Hexose-6-phosphate Dehydrogenase Knock-out Mice Lack 11β-Hydroxysteroid Dehydrogenase Type 1-mediated Glucocorticoid Generation

Abstract

The local generation of active glucocorticoid by NADPHdependent, 11␤-hydroxysteroid dehydrogenase type 1 (11␤-HSD1) oxoreductase activity, has emerged as an important factor in regulating hepatic glucose output and visceral adiposity. We have proposed that this NADPH is generated within the endoplasmic reticulum by the enzyme hexose-6-phosphate dehydrogenase. To address this hypothesis, we generated mice with a targeted inactivation of the H6PD gene. These mice were unable to convert 11-dehydrocorticosterone (11-DHC) to corticosterone but demonstrated increased corticosterone to 11-DHC conversion consistent with lack of 11␤-HSD1 oxoreductase and a concomitant increase in dehydrogenase activity. This increased corticosterone clearance in the knock-out mice resulted in a reduction in circulating corticosterone levels. Our studies define the critical requirement of hexose-6-phosphate dehydrogenase for 11␤-HSD1 oxoreductase activity and add a new dimension to the investigation of 11␤-HSD1 as a therapeutic target in patients with the metabolic syndrome.Corticosteroid hormone action is modulated in a tissue-specific fashion by the expression and activity of two isozymes of 11␤-hydroxysteroid dehydrogenase (11␤-HSD) 3 that interconvert hormonally active cortisol (or corticosterone in rodents) to their inactive derivatives, cortisone/11-dehydrocorticosterone (11-DHC) (1). 11␤-HSD2 acts as a NAD-dependent dehydrogenase, inactivating glucocorticoids and protecting the mineralocorticoid receptor from illegitimate activation by cortisol in mineralocorticoid receptor-rich tissues such as the kidney and colon (2).By contrast, 11␤-HSD1 is a bidirectional enzyme expressed in liver and adipose tissue. It catalyzes both oxidation and oxoreduction of glucocorticoids but acts in vivo predominantly as a NADPH-dependent oxoreductase (1). Independent of circulating glucocorticoid concentrations, the local generation of cortisol/corticosterone by 11␤-HSD1 has emerged as an important factor in regulating hepatic glucose output (by augmenting gluconeogenesis) and visceral adiposity (by increasing adipocyte differentiation). Transgenic mice overexpressing 11␤-HSD1 in liver and adipose tissue recapitulate features of the metabolic syndrome with visceral obesity, hepatic steatosis, glucose intolerance, insulin resistance, hyperlipidemia, and hypertension (3-5). In contrast, knockout (KO) mice lacking 11␤-HSD1 show improved glucose tolerance, enhanced insulin sensitivity, and reduced weight gain when fed a high fat diet (6, 7).11␤-HSD1 has therefore emerged as a novel therapeutic target to treat patients with obesity and insulin resistance. Indeed, selective 11␤-HSD1 inhibitors improve glucose tolerance in diabetic mice (8 -10).These in vivo findings are dependent upon the oxoreductase activity of 11␤-HSD1, which is puzzling because activity studies performed on the purified 11␤-HSD1 enzyme or on cell/tissue homogenates indicate almost exclusive unidirectional dehydrogenase activity (11). We hypothesized that the enzyme hexose-6-phosphate de...

Obesity and corticosteroids: 11β-Hydroxysteroid type 1 as a cause and therapeutic target in metabolic disease

“…11 -HSD1 is widely expressed in many tissues (Ricketts et al, 1998) most highly in liver (Tannin et al, 1991) and at lower levels in adipose tissue (Bujalska, et al, 1997, Rask et al, 2001 and in other organs and cells with high GR expression (Whorwood et al, 1991). The activation potential of 11 -HSD1 is dependent on the provision of NADPH co-factor by the co-localised enzyme hexose-6-phosphate dehydrogenase (H6PDH) (Atanasov et al, 2004, Lavery et al, 2006, in the absence of which 11 -HSD1 acts as a dehydrogenase, inactivating cortisol.…”

MicroRNA‐661 modulates redox and metabolic homeostasis in colon cancer

“…In addition, PKM2 translocation into the nucleus has been described, where it functions as a histone kinase upregulating the expression of c‐Myc and cyclin D1, thereby promoting the Warburg effect and cell cycle progression, respectively (Yang and Lu, 2013). Hexose‐6‐phosphate dehydrogenase (H6PDH), similar to glucose‐6‐phosphate dehydrogenase (G6PD), is important for NADPH production and for the global redox homeostasis (Lavery et al ., 2006). H6PDH is specifically responsible for NADPH generation at the endoplasmic reticulum (ER) lumen, which is also essential for the proper function of ER (Szaraz et al ., 2010).…”

“…In addition, PKM2 translocation into the nucleus leads to the upregulation of c‐Myc and cyclin D1, promoting the Warburg effect and cell cycle progression, respectively. Regardless of H6PD, this is crucial for NADPH production and for the global redox homeostasis (Lavery et al ., 2006; Szaraz et al ., 2010). It has been reported that H6PD knockdown induces autophagy as a survival mechanism up to a threshold of oxidative injury, after which cells undergo apoptosis (Kapuy and Banhegyi, 2013).…”

The role and regulation of 11β-hydroxysteroid dehydrogenase type 1 in the inflammatory response

“…They show increased insulin sensitivity and are protected against metabolic disease (Morton et al, 2001;Morton et al, 2004), show increased angiogenesis following injury (Small et al, 2005) and resist cognitive decline in old age (Yau et al, 2007;Yau et al, 2001). More recently, mice have also been generated which are deficient in hexose-6-phosphate dehydrogenase, the "partner" enzyme to 11β-HSD1 that dictates its enzyme direction through cofactor supply within the endoplasmic reticulum lumen (Lavery et al, 2006). In H6pd -/-mice, the normal reaction direction of 11β-HSD1 is reversed so that it functions exclusively as a dehydrogenase, inactivating glucocorticoids (Lavery et al, 2006).…”

“…More recently, mice have also been generated which are deficient in hexose-6-phosphate dehydrogenase, the "partner" enzyme to 11β-HSD1 that dictates its enzyme direction through cofactor supply within the endoplasmic reticulum lumen (Lavery et al, 2006). In H6pd -/-mice, the normal reaction direction of 11β-HSD1 is reversed so that it functions exclusively as a dehydrogenase, inactivating glucocorticoids (Lavery et al, 2006). Their phenotype is similar to that of Hsd11b1 -/-mice in that they also show increased insulin sensitivity and alterations in glucose and lipid homeostasis .…”