Expression of sulfoglucuronyl (HNK-1) carbohydrate and its binding protein (SBP-1) in developing rat cerebellum

Neurogenesis after traumatic brain injury - The complex role of HMGB1 and neuroinflammation

INTRODUCTION

Traumatic brain injury (TBI) is amongst the leading causes of morbidity and mortality worldwide. Despite evidence of neurogenesis post-TBI, survival and integration of newborn neurons remains impaired. High Mobility Group Box protein 1 (HMGB1) is an 'alarmin' released hyper-acutely following TBI and implicated in hosting the neuro-inflammatory response to injury. It is also instrumental in mediating neurogenesis under physiological conditions. Given its dual role in mediating neuro-inflammation and neurogenesis, it serves as a promising putative target for therapeutic modulation. In this review, we discuss neurogenesis post-TBI, neuro-pharmacological aspects of HMGB1, and its potential as a therapeutic target.

METHODS

PubMed database was searched with varying combinations of the following search terms: HMGB1, isoforms, neurogenesis, traumatic brain injury, Toll-like receptor (TLR), receptor for advanced glycation end-products (RAGE).

RESULTS

Several in vitro and in vivo studies demonstrate evidence of neurogenesis post-injury. The HMGB1-RAGE axis mediates neurogenesis throughout development, whilst interaction with TLR-4 promotes the innate immune response. Studies in the context of injury demonstrate that these receptor effects are not mutually exclusive. Despite recognition of different HMGB1 isoforms based on redox/acetylation status, effects on neurogenesis post-injury remain unexplored. Recent animal in vivo studies examining HMGB1 antagonism post-TBI demonstrate predominantly positive results, but specific effects on neurogenesis and longer-term outcomes remain unclear.

CONCLUSION

HMGB1 is a promising therapeutic target but its effects on neurogenesis post-TBI remains unclear. Given the failure of several pharmacological strategies to improve outcomes following TBI, accurate delineation of HMGB1 signalling pathways and effects on post-injury neurogenesis are vital.

Cerebellar Purkinje cells exhibit increased expression of HMGB-1 and apoptosis in congenital hydrocephalic H-Tx rats

BACKGROUND

Highly integrated anatomic and functional interactions between the cerebrum and the cerebellum during development have been reported. In our previous study, we conducted a proteome analysis to identify the proteins present in the congenital noncommunicating hydrocephalus in the cerebellum. We found higher expression of high-mobility group box-1 protein (HMGB-1) in hydrocephalic H-Tx rats.

OBJECTIVE

We studied the expression pattern of HMGB-1 in the cerebellum.

METHODS

We studied congenital hydrocephalic H-Tx rats aged 1 day and 7 days along with age-matched nonhydrocephalic H-Tx and Sprague-Dawley rats as controls. Gene and protein expressions of HMGB-1 in the cerebellum were assayed by real-time polymerase chain reaction and Western blotting, respectively; furthermore, immunohistochemical analyses were performed by using HMGB-1 (indicator of apoptosis), single-stranded DNA; adhesion factor related to cell migration, HNK-1; and the Purkinje cell-specific antibody, calbindin.

RESULTS

Cytoplasmic HMGB-1 expression observed in Purkinje cells in the 1-day-old hydrocephalic group was stronger than that in the nonhydrocephalic and Sprague-Dawley groups. Double fluorescent staining with single-stranded DNA confirmed that Purkinje cells were undergoing apoptosis. HNK-1 expression was lower in the Purkinje cell layer in the 7-day-old rats in the hydrocephalic group, and Purkinje cells were disrupted in comparison with the control groups. Morphological changes in the cerebellum were observed in the 7-day-old rats in the hydrocephalic group in comparison with the control groups.

CONCLUSION

Our results suggest that cerebellar neuronal cell damage in the early postnatal period may be related to the higher expression of HMGB-1 in the Purkinje cells.

The role of receptor for advanced glycation end products (RAGE) in neuronal differentiation

The receptor for advanced glycation end products (RAGE) is a multiligand receptor protein thought to play an important role in neuronal differentiation. RAGE can bind a number of ligands and activate a variety of signalling pathways that lead to diverse downstream effects. Amphoterin and S100B are endogenous ligands, the interaction of which with RAGE is known to be involved in defined physiological processes. The present study investigated the spatiotemporal pattern of the expression for RAGE and its ligands, amphoterin and S100B, during neuronal differentiation of NT2/D1 cells. In this study, all three proteins were shown to increase with progression of neuronal differentiation as determined by Western blotting, raising the possibility that both amphoterin and S100B may interact with RAGE and have important functions during the process of cell differentiation. Moreover, blocking the activation of RAGE with neutralizing antibody in the presence of retinoic acid disrupted the progression of normal neuronal differentiation. Immunocytochemistry (ICC) studies showed that amphoterin partially colocalized with RAGE within differentiating NT2 cells, whereas S100B showed a high degree of colocalization. This result suggests that S100B is more likely to be the principal ligand for RAGE during the differentiation process and that RAGE and amphoterin might have both independent and combined roles. Moreover, RAGE was expressed only in cells that were committed to a neuronal phenotype, suggesting direct involvement of RAGE in mediating cellular changes within differentiating neuronal cells. Further detailed studies are now required to characterize fully the role of RAGE during the neuronal differentiation period.

Receptor for advanced glycation end products (RAGE) mediates neuronal differentiation and neurite outgrowth

The receptor for advanced glycation end products (RAGE) plays a crucial role in several disease processes, such as diabetes, inflammation, and neurodegeneration. In this article we report multiple roles of RAGE in neuronal differentiation and neurite outgrowth. In retinoic-induced P19 embryonic carcinoma stem cells, silencing the expression of RAGE by RNA interference (RNAi) blocked differentiation of the P19 cells into neuronal cells and enhanced the formation of vimentin-positive fibroblast-like cells. RAGE knockdown inhibited retinoic acid-induced activation and blocked nuclear translocation of NF-kappaB, suggesting RAGE regulates activation of NF-kappaB. RAGE was also shown to be involved in survival of P19 cells during retinoic acid differentiation. Additionally, knockdown of RAGE strongly inhibited neurite outgrowth in retinoic acid-differentiated P19 cells, indicating that RAGE is required for neurite outgrowth of differentiated P19 cells. Retinoic acid-treated P19 cells activated GTPases, Rac1, and Cdc42. This activation of the GTPases was inhibited in RAGE-knockdown cells. In primary cerebellar granule neurons, the knockdown of RAGE also inhibited neurite outgrowth. In these cells, overexpression of dominant-negative forms of Rac1 and Cdc42 inhibited neurite outgrowth, whereas overexpression of constitutively active forms of Rac1 and Cdc42 in RAGE-deficient neurons restored neurite outgrowth, indicating that RAGE mediated neurite outgrowth through the Rac1/Cdc42 pathway. This is the first report on the role of RAGE in cell lines and primary neurons, as determined by RNAi knockdown.

Polysialic acid and HNK-1 are expressed in the adult rat vestibular endorgans

Polysialic acid (PSA) and human natural killer (HNK)-1 carbohydrate epitopes are expressed mainly in developing neurons but also in restricted areas, even in adulthood. In the present study, we demonstrated the expression of PSA and HNK-1 epitopes in adult primary vestibular afferent neurons. In addition, we confirmed the presence of two distinct polysialyltransferases, PST and STX, that form PSA, as well as two types of glucuronyltransferases, GlcAT-P and GlcAT-S involved in the biosynthesis of HNK-1 epitopes in the vestibular endorgans. These results combined suggest that both PSA and HNK-1 carbohydrate epitopes are synthesized and may have an important role in the adult peripheral vestibular endorgans.

Regulated expression and subcellular localization of HMGB1, a chromatin protein with a cytokine function

High mobility group box protein 1 (HMGB1) has been considered as a ubiquitous nuclear protein with an architectural function, but even early reports have described its presence outside of the nucleus. Today, we have only started to understand the extranuclear and extracellular functions of HMGB1: we know that it participates in developmental and differentiation processes, triggers and modulates many of the inflammatory cascades in the body, and may even be involved in the metastatic invasion programme of cancer cells. Given such diverse roles, it is important to know which cells express HMGB1, where, and how much. The present review deals with the expression pattern of HMGB1 and provides evidence that, far from being housekeeping, the HMGB1 gene is tightly regulated. This can have implications for therapeutic intervention on inflammatory diseases as well as cancer.

Amphoterin as an extracellular regulator of cell motility: from discovery to disease

Amphoterin is a ubiquitous and highly conserved protein previously considered solely as a chromatin-associated, nuclear molecule. Amphoterin is released into the extracellular space by various cell types, and plays an important role in the regulation of cell migration, differentiation, tumorigenesis and inflammation. This paper reviews recent research on the mechanistic background underlying the biology of secreted amphoterin, with an emphasis on the role of amphoterin as an autocrine/paracrine regulator of cell migration.

Regulation of expression of sulfoglucuronyl carbohydrate (HNK-1), Amphoterin and RAGE in retinoic acid-differentiated P19 embryonal carcinoma cells

HNK-1 antibody reactive sulfoglucuronyl carbohydrate (SGC) and SSEA-1 antibody reactive Lewis X (Lex) epitope are expressed on several glycolipids, glycoproteins, and proteoglycans of the nervous system and have been implicated in cell-cell recognition, neurite outgrowth, and/or neuronal migration during development. Interaction of SGC with its binding protein Amphoterin and interaction of Amphoterin with a cell-signaling molecule, receptor for advance glycation end product (RAGE) have been suggested to regulate neurite outgrowth and neuronal migration. The regulation of expression of SGC, Lex, Amphoterin, and RAGE was studied in embryonal carcinoma P19 cells after treatment with retinoic acid (RA). The untreated proliferating P19 cells strongly expressed the Lex epitope, which was mostly due to Lex-glycoproteins. P19 cells, when differentiated into neuron-like cells by RA, did not express the Lex epitope, but expressed increasing levels of SGC, with time in culture. Quantitative biochemical analyses showed that in the P19 cells after RA treatment, the amount of SGC-glycoproteins increased at a significantly higher level than sulfoglucuronyl glycolipid-1 (SGGL-1). The increase in the levels of SGGL-1 was due to 16-fold upregulation in the activity of lactosylceramide: N-acetylglucosaminyl-transferase (Lc3 synthase), which synthesizes the key intermediate lactotriosylceramide (Lc3Cer), for lacto- and neolacto-glycolipids. The large increase in the activity of Lc3 synthase appeared to regulate the levels of other neolacto glycolipids, such as Lc3Cer, nLc4Cer, nLc6Cer, disialosyl-nLc4Cer (LD1), and Lex-glycolipids. Strong upregulation of glucuronyl-transferase and modest twofold enhancement in the activity of the glucuronyl-sulfotransferase, which catalyze the final steps in the SGC synthesis, also would account for the large increase in the synthesis SGC-glycoproteins. RA also upregulated the synthesis of Amphoterin and RAGE in P19 cells. SGC, RAGE, and Amphoterin were co-localized in the RA-differentiated neurons. The initiation of neurite outgrowth along with co-ordinated upregulation of Amphoterin, RAGE, SGC-glycoproteins, and SGGLs in RA-treated P19 cells support the hypothesis that these molecules are involved in the neuronal process formation.

HNK-1 sulfotransferase null mice express glucuronyl glycoconjugates and show normal cerebellar granule neuron migration in vivo and in vitro

Sulfoglucuronyl carbohydrate (SGC), reactive with antibody against human natural killer cell antigen, is expressed in several glycolipids, glycoproteins and proteoglycans of the nervous system and has been implicated in cell-cell recognition, neurite outgrowth and neuronal migration during development, through its interaction with SGC-binding protein (SBP) 1. However, sulfotransferase (ST) null mutant mice, which lack SGC, were shown to have normal development with usual gross anatomy of the nervous system and other organs. Failure to observe a severe phenotype in the ST null mice prompted us to determine the compensatory molecular replacement of SGC by analyzing the carbohydrate of glycolipids and glycoproteins of the ST mutant nervous system. In the ST null mice, SGC-containing molecules were absent; instead the precursor glucuronyl carbohydrate (GC)-containing molecules accumulated. Other relevant glycolipids and proteins were not affected. The GC molecules in the mutant were localized at the same anatomical sites in the nervous system as the SGC molecules in the wild type. In vitro binding studies showed that, similar to sulfoglucuronyl glycolipids, glucuronyl glycolipids interacted with SBP-1, but with a lower binding capacity. In vitro studies with explant cultures of cerebellum indicated that neurite outgrowth and cell migration were not significantly affected in the mutant, possibly owing to interaction of SBP-1 with GC molecules. The results suggested that in vivo SBP-1-GC interaction was sufficient to allow normal neurite outgrowth and cell migration in the mutant, giving rise to a wild-type phenotype. However, the role of other compensatory molecules involved in these processes cannot be completely ruled out.

Regulation of sulfoglucuronyl glycolipid synthesis in the developing rat sciatic nerve

Sulfoglucuronyl glycolipids (SGGLs) have been considered as target antigens in demyelinating peripheral neuropathies associated with IgM monoclonal gammopathy. The regulation of expression of SGGLs in the rat sciatic nerve during development was studied by assaying the levels of SGGLs and activities of four glycosyltransferases sequentially involved in their synthesis from lactosylceramide. The levels of SGGLs in the sciatic nerve increased with development and reached a maximum at sixty days after birth. The rate of increase in the level of SGGLs between day 5 to 20 was similar to rate of deposition of myelin in the nerve. Analysis of the activities of the glycosyltransferases showed that only lactotriosylceramide galactosyltransferase (LcOse3Cer-GalTr) increased in parallel with the levels of SGGLs during development. The other three enzymes were not co-relative with the synthesis of SGGLs. The product of LcOse3Cer-GalTr reaction, nLcOse4Cer is the key intermediate for all neolactoglycolipids, particularly NeuAc alpha2-3nLcOse4Cer or nLM1, which is the major ganglioside (60%) of myelin in rat sciatic nerve. The results suggest that in the sciatic nerve SGGLs are mostly associated with Schwann cell myelin and their synthesis is regulated by LcOse3Cer-GalTr, unlike in the cerebral cortex and cerebellum where SGGLs are associated with the neuronal membranes and their synthesis is regulated by lactosylceramide N-acetylglucosaminyltransferase (LcOse2Cer-GlcNAcTr).

Expression and role of sulfoglucuronyl (HNK-1) carbohydrate and its binding protein SBP-1 in developing rat cerebral cortex

Developmental expression of sulfoglucuronyl carbohydrate (SGC) and its binding protein, SBP-1 was studied in the rat cerebral cortex to understand their function. Between embryonic day (ED) 14-19, SBP-1 was strongly expressed in neurons of the ventricular zone and migrating neurons throughout the cortex. SBP-1 declined at birth and by postnatal day (PD) 3 only the latest arriving neurons in the most superficial segment of the cortical plate expressed SBP-1. Between ED 14-16, SGC was expressed in a thin row of glial cells near the ventricles and on their radial processes. Between ED 16-PD 3, SGC was not in neuronal cell soma, but was in neuronal plasma membranes and processes surrounding the neuronal perikarya. The expression of SGC declined similar to SBP-1 and both of them disappeared by PD 7. The expression of SBP-1 and SGC was chronologically coordinated with neuronal migration. SBP-1 was specifically expressed in immature neuronal nuclei and plasma membranes. SBP-1 and SGC were colocalized and were available for interaction with each other on neuronal cell membranes and processes. This was confirmed with isolated neurons in culture. As in vivo, the expression of SBP-1 in neurons declined with time in culture. The dissociated cortical neurons when plated on SBP-1 as a substratum produced extensive neuritic outgrowth. HNK-1, anti-SBP-1 antibodies and sulfoglucuronyl glycolipid, SGGL specifically and severely reduced neurite outgrowth. SBP-1-SGC interactions provide a potential mechanism for guidance and cell signaling, in the processes of neuronal migration and terminal differentiation.