Lecture 20: What are ? How can blood clotting be beneficial?

• Hemostasis: Functions & Goals • Megakaryocytes  platelets • Homeostasis with TPO • Platelet Plug Formation • Positive Feedback • Chemical signals • Clot Formation • Role of platelets & calcium ions • Role of positive feedback • Clotting factors & enzyme cascade • • • Anti-coagulants • Clot Retraction (Tightening) • Fibrinolysis (clot removal) with plasmin & tPA

http://www.uphs.upenn.edu/news/news_releases/200 9/08/fibrin-blood-clot-structure/

10/27/2016 Dr. Casey Self, Biol. 118, Autumn 2016 1 Clotting = Hemostasis: Is this a homeostatic process?

What type of feedback loops are involved?

Goals:

• Close off damaged vessels • Keep blood in a fluid state • Remove clot after restoration of blood vessel

http://www.mhhe.com/biosci/esp/2002_general/Esp/folde r_structure/tr/m1/s7/trm1s7_3.htm - clot animation

10/27/2016 https://online.science.psu.edu/biol141_wc/node/7576 2 How do we go from bleeding wound to stabilized clot?

Collagen exposure Endothelial cell damage

Platelets bind Tissue factor

Platelet factor Ca2+

More platelets aggregate Factor X

There are 13 factors! Prothrombin → Thrombin Where are they made? Where are they found?

10/27/2016 Fibrinogen → Fibrin 3 Where do platelets form? What regulates their production?

Platelet = Thrombocyte

Red Bone Marrow Platelet lives ~9-12 days Why do megakaryocytes develop large rough ER, prior to platelet budding?

Hemocytoblast Megakaryoblast Megakaryocyte Platelets How is platelet production regulated? How does this compare to RBC regulation? Thrombopoeitin = TPO

No negative feedback on X TPO production

Megakaryocytes and X platelets metabolize TPO

10/27/2016 5 There are a lot of clotting factors and platelets have A LOT of receptors. There are many opportunities for regulation.

10/27/2016 6 What do platelets do when they contact a damaged blood vessel wall? Is a platelet plug enough?

Why use positive feedback?

vWF =

http://clinicalgate.com/von-willebrand-disease-and-other-inherited-coagulation http://droualb.faculty.mjc.edu/Course%20Materials/Physiology%20101/Chapte 10/27/2016 r%20Notes/Fall%202011/chapter_15%20Fall%202011.htm 7 Know the events leading to fibrin clot formation (the common pathway). What is calcium’s (Ca2+) role in blood clotting?

Where are these clotting factors produced? What causes hemophilias?

Clot Retraction http://www.youtube.com/watch?v=sZakNWRgw64 10/27/2016 http://droualb.faculty.mjc.edu/Course%20Materials/Physiology%20101/Chapter%20Notes/Fall%202011/chapter_15%20Fall%202011.htm 8 Some anti-coagulant drugs target platelets Aspirin: blocks platelet activation Vitamin E: blocks platelet aggregation Some anti-coagulant drugs target factors Warfarin (coumadin):prevents formation of active Vit. K Heparin: inactivates thrombin

Anti-coagulants are called “blood thinners” by lay persons. Do they decrease blood viscosity? Inactive Vit. K Active Vit. K What risks are associated with their use?

What foods are good sources of Vit. E and Vit. K?

10/27/2016 http://www.youtube.com/watch?v=vEmsaXA-go0 9 How does fibrinogen form fibrin threads?

Factor XIII causes covalent bonds to form between molecules.

10/27/2016 Côté, Lord, Pratt, 1998 10 How does the fibrin (clot) stop blood loss? What is the benefit of the retraction (tightening) of fibrin threads?

Low calcium High calcium

10/27/2016 Versteeg, Heemskerk, Levi, & Reitsma, 2013 11 When & how does fibrinolysis (clot breakdown) occur? FDPs = fibrin degradation products; PAI = plasminogen activator inhibitors; tPA = tissue plasminogen activator

10/27/2016 Bhattacharjee & Bhattacharyya, 2014 12 Why are tPA injections administered to some stroke patients?

If administered 3 – 4.5 hours after stroke

Lansberg et al. 2009. Stroke.

10/27/2016 13 Things to know or review: 1. What is hemostasis? What are the goals? What are the benefits of a vascular spasm? Overall, why is this a negative feedback event? What are the 3 major events? 2. Describe the major steps in platelet development (including location, stem cell, role of TPO & function of a megakaryocyte). Where can the hormone TPO be produced? What factors regulate TPO? Describe the platelet’s structure. How long do platelets survive in blood? 3. Describe the role of positive feedback in platelet plug formation. How does a platelet plug form? How do platelets help initiate the enzyme cascade that leads to formation of the clot? Do anti-coagulants decrease blood viscosity? Describe how Vitamin E & aspirin work as anti-coagulants by targeting platelets. What are good dietary sources of Vitamin E? 4. Describe the function of the enzyme cascade leading to clot formation. Why does this lead to an exponential outcome? Know the role of factor X, calcium in conversion of prothrombin to thrombin. What is the benefit of the positive feedback effect of thrombin in factor X activation? What is hemophilia & how does it affect an individual? 5. Where are many of the clotting factors produced, including fibrinogen? Are the clotting factors present in the blood before injury occurs? Describe the role of Vitamin K in clotting factor production. What foods are sources of Vitamin K? What common drug blocks it? 6. Describe the molecule fibrinogen? How is it able to form long polymers with other fibrinogen molecules to create fibrin (the clot)? What are the advantages of fibrin over platelets alone? What is clot retraction & why is it important? 7. What enzyme converts plasminogen into plasmin in a clot? What does plasmin do? When does fibrinolysis occur normally, relative to clot formation? How does tPA work? 10/27/2016 14 Additional Resources

1. Bhattacharjee P & Bhattacharyya D. (2014) Chapter 1. An insight into the abnormal fibrin clots — its pathophysiological roles. In "Fibrinolysis and Thrombolysis", edited by Kolev K, ISBN 978-953-51-1265-5. http://www.intechopen.com/books/fibrinolysis-and-thrombolysis/an-insight-into-the-abnormal-fibrin- clots-its-pathophysiological-roles

2. Côté HCF, Lord ST, Pratt KP. (1998) γ-Chain dysfibrinogenemias: molecular structure-function relationships of naturally occurring mutations in the γ chain of human fibrinogen. Blood 92(7):2195- 2212

3. Kaushansky K. (2005) The molecular mechanisms that control thrombopoiesis. J Clin Invest. 115(12):3339-3347.

4. Martin JF, Kristensen SD, Mathur A, et al. (2012) The causal role of megakaryocyte–platelet hyperactivity in acute coronary syndromes. Nat Rev Cardiol. 9:658-670.

1. Moyer TP, et al. (2009) Warfarin sensitivity genotyping: a review of the literature and summary of patient experience. Mayo Clinic Proceedings 84(12):1079-1094.

2. Versteeg HH, Heemskerk JWM, Levi M, & Reitsma PH. (2013) New fundamentals in hemostasis. Physiological Reviews 93(1):327-358.

3. Wei A, & Jackson SP. (2008) Boosting platelet production. Nature Medicine 14:917-918

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