Alteration of dopamine release by rat caudate putamen tissues superfused with alpha 2-macroglobulin

Comparative binding of biotinylated neurotrophins to alpha(2)-macroglobulin family of proteins: relationship between cytokine-binding and neuro-modulatory activities of the macroglobulins

Human alpha(2)-macroglobulin (alpha(2)M), pregnancy zone protein (PZP), rat alpha(1)M and acute-phase rat alpha(2)M belong to the alpha(2)M gene family of proteins, which can react covalently with nucleophilic monoamines to yield monoamine-activated (MA) macroglobulins. The MA forms of human alpha(2)M, PZP and rat alpha(2)M have been demonstrated previously to inhibit various neurotrophin-promoted neuronal activities, whereas MA-alpha(1)M is neurostimulatory and all native macroglobulins are generally inactive. The mechanism of neuromodulation is unknown, but it has been postulated that MA macroglobulins might inhibit neurons via their binding and sequestration of neurotrophins. This study employed a novel biotinylation-Western blot technique to compare the neurotrophin-binding properties of the four macroglobulins, and to correlate their binding activities with their known neuro-modulatory activities. In comparison with their respective native counterparts, human and rat MA-alpha(2)M bound slightly more NGF, but significantly less BDNF or NT-3. Native human alpha(2)M and PZP in general have no neuro-modulatory activity, but native PZP bound significantly more NGF, BDNF or NT-3 than either native alpha(2)M or MA-alpha(2)M, which is neuro-inhibitory. It is known that MA-PZP is neuro-inhibitory, but it fails to bind more NGF, BDNF, or NT-3 than native PZP. MA-alpha(1)M is the only macroglobulin known to stimulate NGF-promoted neurite outgrowth, but it bound NGF with similar affinities as native alpha(1)M and rat alpha(2)M; in addition, it bound significantly less BDNF or NT-3 than native alpha(1)M. All the bindings were non-covalent and appeared specific. In conclusion, PZP and rat macroglobulins are versatile carriers of neurotrophins with diverse binding capacities, and the neurotrophin-binding property does not appear to mediate the neuro-modulatory activity of these human and rat macroglobulins.

Rat alpha1-macroglobulin enhances nerve growth factor-promoted neurite outgrowth, TrkA phosphorylation, and gene expression of pheochromocytoma PC12 cells

Monoamine-activated human alpha2-macroglobulin (alpha2M) has been previously demonstrated to inhibit TrkA-, TrkB-, and TrkC-mediated signal transduction. Rat alpha1-macroglobulin (alpha1M) and alpha2M are structural homologues of human alpha2M, but rat alpha1M is distinctly different from rat alpha2M in many ways and its role in the mammalian nervous system is unknown. In this report, monoamine-activated rat alpha1M was demonstrated to enhance in a dose-dependent manner nerve growth factor (NGF)-promoted neurite outgrowth in pheochromocytoma PC12 cells. Monoamine-activated alpha1M by itself, however, was neither neurotrophic nor mitogenic to PC12 cells. To investigate further its possible mode of action, the ability of monoamine-activated alpha1M and normal alpha1M to bind and to activate the NGF receptor (TrkA) was investigated. Monoamine-activated alpha1M formed a more stable complex with TrkA than normal alpha1 M, but the binding of monoamine-activated alpha1M to TrkA was adversely affected by prior stimulation of TrkA with NGF. In addition, monoamine-activated alpha1M enhanced the NGF-promoted TrkA phosphorylation and up-regulated the expression of NGF-inducible immediate-early genes (c-jun and NGFI-A) and delayed-response genes (SCG10 and transin) in PC12 cells; normal alpha1M, in contrast, produced little or no effect. This study demonstrates that alpha1M, the constitutive form of alpha-macroglobulin in the rat, possesses the ability to promote NGF-mediated differentiation in PC12 cells, possibly via its direct action on TrkA receptors and TrkA-mediated signal transduction and gene expression.

Transforming growth factor-alpha's effects on astroglial-cholinergic cell interactions in the medial septal area in vitro are mediated by alpha 2-macroglobulin

We reported previously that two epidermal growth factor receptor ligands, epidermal growth factor and transforming growth factor-alpha, inhibit medial septal cholinergic cell phenotypic expression (choline acetyltransferase and acetylcholinesterase activities) in vitro indirectly via (a) soluble molecule(s) released from astrocytes [Kenigsberg R. L. et al. (1992) Neuroscience 50, 85-97; Kenigsberg R. L. and Mazzoni I. E. (1995) J. Neurosci. Res. 41, 734-744; Mazzoni I. E. and Kenigsberg R. L. (1996) Brain Res. 707, 88-99]. In the present study, we found that this response to transforming growth factor-alpha is mediated, for the most part, by alpha 2-macroglobulin, a potent protease inhibitor with a wide spectrum of biological activities. In this regard, the effects of transforming growth factor-alpha on cholinergic cells can be blocked with immunoneutralizing antibodies raised against alpha 2-macroglobulin. Furthermore, western blot analysis reveals that although alpha 2-macroglobulin is present in conditioned media from control septal cultures, it is more abundant in those treated with transforming growth factor-alpha. In addition, exogenous alpha 2-macroglobulin, both in its native and trypsin-activated forms, can mimic transforming growth factor-alpha's effects on septal cholinergic cell expression. However, while the native antiprotease can slightly but significantly decrease choline acetyltransferase activity, trypsin-activated alpha 2-macroglobulin, in the nanomolar range, induces as marked a decrease in this enzyme activity as that noted with transforming growth factor-alpha. Furthermore, trypsin-activated alpha 2-macroglobulin, like epidermal growth factor/transforming growth factor-alpha, decreases choline acetyltransferase activity by arresting its spontaneous increase that occurs with time in culture, does so in a reversible manner and is not neurotoxic. In addition, trypsin-activated alpha 2-macroglobulin, in the nanomolar range, can affect choline acetyltransferase in a dual manner, up-regulating it at low concentrations while down-regulating it at higher ones. These responses are identical in mixed neuronal-glial and pure neuronal septal cultures. Furthermore, when concentrations of trypsin-activated alpha 2-macroglobulin, which alone decrease choline acetyltransferase, are added simultaneously with nerve growth factor, they serve to potentiate the nerve growth factor-induced increase in enzymatic activity. As GABAergic cell expression is not affected by alpha 2-macroglobulin, it appears that the effects of this protease inhibitor on medial septal neuronal expression are neurotransmitter-specific. Finally, trypsin-activated but not native alpha 2-macroglobulin promotes a dose-dependent aggregation of the septal neurons. This change in morphology, however, is not related to those noted in choline acetyltransferase activity. In summary, these data suggest that the expression of alpha 2-macroglobulin in astroglia from the medial septal nucleus can be controlled by epidermal growth factor receptor ligands to impact the functioning of basal forebrain cholinergic neurons.