Inducible Expression of a Truncated Form of Tau in Oligodendrocytes Elicits Gait Abnormalities and a Decrease in Myelin: Implications for Selective CNS Degenerative Diseases.

The cytoskeleton protein Tau present in oligodendrocytes (OLGs) promotes cellular process outgrowth and myelination; whereas abnormally hyperphosphorylated Tau has been shown to be present in the most debilitating form of multiple sclerosis and in selective dementias. This research examined the functional consequences of expressing a truncated form of Tau in OLGs during the second postnatal life. In particular, this truncated form of Tau (∆Tau) retains the Fyn-binding domain but lacks the microtubule-binding domain. Similar to hyperphosphorylated Tau, ∆Tau cannot bind the cytoskeleton and is missorted. The Cre/loxP recombination system was used to generate transgenic (TG) founder lines, which contain a Floxed LacZ-STOP cassette to prevent expression of enhanced green fluorescence protein (EGFP)-∆Tau. The founder lines were then crossed with a Tamoxifen (TM)-inducible proteolipid protein (PLP)-dependent Cre driver line. Myelin PLP is the major myelin protein in the central nervous system (CNS). TM was given at postnatal day (p) 12 for 3 days, and CNS tissues were collected at p22. Only TG mice with both EGFP-∆Tau and Cre manifested an overt phenotype of loss of balance and stumbles starting around p18. CNS tissues obtained from TM-treated EGFP-∆Tau/Cre double transgenic mice had recombined PCR products, GFP, and diminished brain myelin. GFP was expressed in OLGs, but not in neurons or astrocytes. On the contrary, TM-treated TG mice with only one of the two transgenes, i.e., Cre or Tau, did not have recombinant PCR products, GFP, diminished myelin, or abnormal phenotype. Thus, this inducible model shows for the first time that a non-microtubule-associated Tau protein in OLGs elicits both myelin decrease and gait abnormalities, similar to the occurrence in selective demyelinating and neurodegenerative diseases.