Transcriptional evidence for NMDAR involvement in matrix remodeling and a model of the NMDAR role in PPF. (A) Heat map highlighting differential expression of transcripts for selected ECM and matrix remodeling genes in Pf4-Grin1^−/− MKs compared with WT MKs. Microarray data are shown after z score transformation. (B) Scatterplot showing relative transcript levels of selected matrix remodeling genes detected using Clariom S Pico microarray and by quantitative RT-PCR (RT-qPCR) in Pf4-Grin1^−/− MKs calculated relative to WT MKs (mean ± SEM). Six independent experiments were performed, with a total of 6 biologic replicates per group. Microarray and quantitative PCR data were analyzed using a 2-tailed Student t test; the statistical evidence for each gene was then combined using the Stouffer method for meta-analysis. (C) Hypothetic model of glutamate-NMDAR role in PPF. In maturing MKs, glutamate acting through NMDAR enhances ADP effects on migration and adhesion and supports expression of ECM elements (eg, collagen and fibronectin) and ECM remodeling enzymes (eg, LOX and MMPs). Integrins and mechanosensitive channels (ColR, TRPV4, and Piezo1) detect permissive ECM (eg, type 4 collagen and softer matrices) and induce PPF (Ci). (Cii-iii) Glutamate provides additional localizing signals to guide podosomes and proplatelets inside BM sinusoids along the glutamate gradient. Possible sources of glutamate in the vascular niche include perisinusoidal pericytes and platelet extracellular vesicles (EVs). Col1 a1 and a2, collagen type 1 a1 and a2; ColR, collagen receptors; Cthrc1, collagen triple helix repeat containing 1; Dcn, decorin; EC, endothelial cell; Fn1, fibronectin 1; LOX, lysyl oxidase; P, pericyte; Sparc, secreted protein acidic and cysteine rich; Tgfbi, transforming growth factor β induced.