Several studies have successfully employed GM1 ganglioside to treat animal models of Parkinson's disease (PD), suggesting involvement of this ganglioside in PD etiology. We recently demonstrated that genetically engineered mice (B4galnt1(-/-) ) devoid of GM1 acquire characteristic symptoms of this disorder, including motor impairment, depletion of striatal dopamine, selective loss of tyrosine hydroxylase-expressing neurons, and aggregation of α-synuclein. The present study demonstrates similar symptoms in heterozygous mice (HTs) that express only partial GM1 deficiency. Symptoms were alleviated by administration of L-dopa or LIGA-20, a membrane-permeable analog of GM1 that penetrates the blood-brain barrier and accesses intracellular compartments. Immunohistochemical analysis of paraffin sections from PD patients revealed significant GM1 deficiency in nigral dopaminergic neurons compared with age-matched controls. This was comparable to the GM1 deficiency of HT mice and suggests that GM1 deficiency may be a contributing factor to idiopathic PD. We propose that HT mice with partial GM1 deficiency constitute an especially useful model for PD, reflecting the actual pathophysiology of this disorder. The results point to membrane-permeable analogs of GM1 as holding promise as a form of GM1 replacement therapy.

Several animal autoimmune disorders are suppressed by treatment with the GM1 cross-linking units of certain toxins such as B subunit of cholera toxin (CtxB). Due to the recent observation of GM1 being a binding partner for the endogenous lectin galectin-1 (Gal-1), which is known to ameliorate symptoms in certain animal models of autoimmune disorders, we tested the hypothesis that an operative Gal-1/GM1 interplay induces immunosuppression in a manner evidenced by both in vivo and in vitro systems. Our study of murine experimental autoimmune encephalomyelitis (EAE) indicated suppressive effects by both CtxB and Gal-1 and further highlighted the role of GM1 in demonstrating enhanced susceptibility to EAE in mice lacking this ganglioside. At the in vitro level, polyclonal activation of murine regulatory T (Treg) cells caused up-regulation of Gal-1 that was both cell bound and released to the medium. Similar activation of murine CD4+ and CD8+ effector T (Teff) cells resulted in significant elevation of GM1 and GD1a, the neuraminidase-reactive precursor to GM1. Activation of Teff cells also up-regulated TRPC5 channels which mediated Ca2+ influx upon GM1 cross-linking by Gal-1 or CtxB. This involved co-cross-linking of heterodimeric integrin due to close association of these α4β1 and α5β1 glycoproteins with GM1. Short hairpin RNA (shRNA) knockdown of TRPC5 in Teff cells blocked contact-dependent proliferation inhibition by Treg cells as well as Gal-1/CtxB-triggered Ca2+ influx. Our results thus indicate GM1 in Teff cells to be the primary target of Gal-1 expressed by Treg cells, the resulting co-cross-linking and TRPC5 channel activation contributing importantly to the mechanism of autoimmune suppression.

Calcium is recognized as an important intracellular messenger with a pivotal role in the regulation of many cytosolic and nuclear processes. Gangliosides of various types, especially GM1, are known to have a role in some aspects of Ca 2+ regulation, operating through a variety of mechanisms that are gradually coming to light. The present study provides evidence for a sodium-calcium exchanger in the nuclear envelope of NG108-15 neuroblastoma cells that is potently and specifically activated by GM1. Immunoblot analysis revealed an unusually tight association of GM1 with the exchanger in the nuclear envelope but not with that in the plasma membrane. Exchanger and associated GM1 were located in the inner membrane of the nuclear envelope, suggesting this system could function to transfer Ca 2+ between nucleoplasm and the envelope lumen. The GM1-enhanced exchange was blocked by cholera toxin B subunit while C2-ceramide, a recently discovered inhibitor of the exchanger, blocked all transfer. Exchanger activity was significantly elevated in nuclei isolated from cells that were induced to differentiate by KCl + dibutyryl-cAMP, a treatment previously shown to promote up-regulation of nuclear GM1 in conjunction with axonogenesis. Similar enhancement was achieved by addition of exogenous GM1 to nuclei from undifferentiated cells. These results suggest a prominent role for nuclear GM1 in regulation of nuclear Ca 2+ homeostasis. et al. 1991;Kocsis et al. 1994).The present study was undertaken to determine the specific role of GM1, which was suggested to contribute to this altered regulation of nuclear Ca 2+ (Wu et al. 1995b;Ledeen et al. 1998). We have obtained evidence for the presence of a sodium-calcium (Na-Ca) exchanger in the NE that is strongly associated with and potentiated by GM1. This exchanger was detected by immunocytochemistry in the NE of cortical neurons and NG108-15 cells, and its function demonstrated in isolated nuclei from the latter. ] i , intracellular calcium content; Ctx B, cholera toxin B subunit; Ctx B-FITC, cholera toxin B linked to fluoroisothiocyanate; Ctx B-HRP, cholera toxin B linked to horseradish peroxidase; db-cAMP, dibutyryl cyclic AMP; DMEM, Dulbecco's modified Eagle's medium; DTT, dithiothreitol; HPTLC, high-performance thin-layer chromatography; Membr. Mix, mixture of non-nuclear membranes; NE, nuclear envelope; NPP, nuclear pore protein; PBS, phosphate-buffered saline; SDS-PAGE, sodium dodecyl sulfate polyacrylamide gel electrophoresis.

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Parkinson’s disease (PD) is the second most prevalent late-onset neurodegenerative disorder that affects nearly 1% of the global population aged 65 and older. Whereas palliative treatments are in use, the goal of blocking progression of motor and cognitive disability remains unfulfilled. A better understanding of the basic pathophysiological mechanisms underlying PD would help to advance that goal. The present study provides evidence that brain ganglioside abnormality, in particular GM1, may be involved. This is based on use of the genetically altered mice with disrupted gene Galgt1 for GM2/GD2 synthase which depletes GM2/GD2 and all the gangliotetraose gangliosides that constitute the major molecular species of brain. These knockout mice show overt motor disability on aging and clear indications of motor impairment with appropriate testing at an earlier age. This disability was rectified by L-dopa administration. These mice show other characteristic symptoms of PD, including depletion of striatal dopamine (DA), loss of DA neurons of the substantia nigra pars compacta, and aggregation of alpha synuclein. These manifestations of parkinsonism were largely attenuated by administration of LIGA-20, a membrane permeable analog of GM1 that penetrates the blood brain barrier and enters living neurons. These results suggest that perturbation of intracellular mechanisms mediated by intracellular GM1 may be a contributing factor to PD.