[0001] The present invention refers to a transgenic mouse model of myelin pathologies (or transgenic oligodendrocytes and/or neurons derived thereof). Moreover, the present invention also refers to the use of the mouse model of the invention (or oligodendrocytes and/or neurons derived thereof) in a method for screening candidate compounds for treating myelin pathologies.
1. Transgenic knock-out R-Ras2-/- or double knock-out R-Ras1-/- and R-Ras2-/- mouse model of myelin pathologies, or transgenic oligodendrocytes and/or neurons derived thereof, characterized by the following phenotypic features: a. A 70% to 155% increase of immature oligodendrocytes in the double knock-out R-Ras1-l-R-Ras2-/- transgenic mouse model, with respect to the number of immature oligodendrocytes measured in healthy controls, determined by immunostaining with specific antibodies against Tcf4 and O4 and quantified by fluorescence microscopy; b. At least 50% decrease of mature oligodendrocytes in the double knock-out R-Ras1-l-R-Ras2-/- transgenic mouse model, with respect to the number of mature oligodendrocytes measured in healthy controls, determined by immunostaining with specific antibodies against Olig2 and CC1 and quantified by fluorescence microscopy; c. At least 20% of demyelinated axons in the double knock-out R-Ras1-/-R-Ras2-/- transgenic mouse, and at least 70% of demyelinated axons in the knock-out R-Ras2-/- as compared with heathy controls, determined by electron microscopy; d. Mitochondrial adaptations comprising: i. Increased mitochondrial number per non-myelinated axon of 0.61 ± 0.18 for the knock-out R-Ras2-/- and 0.75 ± 0.23 for the double knock-out R-Ras1-l-R-Ras2-/- as compared with the number of 0.22 ± 0.08 measured in healthy control, determined by electron microscopy; ii. Decreased average mitochondrial area in non-myelinated axons of 0.091 ± 0.05 mm<2> for the knock-out R-Ras2-/- and 0.083 ± 0.03 mm<2> for the double knock-out R-Ras1-/-R-Ras2-/- as compared with the number 0.14 ± 0.08 mm<2> measured in healthy control, determined by electron microscopy; iii. Increased protein expression of the following respiratory chain elements in the double knock-out R-Ras1-l-R-Ras2-/- : ATPsyn fold change of 2.08 ± 0.84, COXIV fold change 2.67 ± 0.21 and UQCRC2 fold change 3.40 ± 0.92, relative to the expression measured in healthy control, determined by western-blot; iv. ADP-stimulated State III in the double knock-out R-Ras1-/-R-Ras2-/- of 31.3 ± 3.1 nmol O/ min / mg protein relative to healthy control, determined with Clark electrode; e. Metabolism alteration in myelin deficient tissues comprising: i. Lactate/pyruvate ratios of 121.75 ± 14.44 for the knock-out R-Ras2<-/-> and 116.19 ± 16.42 for the double knock-out R-Ras1-l-R-Ras2-/- as compared with the number 153.53 ± 18.11 measured in healthy control, determined by gas chromatography-mass spectrometry; ii. Pyruvate amount of 0.027 ± 0.003 for the knock-out R-Ras2<-/-> and 0.024 ± 0.003 for the double knock-out R-Ras1-/-R-Ras2-/- as compared with the number 0.022 ± 0.004 measured in healthy control, determined by gas chromatography-mass spectrometry; iii. Lactate amount of 3.314 ± 0.405 for the knock-out R-Ras2<-/-> and 2.918 ± 0.720 for the double knock-out R-Ras1-/-R-Ras2-/- as compared with the number 3.519 ± 0.640 measured in healthy control, determined by gas chromatography-mass spectrometry; iv. Citrate amount of 0.021 ± 0.004 for the knock-out R-Ras2<-/-> and 0.028 ± 0.010 for the double knock-out R-Ras1-l-R-Ras2-/- as compared with the number 0.028 ± 0.010 measured in healthy control, determined by gas chromatography-mass spectrometry; v. Succinate amount of 0.028 ± 0.004for the knock-out R-Ras2<-/-> and 0.021 ± 0.007 for the double knock-out R-Ras1-/-R-Ras2-/- as compared with the number 0.029 ± 0.007 measured in healthy control, determined by gas chromatography-mass spectrometry; vi. Glycine amount of 0.139 ± 0.057 for the knock-out R-Ras2<-/-> and 0.131 ± 0.040 for the double knock-out R-Ras1-/-R-Ras2-/- as compared with the number 0.146 ± 0.031 measured in healthy control, determined by gas chromatography-mass spectrometry; vii. Lysine amount of 0.003 ± 0.001 for the knock-out R-Ras2<-/-> and 0.004 ± 0.001 for the double knock-out R-Ras1-/-R-Ras2-/- as compared with the number 0.007 ± 0.002 measured in healthy control, determined by gas chromatography-mass spectrometry; viii. Proline amount of 0.035 ± 0.011 for the knock-out R-Ras2<-/-> and 0.040 ± 0.013 for the double knock-out R-Ras1-/-R-Ras2-/- as compared with the number 0.047 ± 0.012 measured in healthy control, determined by gas chromatography-mass spectrometry; f. Axonal degeneration determined by the following parameters: i. ROS increment for the double knock-out R-Ras1<-/->R-Ras2<-/-> of 162.4 ± 53.4% compared to healthy control, determined by western-blot; ii. APP increment for the double knock-out R-Ras1-/-R-Ras2-/- of 154.52 ± 18.71% relative to healthy control, determined by western-blot and confirmed by immunostaining and confocal microscopy; iii. Astrogliosis for the double knock-out R-Ras1-/-R-Ras2-/- of 173.95 ± 24.71% relative to healthy control, determined by immunostaining with antibodies against GFAP and confocal microscopy; iv. Microgliosis for the double knock-out R-Ras1-/-R-Ras2-/- of 131.75 ± 16.08% relative to healthy control, determined by immunostaining with antibodies against Iba1 and confocal microscopy; v. Alteration of the phosphorylation state of the element of the axonal cytoskeleton Tau1: 47.7 ± 22.1% for the knock-out R-Ras2<-/-> and 37.4 ± 3.8% for the double knock-out R-Ras1-/-R-Ras2-/- relative to healthy control, determined by western-blot; vi. Alteration of the phosphorylation state of the element of the axonal cytoskeleton SMI-32: 58.7 ± 25.5% for the double knock-out R-Ras1-/- R-Ras2-/- relative to healthy control, determined by immunostaining and confocal microscopy; vii. Expression of PSA-NCAM 50.0 ± 12.9% for the double knock-out R-Ras1-/-R-Ras2-/- relative to healthy control, determined by immunostaining and confocal microscopy; viii. Increase in apoptotic processes in ganglion cells of 169.02 ± 4.47% for the double knock-out R-Ras1<-/->R-Ras2<-/-> relative to healthy control, determined by immunostaining and confocal microscopy; g. Functional alterations comprising: i. Percentage of correct step sequences over the total number of step cycles of 51.66 ± 27.23 for the double knock-out R-Ras1<-/->R-Ras2<-/->, 61.67 ± 8.81 for the knock-out R-Ras2<-/-> as compared to the percentage determined in healthy control 87.50 ± 6.66, determined by paw-print test; ii. Stride length of 50.30 ± 5.08 mm for the double knock-out R-Rasl<-/-> R-Ras2<-/-> as compared to the healthy control 60.37 ± 3.93 mm, determined by paw-print test; iii. Contrast sensitivity in the range of 0.011-0.355 cycles/degree was significantly weaker for the double knock-out R-Ras1<-/->R-Ras2<-/->, determined by optomotor test. 2. Transgenic knock-out mouse, according to claim 1, characterized in that it is a model of a myelin pathology selected from the group comprising: amyotrophic lateral sclerosis, neuromyelitis optica, multiple sclerosis, Charcot Marie Tooth disease and leukodystrophies. 3. An in vitro method for screening candidate compounds for treating myelin pathologies, which comprises: a) determining in the mouse model or the oligodendrocytes or neurons of claim 1 the level of expression of R-Ras1 and R-Ras2, and the parameters described in claim 1 a) to g) after administering the candidate molecule and b) where, if after administering the candidate molecule, the level of expression of R-Ras1 and R-Ras2 is higher as compared with the level of expression determined before administering the candidate molecule, and the parameters described in claim 1 a) to g) are similar to the values determined in healthy control, this is indicative that the candidate molecule is effective in the treatment myelin pathologies. 4. In vitro method, according to claim 3, wherein the myelin pathology is selected from the group comprising: amyotrophic lateral sclerosis, neuromyelitis optica, multiple sclerosis, Charcot Marie Tooth disease and leukodystrophies. 5. In vitro method for obtaining a transgenic mouse model of myelin pathologies, or transgenic oligodendrocytes and/or neurons derived thereof, which comprises the disruption or inactivation of the gene R-Ras2, or R-Ras1 and R-Ras2, and establishing the parameters described in claim 1 a) to g).