Neurite promoting activity of collagens on embryonic neurons: decreased effect at the postnatal stage

A new in vitro model of the glial scar inhibits axon growth

Astrocytes respond to central nervous system (CNS) injury with reactive astrogliosis and participate in the formation of the glial scar, an inhibitory barrier for axonal regeneration. Little is known about the injury-induced mechanisms underlying astrocyte reactivity and subsequent development of an axon-inhibitory scar. We combined two key aspects of CNS injury, mechanical trauma and co-culture with meningeal cells, to produce an in vitro model of the scar from cultures of highly differentiated astrocytes. Our model displayed widespread morphological signs of astrocyte reactivity, increases in expression of glial fibrillary acidic protein (GFAP), and accumulation of GFAP in astrocytic processes. Expression levels of scar-associated markers, phosphacan, neurocan, and tenascins, were also increased. Importantly, neurite growth from various CNS neuronal populations was significantly reduced when neurons were seeded on the scar-like cultures, compared with growth on cultures of mature astrocytes. Quantification of neurite growth parameters on the scar model demonstrated significant reductions in neuronal adhesion and neurite lengths. Interestingly, neurite outgrowth of postnatal neurons was reduced to a greater extent than that of embryonic neurons, and outgrowth inhibition varied among neuronal populations. Scar-like reactive sites and neurite-inhibitory patches were found throughout these cultures, creating a patchwork of growth-inhibitory areas mimicking a CNS injury site. Thus, our model showed relevant aspects of scar formation and produced widespread inhibition of axonal regeneration; it should be useful both for examining mechanisms underlying scar formation and to assess various treatments for their potential to improve regeneration after CNS injury. (c) 2008 Wiley-Liss, Inc.

Astrocytes express type VIII collagen during the repair process of brain cold injury

We recognized for the first time upregulation of type VIII collagen gene expression during the repair process in the mouse brain cold injury model. Immunohistochemical staining showed that type VIII collagen expression was around the necrotic region, where reactive astrocytes are frequently observed. Cultured astrocytes demonstrated a high expression of type VIII collagen genes. TGF-beta1 enhanced the expression of both alpha1(VIII) and alpha2(VIII) genes by astrocytes in culture. Further, we tested selected biological activities of type VIII collagen, compared with those of type I, IV, and V collagens and fibronectin. Astrocytes adhered to type VIII collagen via receptors requiring metal ions. Astrocyte migration on type VIII collagen was more stimulated than that observed on the other ECM molecules. These data indicate that type VIII collagen plays an important role in glial scar formation during the repair process by astrocytes.

Orientation of human glioblastoma cells embedded in type I collagen, caused by exposure to a 10 T static magnetic field

We investigated the preferred orientation of human glioblastoma cells (A172) following exposure to static magnetic fields (SMF) at 10 Tesla in the presence or absence of collagen. A172 cells embedded in collagen gel were oriented perpendicular to the direction of the SMF. A172 cells cultured in the absence of collagen did not exhibit any specific orientation pattern after 7 days of exposure to the SMF. Thus we succeeded in evoking the magnetic orientation of human glioblastoma cells by exposure to the SMF. Our results suggest that the orientation of glioblastoma cell processes may be due to the arrangement of microtubules under the influence of magnetically oriented collagen fiber.

Intrinsic properties inhibit axonal outgrowth from neonatal rat spinal cord explant

Lumbar spinal cord explants, harvested from neonatal rat pups aged between postnatal day 0 (P0) and P6, were cultured for a period of 48 hrs in the chemically defined medium R(12) on a poly-ethylene-imine (PEI) and on poly-D-lysin (PDL) coated surface. The outgrowth outside the explant was quantified. Lumbar explants from the same rat and embedded in a collagen matrix, and cortical explants from a P0 rat were used as controls. Statistical analysis demonstrated a clear relation between age-at-explantation and the number of neurites in the corona surrounding the explant. The number of outgrowing neurites decreased sharply with age-at-explantation. The average number of neurites per explant obeyed to the expression log (n) = -0.736x + 3.294 on PEI, and log (n) = -0.721x + 2.295 on PDL; x epsilon in [P0 - P6] (n, the number of neurites per explant; x, the age-at-explantation expressed in postnatal days). A similar observed age-related decrease of outgrowth has been described when culturing the lumbar explant inside a collagen matrix. The phenomenon appears to be an intrinsic property of the explant. We review growth inhibitory properties in different models and propose that the phenomenon occurs here at the interface explant-world.

Thy-1 is critical for normal retinal development

In the mammalian retina, Thy-1, the most abundant mammalian neuronal surface glycoprotein, is found predominantly if not exclusively on retinal ganglion cells. We hypothesized that Thy-1 plays a significant role in retinal development. Neurite outgrowth of retinal ganglion cells from Thy-1(-) mice over multiple substrates was compared to that seen with wild-type controls. Adult mouse retinas were histologically compared between Thy-1(-) and three strains of Thy-1 positive mice. Thy-1(-) retinal ganglion cells had significantly less neurite outgrowth than controls. The inner nuclear, inner plexiform, ganglion cell and outer segment/pigment epithelium layers were thinner in Thy-1(-) retinae than in controls. Thy-1 appears to be critical for normal retinal development.

Collagen type IV promotes the differentiation of neuronal progenitors and inhibits astroglial differentiation in cortical cell cultures

In an effort to elucidate the interactions between cells in the developing cortex and their microenvironment, we have employed dissociated cell cultures and immunocytochemistry to analyze the effect of collagen type IV (COL) on the proliferation and differentiation of rat cortical progenitor cells during the period of corticogenesis. COL, present in the proliferative zones throughout the period of neurogenesis, belongs to a group of macromolecular proteins that make up a considerable portion of the extracellular matrix (ECM). We have shown that this ECM molecule inhibits cell proliferation and glial cell differentiation while promoting neuronal differentiation. We have also demonstrated that COL, when applied to the cultures with basic fibroblast growth factor (bFGF), induces glial cell differentiation while continuing to promote neuronal differentiation. These results indicate that cortical progenitor cells respond differentially to local environmental signals, and that components of the ECM are involved in the regulation of corticogenesis.