Gordon's Hypertension

Question 1

What is the BP cutoff for hypertension?

Answer 1

120/80mmHg or below = ideal
140/90mmHg = stage 1/hypertension
160/100mmHg = stage 2/severe hypertension

Question 2

What are the shared diagnostic features of hypoaldosteronism and Gordon’s hypertensions syndrome?

Answer 2

Hypertension
Hyperkalemia
Hyperchloremia
Metabolic acidosis

Question 3

What is the function of aldosterone?

Answer 3

Upregulation of Na+/K+ antiporter on the basolateral membrane of principal cells in the DCT. Increases sodium reabsorption and potassium excretion

Question 4

What are the other main diagnostic features of Gordon’s Hypertension Syndrome?

Answer 4

Low renin
Normal renal function/GFR
High sensitivity to treatment with thiazide diuretics

Question 5

How is chloride ion homeostasis maintained?

Answer 5

KCC channels responsible for chloride ion efflux
NKCC channels responsible for chloride ion influx. This includes the NCC Na+/Cl- cotransporter in the DCT, and the NKCC1/2 Na+/K+/2Cl- cotransporters in the ascending loop of Henle

Question 6

What is the function of a kinase?

Answer 6

Transfers a phosphate from ATP to a protein, forming a phospho-protein that has different activity

Question 7

How are WNK1/4 kinases activated?

Answer 7

By hyperosmotic or hypertonic stress, caused by low intracellular levels of chloride ions

Question 8

What is the target of WNK1/4 and how does it recognise its target?

Answer 8

Recognises SPAK/OSR1 by the conserved CCT domains

Phosphorylation of SPAK/OSR1 on the T loop

Question 9

What is the function of SPAK/OSR1 when activated?

Answer 9

SPAK/OSR1 binds to/recognises the NCC and NKCC2 channels using its CCT domain
It phosphorylates
- the Thr60 residue on the N terminus of the NCC channel
- the NKCC2 channel
Leads to increased activity
Greater Na+/Cl-/K+ absorption
Raised BP

Question 10

How is the activity of WNK1/4 regulated?

Answer 10

The CUL3-KLHL3 E3 ligase complex ubiquitinates it to mark for proteasomal degradation

Question 11

Describe the process of ubiquitination

Answer 11

1. Activation of ubiquitin by E1 (ATP-dependent)
2. Transfer of ubiquitin from E1 to the active site of E2
3. E2 recruits E3 and the target protein
4. E3 catalyses ligation of ubiquitin onto the target protein

Question 12

What are the components of the CUL3-KLHL3 E3 ligase complex?

Answer 12

Cullin 3 - scaffold protein, joined to KLHL3 and Rbx
Kelch-like 3 - (contains BTB domain that interacts with N terminus of CUL3, and is responsible for recruiting WNK1/4)
E3 ubiquitin ligase, E1 and E2
Rbx (ring box protein 1) - recruits E2

Question 13

What are the possible mutations that can lead to Gordon’s Hypertension Syndrome?

Answer 13

WNK1 - cannot be ubiquitinated
WNK4 - missense mutation in C terminal non-catalytic domain where KLHL3 would bind, so cannot be ubiquitinated
The BTB domain of KLHL3 - cannot interact with CUL3
CUL3 - cannot ubiquitinate WNK

All lead to gain of function in WNK1/4

Question 14

Which mutations cause the most severe hypertension phenotype?

Answer 14

KLHL3 or CUL3 - as they regulated both WNKs. If one of the WNK proteins is mutated the other is usually unaffected

Question 15

What is the mechanism of Gitelman’s Syndrome?

Answer 15

Loss of function in the NCC Na+/Cl- cotransporter
Not enough reabsorption of sodium and chloride
Low BP

Question 16

What are the current therapeutic options for Gordon’s Hypertension?

Answer 16

Thiazide Diuretics
Loops diuretics
Low sodium and potassium diet

Question 17

How do thiazide diuretics work and what are the side effects?

Answer 17

Antagonists of the NCC cotransporter
E.g. chlorothiazide

Leads to increased potassium excretion in collecting duct (hypokalemia)
Increased excretion of hydrogen ions (metabolic alkalosis)
Hypercalcaemia

Question 18

How do loop diuretics work and what are the side effects?

Answer 18

Inhibitor of the NKCC2 cotransporter
E.g. Furosemide
Prevents formation of concentration gradient in the medulla, so less reabsorption of water in the collecting duct

Can also cause hypokalemia

Question 19

What are the possible future treatments for Gordon’s Hypertension and what are the benefits?

Answer 19

SPAK inhibitors
Prevents phosphorylation of the NCC and NKCC2

Affects all channels rather than just one
Would not cause hypokalemia

Question 20

Why is chloride ion homeostasis important?

Answer 20

Determines the strength of GABAergic neurotransmission

Question 21

Structure of KLHL3 and function of each part

Answer 21

BTB domain - binds CUL3

Question 22

Structure of WNK1/4 and function of each part

Answer 22

Non catalytic domain towards C terminus - where KLHL3 binds
N terminal catalytic domain - phosphorylates SPAK/OSR1
Coiled coil domain (CCD) - recognises/binds SPAK/OSR1

Question 23

Structure of SPAK/OSR1 and function of each part

Answer 23

T loop kinase domain - where WNK1/4 phosphorylates AND what SPAK/OSR1 uses to phosphorylate NCC and NKCC2
CCT domain - where WNK1/4 binds AND what SPAK/OSR1 uses to bind NCC and NKCC2

Question 24

How does hypoaldosteronism lead to

1. Hyperkalemia
2. Hyperchloremia
3. Metabolic acidosis

Answer 24

1. Reduced Na+/K+ ATPase activity means reduced K+ excretion
2. Increased chloride reabsorption in the collecting duct
3. Increased chloride reabsorption leads to hyperchloremic acidosis

Question 25

How does Gordon’s hypertensions syndrome lead to

1. Hyperkalemia
2. Hyperchloremia
3. Metabolic acidosis

Answer 25

1. Increased K+ reabsorption by NKCC
2. Increased Cl- NCC and NKCC
3. Reduced H+ excretion