C3 Role of leptin in cardiorenal function

Question 1

Different leptin receptors (ObR)

Answer 1

• 6 different isoforms (a-f)
• Generated by alternative splicing
• ObRb most abundant

Question 2

Binding of leptin to ObR

Answer 2

• Creates conformational changes
• Mech of JAK/STAT
  
  • Activates JAK/STAT pathway (phosphorylates JAK2)
  • STAT3 dimerises → translocate to nuclues → alters gene transcription

Question 3

What are the downstream factors of leptin binding to ObR

Answer 3

• JAK/STAT
• MAPK
• PI3K (not via ObR activation)
  
  • All responsible for cell growth, proliferation, differentiation

Question 4

What is a CHOW diet?

Answer 4

• CHOW diet = standard diet (5% fat)

Question 5

What are obob and dbdb mice?

Answer 5

• Ob/ob → mice lacking leptin protein
• Db/db → mice lacking leptin receptor

Question 6

Leptin signalling on BP

Answer 6

• When restored leptin concentrations in Ob/ob and db/db → ↑ in HR/SBP&DBP
  
  • ∴ can turn off leptin signalling → to avoid hypertension associated with obesity

Question 7

Leptin antibodies targeting leptin in the brain

Answer 7

• Leptin antibodies → turn off leptin cell signaling → able to restore BP back to normal

Question 8

Features of kidney filtering

Answer 8

• Reabs, excrete waste, regulates BP
• Filters proteins (<70kD), including albumin at glomerulus
  
  • 0.06%-4% of albumin filter, 96% reabs
  • Podocytes determine what is filtered
    
    • If damaged → alters gaps in b/w podocytes → change what is in filtrate & urine

Question 9

Megalin

Answer 9

• Scavenger R in PCT, a signal transducer
• Binds to many different ligands
  
  • Brings cell inside for degradation or transcytosis (transport to another cell membrane)
• Able to be cleaved → acts as signalling molecule for gene regulation

Question 10

Megalin endocytosis/transcytosis

Answer 10

• Megalin binds to albumin
• Endocytose → degradation pathway
• Or transcytosis of albumin into the blood
• Determines how much protein is being degraded

Question 11

Obesity and Leptin

Answer 11

• x5 [leptin]
• leptin goes into filtrate in glomerulus, but all taken up by megalin → none found in urine

Question 12

Leptin altering glomerulus

Answer 12

• ↑TGF-B1 → ↑collagen (indicates fibrosis damage)
• Also causes hypertrophy

Question 13

Leptin on OK cell line (in PCT)

Answer 13

• Opossum kidney cells (a proximal tubule cell) lack ObR
• ↑Leptin in PCT causes
  
  • ↑ERK1/2
  • ↑AMPK
  • ↑mTOR
  • Does not activate JAK/STAT (as there are no ObR)

Question 14

AMPK

Answer 14

• Regulates cell energy homeostasis
• Adipokines can activate AMPK → ↓inflammation
• In obesity (&diabetes) → ↓AMPK → ↑inflammation

Question 15

Fibrotic pathway of leptin

Answer 15

• Leptin → ↑AMPK → ↑TGF-B1 (also directed ↑ by leptin):
  
  • Inhibits megalin → Albumin endocytosis & degradation
  • ↑activation of local cells → ↑fibrotic damage (from collagen) to PTC

Question 16

Difference of in vitro and in vivo

Answer 16

• In vitro high leptin has opposite effect to in vivo obese rats (also have high leptin)
  
  • But both conditions have elevated leptin from reduced albumin handling