Multimerin 1 supports platelet function in vivo and binds to specific GPAGPOGPX motifs in fibrillar collagens that enhance platelet adhesion

Abstract

Background Multimerin 1 (human: MMRN1, mouse: Mmrn1) is a homopolymeric, adhesive, platelet and endothelial protein that binds to von Willebrand factor and enhances platelet adhesion to fibrillar collagen ex vivo. Objectives To examine the impact of Mmrn1 deficiency on platelet adhesive function, and the molecular motifs in fibrillar collagen that bind MMRN1 to enhance platelet adhesion. Methods Mmrn1‐deficient mice were generated and assessed for altered platelet adhesive function. Collagen Toolkit peptides, and other triple‐helical collagen peptides, were used to identify multimerin 1 binding motifs and their contribution to platelet adhesion. Results MMRN1 bound to conserved GPAGPOGPX sequences in collagens I, II, and III (including GPAGPOGPI, GPAGPOGPV, and GPAGPOGPQ) that enhanced activated human platelet adhesion to collagen synergistically with other triple‐helical collagen peptides (P < .05). Mmrn1−/− and Mmrn1+/− mice were viable and fertile, with complete and partial platelet Mmrn1 deficiency, respectively. Relative to wild‐type mice, Mmrn1−/− and Mmrn1+/− mice did not have overt bleeding, increased median bleeding times, or increased wound blood loss (P ≥ .07); however, they both showed significantly impaired platelet adhesion and thrombus formation in the ferric chloride injury model (P ≤ .0003). Mmrn1−/− platelets had impaired adhesion to GPAGPOGPX peptides and fibrillar collagen (P ≤ .03) and formed smaller aggregates than wild‐type platelets when captured onto collagen, triple‐helical collagen mimetic peptides, von Willebrand factor, or fibrinogen (P ≤ .008), despite preserved, low shear, and high shear aggregation responses. Conclusions Multimerin 1 supports platelet adhesion and thrombus formation and binds to highly conserved, GPAGPOGPX motifs in fibrillar collagens that synergistically enhance platelet adhesion.

Analysis of the Healthy Platelet Proteome Identifies a New Form of Domain-Specific O-Fucosylation

“…We have discovered that the abundant platelet releasate protein MMRN1 is constitutively O- fucosylated at T216 within its EMI domain. MMRN1 is known to have several functions including binding/release of coagulation factor V, thrombus formation ( 73 ), and interaction with collagen via an N-terminal RGD motif ( 74 ). We show that T216 was stoichiometrically fucosylated within the context of a potentially altered POFUT1 O- fucosylation motif (C 1 -X-X-X-X-T-X) derived from its known modification context in EGF-like domains ( 64 ).…”

Proteomic analysis reveals activation of platelet- and fibrosis-related pathways in hearts of ApoE−/− mice exposed to diesel exhaust particles

“…MMRN1 is a member of the EMILIN/multimerin family and is present in ⍺-granules of resting platelets and secretary granules of endothelial cells 58 , 59 . Following platelet activation, MMRN1 is secreted and binds fibrillar collagen to support platelet adhesion and thrombus formation 60 – 62 . GP5 is an abundant glycoprotein at the platelet surface, and is reported to bind collagen and mediate platelet adhesion and aggregation 63 .…”

Novel prognostic matrisome-related gene signature of head and neck squamous cell carcinoma

“…As a platelet protein, multimerin 1 has shown good predictive value as a biomarker for acute myeloid leukemia (Laszlo et al, 2015). Moreover, Mmrn1defected mice showed significantly impaired platelet adhesion and thrombus formation in a ferric chloride injury model compared to the wild-type (Leatherdale et al, 2021). MMRN1 is implicated in several types of cancers, including non-small cell lung cancer (Valk et al, 2010), thyroid carcinoma (Wang et al, 2018;Yang et al, 2021;Zhang et al, 2019), ovarian cancer (Huang et al, 2012), and cervical cancer (Chokchaichamnankit et al, 2019).…”