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CSD has been linked to migraine aura, but a connection to pain symptoms is uncertain. “There’s just a lack of knowledge. We don’t understand migraine pathophysiology,” said Michael G. Harrington, MBChB, who was asked to comment on the study.
“The evidence for altered transport across the barrier in cortical spreading depression and the associated aura of migraine is pretty strong. The evidence for regular migraine, not so. In fact, there’s really no strong evidence for leakage in those people, and so it is still unresolved whether this initial cortical spreading depression that occurs in aura then triggers migraine afterwards, because it’s occurring during the aura. And in people who do not have the aura, is there a silent cortical spreading depression phenomenon with some leakage that triggers the migraine? That question is definitely not answered,” said Dr. Harrington, a research professor of neurology at the University of Southern California, Los Angeles.
Leakage of the BBB might allow passage of nociceptive compounds that could trigger migraine. Loss of BBB integrity has also been seen in other central nervous system pain disorders, suggesting that alterations to BBB functioning could have broader implications.
“In this model that we’re using, we’re seeing loss of overall barrier integrity, which lends itself to a whole cascade of further pathological possibilities,” Jared Wahl, a PhD candidate at the University of Arizona, Tucson, said in an interview. He presented the research at the American Headache Society’s 2021 annual meeting.
A leaky BBB could allow infiltration of a range of substances, but the potential for such a mechanism in migraine pathology is not well understood.
The researchers specifically investigated the potential role of claudin-5 in the tight junction (TJ) region of the BBB. The decision was made in part because the proteins involved in the BBB are difficult to study, and there is some familiarity with claudin-5, according to Mr. Wahl. ”Of all the proteins that are out there, for claudin-5 (there are) somewhat better techniques and products available to work with, and there’s been some previous research done to show that it’s implicated in blood brain barrier pathology. So it seemed like a good candidate to start with investigating this whole possible pathophysiological link between barrier disruption and migration of pronociceptive substances into the CNS during migraine attacks,” he said. The claudin proteins are also the major components of the tight junctions that seal off gaps between endothelial cells along the BBB.
Dynamic changes seen in the in vitro model
To simulate a CSD event, the researchers pulsed cultured cells for 5 minutes with astrocyte-conditioned media, artificial cerebrospinal fluid, KCl, glutamate, altered pH, or adenosine triphosphate (ATP). They used trans endothelial electrical resistance (TEER) to quickly and qualitatively screen for loss of barrier integrity, which is characterized by loss of electrical resistance. To quantify the magnitude of a breach, the researchers applied carbon-14 (C14)–labeled sucrose to one side of the barrier, and determined the amount of labeled sucrose transmitted to the other side of the barrier.
ATP and pH pulses that were outside normal physiological limits led to permeability. The team then used immunocytochemistry assays to visualize the condition of the model BBB, and found discontinuity of the tight junction membranes. Imaging of claudin-5 showed organizational changes within the tight junction, but there was no change in expression level, suggesting that the alterations were due to dynamic reorganization, according to Mr. Wahl.
Transient openings could allow passage of molecules such as bradykinin, calcitonin gene-related peptide (CGRP), and substance P, which could go on to affect the trigeminal nerve complex and trigger a migraine. “That’s sort of the crux of a lot of this migraine research, is gluing this physiological (mechanism) to how it is actually activating the CNS. And this is sort of where we’re going with it at the moment,” said Mr. Wahl.
Next steps
The researchers next plan to generate a cell line with claudin-5 linked to green fluorescent protein, then use confocal microscopy to image claudin-5 in real time as the BBB model responds to a simulated CSD.
Another important step will be to link physiological findings like those presented by Mr. Wahl to migraine-specific mechanisms. The results from this model will need to be expanded to include more than endothelial cells, especially astrocytes, pericytes, and neurons, as well as organoids, brain slices, or in vivo animal models, according to Dr. Harrington. “I think you could try and block the changes in occludin [another protein in the tight junction] or claudin-5 to see if, under the same provocation, that prevented the changes in a migraine model. That would be a direct way of connecting from CSD to migraine,” said Dr. Harrington.
If BBB disruption is confirmed to play an important role in migraine, and claudin-5 or other specific proteins are confirmed to be the cause, it could have clinical implications. A drug that could prevent those changes in the proteins and prevent a leak in the BBB could be a migraine preventative. “That could help prevent things like nociceptive substances migrating into the CNS, and could possibly be a well-tolerated drug target that doesn’t have the side effects or the overuse problems that a lot of stuff on the market has today,” said Mr. Wahl.
CSD has been linked to migraine aura, but a connection to pain symptoms is uncertain. “There’s just a lack of knowledge. We don’t understand migraine pathophysiology,” said Michael G. Harrington, MBChB, who was asked to comment on the study.
“The evidence for altered transport across the barrier in cortical spreading depression and the associated aura of migraine is pretty strong. The evidence for regular migraine, not so. In fact, there’s really no strong evidence for leakage in those people, and so it is still unresolved whether this initial cortical spreading depression that occurs in aura then triggers migraine afterwards, because it’s occurring during the aura. And in people who do not have the aura, is there a silent cortical spreading depression phenomenon with some leakage that triggers the migraine? That question is definitely not answered,” said Dr. Harrington, a research professor of neurology at the University of Southern California, Los Angeles.
Leakage of the BBB might allow passage of nociceptive compounds that could trigger migraine. Loss of BBB integrity has also been seen in other central nervous system pain disorders, suggesting that alterations to BBB functioning could have broader implications.
“In this model that we’re using, we’re seeing loss of overall barrier integrity, which lends itself to a whole cascade of further pathological possibilities,” Jared Wahl, a PhD candidate at the University of Arizona, Tucson, said in an interview. He presented the research at the American Headache Society’s 2021 annual meeting.
A leaky BBB could allow infiltration of a range of substances, but the potential for such a mechanism in migraine pathology is not well understood.
The researchers specifically investigated the potential role of claudin-5 in the tight junction (TJ) region of the BBB. The decision was made in part because the proteins involved in the BBB are difficult to study, and there is some familiarity with claudin-5, according to Mr. Wahl. ”Of all the proteins that are out there, for claudin-5 (there are) somewhat better techniques and products available to work with, and there’s been some previous research done to show that it’s implicated in blood brain barrier pathology. So it seemed like a good candidate to start with investigating this whole possible pathophysiological link between barrier disruption and migration of pronociceptive substances into the CNS during migraine attacks,” he said. The claudin proteins are also the major components of the tight junctions that seal off gaps between endothelial cells along the BBB.
Dynamic changes seen in the in vitro model
To simulate a CSD event, the researchers pulsed cultured cells for 5 minutes with astrocyte-conditioned media, artificial cerebrospinal fluid, KCl, glutamate, altered pH, or adenosine triphosphate (ATP). They used trans endothelial electrical resistance (TEER) to quickly and qualitatively screen for loss of barrier integrity, which is characterized by loss of electrical resistance. To quantify the magnitude of a breach, the researchers applied carbon-14 (C14)–labeled sucrose to one side of the barrier, and determined the amount of labeled sucrose transmitted to the other side of the barrier.
ATP and pH pulses that were outside normal physiological limits led to permeability. The team then used immunocytochemistry assays to visualize the condition of the model BBB, and found discontinuity of the tight junction membranes. Imaging of claudin-5 showed organizational changes within the tight junction, but there was no change in expression level, suggesting that the alterations were due to dynamic reorganization, according to Mr. Wahl.
Transient openings could allow passage of molecules such as bradykinin, calcitonin gene-related peptide (CGRP), and substance P, which could go on to affect the trigeminal nerve complex and trigger a migraine. “That’s sort of the crux of a lot of this migraine research, is gluing this physiological (mechanism) to how it is actually activating the CNS. And this is sort of where we’re going with it at the moment,” said Mr. Wahl.
Next steps
The researchers next plan to generate a cell line with claudin-5 linked to green fluorescent protein, then use confocal microscopy to image claudin-5 in real time as the BBB model responds to a simulated CSD.
Another important step will be to link physiological findings like those presented by Mr. Wahl to migraine-specific mechanisms. The results from this model will need to be expanded to include more than endothelial cells, especially astrocytes, pericytes, and neurons, as well as organoids, brain slices, or in vivo animal models, according to Dr. Harrington. “I think you could try and block the changes in occludin [another protein in the tight junction] or claudin-5 to see if, under the same provocation, that prevented the changes in a migraine model. That would be a direct way of connecting from CSD to migraine,” said Dr. Harrington.
If BBB disruption is confirmed to play an important role in migraine, and claudin-5 or other specific proteins are confirmed to be the cause, it could have clinical implications. A drug that could prevent those changes in the proteins and prevent a leak in the BBB could be a migraine preventative. “That could help prevent things like nociceptive substances migrating into the CNS, and could possibly be a well-tolerated drug target that doesn’t have the side effects or the overuse problems that a lot of stuff on the market has today,” said Mr. Wahl.
CSD has been linked to migraine aura, but a connection to pain symptoms is uncertain. “There’s just a lack of knowledge. We don’t understand migraine pathophysiology,” said Michael G. Harrington, MBChB, who was asked to comment on the study.
“The evidence for altered transport across the barrier in cortical spreading depression and the associated aura of migraine is pretty strong. The evidence for regular migraine, not so. In fact, there’s really no strong evidence for leakage in those people, and so it is still unresolved whether this initial cortical spreading depression that occurs in aura then triggers migraine afterwards, because it’s occurring during the aura. And in people who do not have the aura, is there a silent cortical spreading depression phenomenon with some leakage that triggers the migraine? That question is definitely not answered,” said Dr. Harrington, a research professor of neurology at the University of Southern California, Los Angeles.
Leakage of the BBB might allow passage of nociceptive compounds that could trigger migraine. Loss of BBB integrity has also been seen in other central nervous system pain disorders, suggesting that alterations to BBB functioning could have broader implications.
“In this model that we’re using, we’re seeing loss of overall barrier integrity, which lends itself to a whole cascade of further pathological possibilities,” Jared Wahl, a PhD candidate at the University of Arizona, Tucson, said in an interview. He presented the research at the American Headache Society’s 2021 annual meeting.
A leaky BBB could allow infiltration of a range of substances, but the potential for such a mechanism in migraine pathology is not well understood.
The researchers specifically investigated the potential role of claudin-5 in the tight junction (TJ) region of the BBB. The decision was made in part because the proteins involved in the BBB are difficult to study, and there is some familiarity with claudin-5, according to Mr. Wahl. ”Of all the proteins that are out there, for claudin-5 (there are) somewhat better techniques and products available to work with, and there’s been some previous research done to show that it’s implicated in blood brain barrier pathology. So it seemed like a good candidate to start with investigating this whole possible pathophysiological link between barrier disruption and migration of pronociceptive substances into the CNS during migraine attacks,” he said. The claudin proteins are also the major components of the tight junctions that seal off gaps between endothelial cells along the BBB.
Dynamic changes seen in the in vitro model
To simulate a CSD event, the researchers pulsed cultured cells for 5 minutes with astrocyte-conditioned media, artificial cerebrospinal fluid, KCl, glutamate, altered pH, or adenosine triphosphate (ATP). They used trans endothelial electrical resistance (TEER) to quickly and qualitatively screen for loss of barrier integrity, which is characterized by loss of electrical resistance. To quantify the magnitude of a breach, the researchers applied carbon-14 (C14)–labeled sucrose to one side of the barrier, and determined the amount of labeled sucrose transmitted to the other side of the barrier.
ATP and pH pulses that were outside normal physiological limits led to permeability. The team then used immunocytochemistry assays to visualize the condition of the model BBB, and found discontinuity of the tight junction membranes. Imaging of claudin-5 showed organizational changes within the tight junction, but there was no change in expression level, suggesting that the alterations were due to dynamic reorganization, according to Mr. Wahl.
Transient openings could allow passage of molecules such as bradykinin, calcitonin gene-related peptide (CGRP), and substance P, which could go on to affect the trigeminal nerve complex and trigger a migraine. “That’s sort of the crux of a lot of this migraine research, is gluing this physiological (mechanism) to how it is actually activating the CNS. And this is sort of where we’re going with it at the moment,” said Mr. Wahl.
Next steps
The researchers next plan to generate a cell line with claudin-5 linked to green fluorescent protein, then use confocal microscopy to image claudin-5 in real time as the BBB model responds to a simulated CSD.
Another important step will be to link physiological findings like those presented by Mr. Wahl to migraine-specific mechanisms. The results from this model will need to be expanded to include more than endothelial cells, especially astrocytes, pericytes, and neurons, as well as organoids, brain slices, or in vivo animal models, according to Dr. Harrington. “I think you could try and block the changes in occludin [another protein in the tight junction] or claudin-5 to see if, under the same provocation, that prevented the changes in a migraine model. That would be a direct way of connecting from CSD to migraine,” said Dr. Harrington.
If BBB disruption is confirmed to play an important role in migraine, and claudin-5 or other specific proteins are confirmed to be the cause, it could have clinical implications. A drug that could prevent those changes in the proteins and prevent a leak in the BBB could be a migraine preventative. “That could help prevent things like nociceptive substances migrating into the CNS, and could possibly be a well-tolerated drug target that doesn’t have the side effects or the overuse problems that a lot of stuff on the market has today,” said Mr. Wahl.
FROM AHS 2021