Joachim Kappler

Astroglial neurotrophic and neurite-promoting factors.

Astroglial cells express neurotrophic and/or neurite growth-promoting factors, including (a) peptide growth factors (e.g. nerve growth factors, ciliary neuronotrophic factor, fibroblast growth factor), (b) neurotransmitters (such as glutamate, neuropeptide Y), (c) cell adhesion molecules (e.g. N-CAM) and (d) extracellular matrix proteins (including laminin, fibronectin and proteoglycans). Expression of these molecules is regulated during development and/or after CNS lesions. Some of the astroglial peptide growth factors, including nerve growth factor, basic fibroblast growth factor and ciliary neuronotrophic factor, have been shown to exert protective or even regenerative effects on neurons following traumatic, chemical or ischemic lesions. These observations illustrate the enormous therapeutic potential of astroglia-derived neurotrophic molecules.

Chondroitin/dermatan sulphate promotes the survival of neurons from rat embryonic neocortex.

Recently we have shown that biglycan, a small chondroitin sulphate proteoglycan of the extracellular matrix, supports the survival of cultured neurons from the developing neocortex of embryonic day 15 rats. Here we investigate the structure‐function relationship of this neurotrophic proteoglycan and show that chondroitin/dermatan sulphate chains are the active moieties supporting survival. Heparin, a highly sulphated glucosaminoglycan, is less active than the galactosaminoglycans (chondroitin‐4‐sulphate, chondroitin‐6‐sulphate and dermatan sulphate), whereas hyaluronic acid, an unsulphated glucosaminoglycan, does not support neuron survival. Galactosaminoglycans must be in direct contact with neurons to cause survival. Experiments with elevated potassium concentrations and antagonists of voltage‐gated calcium channels exclude the involvement of membrane depolarization. However, genistein and an erbstatin analogue, which are inhibitors of tyrosine kinases with low specificity, abolished neuron survival in the presence of chondroitin/dermatan sulphate, whereas a selective inhibitor of neurotrophin receptor kinases (K252a) had no suppressive effect. Thus, yet unidentified tyrosine kinases are involved in the chondroitin/dermatan sulphate‐dependent survival of neocortical neurons. In the embryonic stages of rat neocortical development chondroitin sulphate is mainly located in layers I, V and VI and the subplate. Chondroitin sulphate expression is maintained after birth, extends up to cortical layer IV on postnatal day 7, and is down‐regulated until postnatal day 21 concomitant with the period of naturally occurring cell death. The latter observation is consistent with a putative role of chondroitin sulphate in the control of neuron survival during cortical histogenesis.

Purification of a Meningeal Cell-derived Chondroitin Sulphate Proteoglycan with Neurotrophic Activity for Brain Neurons and its Identification as Biglycan

Serum‐free cultures of meningeal fibroblasts synthesize and release a chondroitin sulphate proteoglycan (CSPG) that markedly enhances survival but not adhesion of embryonic rat (embryonic day 15) neocortical neurons in vitro. The active molecule was purified from conditioned medium (meningeal cell‐conditioned medium, MCM) in three steps by means of fast‐performance liquid chromatography fractionation combined with a quantitative microphotometric bioassay: (i) preparative Q‐Sepharose anion exchange chromatography under native conditions; (ii) rechromatography of biologically active Q‐Sepharose fractions on a MonoQ column in the presence of 8 M urea; and (iii) final gel filtration of active MonoQ fractions on Superose 6 in the presence of 4 M guanidinium hydrochloride. Analytical sodium dodecyl sulphate‐polyacrylamide gradient gel electrophoresis of active Superose 6 fractions revealed a single broad glycoprotein band with a molecular mass in the range of 220–340 kDa. Further characterization of the purified molecule with glycosaminoglycan:lyases revealed a core protein of 50 kDa and the nearly complete loss of neurotrophic activity after chondroitinase digestion, whereas heparitinase treatment changed neither electrophoretic mobility nor biological activity. Amino‐terminal sequencing of the purified CSPG core protein revealed identity with the amino acid sequence of rat biglycan. Biglycan purified from bovine cartilage supported neuron survival with virtually the same activity as the CSPG purified from MCM (half‐maximal activity ∼10‐8 M). In conclusion, we isolated a neurotrophic CSPG from meningeal cells with strong survival‐enhancing activity for brain neurons that was identified as biglycan, a molecule not previously related to neural functions.

Collapsin Response Mediator Proteins of Neonatal Rat Brain Interact with Chondroitin Sulfate

Chondroitin sulfate proteoglycans are structurally and functionally important components of the extracellular matrix of the central nervous system. Their expression in the developing mammalian brain is precisely regulated, and cell culture experiments implicate these proteoglycans in the control of cell adhesion, neuron migration, neurite formation, neuronal polarization, and neuron survival. Here, we report that a monoclonal antibody against chondroitin sulfate-binding proteins from neonatal rat brain recognizes collapsin response mediator protein-4 (CRMP-4), which belongs to a family of proteins involved in collapsin/semaphorin 3A signaling. Soluble CRMPs from neonatal rat brain bound to chondroitin sulfate affinity columns, and CRMP-specific antisera co-precipitated chondroitin sulfate. Moreover, chondroitin sulfate and CRMP-4 were found to be localized immuno-histochemically in overlapping distributions in the marginal zone and the subplate of the cerebral cortex. CRMPs are released to culture supernatants of NTera-2 precursor cells and of neocortical neurons after cell death, and CRMP-4 is strongly expressed in the upper cortical plate of neonatal rat where cell death is abundant. Therefore, naturally occurring cell death is a plausible mechanism that targets CRMPs to the extracellular matrix at certain stages of development. In summary, our data indicate that CRMPs, in addition to their role as cytosolic signal transduction molecules, may subserve as yet unknown functions in the developing brain as ligands of the extracellular matrix.

Cultured astrocytes express biglycan, a chondroitin/dermatan sulfate proteoglycan supporting the survival of neocortical neurons.

Astrocyte-conditioned medium (ACM) supports the survival of rat E15 neocortical neurons. Using a microtiter assay for neuronal survival, we demonstrated that part of the survival activity is associated with a proteoglycan fraction obtained after two chromatographic steps: (1) preparative Q-Sepharose anion-exchange chromatography under non-denaturating conditions and (2) MonoQ chromatography in the presence of 8 M urea. Analytical SDS-polyacrylamide gradient gel electrophoresis of pooled active MonoQ-fractions (MQ-pool) revealed a broad proteoglycan band migrating with an apparent M(r) in the range of 150-400 kDa. Digestion of the MQ-pool with chondroitin-ABC-lyase yielded a major core protein of 50 kDa. In Western blots the high molecular weight (150-400 kDa) material as well as the 50 kDa core protein band were immunoreactive to chicken polyclonal antibodies raised against purified biglycan from rat meningeal fibroblasts. Northern blot analysis of total RNA prepared from highly enriched astrocyte cultures revealed a single 2.9 kb biglycan transcript. By using in situ hybridization we demonstrated that essentially all cells in these cultures expressed biglycan mRNA. Furthermore, highly purified biglycan from bovine cartilage was shown to markedly enhance survival of rat neocortical neurons. In conclusion, we have shown that astrocytes synthesize and release the small chondroitin/dermatan sulfate proteoglycan (CS/DSPG) biglycan, a molecule that was found to support survival of neocortical neurons in vitro.

Cerebral Vasomotor Changes in the Transient Syndrome of Headache With Neurologic Deficits and CSF Lymphocytosis (HaNDL)

We report two patients with the recently described transient syndrome of headache with neurologic deficits and CSF lymphocytosis (HaNDL). Transcranial Doppler sonography performed during and after attacks of HaNDL showed asymmetrical decreases or increases in blood flow velocity of the middle cerebral artery, accompanied by increases or decreases in pulsatility suggesting fluctuations of arteriolar tone. The findings demonstrate focal vasomotor disturbances that link the transient headaches and deficits of HaNDL with attacks of migraine.

Developmental regulation of decorin expression in postnatal rat brain

Here, we report on the expression of the small chondroitin/dermatan sulfate proteoglycan decorin in the developing postnatal rat brain. Northern analysis of brain RNA demonstrated decorin transcripts with peak expression on postnatal day 3 followed by a slow decline to the lower adult level. In situ hybridization and immunohistochemistry revealed postnatal decorin expression in the grey matter of neocortex, hippocampus and thalamus, in myelinated fibre tracts and in several mesenchymal tissues (blood vessels, pia mater and the choroid plexus). In the neocortex, decorin is expressed in a specific laminar pattern with intense staining of the cortical plate and its derivatives, which differs remarkably from the distributions observed for other proteoglycans [B. Miller, A.M. Sheppard, A.R. Bicknese, A.L. Pearlman, Chondroitin sulfate proteoglycans in the developing cerebral cortex: the distribution of neurocan distinguishes forming afferent and efferent axonal pathways, J. Comp. Neurol. 355 (1995) 615-28]. Thus, decorin seems to serve yet unknown functions in the developing rat brain parenchyma in addition to its well-established role as a constituent of the mesenchymal extracellular matrix.

Chapter 15 – Astroglial neurotrophic and neurite-promoting factors

Publisher Summary Astroglial cells commonly express glial fibrillary acidic protein in their intermediate filaments, at least at some stage during their development. Astrocytes are present throughout the entire central nervous system (CNS), but their density varies considerably in various regions. The distribution of neurotrophin protein and mRNA in brain suggests that these growth factors are synthesized in target regions of neurotrophin projection fibers, and may support maturation and maintenance for neurotrophin sensitive neurons by receptor-mediated uptake and retrograde axonal transport. Ciliary neurotrophic factor (CNTF) is a very potent survival-enhancing molecule for a variety of neuronal cell populations. A 135 kDa astroglial surface adhesion protein is discovered, which might play a role in astroglial-guided neuronal migration. Astroglia-derived extracellular matrix molecules that influence adhesion, migration, and process formation of neurons are elaborated. Even the sole expression of laminin B2 chain by cultured astrocytes may be sufficient to stimulate neurite outgrowth of PC12-cells.