Brain and Erythrocyte Anion Transporter Protein, Band 3, as a Marker for Alzheimer’s Disease: Structural Changes Detected by Electron Microscopy, Phosphorylation, and Antibodies

Abstract

Band 3, a ubiquitous membrane transport, regulatory, and structural protein, is represented in brain by at least 4 isoforms. Bands 3 in brain performs the same functions as it does in erythrocytes (RBC). It is susceptible to oxidative damage, which, ultimately, terminates its life and that of the cell. We examined the changes band 3 undergoes in Alzheimer’s disease (AD) because our previous studies suggest that band 3 is a pivotal protein in neurological disease. Because we hypothesize that AD is a total body disease, we examined peripheral blood cells as well as brain tissue to determine whether the same changes occur in both. Our results indicate that posttranslational changes occur in RBC band 3 that parallel changes in brain band 3. These include decreased ³²P-phosphate labeling in vitro of band 3 polypeptides in brain and RBC, increased degradation of band 3, alterations in band 3 recognized by polyclonal and monoclonal antibodies, and decreased anion and glucose transport by blood cells. Serum autoantibodies to band 3 peptides 588-602 and 822-839 were increased in AD patients compared to controls. These band 3 residues lie in anion transport/binding regions. This is consistent with alteration of this region in AD since it is recognized as antigenically different by the patients’ immune system. Our data support an immunological component to AD. The finding that changes in RBC in AD reflect those in brain and can be recognized by antibodies should facilitate development of blood tests for diagnosis and monitoring, and early therapy. It is anticipated that identification of molecular sites of posttranslational modification of band 3 will enable us to design specific preventive and treatment strategies, and target drugs to crucial molecular sites.

Immunoregulation of Cellular Life Span

“…This suggested that band 3 existed in normal neurons in, predominately, an unaltered or uncleaved state; and that degradation of band 3 occurred in AD, thus allowing binding of antibodies to pep‐COOH. In other studies, antibodies to band 3 and its peptides bound to structures in AD but not normal brain, as determined by immunoelectron microscopy 100,101. (Reproduced from Saitoh et al 64 with permission.)…”

Protein kinase C as a peripheral biomarker for Alzheimer’s disease

“…Moreover, Band 3 (AE1) , an anion exchanger transmembrane protein ,which is important for organizing the structure of the red blood cells (RBC) membrane, which performs the same functions in brain as it does in erythrocytes (RBC) and which is phosphorylated by PKC, showed similar alteration in brain and RBC of AD patients. These parallel changes included decreased 32P-phosphate labeling, altered conformation of band 3 recognized by polyclonal and monoclonal antibodies and decreased anion transport in RBC (Kay and Goodman, 1997). This finding could suggest that one of the sources of this alteration of a major transport complex in two different cell types is either a general modification in PKC activity or changes in the membrane bilayer, which is stabilized by Band 3 in RCB.…”

Vitamin E prevents oxidative modification of brain and lymphocyte band 3 proteins during aging.

“…The normal lifespan of band 3 correlates with the lifespan of the cell (6,19,20,22,24,25). The breakdown of band 3 and the accumulation of SCA on cells triggers removal of that cell (6,8,9,(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27). Therefore, band 3 is an excellent marker protein for posttranslational modifications during aging and, perhaps, disease.…”

“…To date, our aging studies indicate that the anion transport ability of band 3 decreases in brains and erythrocytes from old mice (10,19,(23)(24)(25)(26)(27). This decreased transport ability precedes obvious structural changes such as band 3 degradation and generation of SCA (10,19,23,(20)(21)(22)(23)(24)(25)(26)(27) and occurs concommitantly with generation of aged/altered band 3.…”