Final Report Summary - ROLPASCI (Role of lysophosphatidic acid in the pathophysiology of spinal cord injury)
Although the spinal cord is well protected by the bones of the spinal column, it can be damaged in many ways: by cut, bruise or compression, and less frequently injured by infection, damaged when its blood supply is cut off, or affected by diseases that alter its nerve function. Any of these spinal cord injuries result in a disruption of the pathways that carry information between brain and body, as well as of neuronal networks related to many physiological functions. As central nervous system (CNS) axons of adult mammals do not regenerate following lesion, and dead cells are not successfully replaced, this results in irreversible functional loss in patients suffering from spinal cord injury (SCI).
The pathophysiology of SCI involves two stages of tissue degeneration known as primary and secondary injury. The first results from the direct mechanical trauma to the spinal cord which is followed by a secondary wave of tissue degeneration that occurs over a period of several weeks that include inflammation and other mechanisms triggered by injury. Secondary tissue damage that occurs after spinal cord injury (SCI) contributes significantly to permanent functional disabilities. Although regeneration of damaged axons and replacement of lost neurons after SCI are important goals, the secondary damage to axons, neuronal cell bodies, myelin and glial cells that follows the initial trauma is likely to be more easily amenable to treatment. Preventing or minimizing such secondary damage after SCI can be expected to substantially reduce the functional disability. The inflammatory response that occurs after SCI strongly contributes to secondary injury. A number of mechanisms underlie the recruitment of leukocytes from the peripheral circulation, and the activation of these cells and endogenous microglia and astrocytes within the injured spinal cord. However, the molecules that trigger these responses are not completely known. Lysophosphatidic acid (LPA) is a potent, biologically active lipid mediator that has many physiological functions, such as cellular ionic homeostasis and regulation of cytoskeleton, proliferation and survival, adhesion and migration. Recent observations suggest that LPA might be also involved in inflammation. Although LPA is involved in several human diseases, little is known about the effects of LPA in the nervous system. In vivo studies have showed that LPA is responsible for the development of neuropathic pain after sciatic nerve injury. Interestingly, a recent work reveals that the administration of the B3 antibody, which binds to LPA and other lysophospholipids preventing them from interacting with their receptors, promotes functional recovery after spinal cord hemisection in mice. Although the hemisection model is not a clinical relevant model of SCI, this study provided the first insights on the potential deleterious actions of LPA in SCI.
Due to the wide variety of LPA receptors it is likely that LPA may exert helpful or harmful effects in the CNS depending on the receptors it signals through, as has been already observed in other lipid mediators such as prostaglandins. There is therefore a need to know which LPA receptors contribute to neurodegeneration, and those, if any, that could mediate neuroprotection. In the present project we aimed at dissecting out the contribution of the three LPA receptors belonging to the endothelial differentiation gene (Edg) family (LPA1-3) to SCI.
We first found that LPA levels rapidly increase in the spinal cord parenchyma after traumatic injury. In order to know the potential effects of a sudden raise of LPA in the CNS, we injected LPA into the intact spinal cord. We found that LPA triggered a rapid and potent activation of the inflammatory response in the spinal cord, which led to demyelination and functional impairment. This results suggested that the increased in LPA levels in the spinal cord after injury, could be contributing to inflammation and demyelination, and consequently, to functional impairments. LPA mediate its effects by signaling via specific LPA receptors, herein we studied the contribution of the Edg family LPA receptors (LPA1-3).
We found that the demyelinating lesion triggered by intraspinal injection of LPA into the intact spinal cord was significantly reduced in the lack of LPA1 and LPA2, suggesting that the activation of these two LPA receptors induces demyelination. Interestingly, we observed that administration of a selective LPA1 antagonist resulted in a greater locomotor skills and myelin preservation after SCI. Similarly, the lack of LPA2 activity lead to improved functional outcomes and to enhanced preservation of myelin and neurons. These data, clearly demonstrated that the increased LPA levels in the spinal cord parenchyma after injury, leads to activation of the LPA receptors known as LPA1 and LPA2, which triggers neuronal cell death, myelin loss, and consequently, functional disabilities. We also found that LPA3 blockade or activation does not mediate any detrimental effect in SCI, suggesting that activation of this LPA receptors does not leads to harmful functions.
We have also studied the mechanisms underlying the detrimental actions of LPA1 and LPA2 in the spinal cord. These studies revealed that toxic effects of LPA were mediated by microglial cells, which release unknown factors that cause the death of oligodendrocytes when LPA activated the receptors LPA1 and LPA2. Moreover, we also found that the activation of neuronal LPA2 induces cell death.
Overall, our data reveal that the increase in LPA levels in the contused spinal cord contributes to demyelination and neuronal loss by signaling through microglia LPA1 and LPA2 and neuronal LPA2. Since microglia activation, as well as myelin and neuronal loss, are key events that occurs in several CNS disorders, targeting LPA receptors may lead to the development of a new pharmacological approach to treat acute SCI in humans, but also a wide range of neurodegenerative disorders.
The pathophysiology of SCI involves two stages of tissue degeneration known as primary and secondary injury. The first results from the direct mechanical trauma to the spinal cord which is followed by a secondary wave of tissue degeneration that occurs over a period of several weeks that include inflammation and other mechanisms triggered by injury. Secondary tissue damage that occurs after spinal cord injury (SCI) contributes significantly to permanent functional disabilities. Although regeneration of damaged axons and replacement of lost neurons after SCI are important goals, the secondary damage to axons, neuronal cell bodies, myelin and glial cells that follows the initial trauma is likely to be more easily amenable to treatment. Preventing or minimizing such secondary damage after SCI can be expected to substantially reduce the functional disability. The inflammatory response that occurs after SCI strongly contributes to secondary injury. A number of mechanisms underlie the recruitment of leukocytes from the peripheral circulation, and the activation of these cells and endogenous microglia and astrocytes within the injured spinal cord. However, the molecules that trigger these responses are not completely known. Lysophosphatidic acid (LPA) is a potent, biologically active lipid mediator that has many physiological functions, such as cellular ionic homeostasis and regulation of cytoskeleton, proliferation and survival, adhesion and migration. Recent observations suggest that LPA might be also involved in inflammation. Although LPA is involved in several human diseases, little is known about the effects of LPA in the nervous system. In vivo studies have showed that LPA is responsible for the development of neuropathic pain after sciatic nerve injury. Interestingly, a recent work reveals that the administration of the B3 antibody, which binds to LPA and other lysophospholipids preventing them from interacting with their receptors, promotes functional recovery after spinal cord hemisection in mice. Although the hemisection model is not a clinical relevant model of SCI, this study provided the first insights on the potential deleterious actions of LPA in SCI.
Due to the wide variety of LPA receptors it is likely that LPA may exert helpful or harmful effects in the CNS depending on the receptors it signals through, as has been already observed in other lipid mediators such as prostaglandins. There is therefore a need to know which LPA receptors contribute to neurodegeneration, and those, if any, that could mediate neuroprotection. In the present project we aimed at dissecting out the contribution of the three LPA receptors belonging to the endothelial differentiation gene (Edg) family (LPA1-3) to SCI.
We first found that LPA levels rapidly increase in the spinal cord parenchyma after traumatic injury. In order to know the potential effects of a sudden raise of LPA in the CNS, we injected LPA into the intact spinal cord. We found that LPA triggered a rapid and potent activation of the inflammatory response in the spinal cord, which led to demyelination and functional impairment. This results suggested that the increased in LPA levels in the spinal cord after injury, could be contributing to inflammation and demyelination, and consequently, to functional impairments. LPA mediate its effects by signaling via specific LPA receptors, herein we studied the contribution of the Edg family LPA receptors (LPA1-3).
We found that the demyelinating lesion triggered by intraspinal injection of LPA into the intact spinal cord was significantly reduced in the lack of LPA1 and LPA2, suggesting that the activation of these two LPA receptors induces demyelination. Interestingly, we observed that administration of a selective LPA1 antagonist resulted in a greater locomotor skills and myelin preservation after SCI. Similarly, the lack of LPA2 activity lead to improved functional outcomes and to enhanced preservation of myelin and neurons. These data, clearly demonstrated that the increased LPA levels in the spinal cord parenchyma after injury, leads to activation of the LPA receptors known as LPA1 and LPA2, which triggers neuronal cell death, myelin loss, and consequently, functional disabilities. We also found that LPA3 blockade or activation does not mediate any detrimental effect in SCI, suggesting that activation of this LPA receptors does not leads to harmful functions.
We have also studied the mechanisms underlying the detrimental actions of LPA1 and LPA2 in the spinal cord. These studies revealed that toxic effects of LPA were mediated by microglial cells, which release unknown factors that cause the death of oligodendrocytes when LPA activated the receptors LPA1 and LPA2. Moreover, we also found that the activation of neuronal LPA2 induces cell death.
Overall, our data reveal that the increase in LPA levels in the contused spinal cord contributes to demyelination and neuronal loss by signaling through microglia LPA1 and LPA2 and neuronal LPA2. Since microglia activation, as well as myelin and neuronal loss, are key events that occurs in several CNS disorders, targeting LPA receptors may lead to the development of a new pharmacological approach to treat acute SCI in humans, but also a wide range of neurodegenerative disorders.