BISC 675Cardiovascular Physiology

Platelets 2

Ulhas P. Naik, Ph.D

Professor and Director

Delaware Cardiovascular Research Center

Overview

• Inside-out signaling- agonist-induced integrin activation

• Outside-in signaling- signaling initiated by binding of fibrinogen to activated integrin

• Clot retraction- mechano-signal transduction

Intracellular Calcium

GPVI (Collagen Receptor) Signaling

Gq

PLC

Ca 2+

Gi

P2Y12

-Adenylyl cyclase

cAMP

ADP

Shape Change

PI3K

Akt Rap1b

Fibrinogen Receptor Activation, Platelet Aggregation, Secretion and Thromboxane Generation

? ?Indirect role

Rho Kinase activation

PKC

Src tyrosinekinase

AR-C69931MX MRS2179

Erk1/2

? RhoA

p160ROCK

P2Y1, PAR1/4TP

TRAP, TXA2

G12/13

YM254890

Thrombin Signaling

Platelet Secretion

Integrin Inside-out Signaling

Integrin Outside-in Signaling

Events Leading to Platelet Aggregation

Platelet Aggregate Stabilization

Calcium- and Integrin-binding Protein 1

CIB1 in Platelet Spreading

Discoid Spiky Partially spread Spread

CIB1 is Needed for Lamellipodia Formation

-DMSO

Anti-CIB1cIgG

+DMSO

CIB1 Deletion Affects Platelet Spreading on Immobilized Fibrinogen

Ablation of CIB1 Results in Delayed Clot Retraction

JAM-A and Platelet Activation

• JAM-A was originally identified as a receptor for a stimulatory monoclonal antibody, mAb F11 (Naik et al., J. Biochem, 1995)

• JAM-A gene was cloned and shown to localize on chromosome 1 (Naik, et al., J. Cell Sci 2001)

• JAM-A associates with integrin v3 in quiescent endothelial cells (Naik, et al., Blood 2003)

• Mutation of tyrosine 280 to phenylalanine affects JAM-A function (Naik and Naik, J.Cell Sci. 2006)

Ablation of JAM-A Results in Faster Clot Retraction

JAM-A movie

Platelet Storage

• They age rapidly outside the body

• Platelets are easily activated

• Cold temperature also activate platelets

• Needs to be stored at 20-24oC with rocking

• Platelets should be used for transfusion within 3-4 days of isolation

Anti-Platelet Drugs

Aspirin

Aspirin inhibits both COX-1 and COX-2

Inhibition is 170 fold greater for COX1

Platelet express COX1 more than COX2

Anti-ADP Receptors

IIb3 Antagonists

Anti-platelet Therapy

Controlling Cardiovascular Disease Through Platelets