SPARC, an extracellular matrix glycoprotein containing the follistatin module, is expressed by astrocytes in synaptic enriched regions of the adult brain

SPARC overexpression in allogeneic adipose-derived mesenchymal stem cells in dog dry eye model induced by benzalkonium chloride

BACKGROUND

Nowadays, companion and working dogs hold significant social and economic importance. Dry eye, also known as dry keratoconjunctivitis (KCS), a common disease in ophthalmology, can readily impact a dog's working capacity and lead to economic losses. Although there are several medications available for this disease, all of them only improve the symptoms on the surface of the eye, and they are irritating and not easy to use for long periods of time. Adipose-derived mesenchymal stem cells (ADMSC) are promising candidates for tissue regeneration and disease treatment. However, long-term in vitro passaging leads to stemness loss of ADMSC. Here, we aimed to use ADMSC overexpressing Secreted Protein Acidic and Rich in Cysteine (SPARC) to treat 0.25% benzalkonium chloride-treated dogs with dry eye to verify its efficacy. For in vitro validation, we induced corneal epithelial cell (HCECs) damage using 1 µg/mL benzalkonium chloride.

METHODS

Fifteen male crossbred dogs were randomly divided into five groups: normal, dry eye self-healing control, cyclosporine-treated, ADMSC-CMV-treated and ADMSC-OESPARC-treated. HCECs were divided into four groups: normal control group, untreated model group, ADMSC-CMV supernatant culture group and ADMSC-OESRARC supernatant culture group.

RESULTS

SPARC-modified ADMSC had the most significant effect on canine ocular surface inflammation, corneal injury, and tear recovery, and the addition of ADMSC-OESPARC cell supernatant also had a salvage effect on HCECs cellular damage, such as cell viability and cell proliferation ability. Moreover, analysis of the co-transcriptome sequencing data showed that SPARC could promote corneal epithelial cell repair by enhancing the in vitro viability, migration and proliferation and immunosuppression of ADMSC.

CONCLUSION

The in vitro cell test and in vivo model totally suggest that the combination of SPARC and ADMSC has a promising future in novel dry eye therapy.

Interplay between hevin, SPARC, and MDGAs: Modulators of neurexin-neuroligin transsynaptic bridges

Hevin is secreted by astrocytes and its synaptogenic effects are antagonized by the related protein, SPARC. Hevin stabilizes neurexin-neuroligin transsynaptic bridges in vivo. A third protein, membrane-tethered MDGA, blocks these bridges. Here, we reveal the molecular underpinnings of a regulatory network formed by this trio of proteins. The hevin FS-EC structure differs from SPARC, in that the EC domain appears rearranged around a conserved core. The FS domain is structurally conserved and it houses nanomolar affinity binding sites for neurexin and neuroligin. SPARC also binds neurexin and neuroligin, competing with hevin, so its antagonist action is rooted in its shortened N-terminal region. Strikingly, the hevin FS domain competes with MDGA for an overlapping binding site on neuroligin, while the hevin EC domain binds the extracellular matrix protein collagen (like SPARC), so that this trio of proteins can regulate neurexin-neuroligin transsynaptic bridges and also extracellular matrix interactions, impacting synapse formation and ultimately neural circuits.

The role of astrocyte-mediated plasticity in neural circuit development and function

Neuronal networks are capable of undergoing rapid structural and functional changes called plasticity, which are essential for shaping circuit function during nervous system development. These changes range from short-term modifications on the order of milliseconds, to long-term rearrangement of neural architecture that could last for the lifetime of the organism. Neural plasticity is most prominent during development, yet also plays a critical role during memory formation, behavior, and disease. Therefore, it is essential to define and characterize the mechanisms underlying the onset, duration, and form of plasticity. Astrocytes, the most numerous glial cell type in the human nervous system, are integral elements of synapses and are components of a glial network that can coordinate neural activity at a circuit-wide level. Moreover, their arrival to the CNS during late embryogenesis correlates to the onset of sensory-evoked activity, making them an interesting target for circuit plasticity studies. Technological advancements in the last decade have uncovered astrocytes as prominent regulators of circuit assembly and function. Here, we provide a brief historical perspective on our understanding of astrocytes in the nervous system, and review the latest advances on the role of astroglia in regulating circuit plasticity and function during nervous system development and homeostasis.

Olfactory ensheathing cells facilitate neurite sprouting and outgrowth by secreting high levels of hevin

Transplantation of olfactory ensheathing cells (OECs) has been shown to enhance synapse formation. However, the mechanisms underlying this effect are not completely understood. We performed profiling of the OEC and astrocyte secretomes via a proteomics approach, in case hevin secreted by astrocytes might be involved in the formation of synapses. Semi-quantitative proteomic analysis revealed that 25 proteins were highly expressed, and 22 were weakly expressed in OEC conditioned medium compared with astrocyte conditioned medium. These molecules are highly associated with neural differentiation and regeneration, enzyme regulatory activity, and growth factor binding. The quantification data of clusterin, fibronectin, hevin, insulin-like growth factor binding protein 2 and secreted protein acidic and rich in cysteine were further confirmed by western blotting. Moreover, the addition of hevin in the culture medium improved neurite sprouting and outgrowth of differentiated neural stem cells. The greater expression of hevin in OEC conditioned medium than in astrocyte conditioned medium was associated with a greater capacity of synaptic formation. Thus, our results indicate that soluble factors secreted by OECs provide a permissive environment for nerve repair, and hevin is one of the key molecules facilitating neurite sprouting and outgrowth.

Cartography of hevin-expressing cells in the adult brain reveals prominent expression in astrocytes and parvalbumin neurons

Hevin, also known as SPARC-like 1, is a member of the secreted protein acidic and rich in cysteine family of matricellular proteins, which has been implicated in neuronal migration and synaptogenesis during development. Unlike previously characterized matricellular proteins, hevin remains strongly expressed in the adult brain in both astrocytes and neurons, but its precise pattern of expression is unknown. The present study provides the first systematic description of hevin mRNA distribution in the adult mouse brain. Using isotopic in situ hybridization, we showed that hevin is strongly expressed in the cortex, hippocampus, basal ganglia complex, diverse thalamic nuclei and brainstem motor nuclei. To identify the cellular phenotype of hevin-expressing cells, we used double fluorescent in situ hybridization in mouse and human adult brains. In the mouse, hevin mRNA was found in the majority of astrocytes but also in specific neuronal populations. Hevin was expressed in almost all parvalbumin-positive projection neurons and local interneurons. In addition, hevin mRNA was found in: (1) subsets of other inhibitory GABAergic neuronal subtypes, including calbindin, cholecystokinin, neuropeptide Y, and somatostatin-positive neurons; (2) subsets of glutamatergic neurons, identified by the expression of the vesicular glutamate transporters VGLUT1 and VGLUT2; and (3) the majority of cholinergic neurons from motor nuclei. Hevin mRNA was absent from all monoaminergic neurons and cholinergic neurons of the ascending pathway. A similar cellular profile of expression was observed in human, with expression of hevin in parvalbumin interneurons and astrocytes in the cortex and caudate nucleus as well as in cortical glutamatergic neurons. Furthermore, hevin transcript was enriched in ribosomes of astrocytes and parvalbumin neurons providing a direct evidence of hevin mRNAs translation in these cell types. This study reveals the unique and complex expression profile of the matricellular protein hevin in the adult brain. This distribution is compatible with a role of hevin in astrocytic-mediated adult synaptic plasticity and in the regulation of network activity mediated by parvalbumin-expressing neurons.

Cell adhesion and matricellular support by astrocytes of the tripartite synapse

Astrocytes contribute to the formation, function, and plasticity of synapses. Their processes enwrap the neuronal components of the tripartite synapse, and due to this close interaction they are perfectly positioned to modulate neuronal communication. The interaction between astrocytes and synapses is facilitated by cell adhesion molecules and matricellular proteins, which have been implicated in the formation and functioning of tripartite synapses. The importance of such neuron-astrocyte integration at the synapse is underscored by the emerging role of astrocyte dysfunction in synaptic pathologies such as autism and schizophrenia. Here we review astrocyte-expressed cell adhesion molecules and matricellular molecules that play a role in integration of neurons and astrocytes within the tripartite synapse.

Secreted Protein Acidic and Rich in Cysteine in Ocular Tissue

Secreted protein acidic and rich in cysteine (SPARC), also known as osteonectin or BM-40, is the prototypical matricellular protein. Matricellular proteins are nonstructural secreted proteins that provide an integration between cells and their surrounding extracellular matrix (ECM). Regulation of the ECM is important in maintaining the physiologic function of tissues. Elevated levels of SPARC have been identified in a variety of diseases involving pathologic tissue remodeling, such as hepatic fibrosis, systemic sclerosis, and certain carcinomas. Within the eye, SPARC has been identified in the trabecular meshwork, lens, and retina. Studies have begun to show the role of SPARC in these tissues and its possible role, specifically in primary open-angle glaucoma, cataracts, and proliferative vitreoretinopathy. SPARC may, therefore, be a therapeutic target in the treatment of certain ocular diseases. Further investigation into the mechanism of action of SPARC will be necessary in the development of SPARC-targeted therapy.

Astrocyte-secreted matricellular proteins in CNS remodelling during development and disease

Matricellular proteins are secreted, nonstructural proteins that regulate the extracellular matrix (ECM) and interactions between cells through modulation of growth factor signaling, cell adhesion, migration, and proliferation. Despite being well described in the context of nonneuronal tissues, recent studies have revealed that these molecules may also play instrumental roles in central nervous system (CNS) development and diseases. In this minireview, we discuss the matricellular protein families SPARC (secreted protein acidic and rich in cysteine), Hevin/SC1 (SPARC-like 1), TN-C (Tenascin C), TSP (Thrombospondin), and CCN (CYR61/CTGF/NOV), which are secreted by astrocytes during development. These proteins exhibit a reduced expression in adult CNS but are upregulated in reactive astrocytes following injury or disease, where they are well placed to modulate the repair processes such as tissue remodeling, axon regeneration, glial scar formation, angiogenesis, and rewiring of neural circuitry. Conversely, their reexpression in reactive astrocytes may also lead to detrimental effects and promote the progression of neurodegenerative diseases.

Osteonectin Expression in Surrounding Stroma of Craniopharyngiomas

Craniopharyngioma is an epithelial tumor of the sellar region with a high survival rate but a high rate of recurrence, especially in children. Hypothalamic involvement, tumor recurrence, and multiple treatments result in clinical deterioration and impaired quality of life. Using immunohistochemistry, we investigated the expression pattern of osteonectin, a marker of tumor invasion and aggressive behavior, in 43 cases of craniopharyngioma. We observed a positive correlation of osteonectin expression in connective-type stromal tissue surrounding the epithelial tumor cells of craniopharyngioma with the extent of central nervous system infiltration and recurrence rate ( P < .001). Given the previous success of chemotherapeutic agents that target the tumor microenvironment, our findings on osteonectin expression in stroma of craniopharyngiomas might, hopefully, be a guide to find newer prognostic markers capable of estimating the risk of progression or recurrence. They may also aid in the development of therapeutics that target tumor microenvironment to improve patient outcome.

Hippocampal SPARC regulates depression-related behavior

SPARC (secreted protein acidic and rich in cysteine) is a matricellular protein highly expressed during development, reorganization and tissue repair. In the central nervous system, glial cells express SPARC during development and in neurogenic regions of the adult brain. Astrocytes control the glutamate receptor levels in the developing hippocampus through SPARC secretion. To further characterize the role of SPARC in the brain, we analyzed the hippocampal-dependent adult behavior of SPARC KO mice. We found that SPARC KO mice show increased levels of anxiety-related behaviors and reduced levels of depression-related behaviors. The antidepressant-like phenotype could be rescued by adenoviral vector-mediated expression of SPARC in the adult hippocampus, but anxiety-related behavior persisted in these mice. To identify the cellular mechanisms underlying these behavioral alterations, we analyzed neuronal activity and neurogenesis in the dentate gyrus (DG). SPARC KO mice have increased levels of neuronal activity, evidenced as more neurons that express c-Fos after a footshock. SPARC also affects cell proliferation in the subgranular zone of the DG, although it does not affect maturation and survival of new neurons. SPARC expression in the adult DG does not revert the proliferation phenotype in KO mice, but our results suggest a role of SPARC in limiting the survival of new neurons in the DG. This work suggests that SPARC could affect anxiety-related behavior by modulating neuronal activity, and that depression-related behavior is dependent upon the adult expression of SPARC, which affects adult brain function by mechanisms that need to be elucidated.

The Function of SPARC as a Mediator of Fibrosis

Fibrosis is a common end-point of a number of different diseases such as hypertension, diabetes, liver cirrhosis, and those associated with chronic inflammation. Fibrosis is characterized by excessive deposition of extracellular matrix that interferes with normal tissue architecture and function. Increased expression of secreted protein acidic and rich in cysteine (SPARC) in fibrotic tissues has been reported in numerous studies. SPARC is a 43 kDa collagen-binding protein secreted from several different cell types into the extracellular matrix and has been shown to be anti-proliferative and counter-adhesive in vitro. SPARC is a matricellular protein; meaning SPARC is secreted into the extracellular space but does not serve a structural function. Instead, SPARC modulates interactions between cells and the surrounding extracellular matrix. In animal models of fibrotic disease and in human fibrotic tissues, elevated expression of SPARC has been reported in many tissues including heart, lungs, kidneys, liver, dermis, intestine, and eyes. In this review, we will summarize current studies that have examined the expression and functional importance of SPARC in various animal models of fibrosis and in human tissues. Although cellular mechanisms of SPARC in fibrosis remain to be fully elucidated, the studies summarized here provide impetus to further explore the efficacy of SPARC as a potential target for reducing fibrosis.

SPARC prevents maturation of cholinergic presynaptic terminals

Secreted Protein Acidic and Rich in Cysteine (SPARC) is a matricellular protein produced by glial cells. Although it is highly expressed in synaptogenic areas in the developing nervous system, it is still unclear whether this molecule displays an action on synaptic activity. We show that nanomolar concentrations of SPARC favour a more efficient synapse formation and increase short term depression in single cell cholinergic microcultures. The change in synaptic plasticity, which is also observed when SPARC is locally secreted on stable synapses for 24-48 h, is caused by a high release probability and a reduction in the size of the rapidly releasable pool of vesicles. Both features are attributable to synapses operating at an immature stage as demonstrated by correlative electrophysiology and electron microscopy experiments. Presynaptic terminals developed in the presence of SPARC display few cytoplasmic vesicles and two to threefold decrease in the number of docked vesicles at active zones. At the postsynaptic level, the analysis of miniature excitatory postsynaptic currents suggests SPARC has little effect on the number of nicotinic receptors but might alter their composition. The widespread distribution of SPARC makes current findings potentially relevant to other excitatory synapses and development of neuronal circuits.

Control of excitatory CNS synaptogenesis by astrocyte-secreted proteins Hevin and SPARC

Astrocytes regulate synaptic connectivity in the CNS through secreted signals. Here we identified two astrocyte-secreted proteins, hevin and SPARC, as regulators of excitatory synaptogenesis in vitro and in vivo. Hevin induces the formation of synapses between cultured rat retinal ganglion cells. SPARC is not synaptogenic, but specifically antagonizes synaptogenic function of hevin. Hevin and SPARC are expressed by astrocytes in the superior colliculus, the synaptic target of retinal ganglion cells, concurrent with the excitatory synaptogenesis. Hevin-null mice had fewer excitatory synapses; conversely, SPARC-null mice had increased synaptic connections in the superior colliculus. Furthermore, we found that hevin is required for the structural maturation of the retinocollicular synapses. These results identify hevin as a positive and SPARC as a negative regulator of synapse formation and signify that, through regulation of relative levels of hevin and SPARC, astrocytes might control the formation, maturation, and plasticity of synapses in vivo.

Proteomic Characterization of Cerebrospinal Fluid from Ataxia-Telangiectasia (A-T) Patients Using a LC/MS-Based Label-Free Protein Quantification Technology

Cerebrospinal fluid (CSF) has been used for biomarker discovery of neurodegenerative diseases in humans since biological changes in the brain can be seen in this biofluid. Inactivation of A-T-mutated protein (ATM), a multifunctional protein kinase, is responsible for A-T, yet biochemical studies have not succeeded in conclusively identifying the molecular mechanism(s) underlying the neurodegeneration seen in A-T patients or the proteins that can be used as biomarkers for neurologic assessment of A-T or as potential therapeutic targets. In this study, we applied a high-throughput LC/MS-based label-free protein quantification technology to quantitatively characterize the proteins in CSF samples in order to identify differentially expressed proteins that can serve as potential biomarker candidates for A-T. Among 204 identified CSF proteins with high peptide-identification confidence, thirteen showed significant protein expression changes. Bioinformatic analysis revealed that these 13 proteins are either involved in neurodegenerative disorders or cancer. Future molecular and functional characterization of these proteins would provide more insights into the potential therapeutic targets for the treatment of A-T and the biomarkers that can be used to monitor or predict A-T disease progression. Clinical validation studies are required before any of these proteins can be developed into clinically useful biomarkers.

Astrocytes control glutamate receptor levels at developing synapses through SPARC-beta-integrin interactions

Neurons recruit numerous mechanisms to facilitate the development of synaptic connections. However, little is known about activity-dependent mechanisms that control the timing and fidelity of this process. Here we describe a novel pathway used by neurons to regulate glutamate receptors at maturing central synapses. This pathway relies on communication between neurons and astrocytes and the ability of astrocytes to release the factor SPARC (secreted protein, acidic and rich in cysteine). SPARC expression is dynamically regulated and plays a critical role in determining the level of synaptic AMPARs. SPARC ablation in mice increases excitatory synapse function, causes an abnormal accumulation of surface AMPARs at synapses, and impairs synaptic plasticity during development. We further demonstrate that SPARC inhibits the properties of neuronal β3-integrin complexes, which are intimately coupled to AMPAR stabilization at synapses. Thus neuron-glial signals control glutamate receptor levels at developing synapses to enable activity-driven modifications of synaptic strength.

Differential expression patterns of OCC1-related, extracellular matrix proteins in the lateral geniculate nucleus of macaque monkeys

The extracellular matrix (ECM) plays important roles in the development and plasticity of the central nervous system, and it has been shown that it regulates reorganization of the neuronal network. We have found that expression of OCC1, testican-1, testican-2, testican-3, SPARC and SC1 mRNAs, which encode members of the OCC1-related family of ECM proteins, exhibits distinct activity-dependent expression patterns in the adult macaque visual cortex. This finding suggests that OCC1-related proteins play crucial roles in the visual processing pathway. In the present study, we examined mRNA expression patterns of OCC1-related genes in the dorsal lateral geniculate nucleus (dLGN) of macaques. The mRNAs of testican-1 and testican-2 were strongly expressed in both excitatory projection neurons and GABAergic interneurons in the dLGN. Expression of testican-3 mRNA, which is predominantly observed in GABAergic interneurons in the cortex, was restricted to excitatory projection neurons in the dLGN. SPARC mRNA was strongly, and exclusively, expressed in glial cells in the dLGN. Interestingly, neuronal SC1 mRNA expression was abundantly observed in intercalated, koniocellular layers of the dLGN, while it was preferentially observed in blob regions of the primary visual area that receives color coding K-pathway projection from dLGN koniocellular layers, suggesting a pathway preference of expression. Finally, monocular inactivation experiments demonstrated that expression of testican-1, testican-2 and testican-3 mRNAs in the dLGN is dependent on sensory activity. Given their differential expression patterns and activity dependence, products of OCC1-related genes may modulate visual processing and plasticity at the level of the dLGN and the visual cortex.

Synergistic effects of osteonectin and brain-derived neurotrophic factor on axotomized retinal ganglion cells neurite outgrowth via the mitogen-activated protein kinase-extracellular signal-regulated kinase 1/2 pathways

Our previous study identified osteonectin (ON) in a screen of factors made by Schwann cells (SCs) which promoted peripheral and central neurons survival and neuritogenesis, however, the mechanisms of ON promoting effects are largely unknown. In the present study, we investigated the effects of ON-deficient SC-conditioned medium (SCCM) and molecular mechanisms of ON, in regulating retinal ganglion cells (RGCs) survival and neurite outgrowth. Neonatal rat RGCs and SCs were purified by immunopanning technique. RGC survival and neuritogenesis reduced significantly when treated with either ON-null mice SCCM or ON-immunodepleted (IP) SCCM (P<0.05). In contrast to wild type SCCM, in the presence of a tyrosine kinase receptor (Trk) inhibitor (K252a), ON-null mice SCCM-induced neuritogenesis were further reduced by 24%. The Trk-mediated signaling pathways became more sensitive to K252a inhibition in the absence of ON. We also showed the synergistic effects of ON and brain-derived neurotrophic factor (BDNF) in promoting RGCs growth and the involvement of ON in two major neurotrophin-mediated signaling pathways, PI-3K-Akt and MAPK-Erk1/2. ON alone activated Akt phosphorylation and increased survival. Blockage of TrkB signalling pathway by TrkB-Fc chimera (BDNF scavenger) or K252a in ON-treated cultures reduced Akt-P level significantly. This suggests that ON induces BDNF synthesis and secretion from RGCs. The enhancement of neuritogenesis and Erk1/2 phosphorylation by ON in BDNF-treated cultures further demonstrate the signaling pathways responsible for the synergistic effect of ON on BDNF-induced neurite outgrowth. To the best of our knowledge, this is the first report showing the synergistic effects of ON on classical neurotrophins which participate in the same signalling pathways in regulating RGC neurite outgrowth.

The role of astrocyte-secreted matricellular proteins in central nervous system development and function

Matricellular proteins, such as thrombospondins (TSPs1-4), SPARC, SPARC-like1 (hevin) and tenascin C are expressed by astrocytes in the central nervous system (CNS) of rodents. The spatial and temporal expression patterns of these proteins suggest that they may be involved in important developmental processes such as cell proliferation and maturation, cell migration, axonal guidance and synapse formation. In addition, upon injury to the nervous system the expression of these proteins is upregulated, suggesting that they play a role in tissue remodeling and repair in the adult CNS. The genes encoding these proteins have been disrupted in mice. Interestingly, none of these proteins are required for survival, and furthermore, there are no evident abnormalities at the gross anatomical level in the CNS. However, detailed analyses of some of these mice in the recent years have revealed interesting CNS phenotypes. Here we will review the expression of these proteins in the CNS. We will discuss a newly described function for thrombospondins in synapse formation in the CNS in detail, and speculate whether other matricellular proteins could play similar roles in nervous system development and function.

Synergistic effects of osteonectin and NGF in promoting survival and neurite outgrowth of superior cervical ganglion neurons

Schwann cells (SCs) play a major role in the successful regeneration of peripheral nerves regeneration. Here we examined the effects of osteonectin (ON), a major factor secreted by SCs, on survival and neuritogenesis of mouse superior cervical ganglion (SCG) neurons. SC conditioned medium (SCCM) not only promoted the survival and neuritogenesis of SCG neurons at a level comparable to nerve growth factor (NGF) but also doubled the neurite length of NGF-treated SCG neurons. SCCM neuritogenic effects were not blocked by the tyrosine kinase receptor (Trk) inhibitor K252a demonstrating that these are not due solely to classical neurotrophic factors. Anti-ON neutralizing antibody diminished the SCCM-induced survival and neuritogenesis significantly. In the presence of K252a, the SCCM neuritogenic effects were blocked completely by anti-ON which suggests synergistic effects of ON with Trk-mediated growth factors. ON alone increased the survival and neurite outgrowth of SCG neurons significantly at high density cultures. ON at low concentration acts synergistically with NGF which induced maximum survival and neurite outgrowth (>50% increase). However, ON at high concentration was detrimental to survival (64% decrease) and neurite outgrowth (87% decrease) even in the presence of NGF. The well documented counter-adhesive effect of ON may account for this observation. Nevertheless, the growth promoting effects of ON became more pronounced as the cell density increased which suggests a possible interaction of ON with growth factors secreted by SCG neurons (autocrine or paracrine effects). Taken together, our study indicates that ON plays important roles in nervous system repair through its synergistic effects with growth factors.

Post-ischemic hypothermia attenuates loss of the vascular basement membrane proteins, agrin and SPARC, and the blood-brain barrier disruption after global cerebral ischemia

Vascular basement membrane (BM) stabilizes brain vessels and inhibits endothelial cell cycle. Cerebral ischemia causes BM breakdown with the loss of structural BM components including collagens and laminins. In this study, the expression changes of the BM proteoglycan agrin, and the non-structural BM constituent SPARC (BM-40, osteonectin), were studied in brain vessels after global cerebral ischemia. A transient 20-min forebrain ischemia followed by 1, 6 or 24 h of reperfusion was induced in adult Sprague-Dawley rats by combined bilateral common carotid artery occlusion and hypotension (42-45 mm Hg). In a separate group of animals, a mild (32 degrees C) post-ischemic hypothermia was induced for 6 h, starting immediately after ischemia. RNA from approximately 500 brain vessels (20-100 microm) extracted by laser-capture microdissection (LCM) microscopy was used to determine the expression of proteoglycans agrin and SPARC mRNAs by quantitative PCR (Q-PCR). Protein expression was determined by immunohistochemistry in adjacent tissue sections. The BBB permeability was assessed using (3)H-sucrose as an in vivo tracer and by examining fibrinogen immunoreactivity in tissue sections. A transient global brain ischemia resulted in a significant (ANOVA, p<0.05; 6 animals/group) reduction in agrin and SPARC mRNAs in LCM-captured brain vessels 24 h after reperfusion. A time-dependent loss of agrin and SPARC from the BM during reperfusion was also observed by immunochemistry. A 6-h post-ischemic hypothermia reduced SPARC and agrin mRNA and protein losses, BBB transfer constant for (3)H-sucrose as well as fibrinogen extravasation 24 h after reperfusion. It is conluded that a transient post-ischemic hypothermia stabilizes brain vessels and reduces BBB disruption in part by preventing proteolytic degradation of regulatory BM constituents, SPARC and agrin.

The extracellular matrix protein SC1/hevin localizes to excitatory synapses following status epilepticus in the rat lithium-pilocarpine seizure model

The epileptic brain is characterized by increased susceptibility to neuronal hyperexcitability. The rat lithium-pilocarpine model, which mimics many features of temporal lobe epilepsy, has been used to study processes leading to the development of recurrent seizures. After a prolonged seizure episode, termed status epilepticus (SE), neural changes occur during a period known as epileptogenesis and include neuronal cell death, reactive gliosis, axonal sprouting, and synaptogenesis. Extracellular matrix adhesion molecules are important regulators of synaptogenesis and axonal sprouting resulting from SE. SC1, also known as hevin, is an antiadhesive extracellular matrix molecule that localizes to synapses in the mammalian brain. In this study, the distribution of SC1 protein in neurons following SE was examined using the lithium-pilocarpine model. SC1 protein levels in neuronal cell bodies showed a transient decrease at 1 day post-SE, which coincided with an increase of SC1 in the synapse-rich neuropil that was identified with the synaptic marker synaptophysin. Immunoelectron microscopy confirmed the decrease of SC1 signal in neurons at 1 day post-SE and showed that SC1 remained localized to postsynaptic elements throughout the seizure time course. Increased colocalization of SC1 was detected with the excitatory synaptic markers vesicular glutamate transporter 1 (VGLUT1), AMPA receptor subunit GluR1, and N-methyl-D-aspartate receptor subunit NR1, but not with the inhibitory synaptic markers vesicular gamma-aminobutyric acid (GABA) transporter (VGAT) and GABA(A) receptor subunit beta2 (GABA(A) beta2), which could reflect enhanced association of SC1 with excitatory synapses. These findings suggest that SC1 may be involved in synaptic modifications underlying epileptogenesis.

Differential expression patterns of occ1-related genes in adult monkey visual cortex

We have previously revealed that occ1 is preferentially expressed in the primary visual area (V1) of the monkey neocortex. In our attempt to identify more area-selective genes in the macaque neocortex, we found that testican-1, an occ1-related gene, and its family members also exhibit characteristic expression patterns along the visual pathway. The expression levels of testican-1 and testican-2 mRNAs as well as that of occ1 mRNA start of high in V1, progressively decrease along the ventral visual pathway, and end of low in the temporal areas. Complementary to them, the neuronal expression of SPARC mRNA is abundant in the association areas and scarce in V1. Whereas occ1, testican-1, and testican-2 mRNAs are preferentially distributed in thalamorecipient layers including “blobs,” SPARC mRNA expression avoids these layers. Neither SC1 nor testican-3 mRNA expression is selective to particular areas, but SC1 mRNA is abundantly observed in blobs. The expressions of occ1, testican-1, testican-2, and SC1 mRNA were downregulated after monocular tetrodotoxin injection. These results resonate with previous works on chemical and functional gradients along the primate occipitotemporal visual pathway and raise the possibility that these gradients and functional architecture may be related to the visual activity–dependent expression of these extracellular matrix glycoproteins.

SPARC is expressed by macroglia and microglia in the developing and mature nervous system

SPARC (secreted protein, acidic and rich in cysteine) is a matricellular protein that is highly expressed during development, tissue remodeling, and repair. SPARC produced by olfactory ensheathing cells (OECs) can promote axon sprouting in vitro and in vivo. Here, we show that in the developing nervous system of the mouse, SPARC is expressed by radial glia, blood vessels, and other pial-derived structures during embryogenesis and postnatal development. The rostral migratory stream contains SPARC that becomes progressively restricted to the SVZ in adulthood. In the adult CNS, SPARC is enriched in specialized radial glial derivatives (Müller and Bergmann glia), microglia, and brainstem astrocytes. The peripheral glia, Schwann cells, and OECs express SPARC throughout development and in maturity, although it appears to be down-regulated with maturation. These data suggest that SPARC may be expressed by glia in a spatiotemporal manner consistent with a role in cell migration, neurogenesis, synaptic plasticity, and angiogenesis.

Newly born dentate granule neurons after pilocarpine-induced epilepsy have hilar basal dendrites with immature synapses

Neurogenesis in the subgranular zone of the dentate gyrus persists throughout the lifespan of mammals, and the resulting newly born neurons are incorporated into existing hippocampal circuitry. Seizures increase the rate of neurogenesis in the adult rodent brain and result in granule cells in the dentate gyrus with basal dendrites. Using doublecortin (DCX) immunocytochemistry to label newly generated neurons the current study focuses on the electron microscopic features of DCX-labeled cell bodies and dendritic processes in the dentate gyrus of rats with pilocarpine-induced epilepsy. At the base of the granule cell layer clusters of cells that include up to six DCX-labeled cell bodies were observed. The cell bodies in these clusters lacked a one-to-one association with an astrocyte cell body and its processes, a relationship that is typical for newly born granule cells in control rats. Also, DCX-labeled basal dendrites in the hilus had immature synapses while those in control rats lacked synapses. These results indicate that increased neurogenesis after seizures alters the one-to-one relationship between astrocytes and DCX-labeled newly generated neurons at the base of the granule cell layer. The data also suggest that the synapses on DCX-labeled hilar basal dendrites contribute to the persistence of hilar basal dendrites on neurons born after pilocarpine-induced seizures.

Entorhinal deafferentation induces upregulation of SPARC in the mouse hippocampus

SPARC is a matricellular protein that modulates cell-cell and cell-matrix interactions by virtue of its antiproliferative and counteradhesive properties. Here, we report the denervation-induced upregulation of SPARC mRNA and protein in the mouse hippocampus following transections of the entorhinal afferents. Northern blot analysis showed that SPARC mRNA was upregulated in a transient manner in the deafferented mouse hippocampus. In situ hybridization and immunohistochemistry confirmed the temporal upregulation of both SPARC mRNA and protein specifically in the denervated areas, which initiated at 7 days postlesion, reached the maximum at 15 as well as 30 days postlesion, and subsided towards normal levels by 60 days postlesion. Double labeling by either a combination of in situ hybridization for SPARC mRNA with immunohistochemistry for glial fibrillary acidic protein or double immunofluorescence staining for both proteins in the hippocampus revealed that SPARC-expressing cells are reactive astrocytes. In respect to the spatiotemporal alterations of SPARC expression in the denervated hippocampus, we suggest that SPARC may be involved in modulation of the denervation-induced plasticity processes such as glial cell proliferation, axonal sprouting and subsequent synaptogenesis in the hippocampus following entorhinal deafferentation.

Osteonectin is a Schwann cell-secreted factor that promotes retinal ganglion cell survival and process outgrowth

We have investigated the factors made by Schwann cells (SCs) that stimulate survival and neurite outgrowth from postnatal rat retinal ganglion cells (RGCs). These effects are preserved under K252a blockade of the Trk family of neurotrophin receptors and are not fully mimicked by the action of a number of known trophic factors. To identify novel factors responsible for this regenerative activity, we have used a radiolabelling assay. Proteins made by SCs were labelled radioactively and then fed to purified RGCs. The proteins taken up by the RGCs were then isolated and further characterized. Using this assay we have identified a major 40 kDa factor taken up by RGCs, which was microsequenced and shown to be the matricellular protein osteonectin (ON). Using an in vitro assay of purified RGCs we show that ON promotes both survival and neurite outgrowth. We conclude that ON has a potential new role in promoting CNS repair.

Expression of tenascin-C long isoforms is induced in the hypothalamus by FGF-1

Fibroblast growth factor (FGF)-1 modulates various brain functions, such as the hypothalamic control of feeding. In the rat, we examined the effect of intracerebroventricularly infused FGF-1 on the hypothalamic expression of tenascin-C, a selective mediator of neuron-glial interaction. In situ hybridization revealed little tenascin-C mRNA expression in control brains, but greatly increased expression in ependymal cells around the third ventricle in the FGF-1-infused rats. Reverse transcription-linked PCR analysis of hypothalamic mRNA revealed an FGF-1-induced expression not of the shortest isoform of tenascin-C, but of the long isoforms (with additional fibronectin type III-domain insertions). Quantitative analysis by real time PCR revealed that this induction was transient and dose-dependent. Specific modulation of hypothalamic neuron-glial interactions by tenascin-C may mediate FGF-1-induced feeding suppression.

[Microinfusion experiment for mice and its application to pharmacological studies]

It is urgently necessary to clarify functions of uncharacterized proteins. To understand life processes, we must investigate the functions and networks of proteins expressed from genomic DNA. In the near future, microinfusion experiments will become a more important method for analyzing uncharacterized function of proteins in vivo. Here we provide a practical manual for performing microinfusion experiments in mice. We also describe our experiment in which we performed a single injection of morphine following Secreted Protein Acidic and Rich in Cysteine (SPARC) infusion into the basolateral amygdala of previously uninjected mice and found markedly enhanced locomotor activity. We discuss the utility of microinfusion experiments in mice.

Induction of SC1 mRNA encoding a brain extracellular matrix glycoprotein related to SPARC following lesioning of the adult rat forebrain

SC1 is an extracellular matrix (ECM) glycoprotein related to SPARC which exhibits anti-adhesive properties. ECM molecules are thought to play important roles in influencing cell shape, proliferation and migration during neurogenesis. Following localized injury to the adult rat forebrain, a biphasic induction of SC1 mRNA was apparent, namely a rapid, transient induction at 1 day post-lesion in cortical neurons which border the lesion site followed by a more prolonged induction in astrocytes which are proximal to the wound site. A similar SC1 induction pattern was observed in the hippocampus in response to the injury. SPARC mRNA exhibits a divergent pattern of induction because it is induced in mature blood vessels close to the lesion and in blood vessels which develop following the trauma. Thus mRNAs encoding the related ECM glycoproteins SC1 and SPARC are induced in different cell populations in the adult forebrain during the neural response to localized injury.

Analysis of human follistatin structure: identification of two discontinuous N-terminal sequences coding for activin A binding and structural consequences of activin binding to native proteins

A primary physiological function of follistatin is the binding and neutralization of activin, a transforming growth factor-beta family growth factor, and loss of function mutations are lethal. Despite the critical biological importance of follistatin's neutralization of activin, the structural basis of activin's binding to follistatin is poorly understood. The purposes of these studies were 1) to identify the primary sequence(s) within the N-terminal domain of the follistatin coding for activin binding, and 2) to determine whether activin binding to the native protein causes changes in other structural domains of follistatin. Synthetic peptide mimotopes identified within a 63-residue N-terminal domain two discontinuous sequences capable of binding labeled activin A. The first is located in a region (amino acids 3-26) of follistatin, a site previously identified by directed mutagenesis as important for activin binding. The second epitope, predicted to be located between amino acids 46 and 59, is newly identified. Although the sequences 3-26 and 46-59 code for activin binding, native follistatin only binds activin if disulfide bonding is intact. Furthermore, pyridylethylation of Cys residues followed by N-terminal sequencing and amino acid analysis revealed that all of the Cys residues in follistatin are involved in disulfide bonds and lack reactive free sulfhydryl groups. Specific ligands were used to probe the structural effects of activin binding on the other domains of the full-length molecule, comprised largely of the three 10-Cys follistatin module domains. No effects on ligand binding to follistatin-like module I or II were observed after the binding of activin A to native protein. In contrast, activin binding diminished recognition of domain III and enhanced that of the C domain by their respective monoclonal antibody probes, indicating an alteration of the antigenic structures of these regions. Thus, subsequent to activin binding, interactions are likely to occur between regions of follistatin located in different domains and separated by considerable lengths of linear sequence. Such interactions could have important functional significance with respect to the structural heterogeneity of naturally occurring follistatins.

Increased sensitivity to the stimulant effects of morphine conferred by anti-adhesive glycoprotein SPARC in amygdala

Repeated administration of morphine substantially increases its locomotor-enhancing activity, a phenomenon termed locomotor sensitization. Here we show that secreted protein acidic and rich in cysteine (SPARC), an anti-adhesive glycoprotein present in the basolateral amygdala, contributes to the establishment of locomotor sensitization. The morphine-induced increase in SPARC levels in the basolateral amygdala persisted after morphine withdrawal and coincided with the duration of locomotor sensitization. Moreover, a single injection of morphine after SPARC infusion into the basolateral amygdala of previously uninjected mice substantially enhanced locomotor activity. Thus, SPARC may be an important element for establishing locomotor sensitization to morphine.

Localization of secreted protein acidic and rich in cysteine (SPARC) expression in the rat eye

Secreted protein acidic and rich in cysteine (SPARC) is a secreted glycoprotein protein which modulates cell shape and cell-matrix interactions and has been implicated in the regulation of angiogenesis, vascular permeability and cataract formation. In situ hybridization and immunohistochemical studies for SPARC were performed to determine the cell and tissue distribution of SPARC in rat eye. Studies demonstrated SPARC mRNA and protein co-localization at all sites. In the retina SPARC mRNA and protein were localized predominantly to the Müller and ganglion cells. Within the choroid, SPARC was found in vascular endothelial cells and fibroblasts; in the sclera SPARC was present in blood vessels and fibroblasts. SPARC was also present in the non-pigmented epithelial cells of the ciliary body, and in the epithelium of the lens capsule and cornea. The demonstrated anatomical distribution of SPARC in the rat eye is consistent with several of the biological functions ascribed to this matricellular protein and provides a rational basis for its examination in pathological conditions.

Extracellular matrix-associated protein Sc1 is not essential for mouse development

Sc1 is an extracellular matrix-associated protein whose function is unknown. During early embryonic development, Sc1 is widely expressed, and from embryonic day 12 (E12), Sc1 is expressed primarily in the developing nervous system. This switch in Sc1 expression at E12 suggests an importance for nervous-system development. To gain insight into Sc1 function, we used gene targeting to inactivate mouse Sc1. The Sc1-null mice showed no obvious deficits in any organs. These mice were born at the expected ratios, were fertile, and had no obvious histological abnormalities, and their long-term survival did not differ from littermate controls. Therefore, the function of Sc1 during development is not critical or, in its absence, is subserved by another protein.

SPARC, a matricellular glycoprotein with important biological functions

SPARC (secreted protein, acidic and rich in cysteine) is a unique matricellular glycoprotein that is expressed by many different types of cells and is associated with development, remodeling, cell turnover, and tissue repair. Its principal functions in vitro are counteradhesion and antiproliferation, which proceed via different signaling pathways. SPARC consists of three domains, each of which has independent activity and unique properties. The extracellular calcium binding module and the follistatin-like module have been recently crystallized. Specific interactions between SPARC and growth factors, extracellular matrix proteins, and cell surface proteins contribute to the diverse activities described for SPARC in vivo and in vitro. The location of SPARC in the nuclear matrix of certain proliferating cells, but only in the cytosol of postmitotic neurons, indicates potential functions of SPARC as a nuclear protein, which might be involved in the regulation of cell cycle progression and mitosis. High levels of SPARC have been found in adult eye, and SPARC-null mice exhibit cataracts at 1-2 months of age. This animal model provides an excellent opportunity to confirm and explore some of the properties of SPARC, to investigate cataractogenesis, and to study SPARC-related family proteins, e.g., SC1/hevin, a counteradhesive matricellular protein that might functionally compensate for SPARC in certain tissues.(J Histochem Cytochem 47:1495-1505, 1999)

Molecular cloning of testican-2: defining a novel calcium-binding proteoglycan family expressed in brain

We have screened a human cDNA library using an expressed sequence tag related to the BM-40/secreted protein, acidic and rich in cysteine (SPARC)/osteonectin family of proteins and isolated a novel cDNA. It encodes a protein precursor of 424 amino acids that consists of a signal peptide, a follistatin-like domain, a Ca2+-binding domain, a thyroglobulin-like domain, and a C-terminal region with two putative glycosaminoglycan attachment sites. The protein is homologous to testican-1 and was termed testican-2. Testican-1 is a proteoglycan originally isolated from human seminal plasma that is also expressed in brain. Northern blot hybridization of testican-2 showed a 6.1-kb mRNA expressed mainly in CNS but also found in lung and testis. A widespread expression in multiple neuronal cell types in olfactory bulb, cerebral cortex, thalamus, hippocampus, cerebellum, and medulla was detected by in situ hybridization. A recombinant fragment consisting of the Ca2+-binding EF-hand domain and the thyroglobulin-like domain of testican-2 showed a reversible Ca2+-dependent conformational change in circular dichroism studies. Testican-1 and -2 form a novel Ca2+-binding proteoglycan family built of modular domains with the potential to participate in diverse steps of neurogenesis.

Follistatin: a multifunctional regulatory protein

Follistatin was first described in 1987 as a follicle-stimulating hormone inhibiting substance present in ovarian follicular fluid. We now know that this effect of follistatin is only one of its many properties in a number of reproductive and nonreproductive systems. A majority of these functions are facilitated through the affinity of follistatin for activin, where activin's effects are neutralized through its binding to follistatin. As such, the interplay between follistatin and activin represents a powerful regulatory mechanism that impinges on a variety of cellular processes within the body. In this review we focus on the biochemical characteristics of follistatin and its interaction with activin and discuss the emerging role of these proteins as potent tissue regulators in the gonad, pituitary gland, pregnancy membranes, vasculature, and liver. Consideration is also given to the larger family of proteins that contain follistatin-like modules, in particular with regard to their functional and structural implications.

SPARC/osteonectin mRNA is induced in blood vessels following injury to the adult rat cerebral cortex

Recently we described the pattern of expression of the anti-adhesive glycoprotein SPARC/osteonectin in the developing and adult brain. SPARC mRNA was present in developing blood vessels during neurogenesis, but was not detected in the mature vasculature. We have now examined the effect of a lesion to the adult rat cerebral cortex on the expression of SPARC by in situ hybridization. SPARC mRNA was increased in the zone proximal to the wound at 3 to 10 days after cortical brain injury. During this period, SPARC was induced in mature blood vessels close to the lesion site and in blood vessels which develop following injury. These results suggest a role for SPARC in the process of angiogenesis following injury to the adult cerebral cortex.

SPARC is expressed by ganglion cells and astrocytes in bovine retina

SPARC (secreted protein, acidic and rich in cysteine)/osteonectin is a matricellular, counteradhesive glycoprotein that disrupts cell-matrix interactions, interacts with growth factors and components of extracellular matrix, and modulates the cell cycle, but appears to subserve only minor structural roles. SPARC is expressed in a variety of tissues during embryogenesis and remodeling and is believed to regulate vascular morphogenesis and cellular differentiation. Although usually limited in normal adult tissues, SPARC is expressed at significant levels in the adult central nervous system. Using a monoclonal antibody against bovine bone osteonectin, we have determined the localization of SPARC in newborn (3-day-old) and adult (4-8-year-old) normal bovine retinas. SPARC was present in the soma of ganglion cells and strong reactivity was found in ganglion cell axons. Muller cells displayed no immunoreactivity, but SPARC was present in retinal astrocytes that were identified by the astrocyte marker glial fibrillary acidic protein (GFAP). Newborn calf retina showed a staining pattern similar to that of adult retina but exhibited significantly reduced levels of SPARC. Minimal levels of SPARC protein were also detected in some capillaries of the inner retina of both newborn and adult animals, whereas large vessels were negative. The presence of SPARC in the retina was confirmed by Western blotting of retinal extracts. These data indicate that SPARC originating from bot h neurons and glia of the inner retina may be an important modulator of retinal angiogenesis. The increased expression of SPARC in adult relative to newborn retinal tissue also indicates that SPARC has an ongoing role in the maintenance of retinal functions.

Spatiotemporal distribution of SPARC/osteonectin in developing and mature chicken retina

Expression of SPARC (Secreted Protein, Acidic, Rich in Cysteine), a counteradhesive, calcium-binding extracellular matrix (ECM) glycoprotein, is associated with several morphogenetic events during early development. In this study, changes in the spatiotemporal distribution of SPARC transcripts and the protein during chicken retinal development were documented by in situ hybridization and indirect immunofluorescence microscopy. SPARC transcripts were first detected within the proliferating neural ectoderm at embryonic day 4. 5 (E4.5), followed short thereafter (E5) by appearance of SPARC. SPARC was enriched within the inner plexiform layer (IPL) by E10 and within the outer plexiform layer (OPL) by E14, several days after these layers became morphologically distinct. Significant levels of SPARC transcripts were first observed within the ganglion cell layer (GCL) at E17 prior to accumulation of SPARC within the nerve fiber layer, seen first at E20. SPARC protein was first detected within the developing retinal pigment epithelium (RPE) at E10 and increased significantly at RPE cells ceased to proliferate and continued differentiating. Of special note was the restriction of SPARC to the basal-half of the RPE cells. SPARC transcripts were similarly distributed in the adult retina, but at lower levels than in the period just prior to hatching. In the adult retina SPARC was retained in the nerve fiber layer and present in the inner nuclear layer (INL) and outer nuclear layer (ONL), but lost from the IPL and OPL. These changes in expression pattern with time indicate that SPARC is developmentally regulated and therefore may have important function(s) in both morphological development of the retina and functioning of the mature eye.

Cloning and expression of murine SC1, a gene product homologous to SPARC

A number of cDNAs (SC1, QR1, and hevin) have been shown to be similar to SPARC (secreted protein acidic and rich in cysteine), a matricellular protein that regulates cell adhesion, cell cycle, and matrix assembly and remodeling. These proteins are 61-65% identical in the final 200 residues of their C-termini; their N-terminal sequences are related but more divergent. All have an overall acidic pl, with a follistatin-like region that is rich in cysteine, and a Ca+2 binding consensus sequence at the C-terminus. Using degenerate primers representing the most highly conserved region in SPARC, SC1, and QR1, we identified a 300-BP SC1 clone in a primary polymerase chain reaction (PCR) screen of a mouse brain cDNA library. This cDNA was used to obtain a full-length clone, which hybridized to a 2.8-KB RNA abundant in brain. Mouse SC1 displays a similarity of 70% to mouse SPARC at the amino acid level. Northern blot and RNAse protection assays revealed a 2.8-KB mRNA expressed at moderate levels (relative to brain) in mouse heart, adrenal gland, epididymis, and lung, and at low levels in kidney, eye, liver, spleen, submandibular gland, and testis. In contrast to SPARC, in situ hybridization showed expression of SC1 mRNA in the tunica media and/or adventitia of medium and large vessels; transcripts were not detected in capillaries, venules, or large lymphatics. The distribution of transcripts for SC1 was also different from that of SPARC in several organs, including adrenal gland, lung, heart, liver, and spleen. Moreover, SC1 mRNA was not evident in endothelium cultured from rat heart, bovine fetal and adult aorta, mouse aorta, human omentum, and bovine retina. Cultured smooth muscle cells and fibroblasts also failed to express SC1 mRNA. The absence of SC1 transcript in cultured cells indicates that the SC1 gene is potentially sensitive to regulatory factors in serum or to a three-dimensional architecture conferred by the extracellular matrix that is lacking in vitro. In conclusion, the expression of SPARC and SC1 appears to be coincident in specific tissues (e.g., adrenal gland and brain), but these proteins exhibit distinct expression patterns in most organs of the mouse. Because SC1 and SPARC are structurally similar and exhibit counteradhesive effects on cultured cells, their overlapping and/or adjacent expression in most tissues predicts that one protein might compensate functionally, at least in part, for the other.

SC1, a brain extracellular matrix glycoprotein related to SPARC and follistatin, is expressed by rat cerebellar astrocytes following injury and during development

In the nervous system, extracellular matrix components are believed to influence cell shape, proliferation and migration during development and following injury. SC1 is a secreted glycoprotein expressed during neural development and in the adult brain. The molecule shows partial sequence homology to the anti-adhesive extracellular matrix molecule SPARC/osteonectin and to follistatin. We have made a surgical lesion in the adult rat cerebellum and examined changes in SC1 expression at 1 to 14 days after injury. Dual in situ hybridization/immunohistochemistry demonstrated that SC1 mRNA was induced in astrocytes surrounding the wound, reaching maximal levels at 10 days post-lesion. Immunohistochemistry revealed changes in the deposition of SC1 protein in radial fibres of Bergmann glia. SC1 protein was also detected at the border of the lesion, suggesting an association with the glial scar. Double immunohistochemistry with the astrocytic marker GFAP demonstrated that astrocytes also express SC1 during postnatal development.

SC1, a SPARC-related glycoprotein, exhibits features of an ECM component in the developing and adult brain

Although extracellular matrix (ECM) components have been shown to play important roles in the development of the CNS, expression generally decreases in the adult brain. This study examines the expression of the SPARC-related glycoprotein SC1 in the rat brain during postnatal development and in the adult. In situ hybridization analysis indicates that expression of SC1 mRNA increases in a caudal to rostral manner as postnatal neural development proceeds and is found at near maximal levels in the adult brain. SC1 mRNA is expressed in glial-enriched areas of the brain at postnatal day 1 (P1) and P5. Between P10 and P20, SC1 mRNA increases in neuron-enriched regions of the hippocampus, dentate gyrus, and cerebral cortex. Immunohistochemistry in the adult shows that SC1 protein is localized to neurons in these regions and to scattered glial cells. Subcellular fractionation demonstrates that the SC1 116/120 kDa doublet is associated with synaptosomes. SC1 is present in the aqueous phase following extraction of membranes with TX-114, suggesting that it is not a transmembrane protein, a property consistent with other adult brain ECM components. Furthermore in cerebellar granule cells grown in culture, high levels of the 120 kDa component are secreted into the media. These results are consistent with the hypothesis that SC1 is an ECM glycoprotein expressed in both the developing and adult brain.