Jose Gerardo-Nava

Spinal cord organotypic slice cultures for the study of regenerating motor axon interactions with 3D scaffolds

Numerous in-vitro techniques exist for investigating the influence of 3D substrate topography on sensory axon growth. However, simple and cost-effective methods for studying post-natal motor axon interactions with such substrates are lacking. Here, spinal cord organotypic slice cultures (OSC) from post-natal day 7-9 rat pups were presented with spinal nerve roots, or blocks of fibrin hydrogel or 3D microporous collagen scaffolds to investigate motor axon-substrate interactions. By 7-14 days, axons from motor neuronal pools extended into the explanted nerve roots, growing along Schwann cell processes and demonstrating a full range of axon-Schwann cell interactions, from simple ensheathment to concentric wrapping by Schwann cell processes and the formation of compact myelin within a basal lamina sheath. Extensive motor axon regeneration and all stages of axon-Schwann interactions were also supported within the longitudinally orientated microporous framework of the 3D collagen scaffold. In stark contrast, the simple fibrin hydrogel only supported axon growth and cell migration over its surface. The relative ease of demonstrating such motor axon regeneration through the microporous 3D framework by immunofluorescence, two-photon microscopy and transmission electron microscopy strongly supports the adoption of this technique for assaying the influence of substrate topography and functionalization in regenerative bioengineering.

Differential pattern of neuroprotection in lumbar, cervical and thoracic spinal cord segments in an organotypic rat model of glutamate-induced excitotoxicity

Glutamate-induced excitotoxicity is a major contributor to motor neuron (MN) degeneration in disorders such as amyotrophic lateral sclerosis (ALS), stroke and spinal cord injury. Numerous in vitro and in vivo models have been developed to evaluate the efficacy and mode of action of neuroprotective agents. However, the dominance of glutamate receptor-subtype in the different regions of the spinal cord in these models has generally been overlooked. This study first compared the neuroprotective effect of administering glutamate receptor antagonists, (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine (MK-801) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), into a serum-free excitotoxic organotypic in vitro system, on the survival of MNs located in the lumbar area of spinal cord. The poor neuroprotection provided by MK-801 (NMDA (N-methyl-D-aspartate) antagonist) in comparison to CNQX (AMPA/KA (a-amino-3-hydroxy-5-methyl-4-isoxazole propionate/kainate) antagonist), raised the hypothesis that the extent of engagement by glutamate receptor sub-types in the mechanism of excitotoxicity may differ within different populations of MNs. The consequent examination of MN susceptibility to glutamate-induced excitotoxicity in relation to the rostro-caudal level from which MN originated revealed a differential glutamate receptor sub-type dominance at different spinal cord regions (i.e. cervical, thoracic and lumbar). In the cervical and lumbar regions, the AMPA receptor was the main contributor to MN excitotoxicity, whereas in thoracic regions, the NMDA receptor was the main contributor. This study provides a new way of looking at mechanisms leading to glutamate-induced excitotoxicity in MN and may therefore be important for the development of treatment strategies in protection of spinal MNs in neurodegenerative disease and traumatic injury.

Cellular Signature of SIL1 Depletion: Disease Pathogenesis due to Alterations in Protein Composition Beyond the ER Machinery.

SIL1 acts as nucleotide exchange factor for the endoplasmic reticulum chaperone BiP. Mutations of SIL1 cause Marinesco-Sjögren syndrome (MSS), a neurodegenerative disorder. Moreover, a particular function of SIL1 for etiopathology of amyotrophic lateral sclerosis (ALS) was highlighted, thus declaring the functional SIL1-BiP complex as a modifier for neurodegenerative disorders. Thereby, depletion of SIL1 was associated with an earlier manifestation and in strengthened disease progression in ALS. Owing to the absence of appropriate in vitro models, the precise cellular pathophysiological mechanisms leading to neurodegeneration in MSS and triggering the same in further disorders like ALS are still elusive. We found that SIL1 depletion in human embryonic kidney 293 (HEK293) cells led to structural changes of the endoplasmic reticulum (ER) including the nuclear envelope and mitochondrial degeneration that closely mimic pathological alterations in MSS and ALS. Functional studies revealed disturbed protein transport, cytotoxicity with reduced proliferation and viability, accompanied by activation of cellular defense mechanisms including the unfolded protein response, ER-associated degradation pathway, proteolysis, and expression of apoptotic and survival factors. Our data moreover indicated that proteins involved in cytoskeletal organization, vesicular transport, mitochondrial function, and neurological processes contribute to SIL1 pathophysiology. Altered protein expression upon SIL1 depletion in vitro could be confirmed in Sil1-deficient motoneurones for paradigmatic proteins belonging to different functional classes. Our results demonstrate that SIL1-depleted HEK293 cells are an appropriate model to identify proteins modulated by SIL1 expression level and contributing to neurodegeneration in MSS and further disorders like ALS. Thereby, our combined results point out that proteins beyond such involved ER-related protein processing are affected by SIL1 depletion.

Central Nervous System

This chapter reviews the biomaterials that have been developed for application in the central nervous system with particular reference to applications for the treatment of traumatic spinal cord injury (SCI). The pathophysiology of SCI is multi-factorial and extends over weeks and even months. The complex nature of traumatic SCI demands the most effective treatment strategies to encompass a combination of approaches including neuroprotection as well as the possibility of implanting scaffolds capable of promoting axon regeneration and functional recovery. Biomaterials from natural or synthetic materials are currently being developed to meet a number of these challenges. Biomaterials have major advantages for spinal cord repair because of their structural and molecular versatility, but further preclinical development will be required before they may be applied to the clinical situation.

Functional recovery not correlated with axon regeneration through olfactory ensheathing cell-seeded scaffolds in a model of acute spinal cord injury

The implantation of bioengineered scaffolds into lesion-induced gaps of the spinal cord is a promising strategy for promoting functional tissue repair because it can be combined with other intervention strategies. Our previous investigations showed that functional improvement following the implantation of a longitudinally microstructured collagen scaffold into unilateral mid-cervical spinal cord resection injuries of adult Lewis rats was associated with only poor axon regeneration within the scaffold. In an attempt to improve graft-host integration as well as functional recovery, scaffolds were seeded with highly enriched populations of syngeneic, olfactory bulb-derived ensheathing cells (OECs) prior to implantation into the same lesion model. Regenerating neurofilament-positive axons closely followed the trajectory of the donor OECs, as well as that of the migrating host cells within the scaffold. However, there was only a trend for increased numbers of regenerating axons above that supported by non-seeded scaffolds or in the untreated lesions. Nonetheless, significant functional recovery in skilled forelimb motor function was observed following the implantation of both seeded and non-seeded scaffolds which could not be correlated to the extent of axon regeneration within the scaffold. Mechanisms other than simple bridging of axon regeneration across the lesion must be responsible for the improved motor function.

Cetuximab Induces Eme1-Mediated DNA Repair: a Novel Mechanism for Cetuximab Resistance

Overexpression of the epidermal growth factor receptor (EGFR) is observed in a large number of neoplasms. The monoclonal antibody cetuximab/Erbitux is frequently applied to treat EGFR-expressing tumors. However, the application of cetuximab alone or in combination with radio- and/or chemotherapy often yields only little benefit for patients. In the present study, we describe a mechanism that explains resistance of both tumor cell lines and cultured primary human glioma cells to cetuximab. Treatment of these cells with cetuximab promoted DNA synthesis in the absence of increased proliferation, suggesting that DNA repair pathways were activated. Indeed, we observed that cetuximab promoted the activation of the DNA damage response pathway and prevented the degradation of essential meiotic endonuclease 1 homolog 1 (Eme1), a heterodimeric endonuclease involved in DNA repair. The increased levels of Eme1 were necessary for enhanced DNA repair, and the knockdown of Eme1 was sufficient to prevent efficient DNA repair in response to ultraviolet-C light or megavoltage irradiation. These treatments reduced the survival of tumor cells, an effect that was reversed by cetuximab application. Again, this protection was dependent on Eme1. Taken together, these results suggest that cetuximab initiates pathways that result in the stabilization of Eme1, thereby resulting in enhanced DNA repair. Accordingly, cetuximab enhances DNA repair, reducing the effectiveness of DNA-damaging therapies. This aspect should be considered when using cetuximab as an antitumor agent and suggests that Eme1 is a negative predictive marker.

Author Correction: Stem cells from human apical papilla decrease neuro‑inflammation and stimulate oligodendrocyte progenitor differentiation via activin‑A secretion

In the original publication, sixth author’s surname was incorrectly published as “Llyod” instead of “Lloyd”. The correct name should read as “Amy Lloyd”.