Gene expression profiling of brain cortex pericytes from control and Rbpj-knockout mice at P7 and P10

Background: Pericytes are capillary-associated mural cells especially prominent in the central nervous system where they regulate vascular permeability and blood-brain barrier integrity. Despite their relevance for neurovascular unit homeostasis and their involvement in the pathobiology of neurodegenerative diseases, signalling mechanisms responsible for functional specialization and intercellular communication remain elusive. Objectives: The main goal of this study is to understand the relevance of Rbpj (the common downstream mediator of Notch signalling, an important mediator of cell-to-cell communication) in brain pericytes and to identify molecular signatures associated to Rbpj deletion. Methods: We used mouse genetic experiments to knockout Rbpj specifically in pericytes using a mural cell-specific Cre-driver (PdgfrbCreERT2). Inclusion of the Rpl22-HA (RiboTag) construct allowed Cre-mediated HA-labeling of ribosomal proteins and consequent isolation of actively translating mRNA from pericytes. PdgfrbCreERT2 transgenic mice were used to drive recombination of Rpl22-HA (RiboTag) allele and/or Rbpj-lox conditional knockout. Tamoxifen administration from postnatal day 1 (P1) to P3 allowed efficient recombination in pericytes. Brain cortices were collected at P7 or P10 and HA-tagged polyribosomes were immunoprecipitated using anti-HA coated beads. Total RNA was extracted and sequencing libraries prepared. Results: Pericyte-specific Rbpj deletion induces severe changes in the neurovascular unit characterized by defects in vascular morphogenesis, brain hemorrhaging, altered extracellular matrix composition and strong inflammatory responses. Analysis of pericytes translatome of Rbpj-KO mice compared to controls revealed profound changes in pericyte identity, increased expression of vascular smooth muscle cell markers and increased signaling through TGFbeta, among other alterations in mural cell behavior. Brain cortices from 3 mice per group were collected and homogenized. RNA associated to HA-tagged polyribosomes (RiboTag) was purified and used for sequencing library preparation. Mice at postnatal day (P) 7 and P10 were used from the following groups: Control (PdgfrbCreERT2 +/T; Rpl22-HA p/p) vs. Rbpj-KO (PdgfrbCreERT2 +/T; Rpl22-HA p/p; Rbpj-lox p/p).