We experimentally study mechanisms of degeneration and regeneration in the nervous system. To this end, we use several models as well as techniques, to cover different organization levels at diverse tissular locations.
AXONAL DEGENERATION AS A TARGET FOR NEUROPROTECTION
Axonal degeneration is an active mechanism involved in a variety of neurodegenerative conditions triggered by mechanical, metabolic, infectious, toxic, hereditary and inflammatory stimuli. Importantly, axonal degeneration and synapse loss have been proposed as an early event and major contributor to neuronal death in several neurodegenerative conditions, including Parkinson, Alzheimer, Huntington, demyelinating, motoneuron, and prion diseases. Axon degeneration can cause permanent loss of function, so it represents a focus for neuroprotective strategies.
Although axonal degeneration has been extensively studied over the last years, the molecular pathway leading from the injury event to destruction of axons has not been fully determined. Axonal transport defects, local activation of signaling pathways, mitochondrial dysfunction and calcium-dependent proteolysis have all been linked to axonal degeneration. In our laboratory, we have been developing models to study axonal degeneration with potential screening capabilities. Using these methods, we have recently shown that axonal degeneration is dependent on the activation of the mitochondrial permeability transition pore (mPTP). We are currently studying the mechanisms involved in mPTP activation after different stimuli -including mechanical and toxic axonal damage- to characterize some of the critical steps of the axonal degeneration program and understand the progression of axonopathies associated to neurological disorders.
VESICULAR TRANSFER BETWEEN GLIA AND AXONS
Glial cells and neurons have multiple mechanisms for bidirectional comunication. We have shown that transcellular transfer of macromolecules take place from glia to axons after injury (Court et al., 2008) and during axonal regeneration (Court et al., 2011). We are currently studying the communication and macromolecular transfer mechanisms between glial cells and axons mediated by secreted vesicles. Our ultimate goal is to define the role of vesicular transfer between glia and neurons in the regulation of different axonal processes, including local protein synthesis and axonal regeneration in the peripheral and central nervous system.
The intimate communication between neurons and glia has been dramatically demonstrated in several pathological conditions in which primary abnormalities in glial cells have important consequences to neurons. Communication between cells involves the secretion or exposure of proteins from one cell that bind to receptors on neighboring cells. Another mode of communication – involving the release of molecularly defined vesicles – has recently become the subject of increasing interest. We have previously shown that Schwann cell transfer ribosomes to axons. Among the various kinds of vesicular vectors, exosomes are vesicles secreted in a regulated fashion by most cell types upon fusion of multivesicular endosomes with the cellular plasma membrane. It has been shown that exosome transfer is involved in diverse physiological and pathological processes, such as modulation of the immune response, induction of cancer phenotypes and neurodegenerative conditions. In addition, it has been proposed that biochemical analysis of circulating exosomes represent an early diagnostic method for different diseases. Exosomes carry not only proteins but also mRNA, microRNA and organelles, emphasizing their important role in intercellular communication. We are studying the mechanisms involved in exosome release by glial cells in the peripheral nervous system, their cargoes (including proteins, mRNA and miRNA) and the internalization of glia-derived exosomes by axons. Our ultimate goal is to define the role of exosomes in the regulation of different axonal processes, including local protein synthesis and their possible impact in axonal regeneration. In a therapeutic perspective, exosomes derived from glial cells might be used as transfer vector of specific genes or proteins to affected neurons in diseases.
FUNCTIONAL RECOVERY AFTER SPINAL CORD INJURY
Spinal Cord Injuries (SCI) are devastating conditions leading to partial or complete paralysis with tremendous social and economic impacts. Currently there are no effective therapies for functional recovery after SCI. In our lab, we are approaching the problem in both basic and applied research levels using mice and rats as experimental models. In collaboration with Dr. Claudio Hetz at Univeridad de Chile, we have recently demosntrated an important role of the Unfolded Protein Response (UPR) in locomotor recovery after spinal cord injury (see publications: Valuenzuela et al. Cell Death Disease, 2011).
Trauma to the spinal cord results in functional loss or impairment leading to reduced mobility and sensation. Currently there are no effective therapies for functional recovery after SCI. In our lab, we are using two experimental models to approach this important clinical problem. Most injuries to the spinal cord are incomplete and present a partial recovery of locomotor function. Nevertheless the mechanisms involved in this partial locomotor recovery are not completely defined. Recent evidence demonstrates that after SCI, non-damaged neurons have the capability of sprout and partially compensate the function of lost nerve fibers, leading to functional locomotor recovery. Based on this information, we are trying to unravel the mechanisms involved in neuronal sprouting. To evaluate this phenomenon we have implemented a dorso-ventral lateral hemisection in mice that allows us to test the mechanisms involved in the axon collateral extension by using genetic approachs. The understanding of the intrinsic neuronal capability for compensation of altered neuronal circuits might lead to novel therapeutics strategies. In collaboration with Dr. Claudio Hetz at University of Chile, we are studying the functional role of cellular stress responses in neuroprotection and locomotor recovery after SCI. In a more applied level, we are working with the groups of Dr. Miguel Bronfman and Dr. Francisca Bronfman to assess if diverse candidate drugs can increase functional recovery after SCI. To prove this hypothesis, we are using a clip-compression model in rats. In all these studies we use a wide variety of analytical tools, including biochemical analysis, in vivo labeling of neuronal projections, behavioral studies and morphological analysis using optic and electron microscopy.