Metformin inhibits hepatic gluconeogenesis through AMP-activated protein kinase-dependent regulation of the orphan nuclear receptor SHP.
OBJECTIVE
Metformin is an antidiabetic drug commonly used to treat type 2 diabetes. The aim of the study was to determine whether metformin regulates hepatic gluconeogenesis through the orphan nuclear receptor small heterodimer partner (SHP; NR0B2).


METHODS
We assessed the regulation of hepatic SHP gene expression by Northern blot analysis with metformin and adenovirus containing a constitutive active form of AMP-activated protein kinase (AMPK) (Ad-AMPK) and evaluated SHP, PEPCK, and G6Pase promoter activities via transient transfection assays in hepatocytes. Knockdown of SHP using siRNA SHP was conducted to characterize the metformin-induced inhibition of hepatic gluconeogenic gene expression in hepatocytes, and metformin-and adenovirus SHP (Ad-SHP)-mediated hepatic glucose production was measured in B6-Lep(ob/ob) mice.


RESULTS
Hepatic SHP gene expression was induced by metformin, 5-aminoimidazole-4-carboxamide-1-beta-d-ribofuranoside (AICAR), and Ad-AMPK. Metformin-induced SHP gene expression was abolished by adenovirus containing the dominant negative form of AMPK (Ad-DN-AMPK), as well as by compound C. Metformin inhibited hepatocyte nuclear factor-4alpha-or FoxA2-mediated promoter activity of PEPCK and G6Pase, and the inhibition was blocked with siRNA SHP. Additionally, SHP knockdown by adenovirus containing siRNA SHP inhibited metformin-mediated repression of cAMP/dexamethasone-induced hepatic gluconeogenic gene expression. Furthermore, oral administration of metformin increased SHP mRNA levels in B6-Lep(ob/ob) mice. Overexpression of SHP by Ad-SHP decreased blood glucose levels and hepatic gluconeogenic gene expression in B6-Lep(ob/ob) mice.


CONCLUSIONS
We have concluded that metformin inhibits hepatic gluconeogenesis through AMPK-dependent regulation of SHP.
Kim
Yong Deuk
YD
Hormone Research Center, School of Biological Sciences & Technology, Chonnam National University, Gwangju, 500-757, Republic of Korea.
Park
Keun-Gyu
KG
Lee
Yong-Soo
YS
Park
Yun-Yong
YY
Kim
Don-Kyu
DK
Nedumaran
Balachandar
B
Jang
Won Gu
WG
Cho
Won-Jea
WJ
Ha
Joohun
J
Lee
In-Kyu
IK
Lee
Chul-Ho
CH
Choi
Hueng-Sik
HS
D055372:AMP-Activated Protein Kinases; D000818:Animals; D006528:Carcinoma, Hepatocellular; D045744:Cell Line, Tumor; D005943:Gluconeogenesis / Q000187:drug effects*; D022781:Hepatocytes / Q000502:physiology*; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008113:Liver Neoplasms; D008297:Male; D008687:Metformin / Q000494:pharmacology*; D009097:Multienzyme Complexes / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics*; D014162:Transfection
D007004:Hypoglycemic Agents; D009097:Multienzyme Complexes; D034741:RNA, Small Interfering; D018160:Receptors, Cytoplasmic and Nuclear; C099713:nuclear receptor subfamily 0, group B, member 2; D008687:Metformin; D017346:Protein Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases