The 39-to 43-amino acid amyloid 1-protein (A*6), which is progressively deposited in cerebral plaques and blood vessels in Alzheimer disease (AD), is secreted by cultured human cells during normal metabolism. 11993The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

The molecular pathogenesis of bipolar disorder (BPD) is poorly understood. Using human-induced pluripotent stem cells (hiPSCs) to unravel such mechanisms in polygenic diseases is generally challenging. However, hiPSCs from BPD patients responsive to lithium offered unique opportunities to discern lithium's target and hence gain molecular insight into BPD. By profiling the proteomics of BDP-hiPSCderived neurons, we found that lithium alters the phosphorylation state of collapsin response mediator protein-2 (CRMP2). Active nonphosphorylated CRMP2, which binds cytoskeleton, is present throughout the neuron; inactive phosphorylated CRMP2, which dissociates from cytoskeleton, exits dendritic spines. CRMP2 elimination yields aberrant dendritogenesis with diminished spine density and lost lithium responsiveness (LiR). The "set-point" for the ratio of pCRMP2:CRMP2 is elevated uniquely in hiPSC-derived neurons from LiR BPD patients, but not with other psychiatric (including lithium-nonresponsive BPD) and neurological disorders. Lithium (and other pathway modulators) lowers pCRMP2, increasing spine area and density. Human BPD brains show similarly elevated ratios and diminished spine densities; lithium therapy normalizes the ratios and spines. Consistent with such "spine-opathies," human LiR BPD neurons with abnormal ratios evince abnormally steep slopes for calcium flux; lithium normalizes both. Behaviorally, transgenic mice that reproduce lithium's postulated site-of-action in dephosphorylating CRMP2 emulate LiR in BPD. These data suggest that the "lithium response pathway" in BPD governs CRMP2's phosphorylation, which regulates cytoskeletal organization, particularly in spines, modulating neural networks. Aberrations in the posttranslational regulation of this developmentally critical molecule may underlie LiR BPD pathogenesis. Instructively, examining the proteomic profile in hiPSCs of a functional agent-even one whose mechanism-of-action is unknownmight reveal otherwise inscrutable intracellular pathogenic pathways. have proven valuable for studying the molecular pathology of monogenic diseases, one of the technique's greatest challenges has been to offer similar insights into the molecular pathogenesis of polygenic, multifactorial disorders for which the underlying pathophysiology is unknown. The struggle has been to go beyond phenotypic description to discerning underlying molecular mechanisms. Neuropsychiatric illnesses are a prototype for such complex conditions (1-3). They are difficult to model not only because of the likelihood of polygenic influences, but also because of the subjectivity with which these diseases must often be diagnosed, the empirical fashion with which drugs are prescribed, and the heterogeneity of patient response. Of such maladies, bipolar disorder

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We describe a male infant with psychomotor retardation and leukodystrophy who excretes large quantities of N-acetylaspartate in his urine. A high CSF/plasma concentration ratio of N-acetylaspartate indicates that this substance originates in the brain. Fibroblasts from the patient are deficient in aspartoacylase activity. It is proposed that the dysmyelination in the patient may be due to failure of N-acetylaspartate to serve as a carrier of acetyl groups from mitochondria to the cytosol for lipogenesis.

Cell lines transfected with the Swedish Alzheimer's disease amyloid precursor protein APP6701671 mutation release significantly more B-amyloid than wild-type cells. Citron et al. [Proc. Natl. Acad. Sci. USA (1994) in press] have recently shown that fibroblasts carrying the APP670/671 mutation also release more /3-amyloid than control cells [l]. The present study confirms a ca. threefold increase in /3-amyloid release from mutation-bearing fibroblasts. APP mRNA levels did not differ between mutation-bearing and control cells, although mutation-bearing fibroblasts contained significantly more APP751/770 than controls. Mild stress decreased B-amyloid secretion and increased APP751/770 levels in all cell lines. In conclusion, the proportion of APP committed to amyloidogenic processing is increased in fibroblasts from family members with the APP670/671 mutation, and this mutation may also compromise the APP stress response.Key words: Alzheimer's disease; Amyloid precursor protein; APP mRNA; &4myloid; Fibroblast; Foetal calf serum IntioductionAlzheimer's disease is a progressive neurodegenerative disorder defined histopathologically by the excessive accumulation of extracellular proteinaceous deposits (amyloid plaques) and intraneuronal bundles of paired helical filaments (neurofibrillary tangles) throughout the hippocampus and neocortex. A 39-43 amino acid peptide, termed /3-amyloid, has been identified as the major constituent of plaque and cerebrovascular amyloid [2]. This peptide is a metabolite of the amyloid precursor protein (APP), encoded by a gene on chromosome 21 [3]. The identification of pathogenic APP gene mutations in some Alzheimer's disease families has firmly established the importance of APP and /3-amyloid in the aetiology of this disorder [4,51. APP RNA is alternatively spliced in a tissue-specific manner, giving rise to at least ten different mRNA species. These include APP770 with domains showing homology to a Kunitz type protease inhibitor (KPI) and the MRC OX-2 antigen; APP751 which includes the KPI region only; and APP695 which lacks both the KPI and the MRC OX-2 domains [3,&8].Two alternative APP processing routes utilising the as yet We have identified a double mutation in the APP gene resulting in amino acid substitutions of Lys to Asn (codon 670) and Met to Leu (671) in a large Swedish family where Alzheimer's disease is inherited in an autosomal dominant manner [5,16]. Subsequently, it was shown that human kidney 293 and neuroblastoma Ml7 cell lines transfected with this mutation released approximately 7 times more /?-amyloid into culture medium than their wild type counterparts [17,18]. Recently, Citron et al. have shown that /?-amyloid release is increased in fibroblast cell lines from Swedish APP670/671 mutation carriers, co'mpared to control family members [I].In the present study, we quantified B-amyloid release from primary fibroblast cell lines established from heterozygous APP670/671 mutation carriers and control family members using a sensitive ELISA assay [13]. In addi...

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The lower V(max) and K(m) are compatible with a cell membrane disturbance and support the view of schizophrenia as a systemic disorder. The decreased V(max) and K(m) observed in cells from schizophrenic patients probably reflect a genetic trait, as the changes were transmitted through several cell generations of cultured fibroblast.

Human fibroblast cells are an advantageous model to study the transport of amino acids across cell membranes, since one can control the environmental factors. A major problem in all earlier studies is the lack of precise and detailed knowledge regarding the expression and functionality of tyrosine transporters in human fibroblasts. This motivated us to perform a systematic functional characterization of the tyrosine transport in fibroblast cells with respect to the isoforms of system-L (LAT1, LAT2, LAT3, LAT4), which is the major transporter of tyrosine. Ten (n=10) fibroblast cell lines from healthy volunteers were included in the study. Uptake of L-[U-14C] tyrosine in fibroblasts was measured using the cluster tray method in the presence and absence of excess concentrations of various combinations of inhibitors. This study demonstrated that LAT1 is involved in 90% of total uptake of tyrosine and also around 51% of alanine. Not more than 10% can be accounted for by LAT2, LAT3 and LAT4 isoforms. LAT2 seems to be functionally weak in uptake of tyrosine while LAT3 and LAT4 contributed around 7%. 10% could be contributed by system-A (ATA2 isoform). Alanine consequently inhibited the tyrosine transport by up to 60%. Tyrosine transport through the LAT1 isoform has a higher affinity compared to system-L. In conclusion, the LAT1 isoform is the major transporter of tyrosine in human fibroblast cells. Competition between tyrosine and alanine for transport is shown to exist, probably between LAT1 and LAT2 isoforms. This study established fibroblast cells as a suitable experimental model for studying amino acid transport defects in humans.