Connexins Are Critical for Normal Myelination in the CNS

Abstract

Mutations in Cx32, a gap-junction channel-forming protein, result in X-linked Charcot-Marie-Tooth disease, a demyelinating disease of the peripheral nervous system. However, although oligodendrocytes express Cx32, central myelination is unaffected. To explore this discrepancy, we searched for additional oligodendrocyte connexins. We found Cx47, which is expressed specifically in oligodendrocytes, regulated in parallel with myelin genes and partially colocalized with Cx32 in oligodendrocytes. Mice lacking either Cx47 or Cx32 are viable. However, animals lacking both connexins die by postnatal week 6 from profound abnormalities in central myelin, characterized by thin or absent myelin sheaths, vacuolation, enlarged periaxonal collars, oligodendrocyte cell death, and axonal loss. These data provide the first evidence that gap-junction communication is crucial for normal central myelination.

Loss-of-function GJA12/Connexin47 mutations cause Pelizaeus–Merzbacher-like disease

“…In rodents, Cx47 is expressed by rat oligodendrocytes, but not by astrocytes or neurons (Menichella et al 2003;Altevogt and Paul 2004;Kleopa et al 2004). To determine whether human oligodendrocytes express Cx47 in the primate brain in a similar pattern, we immunostained cryosections of autopsied human brains, but poor preservation precluded any definitive conclusions.…”

“…The marked discrepancy between the devastating CNS phenotype in people with PMLD (Uhlenberg et al 2004) and the mild CNS phenotype of mice that are homozygous for a null Gja12/cx47 allele (Menichella et al 2003;Odermatt et al 2003) remains to be explained. The differences in the primary amino acid sequence of mouse and human Cx47 (Suppl.…”

“…The cells were washed in PBS, fixed in acetone at −20°C for 10 min, and blocked for 1 h at RT with 5% fish skin gelatin in PBS containing 0.1% Triton X-100 (TX100). Primary antibodies -a rabbit antiserum (gift of Dr. David Paul, Harvard University, Boston, MA; diluted 1:1500) raised against the C-terminus of mouse Cx47 (Menichella et al 2003), and the two rabbit antisera raised against the C-terminus of human Cx47 described above (diluted 1:2000) -were added to this blocking solution and the samples were incubated overnight at 4°C. Some slides were double-labeled with monoclonal antibodies GRP94 (Abcam Inc., Cambridge, MA, diluted 1:250), 58K protein (Sigma-Aldrich, St. Louis, MO, diluted 1:100), LAMP-2 (RDI division of Fitzgerald Industries Intl., Concord, MA, diluted 1:100) or pancadherin (Abcam Inc., Cambridge, MA, diluted 1:200), which are ER, Golgi, lysosomal and cell surface markers, respectively.…”

“…Anatomical and functional studies of the rodent CNS have demonstrated that astrocytes and oligodendrocytes are coupled by gap junctions (Massa and Mugnaini 1982;Ransom and Kettenmann 1990;Robinson et al 1993;Rash et al 1997), and that each cell type expresses different connexins (Dermietzel et al 1989;Yamamoto et al 1990;Scherer et al 1995;Dermietzel et al 1997;Ochalski et al 1997;Nagy et al 1999;Altevogt et al 2002;Menichella et al 2003;Odermatt et al 2003;Kleopa et al 2004). Astrocyte/astrocyte (A/ A) coupling is likely mediated by Cx43/Cx43 and Cx30/Cx30 homotypic channels, and astrocyte/oligodendrocyte (A/O) coupling is most likely mediated by Cx43/Cx47 and Cx30/ Cx32 heterotypic channels, with an uncertain contribution of Cx26/Cx32 channels (Rash et al 2001;Nagy et al 2003;Altevogt and Paul 2004;Li et al 2004).…”

“…Although CNS myelination in Gja12/cx47-null mice is minimally affected (Menichella et al 2003;Odermatt et al 2003), recessive GJA12/Cx47 mutations cause a devastating dysmyelinating disease in humans, called Pelizaeus-Merzbacher-like disease (PMLD; (Uhlenberg et al 2004;Bugiani et al 2006). PMD itself is an X-linked dysmyelinating disorder caused by mutations in Proteolipid Protein 1 (PLP1), which encodes the main intrinsic membrane protein of CNS myelin (Garbern et al 1999).…”