Amyloid-β regulates gap junction protein connexin 43 trafficking in cultured primary astrocytes

Altered expression and function of astroglial gap junction protein connexin 43 (Cx43) has increasingly been associated to neurotoxicity in Alzheimer disease (AD). Although earlier studies have examined the effect of increased beta-amyloid (A beta) on Cx43 expression and function leading to neuronal damage, underlying mechanisms by which A beta modulates Cx43 in astrocytes remain elusive. Here, using mouse primary astrocyte cultures, we have examined the cellular processes by which A beta can alter Cx43 gap junctions. We show that A beta(25-35) impairs functional gap junction coupling yet increases hemichannel activity. Interestingly, A beta(25-35) increased the intracellular pool of Cx43 with a parallel decrease in gap junction assembly at the surface. Intracellular Cx43 was found to be partly retained in the endoplasmic reticulum-associated cell compartments. However, forward trafficking of the newly synthesized Cx43 that already reached the Golgi was not affected in A beta(25-35)-exposed astrocytes. Supporting this, treatment with 4-phenylbutyrate, a well-known chemical chaperone that improves trafficking of several transmembrane proteins, restored A beta-induced impaired gap junction coupling between astrocytes. We further show that interruption of Cx43 endocytosis in A beta(25-35)-exposed astrocytes resulted in their retention at the cell surface in the form of functional gap junctions indicating that A beta(25-35) causes rapid internalization of Cx43 gap junctions. Additionally, in silico molecular docking suggests that A beta can bind favorably to Cx43. Our study thus provides novel insights into the cellular mechanisms by which A beta modulates Cx43 function in astrocytes, the basic understanding of which is vital for the development of alternative therapeutic strategy targeting connexin channels in AD.