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Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder involving an extensive loss of motoneurons. Aberrant excitability of motoneurons has been implicated in the pathogenesis of selective motoneuronal death in ALS. d -Serine, an endogenous coagonist of N -methyl- d -aspartate receptors, exacerbates motoneuronal death and is increased both in patients with sporadic/familial ALS and in a G93A-SOD1 mouse model of ALS (mSOD1 mouse). More recently, a unique mutation in the d -amino acid oxidase (DAO) gene, encoding a d -serine degrading enzyme, was reported to be associated with classical familial ALS. However, whether DAO affects the motoneuronal phenotype and d -serine increase in ALS remains uncertain. Here, we show that genetic inactivation of DAO in mice reduces the number and size of lower motoneurons with axonal degeneration, and that suppressed DAO activity in reactive astrocytes in the reticulospinal tract, one of the major inputs to the lower motoneurons, predominantly contributes to the d -serine increase in the mSOD1 mouse. The DAO inactivity resulted from expressional down-regulation, which was reversed by inhibitors of a glutamate receptor and MEK, but not by those of inflammatory stimuli. Our findings provide evidence that DAO has a pivotal role in motoneuron degeneration through d -serine regulation and that inactivity of DAO is a common feature between the mSOD1 ALS mouse model and the mutant DAO-associated familial ALS. The therapeutic benefit of reducing d -serine or controlling DAO activity in ALS should be tested in future studies.

D-Serine is an essential coagonist with glutamate for stimulation of N-methyl-D-aspartate (NMDA) glutamate receptors. Although astrocytic metabolic processes are known to regulate synaptic glutamate levels, mechanisms that control D-serine levels are not well defined. Here we show that d-serine production in astrocytes is modulated by the interaction between the D-serine synthetic enzyme serine racemase (SRR) and a glycolytic enzyme, glyceraldehyde 3-phosphate dehydrogenase (GAPDH). In primary cultured astrocytes, glycolysis activity was negatively correlated with D-serine level. We show that SRR interacts directly with GAPDH, and that activation of glycolysis augments this interaction. Biochemical assays using mutant forms of GAPDH with either reduced activity or reduced affinity to SRR revealed that GAPDH suppresses SRR activity by direct binding to GAPDH and through NADH, a product of GAPDH. NADH allosterically inhibits the activity of SRR by promoting the disassociation of ATP from SRR. Thus, astrocytic production of D-serine is modulated by glycolytic activity via interactions between GAPDH and SRR. We found that SRR is expressed in astrocytes in the subiculum of the human hippocampus, where neurons are known to be particularly vulnerable to loss of energy. Collectively, our findings suggest that astrocytic energy metabolism controls D-serine production, thereby influencing glutamatergic neurotransmission in the hippocampus.

Because allelic polymorphism of the major histocompatibility complex class II antigens affects the immune response at several levels, we wished to characterize the contribution of a particular alpha or beta chain in vivo using transgenic mice. We have established and characterized 12 lines of H-2s/s mice carrying from 1 to 65 copies of an Ak beta transgene. The transgene was coexpressed with the endogenous allele in a tissue-specific manner, and Ak beta mRNA expression correlated well with transgene copy number. High copy number (extreme overexpression) of the transgene was associated with a variety of defects, including a significant reduction in Ia cell-surface expression, a severe decrease in B-cell number, abnormal extramedullary granulopoiesis, and an increased susceptibility to infection. In this paper we describe in detail the phenotype associated with high copy numbers of the Ak beta transgene. The defects we have observed may be relevant to similar phenomena seen in other transgenic mice. In addition, these mice have fortuitously provided a system in which to assess the effect of various levels of class II cell-surface expression in the thymus on selection of the T-cell repertoire.

The role of tumor necrosis factor alpha (TNF-alpha) in the pathogenesis of autoimmune diabetes mellitus was tested in the nonobese mouse (NOD) model system. The effects of TNF-alpha were assessed on three levels: (i) insulitis development, (ii) development of overt diabetes, (iii) adoptive transfer of diabetes by splenic lymphocytes. Spontaneous diabetes mellitus was blocked in NOD mice by long-term treatment with recombinant TNF-alpha. Treatment with TNF-alpha caused a significant reduction in the lymphocytic infiltration associated with the destruction of the insulin-producing beta cells. Class II major histocompatibility complex Ia expression by islet cells was not up-regulated by TNF-alpha. Moreover, TNF-alpha was able to suppress the induction of diabetes in adoptive transfer of lymphocytes from diabetic female mice to young nondiabetic male NOD mice. These activities of TNF-alpha were shared by interleukin 1 alpha in this system. These studies have implications for the pathogenesis and therapy of autoimmune diabetes mellitus.