Decreased spinal cord motor neuron numbers in mice depleted of central nervous system copper

Disrupted copper availability in the central nervous system (CNS) is implicated as a significant feature of the neurodegenerative disease amyotrophic lateral sclerosis (ALS). Solute carrier family 31 member 1 (Slc31a1; Ctr1) governs copper uptake in mammalian cells and mutations affecting Slc31a1 are associated with severe neurological abnormalities. Here, we examined the impact of decreased CNS copper caused by ubiquitous heterozygosity for functional Slc31a1 on spinal cord motor neurons in Slc31a1+/- mice. Congruent with the CNS being relatively susceptible to disrupted copper availability, brain and spinal cord tissue from Slc31a1+/- mice contained significantly less copper than wild-type littermates, even though copper levels in other tissues were unaffected. Slc31a1+/- mice had less spinal cord α-motor neurons compared to wild-type littermates, but they did not develop any overt physical signs of motor impairment. By contrast, ALS model SOD1G37R mice had fewer α-motor neurons than control mice and exhibited clear signs of motor function impairment. With the expression of Slc31a1 notwithstanding, spinal cord expression of genes related to copper handling revealed only minor differences between Slc31a1+/- and wild-type mice. This contrasted with SOD1G37R mice where changes in the expression of copper handling genes were pronounced. Similarly, the expression of genes related to toxic glial activation was unchanged in spinal cords from Slc31a1+/- mice but highly upregulated in SOD1G37R mice. Together, results from the Slc31a1+/- mice and SOD1G37R mice indicate that although depleted CNS copper has a significant impact on spinal cord motor neuron numbers, the manifestation of overt ALS-like motor impairment requires additional factors.