Decreased glucose transporter expression triggers BAX-dependent apoptosis in the murine blastocyst.

We report that a decrease in facilitative glucose transporter (GLUT1) expression and reduced glucose transport trigger apoptosis in the murine blastocyst. Inhibition of GLUT1 expression either by high glucose conditions or with antisense oligodeoxynucleotides significantly lowers protein expression and function of GLUT1 and as a result induces a high rate of apoptosis at the blastocyst stage. Similar to wild-type mice, embryos from streptozotocin-induced diabetic Bax -/- mice experienced a significant decrease in glucose transport compared with embryos from non-diabetic Bax -/- mice. However, despite this decrease, these blastocysts demonstrate significantly fewer apoptotic nuclei as compared with blastocysts from hyperglycemic wild-type mice. This decrease in preimplantation apoptosis correlates with a decrease in resorptions and malformations among the infants of the hyperglycemic Bax -/- mice versus the Bax +/+ and +/- mice. These findings suggest that hyperglycemia by decreasing glucose transport acts as a cell death signal to trigger a BAX-dependent apoptotic cascade in the murine blastocyst. This work also supports the hypothesis that increased apoptosis at a blastocyst stage because of maternal hyperglycemia may result in loss of key progenitor cells and manifest as a resorption or malformation, two adverse pregnancy outcomes more common in diabetic women.

GLUT8 is a glucose transporter responsible for insulin-stimulated glucose uptake in the blastocyst.

Mammalian preimplantation blastocysts exhibit insulin-stimulated glucose uptake despite the absence of the only known insulin-regulated transporter, GLUT4. We describe a previously unidentified member of the mammalian facilitative GLUT superfamily that exhibits approximately 20-25% identity with other murine facilitative GLUTs. Insulin induces a change in the intracellular localization of this protein, which translates into increased glucose uptake into the blastocyst, a process that is inhibited by antisense oligoprobes. Presence of this transporter may be necessary for successful blastocyst development, fuel metabolism, and subsequent implantation. Moreover, the existence of an alternative transporter may explain examples in other tissues of insulin-regulated glucose transport in the absence of GLUT4.

Evidence that human immunoglobulin M rheumatoid factors can Be derived from the natural autoantibody pool and undergo an antigen driven immune response in which somatically mutated rheumatoid factors have lower affinities for immunoglobulin G Fc than their germline counterparts.

The question of whether immunoglobulin (Ig)M rheumatoid factors (RF) arise as the result of an abnormal expansion of already existing clones producing natural autoantibodies or emerge as new clones that are somatically mutated owing to an antigen driven immune response has never been conclusively answered. In this study, an inhibition ELISA was utilized to measure the affinities of recombinant antibodies using VH segments reverted back to their closest germline counterparts (germline revertants). In all cases, the somatically mutated parental RFs had a decreased affinity for immunoglobulin (Ig)G Fc compared to the germline revertant, indicating that the antibodies in the germline configuration had the higher affinities. This demonstrates that somatic mutation is not a prerequisite to generate disease associated antibodies. The presence of mutations in the parental IgM RFS suggests that these cells had been involved in a germinal centre reaction. As the germinal centre is the conventional site of the acquisition of mutations during an antigen driven response, these data suggest a role for germinal centres in the generation of the antibody diversity in addition to the selection of higher affinity antibodies. Assuming that only antigen selected cells survive deletion, these data support the hypothesis that IgM RFS can be derived from the natural autoantibody repertoire and result from an antigen driven response. Mechanisms controlling the survival of B cells based on the affinity/avidity of the immunoglobulin receptor are shown to be functional in patients with rheumatoid arthritis.