Gene Expression Analysis in Patients with Cocaine-Induced Midline Destructive Lesions

BACKGROUND AND OBJECTIVES

Cocaine users may present with positive antineutrophil cytoplasmic antibodies (ANCA) and severe midline destructive lesions (CIMDL) which are histologically characterized by massive apoptosis. However, histopathological and laboratory studies suggest that autoimmunity may not be the main pathogenic driver. We analyzed gene expression both in cell lines of nasal mucosa exposed to cocaine and in CIMDL patients to determine whether genetic predisposition might cause such lesions, which are observed in a minority of cocaine abusers.

MATERIALS AND METHODS

The genetic expression profile of nasal mucosa exposed to cocaine was analyzed. Rare variants of expressed genes were searched in patients with CIMDL using exome sequencing and bio-informatics.

RESULTS

We identified 462 genes that were induced by cocaine, mainly related to apoptosis and autophagy in response to oxidative stress. Under the hypothesis that genes linked to the phenotype are also induced by cocaine itself, a rare variants burden test was performed to select genes that were significantly enriched in rare mutations. Next, 11 cocaine abusers with CIMDL and no other relevant medical comorbidities underwent exome sequencing, and 12 genes that were significantly enriched in the burden test and present in at least 10 patients were identified. An in-depth analysis of these genes revealed their involvement in apoptosis, tissue homeostasis, autophagy, and response to oxidative stress.

CONCLUSIONS

Oxidative stress and rare genetic alterations in the response to reactive oxygen species, apoptosis, autophagy, and tissue regeneration are plausible drivers of damage affecting nasal mucosa exposed to cocaine crystals and, consequently, the pathogenic mechanism behind CIMDL.

MPTP-induced model of Parkinson's disease in cytochrome P450 2E1 knockout mice

Evidence for involvement of cytochrome P450 2E1 in the MPTP-induced mouse model of PD has been reported [Vaglini, F., Pardini, C., Viaggi, C., Bartoli, C., Dinucci, D., Corsini, G.U., 2004. Involvement of cytochrome P450 2E1 in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced mouse model of Parkinson's disease. J. Neurochem. 91, 285-298]. We studied the sensitivity of Cyp2e1(-/-) mice to the acute administration of MPTP in comparison with their wild-type counterparts. In Cyp2e1(-/-) mice, the reduction of striatal DA content was less pronounced 7 days after MPTP treatment compared to treated wild-type mice. Similarly, TH immunoreactivity analysis of the substantia nigra of Cyp2e1(-/-) mice did not show any neuronal lesions after MPTP treatment. In contrast to this, wild-type animals showed a minimal but significant lesioning by the toxin as evaluated also by means of non-stereologic computerized assisted analysis of this brain area. Striatal levels of DA metabolites after 7 days were variably affected by the toxin, but consistent differences between the two animal strains were not observed. We evaluated short-term changes in the levels of striatal DA and its metabolites, and we monitored striatal MPP(+) levels. Striatal MPP(+) was cleared more rapidly in Cyp2e1(-/-) mice than in wild-type animals and, consistently, striatal DA content decreased faster in Cyp2e1(-/-) mice than in wild-type animals, and 3-methoxytyramine and HVA levels showed an early and sharp rise. Our findings suggest that Cyp2e1(-/-) mice are weakly sensitive to MPTP-induced brain lesions, markedly in contrast with a protective role of the enzyme as suggested previously. The differences observed between the knockout mice and their wild-type counterparts are modest and may be due to an efficient compensatory mechanism or genetic drift in the colonies.

CYP 2E1 mutant mice are resistant to DDC-induced enhancement of MPTP toxicity

In order to reach a deeper insight into the mechanism of diethyldithiocarbamate (DDC)-induced enhancement of MPTP toxicity in mice, we showed that CYP450 (2E1) inhibitors, such as diallyl sulfide (DAS) or phenylethylisothiocyanate (PIC), also potentiate the selective DA neuron degeneration in C57/bl mice. Furthermore we showed that CYP 2E1 is present in the brain and in the basal ganglia of mice (Vaglini et al., 2004). However, because DAS and PIC are not selective CYP 2E1 inhibitors and in order to provide direct evidence for CYP 2E1 involvement in the enhancement of MPTP toxicity, CYP 2E1 knockout mice (GONZ) and wild type animals (SVI) of the same genetic background were treated with MPTP or the combined DDC + MPTP treatment. In CYP 2E1 knockout mice, DDC pretreatment completely fails to enhance MPTP toxicity, although enhancement of MPTP toxicity was regularly present in the SVI control animals. The immunohistochemical study confirms our results and suggests that CYP 2E1 may have a detoxifying role.

Cytochrome P450 and Parkinson's disease: protective role of neuronal CYP 2E1 from MPTP toxicity

Elucidation of the biochemical steps leading to the 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine (MPTP)-induced degeneration of the nigro-striatal dopamine (DA) pathway has provided new clues to the pathophysiology of Parkinson's Disease (PD). In line with the enhancement of MPTP toxicity by diethyldithiocarbamate (DDC), here we demonstrate how other CYP450 (2E1) inhibitors, such as diallyl sulfide (DAS) or phenylethylisothiocyanate (PIC), also potentiate the selective DA neuron degeneration in C57/bl mice. In order to provide direct evidence for this isozyme involvement, CYP 2E1 knockout mice were challenged with MPTP or the combined treatment. Here we show that these transgenic mice have a low sensitivity to MPTP alone, similarly to the wild type SVI, suggesting that it is likely that transgenic mice compensate for the missing enzyme. However, in these CYP 2E1 knockout mice, DDC pretreatment completely fails to enhance MPTP toxicity; this enhancement is instead regularly present in the SVI control animals. This study indicates that the occurrence of CYP 2E1 in C57/bl mouse brain is relevant for MPTP toxicity, and suggests that this isozyme may have a detoxificant role related to the efflux transporter of the toxin.

Loss of Mtmr2 phosphatase in Schwann cells but not in motor neurons causes Charcot-Marie-Tooth type 4B1 neuropathy with myelin outfoldings

Mutations in MTMR2, the myotubularin-related 2 gene, cause autosomal recessive Charcot-Marie-Tooth type 4B1 (CMT4B1). This disorder is characterized by childhood onset of weakness and sensory loss, severely decreased nerve conduction velocity, demyelination in the nerve with myelin outfoldings, and severe functional impairment of affected patients, mainly resulting from loss of myelinated fibers in the nerve. We recently generated Mtmr2-null(neo) mice, which show a dysmyelinating neuropathy with myelin outfoldings, thus reproducing human CMT4B1. Mtmr2 is detected in both Schwann cells and neurons, in which it interacts with discs large 1/synapse-associated protein 97 and neurofilament light chain, respectively. Here, we specifically ablated Mtmr2 in either Schwann cells or motor neurons. Disruption of Mtmr2 in Schwann cells produced a dysmyelinating phenotype very similar to that of the Mtmr2-null(neo) mouse. Disruption of Mtmr2 in motor neurons does not provoke myelin outfoldings nor axonal defects. We propose that loss of Mtmr2 in Schwann cells, but not in motor neurons, is both sufficient and necessary to cause CMT4B1 neuropathy. Thus, therapeutical approaches might be designed in the future to specifically deliver the Mtmr2 phospholipid phosphatase to Schwann cells in affected nerves.

Pcp4l1, a novel gene encoding a Pcp4-like polypeptide, is expressed in specific domains of the developing brain

We report the cloning of a novel mouse gene (Pcp4l1) that encodes a polypeptide with significant sequence similarity to the Purkinje cell protein 4 gene (Pcp4) and describe its expression pattern during mouse development. Similar to Pcp4, the Pc4l1 gene product is characterized by the presence of an IQ domain and is highly conserved across evolution. RNA in situ hybridization reveals instead that Pcp4l1 has a distinct pattern of expression: it is only expressed in the central nervous system (CNS), and is first detected at E9.5 in the mesencephalic and metencephalic roof plate as well as in the isthmus, in a region that overlaps the expression domains of Pax2, Fgf8 and Wnt1. Thus, the early Pcp4l1 expression pattern coincides with the regional expression of well-characterized patterning molecules in the organizing centers of the developing brain. Starting at midgestation, Pcp4l1 is mainly expressed in the structures of the circumventricular organs, including the subcommissural organ, the rhombencephalic and telencephalic choroid plexi, and the pineal gland. In the adult brain, this transcript is also detected in laminar as well as in several nuclear structures of the CNS.

Expression of laminin receptors in schwann cell differentiation: evidence for distinct roles

Schwann cells require laminin-2 throughout nerve development, because mutations in the alpha2 chain in dystrophic mice interfere with sorting of axons before birth and formation of myelin internodes after birth. Mature Schwann cells express several laminin receptors, but their expression and roles in development are poorly understood. Therefore, we correlated the onset of myelination in nerve and synchronized myelinating cultures to the appearance of integrins and dystroglycan in Schwann cells. Only alpha6beta1 integrin is expressed before birth, whereas dystroglycan and alpha6beta4 integrin appear perinatally, just before myelination. Although dystroglycan is immediately polarized to the outer surface of Schwann cells, alpha6beta4 appears polarized only after myelination. We showed previously that Schwann cells lacking beta1 integrin do not relate properly to axons before birth. Here we show that the absence of beta1 before birth is not compensated by other laminin receptors, whereas coexpression of both dystroglycan and beta4 integrin is likely required for beta1-null Schwann cells to myelinate after birth. Finally, both beta1-null and dystrophic nerves contain bundles of unsorted axons, but they are predominant in different regions: in spinal roots in dystrophic mice and in nerves in beta1-null mice. We show that differential compensation by laminin-1, but not laminin receptors may partially explain this. These data suggest that the action of laminin is mediated by beta1 integrins during axonal sorting and by dystroglycan, alpha6beta1, and alpha6beta4 integrins during myelination.

Dopamine agonists and analogues have an antiproliferative effect on CHO-K1 cells

Epidemiological studies have shown a reduced incidence of cancer in Parkinson's disease. Since nearly all parkinsonian patients with clinical impairment are treated with L-beta-3,4-dihydroxyphenylalanine (L-DOPA) and dopamine (DA)ergic agonists, a possibility exists that these therapeutic agents can influence the risk of cancer. We studied the antiproliferative effect of these therapeutic agents (and substances structurally correlated) on Chinese hamster ovary (CHO)-K1 cell growth. Among the compounds tested, apomorphine proved to be the most potent inhibitor of CHO-K1 cell growth, with an EC(50) of 3.35 +/- 0.12 micro M. The apomorphine analogues, apocodeine and hydroxyethylnorapomorphine, were less active as inhibitors of CHO-K1 cell growth. The activity of DA, 6-hydroxydopamine (6-OHDA), phenylethylamine (PEA), L-DOPA and bromocriptine as antiproliferative was one order of magnitude lower than that of apomorphine while pergolide was ineffective. To test whether or not the oxidative potential of these compounds was important for their antiproliferative effect, several antioxidants were assayed. Among them glutathione (GSH) and dithiothreitol (DTT) were effective in reversing the anti-proliferative effect of apomorphine, DA, 6-OHDA and PEA, conversely they did not work with bromocriptine. GSH and DTT are sulphydryl-reducing agents; while their effect could explain the efficacy against apomorphine, DA and 6-OHDA, it is difficult to understand why they should have any effect on PEA as this substance does not react with sulphydryl groups. The oxidative potential as a mechanism of action was also questioned by the results obtained with dihydrorhodamine 123, a probe that changes its fluorescent emission wave when oxidized. None of the compounds, with the exception of 6-OHDA, had any effect on the fluorescent emission wave of the probe at the maximal concentrations used to inhibit CHO-K1 cell growth. At concentrations five times higher, apomorphine and DA generated reactive oxygen species but PEA and bromocriptine did not. These data demonstrate that the antiproliferative effect of these compounds is not due to their oxidative potential, but another mechanism must be postulated.

Apomorphine has a potent antiproliferative effect on Chinese hamster ovary cells

Apomorphine is a potent non selective agonist at the D1 and D2 dopamine receptors acting both pre- and post-synaptically. In this report we describe a novel function of apomorphine, independent from its dopaminergic activity. Apomorphine inhibits Chinese hamster ovary (CHO)-K1 cell proliferation in a dose-dependent manner. The EC50 of apomorphine-induced inhibition of CHO-K1 cell proliferation determined by cell counting was 3.24 +/- 0.07 microM. Remarkably, the dose-response curve obtained by measuring the incorporation of [3H]thymidine was practically identical to the previous one giving an EC50 of 3.52 +/- 0.04 microM. The dopaminergic antagonists SCH23390 and spiperone at a concentration of 10 microM (well beyond their Kd values for the dopamine D1- and D2-like receptors respectively) were not able to antagonize the effect of apomorphine on CHO-K1 cell proliferation. Apomorphine exerts its effect early during incubation; CHO-K1 cells exposed to apomorphine for a period as short as 1 h and then allowed to grow for three days were significantly reduced in number with respect to untreated control cells. After four hours of exposition to apomorphine (10 microM) the antiproliferative effect was similar to that seen when this compound was present in the bath for all three days. Concentrations of apomorphine higher than 10 microM induced cell death, and the colony was completely destroyed at 50 microM. Cytometric analyses showed a significant accumulation of CHO-K1 cells in the G2/M phase.

The embryonic expression pattern of 40 murine cDNAs homologous to Drosophila mutant genes (Dres): a comparative and topographic approach to predict gene function

Nature often utilizes the same metabolic 'core groups' of interacting genes or 'pathways' in completely different organs, tissues and cellular compartments. Deciphering the physiological role of a particular gene in a living organism is therefore critical to understanding not only how a gene/protein works, but also where (in which tissue/organ) and when (at what developmental stage) it functions. We have performed systematic RNA in situ hybridization on a subset of murine genes homologous to Drosophila mutant genes, called Drosophila -related expressed sequences (Dres). This approach combines functional information derived from cross-species sequence comparisons and biochemical, physiological and pathological studies performed in the fly with knowledge of the spatial and temporal distribution of gene expression. Forty murine Dres were tested by RNA in situ hybridization on sagittal, coronal and transverse sections at three developmental stages, E10.5, E12.5 and E17.5. For some of them, whole mount in situ hybridization was performed at earlier stages. These data are valuable for establishing how the function of these genes and the genetic programs underlying the development of a particular tissue or organ have evolved during evolution. For example, six Dres genes showed restricted expression domains within the murine retina, suggesting a different role for each of these genes in eye development and functioning. Furthermore, the information derived from this combined approach will be instrumental in predicting the phenotypic consequences of gene dysfunction in both mouse mutants and human genetic diseases.

L-deprenyl fails to protect mesencephalic dopamine neurons and PC12 cells from the neurotoxic effect of 1-methyl-4-phenylpyridinium ion

L-Deprenyl, a monoamine oxidase (MAO)-B inhibitor, appears to slow down the progression of Parkinson's disease. While inhibition of MAO-B activity can account for some of the effects of this substance, the basis by which L-deprenyl slows the progression of the disease remains controversial. In recent years, a new mechanism of action has emerged that may explain the ability of L-deprenyl to increase neuronal survival. L-deprenyl has been reported to modify gene expression and protein synthesis in astrocytes and PC12 cells. In this study, we tested the ability of L-deprenyl to protect mouse mesencephalic cells from the toxicity of the 1-methyl-4-phenyl pyridinium ion (MPP+). We exposed mouse mesencephalic cell cultures to L-deprenyl (10 microM) and, 24 h later, to MPP+ (2.5 microM). On the fifth day after L-deprenyl and MPP+ exposition, cells were washed free of drugs, and the following day they were tested for dopamine uptake, intracellular dopamine content and tyrosine hydroxylase immunoreactivity. The experiments were performed either in the presence or in the absence of glia. It was found that L-deprenyl pretreatment failed to achieve any protection against MPP+ toxicity. The fall in dopamine uptake and intracellular dopamine content, and the diminution of tyrosine hydroxylase immunoreactivity observed in cells pretreated with L-deprenyl and then given MPP+ were not significantly different from the values observed in cells treated with MPP+ alone. Additional experiments performed in PC12 cells, confirmed the failure of L-deprenyl to abolish the toxicity of MPP+. Our data seem to be at variance with previous reports demonstrating that the MAO-B inhibitor L-deprenyl protects dopaminergic neurons against MPP+ toxicity [12,20]; furthermore they do not support alternative mechanisms of action of L-deprenyl against MPP+ toxicity.

Emx1 and Emx2 show different patterns of expression during proliferation and differentiation of the developing cerebral cortex in the mouse

Insights into the complex structure of the forebrain and its regulation have recently come from the analysis of the expression of genes that are likely to be involved in regionalization of this structure. We cloned four new homeo box genes, Emx1, Emx2, Otx1 and Otx2, and showed that in day 10 mouse embryos their expression domains are continuous regions of the developing brain contained within each other in the sequence Emx1 < Emx2 < Otx1 < Otx2. Recently Otx1 has been found to be specifically expressed during neurogenesis of layer 5 and 6 in the developing cerebral cortex. In order to better understand the role of Emx1 and Emx2 in the maturation of the cortex we analysed by in situ hybridization their expression patterns in the developing mouse cerebral cortex, from embryonic day 12.5 to adulthood. We found that Emx2 is expressed exclusively in proliferating cells of the ventricular zone whereas Emx1 is expressed in both proliferating and differentiated neurons, throughout the cortical layers and during all the developmental stages examined. Therefore, Emx2 gene products might control some biological parameters of the proliferation of cortical neuroblasts or of the subsequent cell migration of postmitotic neurons, leaving the cortical germinal zone. Conversely, Emx1 expression, which is confined exclusively to the dorsal telencephalon, characterizes most cortical neurons during proliferation, differentiation, migration and postnatal development and maturation.

Role of excitatory amino-acids in diethyldithiocarbamate-induced cell death in mesencephalic cultures

The effects of diethyldithiocarbamate (DDC) and DDC plus glutamate on mesencephalic cell cultures were investigated. DDC 10 microM was toxic for cell cultures as assessed by observation under a phase-contrast microscope and the drop in [3H]dopamine uptake. Moreover, DDC 1 microM greatly potentiated cell death induced by glutamate 10 and 50 microM. (+)MK801, a selective non-competitive antagonist of NMDA receptors, completely prevented the toxicity of the two neurotoxins.

Chinese hamster ovary cells deficient or proficient in O6-alkylguanine-DNA alkyltransferase activity are equally sensitive to X-rays

In mammalian cells, under aerobic conditions, ionizing radiations and radiomimetic chemical agents can induce an enzymatic activity involved in DNA repair, O6-alkylguanine-DNA alkyltransferase (O6-AT). This catalytic protein is active against alkyl-radical-induced DNA damages. This induction was proposed to be linked to the formation of hydroxyl radicals. The possible involvement of O6-AT in the defense mechanism of the cell against aerobic radiation damage was investigated by comparing the X-ray sensitivity of two Chinese hamster ovary (CHO) cell lines, the first deficient (CHO mex-) and the second proficient by transfection of O6-AT (CHO mex+). The colony-forming ability after X-irradiation was appreciably reduced in CHO mex- in comparison to CHO mex+ cells. Nevertheless, pretreatment of proficient cells with O6-methylguanine, a specific inhibitor of O6-AT, reduced the DNA repair activity but did not modify the degree of sensitivity to X-rays of the CHO mex+ cells. Since the glutathione concentrations as well as the DNA damage amounts induced by X-irradiation were comparable in the variously treated cell lines, these results suggest that the observed induction of O6-AT by ionizing radiation in aerobic conditions could be a generalized rather than a specific response to damage by radicals.

The ability of liver extracts from different-aged rats to repair ‘mis-instructive’ and ‘non-instructive’ lesions of DNA

The ability to repair 'mis-instructive', O6-methylguanine, and 'non-instructive', AP sites, DNA lesions in Fischer 344 rat livers at various ages was determined. Different behaviours were observed. While the AP-endodesoxyribonuclease enzymes displayed a high constant level throughout the animals' lifetime, the O6-methylguanine-DNA methyltransferase activity presented a stepwise modulation (DNA normalisation of results): the O6-MT activity significantly increased within the first month of animal life and enhanced again after 6 months reaching a maximum plateau in the 12-18-month-old animals. Thereafter a net significant decrease of O6-MT enzyme was detected in the 24-month-old group. While the repair of the widely formed AP sites appeared uniformly efficient like 'house keeping' functions, the removal of the rare precancerous O6-methylguanine is age-dependent indicating a decreased protection of the youngest and oldest animals against this 'mis-instructive' damage. However, any extrapolation of the age-associated cancer risk needs further assessment.

[The apomorphine test for diagnosis of parkinsonian syndrome]

Apomorphine is a powerful dopaminergic drug, able to improve cardinal symptoms of Parkinson's disease in few minutes, when injected subcutaneously. We administered different doses of apomorphine s.c. against placebo in 25 patients with a Parkinsonian syndrome, with the aim of discriminating Parkinson's disease from other Parkinsonism. A positive response to apomorphine was predictive (88%) of good responsiveness to levodopa therapy. Our data, together with those of other groups, indicate that apomorphine test is a useful tool in the diagnosis of Parkinsonian syndromes.