Impaired deoxyribonuclease activity in monoglandular and polyglandular autoimmunity.

OBJECTIVE: The enzyme desoxyribonuclease (DNase) degrades DNA during early apoptosis. Impaired DNase activity might increase susceptibility to autoimmune diseases. This study examined for the first time DNase activity in endocrine autoimmunity. METHODS: Included were 112 patients with monoglandular (MGA) or polyglandular autoimmunity (PGA), their 93 healthy relatives, and 41 healthy controls. Serum DNase activity was quantified with a solid phase enzyme immunometric assay comprising degradation of the specific immobilized DNase substrate, formation of enzyme conjugate complexes using horseradish peroxidase conjugate solution, and enzymatic colour reaction. RESULTS: The Bland-Altman plot of the interassay differences suggested good reproducibility (n=96). Compared to healthy controls (median 9.8, range 5.2-16.7 ng/ml), DNase activity was markedly lowered in patients with endocrine autoimmunity (5.8, 2.6-26.2 ng/ml; p<0.0001). Corresponding values in the following MGA, PGA, and relatives groups were 4.8 (2.8-19.0) ng/ml, 7.9 (2.6-26.2) ng/ml, and 8.4 (1.5-19.0) ng/ml, respectively. When MGA patients were splitted up by disease, patients with type 1 diabetes had the lowest DNase activity (3.6, 3.2-3.9 ng/ml) which positively correlated with HbA1c in females (r=0.486, p=0.041). Pathological reduction of DNase activity (below 5 ng/ml) was noted in 54%, 31%, 24%, and 0% of MGA, PGA, relatives, and controls, respectively. Anti-ds-DNA and anti-nucleosome antibodies were negative in the patients with MGA and PGA. CONCLUSIONS: These findings indicate the potential relevance of DNase activity in patients with monoglandular and polyglandular autoimmunity and their clinically healthy relatives. The impaired DNase activity might reduce removal of circulating self- or pathogen-derived DNA thereby favoring autoimmune mechanisms by Toll-like receptor 9 co-activation.

Expression of the Na+-D-glucose cotransporter SGLT1 in neurons.

In brains of the rabbit, pig, and human, expression of the high-affinity Na+-D-glucose cotransporter SGLT1 and of the protein RS1, which alters the activity of SGLT1, was demonstrated. In situ hybridization showed that SGLT1 and RS1 are transcribed in pyramidal cells of brain cortex and hippocampus and in Purkinje cells of cerebellum. In neurons of pig brain SGLT1 protein was demonstrated by western blotting with synaptosomal membranes and by immunohistochemistry, which showed SGLT1 in pyramidal and Purkinje cells. To test whether SGLT1 in neurons may be activated during increased D-glucose consumption, an epileptic seizure was induced in rat brain, and the uptake of specific nonmetabolized substrates of SGLT1 [[14C]methyl-alpha-D-glucopyranoside ([14C]AMG)] and of Na+-independent transporters [2-deoxy-D-[14C] glucose ([14C]2-DG)] was analyzed by autoradiography. During the seizure the uptake of AMG and 2-DG was increased in the focus. Within two hours after the seizure 2-DG uptake in the focus returned to normal. In contrast, the AMG uptake in the focus area was still increased 1 day later. The data show that the high-affinity Na+-D-glucose cotransporter SGLT1 is expressed in neurons and can be up-regulated.

Cloning of a membrane-associated protein which modifies activity and properties of the Na(+)-D-glucose cotransporter.

An expression library from porcine kidney cortex was screened with a monoclonal antibody (R4A6) which stimulates high-affinity phlorizin binding in kidney and intestine but does not react with the membrane protein (SGLT1) which mediates Na(+)-coupled transport of D-glucose (Hediger, M.A., Coady, M.J., Ikeda, T.S., and Wright, E.M. (1987) Nature 330, 379-381). A cDNA (RS1) was obtained which codes for a hydrophilic M(r) 66,832 polypeptide and contains a predicted hydrophobic alpha-helix at the COOH terminus. After expression in Xenopus oocytes RS1 protein was found associated with the plasma membrane. RS1-homologous mRNAs were detected in renal outer cortex and outer medulla, small intestine, liver, and LLCPK1 cells, but not in skeletal muscle, heart muscle, Madin-Darby canine kidney (MDCK) cells, renal inner medulla, and Xenopus oocytes. After nondenaturing gel electrophoresis of renal brush-border membranes comigration of RS1- and SGLT1-homologous proteins as a high molecular weight complex was demonstrated. RS1 altered the expression of Na(+)-glucose cotransport by SGLT1 in Xenopus oocytes. There was no effect on the expression of the nonhomologous transporters for Na(+)-gamma-aminobutyric acid cotransport and for Na(+)-independent glucose transport. However, RS1 also changed the expression of the SGLT1-homologous Na(+)-myo-inositol cotransporter from MDCK cells. The Vmax of methyl-alpha-D-glucopyranoside (AMG) transport expressed after injection of a small amount of SGLT1-cRNA was increased 40-fold when a stoichiometric amount of RS1-cRNA was coinjected. In addition the voltage and glucose dependence of expressed AMG uptake and the concentration dependence of transport inhibition by phlorizin were changed when stoichiometric amounts of RS1-cRNA were coinjected with SGLT1-cRNA. Thus with SGLT1 one apparent transport site (K0.5 about 100 microM) and one apparent phlorizin inhibition site (Ki about 5 microM) was observed whereas with SGLT1 plus RS1 two apparent transport sites (K0.5(1) about 20 microM, K0.5(2) about 1 mM) and two apparent phlorizin inhibition sites (Ki(1) about 0.3 microM, Ki(2) about 30 microM) were found as has been described in brush-border membrane vesicles of kidney and intestine (see e.g. Koepsell, H., Fritzsch, G., Korn, K., and Madrala, A. (1990) J. Membr. Biol. 114, 113-132). The data suggest that the Na(+)-D-glucose cotransporter and possibly also other SGLT1-type Na(+)-cotransporters contain RS1-type regulatory subunits.