Periodic Reporting for period 1 - EFHHBBBMS (Endothelial Hedgehog autocrine signaling at the Blood Brain Barrier controls inflammatory CentralNervous System lesion size and severity through Gas1 co-receptor modulation.)
Periodo di rendicontazione: 2019-01-15 al 2021-01-14
In a healthy individual, the central nervous system (CNS) parenchyma is protected from the peripheral circulation by the blood–brain barrier (BBB). Importantly, during multiple sclerosis, the abnormal permeability of the BBB allows penetration into the CNS of inflammatory cells and plasmatic proteins which drive lesion formation. Previous studies have identified the Hedgehog (HH) pathway as a regulator of BBB integrity in multiple sclerosis, HIV, and stroke and we showed that desert hedgehog (DHH) is expressed constitutively at the BBB in adults. Interestingly, a wealth of literature has enabled a change in the vision of BBB structure and integrity, which has expanded to include contributions from both barrier properties of the vascular endothelial cells and the astrocytic end feet of the neurovascular unit. While it is now well established that BBB breakdown leads to soluble factor and inflammatory cell infiltration into the CNS during neuropathology, the role of the Glia Limitans is more complex. Indeed, astrocytes, described as reactive, may demonstrate opposing roles in both recruiting and restricting neuroinflammatory infiltration depending on the context. Specifically, in multiple sclerosis, it has been shown that reactive astrocytes, on one hand, produce pro-inflammatory and pro-permeability factors and on the other hand, neuroprotective factors. Astrocyte barrier properties are not as well characterized as those of the BBB. However, several groups have highlighted barrier properties at the Glia Limitans which is also required for immune cell trafficking across the neurovascular unit. Strikingly, our recent work has given considerable attention to a new property of reactive astrocytes: the expression of tight junction proteins, notably Claudin4, under inflammatory conditions. This result provides yet another argument in favor of astrocytic barrier properties.The first objective of our study was to decipher the role of Dhh in maintaining BBB tightness. The second objective was to demonstrate that a double barrier system comprising both the BBB and Glia Limitans is implemented in the CNS and regulated by a crosstalk going from endothelial cell to astrocytes using endothelial Dhh knockdown as a model of permeable BBB.
Here, we first demonstrate that endothelial Dhh expression is down-regulated during neuroinflammation and is necessary to maintain BBB tightness. We then show that BBB opening, induced by Dhh knockdown, drives astrocyte Claudin4 expression, conferring barrier properties to the Glia Limitans both under physiological conditions and during pathology. Together, these data identify the neurovascular unit as a double barrier system whose function is controlled by the crosstalk between endothelial cells and astrocytes.
The main project data focusing on the gliovascular double barrier system function has been published in an open access, generalist journal: Plos Biology (doi: 10.1371/journal.pbio.3000946). In parallel, we also published two papers in specialized journals (Atherosclerosis, Thrombosis, Vascular Biology and Cardiovascular Research), focusing respectively on the Hedgehog co-receptors CDON and GAS1 (doi: 10.1161/ATVBAHA.120.314441) and SHH astrocytic secretion at the Glia Limitans (doi: 10.1093/cvr/cvaa285) in condition of neuro-inflammation. We also increased our visibility by sharing our results on social networks notably Twitter (https://twitter.com/chapoulyc(si apre in una nuova finestra), ORCID and LinkedIn. Finally, to gain visibility, we actively participated to the Bordeaux scientific life promoting the U1034 research program during the University summer school, encouraging Master and PhD students to join our laboratory. Finally, we were greatly involved in the actions led by the french multiple sclerosis research foundation (ARSEP). Since 2018, we received in our lab, ARSEP donators and patients suffering from multiple sclerosis in order to present and explain to them our research. We also participated yearly to the “world multiple sclerosis day” which brings awareness on this disease.
The main project data focusing on the gliovascular double barrier system function has been published in an open access, generalist journal: Plos Biology (doi: 10.1371/journal.pbio.3000946). In parallel, we also published two papers in specialized journals (Atherosclerosis, Thrombosis, Vascular Biology and Cardiovascular Research), focusing respectively on the Hedgehog co-receptors CDON and GAS1 (doi: 10.1161/ATVBAHA.120.314441) and SHH astrocytic secretion at the Glia Limitans (doi: 10.1093/cvr/cvaa285) in condition of neuro-inflammation. We also increased our visibility by sharing our results on social networks notably Twitter (https://twitter.com/chapoulyc(si apre in una nuova finestra), ORCID and LinkedIn. Finally, to gain visibility, we actively participated to the Bordeaux scientific life promoting the U1034 research program during the University summer school, encouraging Master and PhD students to join our laboratory. Finally, we were greatly involved in the actions led by the french multiple sclerosis research foundation (ARSEP). Since 2018, we received in our lab, ARSEP donators and patients suffering from multiple sclerosis in order to present and explain to them our research. We also participated yearly to the “world multiple sclerosis day” which brings awareness on this disease.
Neurodegeneration represents a major public health issue as life expectancy increases. As of today, it concerns 1 individual out of 4 in Europe and represents about 800 billion euros of health expenditures. Presently, it is commonly accepted that the BBB is the sole line of defense of the CNS, restricting access to the parenchyma to peripheral attacks in the context of neuro-degeneration. However, with EFHHBBBMS, we bring a different perspective on CNS barrier organization, unveiling the existence of two independent, dissociable effects of the astrocyte and endothelial barriers in the CNS. For the first time, we demonstrate that BBB breakdown is sufficient to induce chronic barrier properties at the Glia Limitans and we highlight a crosstalk from endothelial cells to astrocytes which restrict access to the parenchyma to plasmatic proteins and inflammatory cells during neuropathology. Thus explain that the main approach which focuses on targeting BBB to limit or to facilitate access to the parenchyma has failed so far as it is more likely that playing on BBB status impact Glia Limitans barrier properties. Consequently, on a large scale, our project has wide implications for CNS access in neuropathology as well as drug delivery by manipulating both the BBB and Glia Limitans in combination. Indeed, taking into account both components of the gliovascular unit is of translational interest notably to limit CNS parenchymal access to pathogenic agents by strengthening the Glia Limitans once the BBB is open, in cardiovascular diseases such as brain ischemic strokes, neuro-infections and neuro-degeneration (Parkinson’s/Alzheimer’s diseases, vascular dementia) or to facilitate parenchymal access to drugs, by opening the BBB and Glia Limitans together, in CNS tumor treatment. Along similar lines, it is unknown how the barrier properties of the Glia Limitans may impact the pharmacokinetics of drugs that must enter the CNS parenchyma in conditions such as multiple sclerosis, which may account for treatment failure.
To highlight the project progression, we regularly applied to congresses related to our field (neurovascular biology, neuropathology and Hh pathway); amongst others, we participated to international (International Vascular Biology Meeting) and national conferences (Société d’Etude des Interfaces Sang Cerveau and the Société Française d’Angiogenèse). It gave us the opportunity to present the project to our pairs, using different supports (posters and power point presentations), to get a critical lecture and new perspectives for our research and to develop our network among some of the most talented researchers worldwide.
To highlight the project progression, we regularly applied to congresses related to our field (neurovascular biology, neuropathology and Hh pathway); amongst others, we participated to international (International Vascular Biology Meeting) and national conferences (Société d’Etude des Interfaces Sang Cerveau and the Société Française d’Angiogenèse). It gave us the opportunity to present the project to our pairs, using different supports (posters and power point presentations), to get a critical lecture and new perspectives for our research and to develop our network among some of the most talented researchers worldwide.