IL-6 alone had no influence on tau phosphorylation (Fig. 1A,B, compare lanes 1, 5 and 6). Prestimulation with IL-6 for 42 or 66 h prior to a 6 h challenge with glutamate did neither enhance nor reduce the glutamateinduced dephosphorylation of tau (Fig. 1, compare lanes 2 with 6 and 10, lanes 3 with 7 and 11, lanes 4 with 8 and 12). We also investigated the ability of IL-6 to block the effect of glutamate after shorter periods of prestimulation (5 min, 18 h; Fig. 2). Interestingly IL-6 has been shown to protect hippocampal neurons against glutamate toxicity under these conditions [19]. However, neither a prestimulation for 5 min (Fig. 2, lane 3) nor 18 h (Fig. 2, lane 4) altered the glutamate-induced dephosphorylation of tau. The unaltered glutamate-induced dephosphorylation is again obvious in the disappearance of the AT8-positive (Fig. 2A) and the appearance of the BT-2-reactive band (Fig. 2B) after a 6 h challenge with glutamate. Again, prolonged stimulation with IL-6 (48 h, 72 h) showed no inhibiting effect (Fig. 2, lanes 5 and 6). In conclusion, our experiments did neither show any influence of IL-6 itself on the phosphorylation of tau nor on the glutamate-induced dephosphorylation of tau. The inability of IL-6 to prevent the glutamate-induced dephosphorylation is interesting, because IL-6 has previously
Fig. 1. The effects of IL-6 and glutamate on tau phosphorylation. Western blots were incubated with AT8 (A) or BT2 (B). Protein samples were loaded in the same order on both gels. 100 U/ml IL-6 was added 48 or 72 h before harvesting. Stimulation with various concentrations of glutamate started 6 h before harvesting. Treatments of primary hippocampal neurons were as follows: lane 1, untreated; lanes 2–4, 200, 100 or 50 mM glutamate; lane 5, IL-6 for 48 h; lanes 6–8, IL-6 for 48 h plus 200, 100 or 50 mM glutamate; lane 9, IL-6 for 72 h; lanes 10–12, IL-6 for 72 h plus 200, 100 or 50 mM glutamate. The arrow in (A) marks the AT8 immunoreactive band which is present in the control (lane 1) and after IL-6 treatment (lanes 5 and 9) but disappears dose dependently after glutamate stimulation. The arrow in (B) marks the band of dephosphorylated tau which appears after glutamate treatment.
M. Hu¨ll et al. / Neuroscience Letters 261 (1999) 33–36
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mice expressing IL-6 in a brain specific manner [3,11,18]. However the molecular mechanisms that may mediate the pathogenic effects of IL-6 in AD remain to be resolved. The technical assistance of Sandra Hess and the helpful discussion with Alexander Craig are gratefully acknowledged. This work was supported in part by grants of the Deutsche Forschungsgemeinschaft (Fi 683/1-1 and SFB 505/B1).
Fig. 2. The effect of IL-6 on glutamate-induced tau dephosphorylation. Western blots were incubated with AT8 (A), BT2 (B) or a phosphorylation insensitive polyclonal antibody (C). Protein samples were loaded in the same order on all three gels. Lane 1, untreated control; lanes 2–6 after treatment for 6 h with 1 mM glutamate. IL-6 was added 5 min (lane 3), 18 h (lane 4), 42 h (lane 5) and 66 h (lane 6) prior to the treatment with glutamate. The arrow in (A) marks the AT8 positive band in the control (lane 1) which disappears after glutamate stimulation. The arrow in (B) marks the band of dephosphorylated tau which appears after glutamate treatment. The arrow in C marks a band of tau proteins with a lower apparent molecular weight after glutamate treatment. This amount of the total tau immunoreactivity is shifted from the tau immunoreactivity at approximately 58 kDa indicating a loss of phosphorylation.
been shown to protect hippocampal neurons against glutamate toxicity [19]. Thus, the role of IL-6 in AD is presumably not related to tau pathology. During recent years, a divergent role of IL-6 in the CNS has been emerging. IL-6 and its receptor have been found in the hippocampus which argues for a physiological role of IL-6 in neuronal metabolismus [7]. Furthermore neurotransmitters and prostaglandins have been shown to induce IL-6 in glial cells [6,12]. However, the effects of IL-6 on neurons have only partially been characterized. Cultured hippocampal neurons show no altered short time survival in the presence of IL-6, but seem to degenerate faster in long-time cultures [1]. A pathogenic role of IL-6 in AD is indicated by its presence in the brains of AD patients and by the marked neurodegeneration that has been observed in transgenic
[1] Araujo, D.M. and Cotman, C.W., Trophic effects of interleukin4, -7 and -8 on hippocampal neuronal cultures: potential involvement of glial derived factors, Brain Res., 600 (1993) 49–55. [2] Braak, H. and Braak, E., Frequency of stages of Alzheimerrelated lesions in different age categories, Neurobiol. Aging, 18 (1997) 351–357. [3] Campbell, I.L., Abraham, C.R., Masliah, E., Kemper, P., Inglis, J.D., Oldstone, M.B.A. and Mucke, L., Neurologic disease induced in transgenic mice by cerebral overexpression of interleukin 6, Proc. Natl. Acad. Sci. USA, 90 (1993) 10061–10065. [4] Davis, D.R., Brion, J.P., Couck, A.M., Gallo, J.M., Hanger, D.P., Ladhani, K., Lewis, C., Miller, C.C., Rupniak, T., Smith, C. and Anderton, B.H., The phosphorylation state of the microtubuleassociated protein tau as affected by glutamate, colchicine and beta-amyloid in primary rat cortical neuronal cultures, Biochem. J., 309 (1995) 941–949. [5] Ferreira, A., Lu, Q., Orecchio, L. and Kosik, K.S., Selective phosphorylation of adult tau isoforms in mature hippocampal neurons exposed to fibrillar A beta, Mol. Cell Neurosci., 9 (1997) 220–234. [6] Fiebich, B.L., Hu¨ll, M., Lieb, K., Gyufko, K., Berger, M. and Bauer, J., Prostaglandin E2 induces interleukin-6 synthesis in human astrocytoma cells, J. Neurochem., 68 (1997) 704–709. [7] Gadient, R.A. and Otten, U., Expression of interleukin-6 (IL-6) and interleukin-6 receptor (IL-6R) mRNAs in rat brain during postnatal development, Brain Res., 637 (1994) 10–14. [8] Goedert, M., Tau protein and the neurofibrillary pathology of Alzheimer’s disease, Ann. N.Y. Acad. Sci., 777 (1996) 121– 131. [9] Goedert, M., Jakes, R. and Vanmechelen, E., Monoclonal antibody AT8 recognises tau protein phosphorylated at both serine 202 and threonine 205, Neurosci. Lett., 189 (1995) 167–170. [10] Griffin, W.S.T., Stanley, L.C., Ling, C., White, L., MacLeod, V., Perrot, L.J., White, C.L. and Araoz, C., Brain interleukin 1 and S-100 immunoreactivity are elevated in Down syndrome and Alzheimer disease, Proc. Natl. Acad. Sci. USA, 86 (1989) 7611–7615. [11] Hu¨ll, M., Strauss, S., Volk, B., Berger, M. and Bauer, J., Interleukin-6 is present in early stages of plaque formation and is restricted to the brains of Alzheimer’s disease patients, Acta Neuropathol. (Berl.), 89 (1995) 544–551. [12] Maimone, D., Cioni, C., Rosa, S., Macchia, G., Aloisi, F. and Annunziata, P., Norepinephrine and vasoactive intestinal peptide induce IL-6 secretion by astrocytes: synergism with IL1beta and TNFalpha., J. Neuroimmunol., 47 (1993) 73–82. [13] Olney, J.W., Wozniak, D.F. and Farber, N.B., Excitotoxic neurodegeneration in Alzheimer disease: new hypothesis and new therapeutic strategies, Arch. Neurol., 54 (1997) 1234–1240. [14] Qiu, Z., Parsons, K.L. and Gruol, D.L., Interleukin-6 selectively enhances the intracellular calcium response to NMDA in developing CNS neurons, J. Neurosci., 15 (1995) 6688–6699. [15] Rogers, J., Webster, S., Lue, L.F., Brachova, L., Civin, W.H., Emmerling, M., Shivers, B., Walker, D. and McGeer, P., Inflammation and Alzheimer’s disease pathogenesis, Neurobiol. Aging, 17 (1996) 681–686.
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[16] Strauss, S., Bauer, J., Ganter, U., Jonas, U., Berger, M. and Volk, B., Detection of interleukin 6 and alpha-2-macroglobulin immunoreactivity in cortex and hippocampus of Alzheimer’s disease patients, Lab. Invest., 66 (1992) 223–230. [17] Wisniewski, H.M. and Terry, R.D., Reexamination of the pathogenesis of the senile plaque, Prog. Neuropathol., 2 (1973) 1– 26. [18] Wood, J.A., Wood, P.L., Ryan, R., Graff-Radford, N.R., Pilapil,
C., Robitaille, Y. and Quirion, R., Cytokine indices in Alzheimer’s temporal cortex: no changes in mature IL-1 beta or IL-1 RA but increases in the associated acute phase proteins IL-6, alpha-2-macroglobulin and C-reactive protein, Brain Res., 629 (1993) 245–252. [19] Yamada, M. and Hatanaka, H., Interleukin-6 protects cultured rat hippocampal neurons against glutamate-induced cell death, Brain Res., 643 (1994) 173–180.