Plasticity of Na,K-ATPase isoform expression in cultures of flat astrocytes: Species differences in gene expression

The Na,K-ATPase plays an active role in glial physiology, contributing to K⁺ uptake as well as to the Na⁺ gradients used by other membrane carriers. There are multiple isoforms of Na,K-ATPase α and β subunits, and different combinations result in different affinities for Na⁺ and K⁺. Isoform choice should thus influence K⁺ and Na⁺ homeostasis in astrocytes. Prior studies of astrocyte Na,K-ATPase subunit composition have produced apparently conflicting results, suggesting plasticity of gene expression. Purified flat astrocytes from the cerebral cortex and cerebellum of both mouse and rat were systematically investigated here. Using antibodies specific for the α1, α2, α3, β1, β2, and β3 subunits, isoform level was assessed with Western blots, and cellular distribution was visualized with immunofluorescence. Although α1 was always expressed, differences were observed in the expression of α2 and β2, subunits that can be expressed in astrocytes in vivo and in coculture with neurons. In addition, abundant α subunit was expressed in rat astrocytes and in mouse cerebellar astrocytes without an equivalent level of any of the known β isoforms, suggesting that an additional β subunit important for glia is yet to be discovered. Conditions that have been shown to increase Na,K-ATPase activity in astrocyte cultures, such as dibutyryl cAMP, high extracellular K⁺, and glutamate, did not specifically induce missing subunits, suggesting that cellular interactions are required to alter the ion transporter phenotype. GLIA 24:257–271, 1998.© 1998 Wiley-Liss, Inc.     

Favorably skewed X‐inactivation accounts for neurological sparing in female carriers of Menkes disease

Desai V, Donsante A, Swoboda KJ, Martensen M, Thompson J, Kaler SG. Favorably skewed X‐inactivation accounts for neurological sparing in female carriers of Menkes disease. Classical Menkes disease is an X‐linked recessive neurodegenerative disorder caused by mutations in ATP7A, which is located at Xq13.1‐q21. ATP7A encodes a copper‐transporting P‐type ATPase and plays a critical role in development of the central nervous system. With rare exceptions involving sex chromosome aneuploidy or X‐autosome translocations, female carriers of ATP7A mutations are asymptomatic except for subtle hair and skin abnormalities, although the mechanism for this neurological sparing has not been reported. We studied a three‐generation family in which a severe ATP7A mutation, a 5.5‐kb genomic deletion spanning exons 13 and 14, segregated. The deletion junction fragment was amplified from the proband by long‐range polymerase chain reaction and sequenced to characterize the breakpoints. We screened at‐risk females in the family for this junction fragment and analyzed their X‐inactivation patterns using the human androgen‐receptor (HUMARA) gene methylation assay. We detected the junction fragment in the proband, two obligate heterozygotes, and four of six at‐risk females. Skewed inactivation of the X chromosome harboring the deletion was noted in all female carriers of the deletion (n = 6), whereas random X‐inactivation was observed in all non‐carriers (n = 2). Our results formally document one mechanism for neurological sparing in female carriers of ATP7A mutations. Based on review of X‐inactivation patterns in female carriers of other X‐linked recessive diseases, our findings imply that substantial expression of a mutant ATP7A at the expense of the normal allele could be associated with neurologic symptoms in female carriers of Menkes disease and its allelic variants, occipital horn syndrome, and ATP7A‐related distal motor neuropathy.