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Table 1 Major components of lipolysis pathways in adipose tissue (AT) of dairy cows

From: Adipose tissue lipolysis and remodeling during the transition period of dairy cows

Protein(s)

Encoding gene(s)

Activation stimulus

Function(s)

Transition period dynamics

Catecholamines (adrenaline and noradrenaline)

 

Metabolic stress [125]

- Bind to βAR on the adipocyte cell surface and initiate the lipolytic cascade [33]

- Plasma adrenaline and noradrenaline:

- Increase during the dry period and immediately before calving

- Decrease slightly after calving until 60 d in lactation [62]

Adipocyte β-adrenergic receptors (βAR), types: β1R, β2R, and β3R.

B1AR

B2AR

B3AR

Catecholamine binding

- Activate adenylyl cyclases that convert ATP to cAMP, and induce PKA activation that, in turn, phosphorylates PLIN1 initiating the lipolytic cascade

- βAR are increased in abdominal adipose and during increased rate of lipolysis [33]

- βAR increase during first month after parturition and are positively associated with milk production [27]

- B2AR decreases immediately after parturition and increases after peak lactation [27]

Perilipin-1

PLIN1

PKA

- Protects the lipid droplet from hydrolytic activity of HSL

- Decreases during first 3 wks following parturition compared to other periods of the lactation cycle [21]

α/β hydrolase domain-containing protein 5 (ABHD5/CGI-58)

ABHD5

Phosphorylation of PLIN1

- Increases the activity of ATGL and provides increased DAG substrate for PKA-activated HSL

- Decreased gene expression after calving

- Protein abundance remains unchanged through the transition period [21]

Adipose tissue triglyceride lipase (ATGL)

PNPLA2

ABHD5/CGI-58

- Hydrolysis of TAG c

- Decreased gene expression during the last week of gestation and first week of lactation compared to the dry period and mid lactation

- Lower protein abundance around parturition compared to the dry period [21, 22]

Hormone sensitive lipase (HSL)

LIPE

Activation of PKA

- Hydrolyzes DAG b, releasing free fatty acid and MAG a

- Activity varies depending on anatomical location of AT

- Decreased gene expression during the first 3 wks following parturition compared to the dry period [23]

- Protein content unchanged through the transition period [21, 123]

Fatty acid-binding protein (aP2/FABP4)

FABP4

Association with HSL

- Transports fatty acids to the plasma membrane

- Increased gene expression during induced milk fat depression [126]

Monoglyceride lipase (MGL)

MGll

DAG b hydrolysis by HSL

- Hydrolyzes MAG a, releasing glycerol

- Decreased gene expression during the first 3 wks of lactation [27]

- Protein content currently unknown in cattle

  1. a MAG: Monoglycerol
  2. b DAG: Diglycerol
  3. c TAG: Triglycerol