Collagens as New Players in Nervous System Diseases

The binomial nervous system involves the central nervous system (CNS), comprising the brain and the spinal cord, and the peripheral nervous system (PNS). Both divisions of the nervous system contain electrically excitable neurons as well as a number of supporting neuroglial cells, which include oligodendrocytes, astrocytes, microglia, choroid plexus ependymal cells in the CNS, and satellite and Schwann cells in the PNS. Connective tissues rich in fibrillar collagens form the outermost cover for the nervous system proper. Moreover, there are rich basement membranes (BM) surrounding all nervous system tissues and vessels within these structures. BMs compartmentalize nervous tissues and contribute to selective barrier and filtration functions essential for brain homeostasis. While BMs are absent from the brain parenchyma, there are extracellular matrices (ECM) in these regions that remain under-explored. The composition and types of matrices differ substantially in different parts of the nervous system. ECMs are significantly abundant during development, guiding cellular migration and differentiation as well as axon navigation and synaptogenesis. Additionally, ECMs promote neuronal health, contribute to synaptic homeostasis and plasticity, and are upregulated in response to disease and trauma. It is for these reasons that the mutation and malfunction of collagens have been linked to neurodevelopmental, degenerative, and psychiatric disorders as well as motor and sensory dysfunction. In recent years, it has become clear that collagens, constituting a major family of ECM proteins, and other extracellular components are generated not only by glial cells but also by neurons. The functions and expression patterns of the collagen superfamily members in the nervous system are summarized in this chapter, where we focus on their roles in vitro and in vivo in a number of animal models, and in human diseases of the nervous system.