Because of their neuroprotective properties, cannabinoids are being investigated in neurodegenerative disorders, mainly in preclinical studies. These disorders also include amyotrophic lateral sclerosis (ALS), a degenerative disease produced by the damage of the upper and lower motor neurons leading to muscle denervation, atrophy and paralysis. The studies with cannabinoids in ALS have been conducted exclusively in a transgenic mouse model bearing mutated forms of human superoxide dismutase-1, the first gene that was identified in relation with ALS. The present study represents the first attempt to investigate the endocannabinoid system in an alternative model, the transgenic mouse model of TAR-DNA binding protein-43 (TDP-43), a protein related to ALS and also to frontotemporal dementia. We used these mice for behavioral and histological characterization at an early symptomatic phase (70–80 days of age) and at a post-symptomatic stage (100–110 days of age). TDP-43 transgenic mice exhibited a worsened rotarod performance at both disease stages. This was accompanied by a loss of motor neurons in the spinal cord (measured by Nissl staining) and by reactive microgliosis (measured by Iba-1 immunostaining) at the post-symptomatic stage. We also detected elevated levels of the CB2 receptor (measured by qRT-PCR and western blotting) in the spinal cord of these animals. Double-staining studies confirmed that this up-regulation occurs in microglial cells in the post-symptomatic stage. Some trends towards an increase were noted also for the levels of endocannabinoids, which in part correlate with a small reduction of FAAH. Some of these parameters were also analyzed in the cerebral cortex of TDP-43 transgenic mice, but we did not observe any significant change, in agreement with the absence of anomalies in cognitive tests. In conclusion, our data support the idea that the endocannabinoid signaling system, in particular the CB2 receptor, may serve for the development of a neuroprotective therapy in TDP-43-related disorders. We are presently engaged in pharmacological experiments to investigate this possibility.
Figure S1Representative blots for CB2 receptors and FAAH, always corresponding to tissues from females. Bottom panels are the total protein bands transferred to a PVCF membrane that were used as loading controls. (PPTX 3947 kb)
Figure S2Behavioral recording in the Water Morris test of TDP-43 transgenic and wild-type male mice at the postsymptomatic (100-110 days after birth) stage. Values are means ± SEM for 6-8 animals per group. Data were assessed by the unpaired Student’s t-test. (PPTX 73 kb)
Figure S3Immunofluorescence for CB2 receptors (magnification was 40x) showing a complete loss of immunostaining in the spinal cord of CB2 receptor-knockout mice when compared with the signal found in wild-type mice and, in particular, TDP-43 transgenic mice at the postsymptomatic (100-110 days after birth) stage. Immunostainings were repeated in at least 3 animals per group. (PPTX 241 kb)