Nischarin inhibition alters energy metabolism by activating AMP-activated protein kinase

Abstract

Nischarin (Nisch) is a key protein functioning as a molecular scaffold and thereby hosting interactions with several protein partners. To explore the physiological importance of Nisch, here we generated Nisch loss-of-function mutant mice and analyzed their metabolic phenotype. Nisch-mutant embryos exhibited delayed development, characterized by small size and attenuated weight gain. We uncovered the reason for this phenotype by showing that Nisch binds to and inhibits the activity of AMP-activated protein kinase (AMPK), which regulates energy homeostasis by suppressing anabolic and activating catabolic processes. The Nisch mutations enhanced AMPK activation and inhibited mechanistic target of rapamycin signaling in mouse embryonic fibroblasts as well as in muscle and liver tissues of mutant mice. Nisch-mutant mice also exhibited increased rates of glucose oxidation with increased energy expenditure, despite reduced overall food intake. Moreover, the Nisch-mutant mice had reduced expression of liver markers of gluconeogenesis associated with increased glucose tolerance. As a result, these mice displayed decreased growth and body weight. Taken together, our results indicate that Nisch is an important AMPK inhibitor and a critical regulator of energy homeostasis, including lipid and glucose metabolism.

Knockout model reveals the role of Nischarin in mammary gland development, breast tumorigenesis and response to metformin treatment

“…41 Previously, we have shown that Nischarin interacts with AMPK and affects AMPK functions in mouse embryonic fibroblasts (MEFs), where we showed that deletion of Nischarin in MEFs enhances AMPK phosphorylation. 18 These data seemingly are contradictory with the current data. Although we do not know the exact reason for these differences, we suspect that acquiring cancer phenotype due to the presence of PyMT gene somehow underlies these changes.…”

“…44 Furthermore, IQGAP1 has been shown to promote carcinogenesis 42 and thus suggested to be a rheostat at the interface of cancer and diabetes. Our published data indicate that Nischarin mutation enhances AMPK activation in mouse embryonic fibroblasts to regulate energy homeostasis, 18 while the current study shows the activation is low in Nischarin mutant PyMT tumors to regulate tumor growth. Hence, Nischarin may likely function as a rheostat for balancing AMPK activation in energy homeostasis of embryonic fibroblasts and tumorigenesis of cancer cells.…”

“…All procedures were approved by the Institutional Animal Care and Use Committee of the LSU Health Science Center at New Orleans. We crossed female Nischarin heterozygous (leucine-rich-repeat [LRR] deleted) mice 18…”

“…Oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) in WT, Het and null PyMT primary tumor cells were measured at 37 C using the Seahorse 24XF instrument (Seahorse Biosciences, North Billerica, MA) as previously described. 18 Briefly, cells were seeded onto a 24-well tissue culture plate at a density of 40,000 cells per well for 16 hr. Cells were then changed to unbuffered XF assay media at pH 7.4 supplemented with 25 mM glucose and 1 mM sodium pyruvate.…”

“…To assess the role of Nischarin in mammary development and tumorigenesis in vivo, we generated mice with a Nisch allele in which the exons 7-10 (LRR region) were flanked with recombination sites (Nischarin fl/fl ). 18 The phenotype in Nisch mutant mice with respect to cancer has not been reported to date. Nischarin fl/fl mice were crossed with CMV-Cre mice resulting in Nischarin deletion in all tissues.…”