Our research group is applying tissue engineering and regenerative medicine principles to understand how we can repair peripheral nerves and the injured spinal cord.
We combine cells and biomaterials to create nerve repair conduits to treat nervous system injuries. Using in vitro and in vivo systems we are investigating the biological reactions which impede regeneration with the goal to develop novel therapies to increase neuronal survival and reduce target organ atrophy. Magnetic resonance imaging, a non-invasive method of assessing neuronal survival and regeneration, is combined with histochemical, biochemical and molecular methods to assess the efficacy of our treatments. Our "bench to bedside" approach is facilitated by new research and human cell culturing facilities at the University Hospital of Umeå.
Cells and biomaterials for the injured nervous system
Nerve injuries affect several hundred thousand people every year in Europe and despite some advances in surgical procedures almost all patients are left with some form of disability. Currently clinical treatment of extensive peripheral nerve injuries involves bridging the defect with a nerve autograft taken from elsewhere in the body. This helps to guide some of the regenerating nerve axons across the gap and towards the distal target organs. However, even in this "best case scenario", functional recuperation of muscle movement and skin sensitivity is very often poor. This loss of function and the added morbidity for the patient due to the need to retrieve a nerve for the graft is far from ideal and has prompted the search for new approaches. Compared with peripheral nervous system traumas, the injured spinal cord shows profound pathology and very limited regeneration. Depending on the level of damage, spinal cord injury can interfere with breathing, bowel and bladder function, sensation, and result in paraplegia or quadriplegia. Beyond minimizing the immediate damage and the subsequent changes evoked by inflammation and axonal disconnection, the key objective of spinal cord injury research is the induction of functional re-innervation.
We are developing novel tissue engineering methods to help repair both peripheral nerves and the injured spinal cord. We are using a combination of cells and biomaterials to create nerve repair conduits within which the regrowing axons are directed by path-finding cues and stimulating molecules. Adult stem cells are isolated from adipose, bone marrow and dental tissues. We are investigating the neurotrophic, angiogenic and immunomodulatory activities of these cells to find the best cell types to treat different nerve injuries. We have shown that these stem cells can be stimulated to become like glial cells which help repair the damaged nervous system. When the stem cells are injected into the spinal cord or transplanted within nerve repair conduits we have shown that they promote axon regeneration, enhance myelination and reduce inhibitory scarring and inflammation. We are using various types of nerve conduit materials, including naturally occurring molecules such as fibrin and poly-3-hydroxybutyrate (PHB) and also collaborate with biomaterials scientists developing novel synthetic structures. We showed in a double blind clinical trial performed together with colleagues at University Hospital Umeå that PHB may be advantageous as compared to epineural suturing for treating median and ulnar nerve injuries.
Functional recovery after injury is limited by many factors related to the biology of the nervous system, including the extent of nerve cell survival after the injury, the rate and quality of axonal outgrowth, the orientation and specificity in growth of regenerating axons, production of scar molecules and the survival and state of the end organs. Using experimental in vivo peripheral nerve injury models we have characterised the time-course and quantity of sensory neuronal cell death in dorsal root ganglia and we have also studied this after upper limb nerve injury in patients. We are investigating the apoptotic signalling mechanisms which lead to the cell death and elucidating the role of microRNAs, important post transcriptional regulators, in controlling how these processes are activated or repressed. Similarly, by using laser microdissection and qRT-PCR we are trying to understand why certain populations of neurons can regenerate but others do not. We also use in vitro cultures of glial cells (Schwann cells, astrocytes and microglia) to investigate how these cells contribute to axonal outgrowth in the peripheral and central nervous systems.
We have shown that application of exogenous neurotrophins can prevent retrograde degeneration of sensory and motor neurons after peripheral nerve injury, and neurons of the long spinal tracts after spinal cord injury. However, known side effects of neurotrophins on synaptic connections and axonal transport, complicates their clinical application. We have therefore investigated other drugs including the antioxidants acetyl-L-carnitine and N-acetyl-cysteine which we showed could provide neuroprotection after nerve trauma. We also study how muscles respond to nervous system injury. A denervated muscle atrophies and this is reversible if the muscle is reinnervated without delay. However, the injury often occurs at a significant distance from the muscle, and the regrowing nerve may take months to reach and reinnervate the muscle. This results in a terminal and irreversible atrophy, muscle fibre cell death, fibrosis and consequent loss of motor function. We have shown that injections of stem cells in denervated muscle can reduce damage and we are now determining the mechanisms behind these effects.
There are a lack of non-invasive methods for reliable clinical evaluation of the extent of neuronal cell death and assessments of novel neuroprotective interventions. By developing MRI to assess neuronal cell death we hope to meet the clinical demands for a non-invasive, safe, well-tolerated technique not involving radiation. Furthermore, experimental studies estimating neuronal cell death typically require that animals are sacrificed for histological analysis. The introduction of MRI based assessment of neuronal cell death enables the animals to be followed longitudinally making results more reliable. In previous animal experiments we have found a strong correlation between the decrease in DRG-volume estimated with MRI and the morphological volume decrease after peripheral nerve injury. We have also compared stereological methods and volumetric MRI of DRG in histological quantification and objective clinical assessment of human brachial plexus sensory neurons. Our results demonstrated a strong correlation of neuronal counts and histological DRG volumes with volumetric MRI results in the human volunteers. Our ongoing objectives are to develop clinically relevant MRI -based techniques for the early differential diagnosis of brachial plexus injury (BPI) and assessment of novel neuroprotective treatments. We are currently developing the MRI techniques (structural and diffusion tensor imaging) to assess degeneration and regeneration after BPI; from the peripheral nerve, dorsal root ganglia, the spinal cord, to neuroplastic changes in gray and white matter of the brain. We are using the MRI techniques to differentiate between preganglionic and postganglionic plexus injuries in both experimental animals and patients. We are evaluating the sensitivity of these MRI techniques to detect effects of different neuroprotective treatment strategies (e.g. early nerve reconstruction, adult stem cells and antioxidants) after preganglionic and postganglionic plexus injuries in both animals and humans.