Mechanisms of regulation of the

hemostatic system

• Platelet functioning (adhesion, activation, aggregation) – cell hemostasis• Blood clotting – plasma hemostasis• Blood flow – carrier

Alexey Tokarev, PhD

Federal Research and Clinical Centre of Pediatric Hematology, Oncology and Immunology, National Research Center for Hematology

(Ministry of Health and Social Development of Russian Federation, Moscow)

Hemostatic plug (health) and thrombus (disease) formation

1/3

Platelet cross-flow distribution

Tokarev et al., Biophys. J., 2011b

wal

l wall

• Eulerian (PDEs)Modeling approach:

Tokarev et al. 2012. Rus. J Num. Anal. Math. Model.

• Lagrangian (particles)

Tosenberger et al. 2012. Rus. J Num. Anal. Math. Model.

Platelet adhesion

Tokarev et al., Biophys. J., 2011a

Plasma clotting

Fibrin mesh. SEM made by Jean-Claude Bordet (France).

Blood flow

Plug/ thrombus growth

Falati et al (2002)

plateletsplatelets+fibrin

fibrin

• Platelet activation, secretion, aggregation

Ohlmann (2000)

Some general questions:1.Biological: how plug/thrombus growth stops? Can this stopping result from the interaction between platelet and plasma subsystems?2.Methodological: How to mathematically model this complex system in a biology-adequate way? How to deal with platelet activation/signalling? How to connect intra-platelet signalling (detailed model of platelet activation) and changes in platelet properties (simple model of platelet activation)? 2/3

Some general questions:1.What is the mechanism of clotting propagation and stopping?2.How can we properly reduce the dimension of the large system of coupled PDEs (~30 eqs. down to 2-3 eqs.)?

Plasma clotting in non-stirring and slow-flow conditions

Reaction-diffusion PDEs (no flow) Reaction-diffusion-convection PDEs

Slow flow Boundary of fibrin clot (flow-resistant)

Injury

Dashkevich et al. Thrombin propagates in space during blood coagulation as a traveling wave: a new biological excitable medium. Submitted to PNAS.

0,001 2 3 40

50

100 Experiment Theory

Thr

ombi

n ac

tivity

, nM

Distance from the activator, mm

Thrombin concentration wave

3/3

Additional slides

Strong non-uniform platelet distribution across blood flow generally arises due to the finiteness of platelet own size

Tokarev et al., Biophys. J., 2011, 101 (8): 1835-1843.

Platelet

Erythrocyte

Excluded volume

wal

l wall

0,0 0,2 0,4 0,6

01

5

10

15

20 A

<P

>w

all t

o <

P>

axis r

atio

Inflow hematocrit/100%, 0

0,0 0,2 0,4 0,6

01

5

10

15

20 B

Pw

all t

o P

axis r

atio

Inflow hematocrit/100%, 0

Platelet adhesion from blood flow is controlled by near-wall rebounding collisions with erythrocytes

Tokarev et al., Biophys. J., 2011, 100 (4): 799-808.

Convection +

shear-induced

diffusion

Translocation/activation Detachment

Firm adhesion

Pushing out by RBC

Capture

Platelet activation time = const

Platelet activation - pathways

CRPconvulxine

collagen

vW f

G PVI

G PIb

FcR- Syc PLC-2

DAGIP 3

PLC-

PKC

Integrins1st affinity state

(adhesion)

ADPP2Y 1 P2Y 12

G q

G i2

AC

cAM P

PKA

G P1b-vW fTP

PI3K-

Ca2+

âî ëí à

Ca2+

-âî ëí à

Integrins2nd affinity state

(aggregation)

PAR 1

PAR 4

G 12/13

TP

IIa

T xA2

Shape Change

PG H 2

AA

PLA 2

ERK2M APk

p38M APk

Src

Src

100nM

10nM

Rho

Ca2+

50pM / 2s

5nM / 50s

TxS

COX-1

m em brane

???

PLC-

0.3uM 2uM

IP3

DAG

dencetubular system

Ca2+

(áåç Rap1b?)

AA

Âòî ê Ca2+

MEK

CalDAG-GEF1Ca2+

RAP1-GTP

Gz

2A

epinephrine

130/pl

1500/pl

PK

C

RhoA

???Akt/PKB

Gs

PGI2

Src

???

Raf

PI(3,4)P2?

PLC

PI3

K(I

I)?

PI3K-a)PI(3,4,5)P3 ?

PKCCa2+ RIAM

Talin

?

5-HT5-HT2AR

a-granules

Rab4-GTP

vWf,P-selectin

dense granules

TG

| |

RhoA-GTP

SERT

GEF

???- òî ëüêî ÷åðåç ADP?

Platelet activation – phenomenological behaviour

P 0 P 1 P 2

P flow

G PIb/v W f

P2Y 1

PAR 1

stress

TP

PAR 1*P2Y 12

PAR 4*(1+P2Y 12)

ADP

IIa

T xA 2

15 m in

stress

0.3uM2uM

50pM / 2s 5nM / 50s

-gr

collagen

PAR 4

FVa

PAR 1

PLA 2

Ca2+ext

?

P2+P2S0

P 2S 0

P S

PAR1*PAR4**(1+P2Y12)

P2Y 12