Muscle-derived differentiation factor increases expression of the tyrosine hydroxylase gene and enzyme activity in cultured dopamine neurons from the rat midbrain

Development of the main olfactory system and main olfactory epithelium-dependent male mating behavior are altered in Go-deficient mice

In mammals, initial detection of olfactory stimuli is mediated by sensory neurons in the main olfactory epithelium (MOE) and the vomeronasal organ (VNO). The heterotrimeric GTP-binding protein Go is widely expressed in the MOE and VNO of mice. Early studies indicated that Go expression in VNO sensory neurons is critical for directing social and sexual behaviors in female mice [Oboti L, et al. (2014) BMC Biol 12:31]. However, the physiological functions of Go in the MOE have remained poorly defined. Here, we examined the role of Go in the MOE using mice lacking the α subunit of Go Development of the olfactory bulb (OB) was perturbed in mutant mice as a result of reduced neurogenesis and increased cell death. The balance between cell types of OB interneurons was altered in mutant mice, with an increase in the number of tyrosine hydroxylase-positive interneurons at the expense of calbindin-positive interneurons. Sexual behavior toward female mice and preference for female urine odors by olfactory sensory neurons in the MOE were abolished in mutant male mice. Our data suggest that Go signaling is essential for the structural and functional integrity of the MOE and for specification of OB interneurons, which in turn are required for the transmission of pheromone signals and the initiation of mating behavior with the opposite sex.

GT1b ganglioside induces death of dopaminergic neurons in rat mesencephalic cultures

We examined neurotoxicity of GT1b against dopaminergic neurons in vitro. Cultures of mesencephalic cells deprived of serum underwent the loss of 19% of tyrosine hydroxylase immunopositive (TH-ip) neurons. In cultures deprived of serum, treatment with 10-30 microg/ml GT1b attenuated the number of TH-ip neurons by 26-69%, respectively, compared to non-treated cultures. Intriguingly, cultures deprived of serum were more vulnerable to GT1b-induced neurotoxicity. Application of 60 microg/ml GT1b to cultures grown in serum containing media resulted in the loss of 26% of TH-ip neurons, similar to that (28%) observed in serum-deprived cultures treated with 10 microg/ml GT1b. Moreover, in our cultures, absence of nitric oxide (NO) production after GT1b treatment was obvious. The present results strongly suggest direct neurotoxic actions of GT1b against dopaminergic neurons regardless of NO.

Co-grafts of muscle cells and mesencephalic tissue into hemiparkinsonian rats: behavioral and histochemical effects

Extracts from skeletal muscle cell cultures have been shown to increase levels of the enzyme tyrosine hydroxylase (TH) and promote survival of different types of developing neurons in vitro. To determine the effect of muscle cell co-grafts on the survival of dopamine neurons in a rat model of Parkinson's disease, we transplanted an embryonic day (ED)-15 rat mesencephalic cell suspension alone or with neonatal muscle cells into 6-hydroxydopamine (6-OHDA) denervated rat striatum. In parallel experiments conducted in vitro, we cultured ED-15 rat mesencephalon or rat striatum in conditioned medium from neonatal rat muscle cultures (MC-CM). Our results showed that: (A) in vitro, MC-CM increased the number of TH-immunoreactive (TH-IR) neurons in embryonic mesencephalic cultures but did not induce expression of TH in embryonic striatal cultures; (B) in vivo, animals with co-grafts of muscle cells and ED-15 mesencephalon had more TH-IR in the grafted striatum compared to animals that received mesencephalic cells grafts alone, although the graft-induced reversal of circling behavior in response to methamphetamine was the same in both transplanted groups; and (C) grafts of muscle cells alone did not induce TH-IR in the denervated striatum and did not reduce methamphetamine-induced circling. These findings suggest that in vivo, neonatal muscle cells secrete factors that promote survival and/or outgrowth of fetal midbrain dopamine cells and improve the levels of TH-IR in grafted striatum.

Genetic regulatory elements introduced into neural stem and progenitor cell populations

The genetic manipulation of neural cells has advantage in both basic biology and medicine. Its utility has provided a clearer understanding of how the survival, connectivity, and chemical phenotype of neurones is regulated during, and after, embryogenesis. Much of this achievement has come from the recent generation by genetic means of reproducible and representative supplies of precursor cells which can then be analyzed in a variety of paradigms. Furthermore, advances made in the clinical use of transplantation for neurodegenerative disease have created a demand for an abundant, efficacious and safe supply of neural cells for grafting. This review describes how genetic methods, in juxtaposition to epigenetic means, have been used advantageously to achieve this goal. In particular, we detail how gene transfer techniques have been developed to enable cell immortalization, manipulation of cell differentiation and commitment, and the controlled selection of cells for purification or safety purposes. In addition, it is now also possible to genetically modify antigen presentation on cell surfaces. Finally, there is detailed the transfer of therapeutic products to discrete parts of the central nervous system (CNS), using neural cells as elegant and sophisticated delivery vehicles. In conclusion, once the epigenetic and genetic controls over neural cell production, differentiation and death have been more fully determined, providing a mixture of hard-wired elements and more flexibly expressed characteristics becomes feasible. Optimization of the contributions and interactions of these two controlling systems should lead to improved cell supplies for neurotransplantation.

Tyrosine hydroxylase expression in primary cultures of olfactory bulb: role of L-type calcium channels

Sensory activity mediates regulation of tyrosine hydroxylase (TH), the first enzyme in the dopamine biosynthetic pathway, in the rodent olfactory bulb. The current studies established for the first time primary cultures of neonatal mouse olfactory bulb expressing TH and tested whether L-type calcium channels mediate the activity-dependent regulation of the dopamine phenotype. After 1 d in vitro (DIV), a small population of TH-immunostained neurons that lacked extensive processes could be demonstrated. After an additional 2 DIV in serum-free medium, the number of TH neurons had doubled, and they exhibited long interdigitating processes. Membrane depolarization for 48 hr with 50 mM KCl produced a further 2.4-fold increase in the number of TH-immunoreactive neurons compared with control cultures. Increased TH neuron number required at least 36 hr of exposure to KCl. Forskolin, which increases intracellular cAMP levels, induced a 1.5- to 1.6-fold increase in the number of TH-immunostained neurons. Combined treatment with KCl and forskolin was not additive. Nifedipine, an L-type calcium channel blocker, completely prevented the depolarization-mediated increase in TH expression but did not block the response to forskolin. Treatment with Bay K8644, an L-type calcium channel agonist, also significantly increased the number of TH-expressing neurons. Depolarization also induced alterations in neuritic outgrowth, resulting in a stellate versus an elongate morphology that, in contrast, was not prevented by nifedipine. These results are the first demonstration that in vitro, as in vivo, depolarization increases TH expression in olfactory bulb and that L-type calcium channels mediate this activity-dependent regulation of the dopamine phenotype.

Melatonin rescues dopamine neurons from cell death in tissue culture models of oxidative stress

Dopamine (DA) neurons are uniquely vulnerable to damage and disease. Their loss in humans is associated with diseases of the aged, most notably, Parkinson's Disease (PD). There is now a great deal of evidence to suggest that the destruction of DA neurons in PD involves the accumulation of harmful oxygen free radicals. Since the antioxidant hormone, melatonin, is one of the most potent endogenous scavengers of these toxic radicals, we tested its ability to rescue DA neurons from damage/death in several laboratory models associated with oxidative stress. In the first model, cells were grown in low density on serum-free media. Under these conditions, nearly all cells died, presumably due to the lack of essential growth factors. Treatment with 250 microM melatonin rescued nearly all dying cells (100% tau+ neurons), including tyrosine hydroxylase immunopositive DA neurons, for at least 7 days following growth factor deprivation. This effect was dose and time dependent and was mimicked by other antioxidants such as 2-iodomelatonin and vitamin E. Similarly, in the second model of oxidative stress, 250 microM melatonn produced a near total recovery from the usual 50% loss of DA neurons caused by neurotoxic injury from 2.5 microM 1-methyl-4-phenylpyridine (MPP+). These results indicate that melatonin possesses the remarkable ability to rescue DA neurons from cell death in several experimental paradigms associated with oxidative stress.

Dopamine differentiation factors increase striatal dopaminergic function in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned mice

We have previously shown that muscle-derived differentiation factors (MDF) and human recombinant acidic fibroblast growth factor (aFGF) have beneficial behavioral and neurochemical effects on the nigrostriatal dopaminergic neurons of 6-hydroxy-dopamine (6-OHDA)-lesioned rats (Jin and Iacovitti: Neurobiol Dis 2:1-12, 1995). In the present study, we determined the effects of similar treatments on mice treated with the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Five days after unilateral striatal infusion of MDF or aFGF into MPTP-lesioned mice, striatal tyrosine hydroxylase (TH) activity and dihydroxyphenylacetic acid (DOPAC) levels were bilaterally increased (20-35%) compared to untreated (lesion only) or control (phosphate buffered saline + bovine serum albumin) mice. These increases, however, were not accompanied by change in dopamine (DA) levels, indicating an elevation of DA synthesis (TH/DA) and turnover (DOPAC/DA). The present findings that MDF and aFGF may have neurochemical effects in vivo on the lesioned nigrostriatal dopaminergic system suggest their potential pharmacological role in the treatment of Parkinson's disease.

Potential of neurotrophic factors in therapy of Parkinson's disease

Neurotrophic factors of dopaminergic neurons may represent a potential neuroprotective therapy for PD. This article reviews published experiments that demonstrate the effects of neurotrophic factors on dopaminergic neurons in vitro and in vivo. At present this issue is predominantly investigated in basic neuroscientific research. Its possible future clinical relevance is discussed.

Brain-derived neurotrophic factor works coordinately with partner molecules to initiate tyrosine hydroxylase expression in striatal neurons

Previous studies demonstrated that the cooperative interaction of acidic fibroblast growth factor (aFGF) and a partner molecule could induce the novel expression of the catecholamine (CA) biosynthetic enzyme, tyrosine hydroxylase (TH) in striatal neurons [Du and Iacovitti, J. Neurosci., in press; Du et al., J. Neurosci., 14 (1994) 7688-7694; Iacovitti et al., submitted]. The present study demonstrates that in addition to aFGF, brain-derived neurotrophic factor (BDNF) is also capable of moderate levels of TH induction (30% TH+ striatal neurons) when administered at high concentrations (100 ng/ml). As with aFGF, BDNF's activity depended on its coupling to an appropriate partner molecule; the most potent of which were 10 microM dopamine (DA) and 50 microM mazindol. BDNF + DA-induced TH expression was first evident after at 12 h; peaked by 18 h and declined by 4 days in culture. Cyclohexamide eliminated nearly all and alpha-amanitin reduced by half the TH induction elicited by DA and BDNF; indicating that both de novo transcription and translation were required for increased expression. In contrast with aFGF and BDNF, other putative dopamine differentiation factors, such as glial-derived neurotrophic factor (GDNF) and ciliary neurotrophic factor (CNTF), were able to elicit barely detectable (10%) levels of TH induction, regardless of the partner molecule used. These studies suggest that aFGF and/or BDNF may work coordinately with partner molecules to initiate TH expression; while a number of factors including, CNTF and GDNF, may be involved in its subsequent modulation.

Purification of dopamine neurons by flow cytometry

The heterogeneity and preponderence of other cell types present in cultures has greatly impeded our ability to study dopamine neurons. In this report, we describe methods for isolating nearly pure dopamine neurons for study in culture. To do so, the lipid-soluble dye, 1,1'-dioctadecyl-3,3,3'3'-tetramethylindocarbocyanine perchlorate (diI) was injected into the embryonic rat striata where it was taken up by nerve terminals and transported overnight back to the innervating perikarya in the ventral midbrain. Midbrain cells were then dissected, dissociated and separated on the basis of their (rhodamine) fluorescence by flow cytometry. Nearly all cells recovered as fluorescent positive (> 98%) were also immunoreactive for the dopamine specific enzyme tyrosine hydroxylase (80%-96%). Little contamination by other cells types was observed after labeling for specific neuronal and glial markers. Purified dopamine neurons continued to thrive and elaborate neuronal processes for at least 3 days in culture. Using this new model, it may now be possible to directly study the cellular and molecular processes regulating the survival and functioning of developing, injured and transplanted dopamine neurons.

GM1 ganglioside partially rescues cultured dopaminergic neurons from MPP(+)-induced damage: dependence on initial damage and time of treatment

GM1 ganglioside is believed to be important in promoting the recovery of neurons from injury. The present study assesses the ability of GM1 to repair or prevent the damage of dopamine neurons caused by the neurotoxin 1-methyl-4-phenylpyridinium (MPP+). Treatment of mesencephalic cell cultures with 2.5 microM MPP+ resulted in the loss of 30% of tyrosine hydroxylase (TH) immunoreactive neurons. In contrast, cultures administered 100 microM GM1 ganglioside for 3 days after toxin treatment contained nearly control numbers of TH+ neurons (97%). This reparative effect of GM1 was reflected in parallel increases in TH enzyme activity, dopamine and dopac levels. Cultures sustaining greater insult from higher doses of MPP+ (5.0-10.0 microM) did not benefit from ganglioside treatment, suggesting that rescue by GM1 depended on the degree of initial damage to cells. Moreover, the timing of ganglioside treatment was critical; pretreatment with GM1 alone did not prevent or attenuate the damage caused by subsequent incubation in 2.5 microM MPP+.

Neural transplantation, trophic factors and Parkinson's disease

Part 1 of this update on new restorative therapeutic strategies against Parkinsons's disease focuses on transplantation of dopamine-secreting tissue. Special emphasis is put on clinical trials with fetal mesencephalic cells. Problems and potential alternative approaches are discussed. Part 2 emphasizes progress in the related field of neurotrophic factors for dopaminergic midbrain neurons.

Growth factors in Parkinson's disease

The etiology of Parkinson's disease, one of the most frequent neurodegenerative disorders in human, is unknown. New hopes concerning satisfactory therapies include transplants of autologous adrenal medullary chromaffin tissue, fetal mesencephalic dopaminergic neurons, and local application of growth factors with a neurotrophic capacity. A large body of evidence supports the notion that neurons require trophic support not only during a limited period of ontogenesis, but during their whole lifespan. Relevant molecules promote survival, transmitter synthesis and other differentiated properties, and become crucially important when a neuron is metabolically or toxically impaired. Several molecules, most of which occur in the striatum and the substantia nigra, have been identified that protect lesioned dopaminergic nigrostriatal neurons in culture or in animal models of Parkinson's disease. These include members of the neurotrophin, fibroblast growth factor, and insulin-like growth factor families as well as epidermal growth factor/transforming growth factor alpha, interleukins and ciliary neurotrophic factor. Whether their effects are merely pharmacological, or reflect a physiological role in the nigrostriatal system, is unclear as yet. This article reviews experiments that document the trophic effects of these factors on dopaminergic neurons and discusses their possible physiological and therapeutic relevance.

Centrally active differentiation factors in the nervous system

The adult mammalian brain is a remarkably heterogeneous structure comprised of more than 50 biochemically distinct types of neurons. This phenotypic diversity is established during development, not only as the result of genetic but also epigenetic influences. It is believed that extracellular proteins, called differentiation factors, both instruct neurons in their original choice of neurotransmitter substance and, in certain situations, revise those biochemical decisions. The first candidate differentiation factor in the brain has only recently been proposed. This muscle-derived substance has the unique ability, in culture, to initiate expression of genes associated with catecholamine transmitter synthesis in non-catecholamine neurons of the brain. Because it also amplifies expression in cultured catecholamine-producing neurons in vitro and in vivo, it may prove to be an important therapeutic agent in diseases involving catecholamine shortages.