TAG metabolism Flashcards
old glycerol-phosphate/ kennedy pathway
glycerol-3-phosphate + FA-CoA catalyzed by GPAT–> lysophosphatidate +FA CoA catalyzed by AGPAT –> phosphatidate catalyzed by PAP –> diacylglycerol + FA CoA catalyzed by DGAT –> TAG
diseases involving GPATs
none known currently
how many AGPATs are there, and where are they expressed?
5 AGPATs, expressed in all tissues (AGPAT2 highest in adipose), and all localized to the ER
AGPAT diseases
lack of AGPAT2 gives rise to Berardinelli-Seip syndrome
what is Berardinelli-Seip syndrome?
disease of abnormal fat accumulation; mutations in AGPAT2 gene–>almost no AGPAT activity; occurence: 1 in 10 million (very rare); various ethnic origins;
symptoms of BS syndrome?
TG accumulates in liver and muscle; diabetes, hypertriglyceridemia–> risk factor for heart disease
BS therapy?
restriction of dietary fat; minimize need to store TAG in adipose tissue so it doesn’t go to liver and muscle
stages of liver damage in BS/abnormal fat accumulation in liver?
steatosis (fat deposits= liver enlargement); fibrosis (scar tissue forms)–>cirrhosis (growth of connective tissues destroys liver cells)
fld mouse
fatty liver dystrophy; adipose tissue deficieny, small is size; enlarged pale liver (due to accumulation of TAGs); hypertriglyceridemia (prone to athersclerosis;
what causes fld mouse?
mutation in lipin (lipin=PAP)
lipin mutations in humans?
have been observed; however, no fat dystrophy
however, humans that have mutations in lipin gene–>have excessive accumulation of myoglobin in the circulation–very odd
how was DGAT knocked out in mice?
replacement of specific region of a gene by hom recomb to make a nonfunctional protein–> replace gene with neo (a marker); targeting vector introduced into mouse mebryonic stem cells via electroporation (rare event)–> incorporate–>select cell with KO–>grow on plates
what happens in DGAT1 KO mice?
do not become obese on high fat diet; still synthesize TAGs (to a lesser degree)
how can DGAT KO mice still have TAGs?
there is another DGAT which was inhibited at high Mg conc in the assay–> not present that high in actual mice
DGAT1 is an integral membrane protein in the ER membrane, but mainly found in ER lumen
ya
DGAT2 is also an IM protein in the ER, but mainly found on the cytosolic side
ya
what happens to DGAT2 KO mice?
die within hours of birth
–>DGAT2 maintains the skin permeability barrier–>DGAT2 -/- mice become dehydrated and cannot contain the water
link between DGAT2 and skin barrier function?
lamellar membranes are not ordered–>allows lots of water to pass through; proper lamellar function is based on 3 lipids: cholesterol, linoleic acid, and ceramide
–linoleic acid is the most important in maintaining the integrity of the skin barrier–>TGs need to be incorporated into linoleic acid by DGAT2, but without no incorporation happens–> faulty membrane
DGAT1 knockout experiment in humans
dGAT1 inhibitor given orally, TAG levels in blood measured after a meal, with and without inhibitor–> drug will inhibit TAG absorption
how does DGAT1 inhibitor function?
inhibits TAG reabsorption by inhibiting resynthesis in the small intestine
where is DGAT1 found?
in small instestine and adipose tissue
DGAT1 -/- in humans symptoms
days after birth, children has frequent vomiting, diarrhea, low body weight, loss of protein, dehydration
mutation of DGAT1–> a T turned to a C; having one good copy is sufficient, but being homozygous leads to problems
–> T to C mutation (in intron) causes skipping of exon 8; in frame deletion, 25 amino acids, but the active site is still present–>removing the exon 8 causes its rapid degradation
ya
still possible to reduce DGAT2 activity in mice–>keep one good copy, happy healthy mice
ya
