Vascular basement membrane laminins contribute to the functional integrity of the blood vessels

Tushar  Deshpande 1 *,  Jula  Huppert 1 *†,  Sai-Kiran  Samawar 1 ,  Kishan  Kapupara 1 ,  Sharang Ghavampour , Jian Song 1 , Ralf Adams 2 , Hyun-Woo Jeong 2 , Lydia Wachsmuth 3 , Cornelius Faber 3 , Lingzhang Meng 1 , Jens Soltwisch 4  , Melanie-Jane Hannocks 1 , Rupert Hallmann 1  and Lydia Sorokin 1

The  neurovascular  unit  (NVU)  is  the  interconnection  between  the  blood  vessels  and  the surrounding  neurons  and  is  constituted  by  several  cell  layers,  including  endothelium, perivascular cells, astrocytes, and neurons, but also acellular layers that are mainly basement membranes (BMs). BMs underlie endothelium, encase pericytes and smooth muscle cells and mark the pial border and, as such, are in contact with several cellular layers of the NVU. Laminins are essential components of vascular BMs, but little is known about their contribution to the NVU. In the brain, laminin α4 and α5 occur in endothelial and mural BMs. To define their contribution to NVU integrity, we analysed blood vessel enriched, neuron depleted samples from  laminin  α4  knock  out  (Lama4 -/- )  and  endothelial-specific  laminin  α5  knock  out  (Tek-cre:Lama5 -/- ) mice using single cell RNA sequencing. The data was clustered into endothelial, mural and myeloid cell types and unsupervised clustering revealed several sub-types of each category  that  were  altered  in  the  laminin  knock  out  mice.  Lama4 -/-   endothelium  showed enhanced large artery and reduced postcapillary venule sub-clusters. Accordingly, mural cells of Lama4 -/-  mice presented augmented contractile gene signatures. Although devoid of laminin expression, resident myeloid cells exhibited an activated phenotype in Lama4 -/- . Analysis of Tek-cre:Lama5 -/-  samples exhibited the opposite molecular and cellular phenotype to Lama4 -/- , with enhanced postcapillary venule marker expression and reduced contractile nature of perivascular  cells.  However  myeloid  cell  populations  were  not  altered  in  Tek-cre:Lama5 -/-  samples compared to WT controls. Our data suggest direct and indirect roles for vascular laminins  in  the  intercommunication  between  the  endothelium,  mural  cells  and  myeloid populations associated with the arterial wall, all of which are required for the functional integrity of the NVU.

Author affiliations
1 Institute of Physiological Chemistry and Pathobiochemistry and Cells-in-Motion Interfaculty Centre (CiMIC), University of Muenster, Germany; 
2 Department of Tissue Morphogenesis, Max-Planck-Institute  for  Molecular  Biomedicine,  Muenster,  Germany. 
3 Clinical  Radiology, University of Muenster, Germany; 
4 Institute of Hygiene, University of Muenster, Germany