Form of dual-specificity tyrosine-(Y)-phosphorylation-regulated kinase 1A nonphosphorylated at tyrosine 145 and 147 is enriched in the nuclei of astroglial cells, adult hippocampal progenitors, and some cholinergic axon terminals

Compelling lines of evidence indicate that overexpression of dual-specificity tyrosine-(Y)-phosphorylation regulated kinase 1A (DYRK1A) in subjects with trisomy 21 (Down syndrome[DS]) contributes to the abnormal structure and function of the DS brain. In the present study, we used a novel, phospho-dependent antibody recognizing DYRK1A only with nonphosphorylated tyrosine 145 and 147 (DYRK1A Tyr-145/147P(-)), to investigate the expression pattern of this DYRK1A species in trisomic and disomic human and mouse brains. Immunoblotting and dephosphorylation experiments demonstrated higher levels of DYRK1A Tyr-145/147P(-) in postnatal trisomic brains in comparison with controls (by ∼40%) than those of the DYRK1A visualized by three other N- and C-terminally directed antibodies to DYRK1A. By immunofluorescence, the immunoreactivity to DYRK1A Tyr-145/147P(-) was the strongest in the nuclei of astroglial cells, which contrasted with the predominantly neuronal localization of DYRK1A visualized by the three other antibodies to DYRK1A we used. In addition, DYRK1A Tyr-145/147P(-) was enriched in the nuclei of neuronal progenitors and newly born neurons in the adult hippocampal proliferative zone and also occurred in some cholinergic axonal terminals. Our data show a distinctive expression pattern of DYRK1A forms nonphosphorylated at Tyr-145 and Tyr-147 in the brain tissue and suggest that DS subjects may exhibit not only upregulation of total DYRK1A, but also more subtle differences in phosphorylation levels of this kinase in comparison with control individuals.

Distribution of tripeptidyl peptidase I in human tissues under normal and pathological conditions

Tripeptidyl peptidase I (TPP I) is a lysosomal exopeptidase that cleaves tripeptides from the free N-termini of oligopeptides. Mutations in this enzyme are associated with the classic late-infantile form of neuronal ceroid lipofuscinosis (CLN2), an autosomal recessive disorder leading to severe brain damage. To gain more insight into CLN2 pathogenesis and the role of TPP I in human tissues in general, we analyzed the temporal and spatial distribution of TPP I in the brain and its localization in internal organs under normal and pathological conditions. We report that TPP I immunoreactivity appears in neurons late in gestation and increases gradually in the postnatal period, matching significantly the final differentiation and maturation of neural tissue. Endothelial cells, choroid plexus, microglial cells, and ependyma showed TPP I immunostaining distinctly earlier than neurons. Acquisition of the adult pattern of TPP I distribution in the brain at around the age of 2 years correlates with the onset of clinical signs in CLN2 subjects. In adults, TPP I was found in all types of cells in the brain and internal organs we studied, although the intensity of TPP I labeling varied among several types of cells and showed a noticeable predilection for cells and/or organs associated with peptide hormone and neuropeptide production. In addition, TPP I immunoreactivity was increased in aging brain, neurodegenerative and lysosomal storage disorders, and some differentiated neoplasms and was reduced in ischemic/anoxic areas and undifferentiated tumors. These findings suggest that TPP I is involved in general protein turnover and that its expression may be controlled by various regulatory mechanisms, which highlights the importance of this enzyme for normal function of cells and organs in humans.

Tripeptidyl-peptidase I in neuronal ceroid lipofuscinoses and other lysosomal storage disorders

The classic late infantile form of neuronal ceroid lipofuscinosis (CLN2, cLINCL) is associated with mutations in the gene encoding tripeptidyl-peptidase I (TPP-I), a lysosomal aminopeptidase that cleaves off tripeptides from the free N-termini of oligopeptides. To date over 30 different mutations and 14 polymorphisms associated with CLN2 disease process have been identified. In the present study, we analysed the molecular basis of 15 different mutations of TPP-I by using immunocytochemistry, immunofluorescence, Western blotting, enzymatic assay and subcellular fractionation. In addition, we studied the expression of TPP-I in other lysosomal storage disorders such as CLN1, CLN3, muccopolysaccharidoses and GM1 and GM2 gangliosidoses. Our study shows that TPP-I is absent or appears in very small amounts not only in cLINCL subjects with mutations producing severely truncated protein, but also in individuals with missense point mutations, which correlates with loss of TPP-I activity. Of interest, small amounts of TPP-I were detected in lysosomal fraction from fibroblasts from cLINCL subject with protracted form. This observation suggests that the presence of small amounts of TPP-I in lysosomes is able to delay significantly CLN2 disease process. We also show that TPP-I immunoreactivity is increased in the brain tissue of CLN1 and CLN3 subjects, stronger in glial cells and macrophages than neurons. Less prominent increase of TPP-I staining was found in muccopolysaccharidoses and GM1 and GM2 gangliosidoses. These data suggest that TPP-I participates in lysosomal turnover of proteins in pathological conditions associated with cell/tissue injury.

CLN3 disease process: missense point mutations and protein depletion in vitro

Although the CLN3 gene associated with the disease process in subjects with the juvenile form of neuronal ceroid lipofuscinosis was discovered in 1995, our knowledge of the physiological function of its gene product, CLN3 protein, is still incomplete. To gain more insight into the structural properties and function of CLN3 protein we studied at present: i) how the naturally occurring point mutations Arg334Cys and Leu101Pro affect the biological properties of CLN3 protein, and ii) whether depletion of CLN3 protein synthesis by using an antisense approach induces a distinct phenotype in cells of neuronal origin in vitro. Here we report that although both CLN3 mutant proteins are targeted to lysosomes, thus similar to wild-type CLN3 protein, they are devoid of the biological activity of wild-type CLN3 protein such as its effect on lysosomal pH or intracellular processing of amyloid-beta protein precursor and cathepsin D in vitro. The Leu101Pro mutation affected significantly the maturation and stability of CLN3 protein. The Arg334Cys mutation influenced mildly the maturation and turnover of CLN3 protein, but at the same time abolished the function of CLN3 protein in vitro, which suggests that the Arg334 may constitute a part of the active site of CLN3 protein. In addition, we show that depletion of CLN3 protein synthesis in human neuroblastoma cells in vitro induces outgrowth of long cellular processes and formation of cellular aggregates and affects the viability of these cells. This finding suggests that CLN3 protein is implicated in biological processes associated with the differentiation of cells of neuronal origin.

Sodium dodecyl sulfate-resistant complexes of Alzheimer's amyloid beta-peptide with the N-terminal, receptor binding domain of apolipoprotein E

Immunocytochemical, biochemical, and molecular genetic studies indicate that apolipoprotein E (apoE) plays an important role in the process of amyloidogenesis-beta. However, there is still no clear translation of these data into the pathogenesis of amyloidosis-beta. Previous studies demonstrated sodium dodecyl sulfate (SDS)-resistant binding of apoE to the main component of Alzheimer's amyloid-A beta and modulation of A beta aggregation by apoE in vitro. To more closely characterize apoE-A beta interactions, we have studied the binding of thrombolytic fragments of apoE3 to A beta in vitro by using SDS-polyacrylamide gel electrophoresis and intrinsic fluorescence quenching. Here we demonstrate that SDS-resistant binding of A beta is mediated by the receptor-binding, N-terminal domain of apoE3. Under native conditions, both the N- and C-terminal domains of apoE3 bind A beta; however, the former does so with higher affinity. We propose that the modulation of A beta binding to the N-terminal domain of apoE is a potential therapeutic target for the treatment of amyloidosis-beta.

CLN3 protein regulates lysosomal pH and alters intracellular processing of Alzheimer's amyloid-beta protein precursor and cathepsin D in human cells

Maintenance of the appropriate pH in the intracellular vacuolar compartments is essential for normal cell function. Here, we report that CLN3 protein, which is associated with the juvenile form of neuronal ceroid lipofuscinosis (JNCL), participates in lysosomal pH homeostasis in human cells. We show that CLN3 protein increases lysosomal pH in cultured human embryonal kidney cells, whereas inhibition of CLN3 protein synthesis by antisense approach acidifies lysosomal compartments. These changes in lysosomal pH are sufficient to exert a significant biological effect and modify intracellular processing of amyloid-beta protein precursor and cathepsin D, model proteins whose metabolism is influenced by the pH of acidic organelles. Mutant CLN3 protein (R334C) that is associated with the classical JNCL phenotype was devoid of biological activities of wild-type CLN3 protein. These data suggest that the pathogenesis of juvenile neuronal ceroid lipofuscinosis is associated with altered acidification of lysosomal compartments. Furthermore, our study indicates that CLN3 protein affects metabolism of proteins essential for cell functions, such as amyloid-beta protein precursor, implicated in Alzheimer's disease pathogenesis.

Nasoethmoidal encephalomeningocele demonstrated by cisternography: case report

A mass at the base of the nose, suspected of containing a nasoethmoidal encephalomeningocele, was shown to communicate with the cerebrospinal fluid by cisternography. The diagnosis of encephalomeningocele was confirmed at surgery.