Old Tricks

Something very intriguing came in over the weekend from PLoSONE. It was a study comparing neuromuscular junctions between age and ALS. It turns out that the same muscles susceptible to denervation in ALS are likewise susceptible to denervation with age. Autonomic muscles (those that act without your conscious input) and muscles innervated directly from the brain (eg your eyes and certain facial muscles) are extraordinarily resistant to age- and ALS-related denervation. Something that struck me was the finding that TDP43 was mislocalized in aged motor neurons very similarly to ALS motor neurons. TDP43 is normally found in the nucleus but in ALS it is found in the cytoplasm where it is cleaved by caspases and a 25 kilodalton fragment aggregates in a form that apparently gains a toxic function.

TDP43 mislocalization has also been found by the symptomatic phase in the SOD1 mouse model (although earlier and more recent reports are somewhat contradictory on this point). Another protein found upregulated in the SOD1 mouse is CRMP4a, a subprotien of the CRMP family. CRMP4 is normally involved in learning, neurite outgrowth, and building functional circuitry within the brain. However, the Duplan, et al., 2010 study referenced above found upregulation or overexpression of CRMP4a is deadly specific to motor neurons. In the subject study of this post, Valdez, et al., 2012, CRMP4a was also found upregulated in the same types of motor neurons of normally-aged mice as those which degenerate in ALS mice. CRMPs are known to change due to age.

Inflammation is present in all neurodegenerative diseases. One of the primary drivers of ALS is thought to be neuroinflammation. Multiple animal models of ALS, including data in humans, show neuroinflammation. As the subject study shows, TDP43 and CRMP4 is upregulated in both aging and ALS. Taking one step further, aging and ALS have another thing in common: Inflammation.