Annexin A6 Is Critical to Maintain Glucose Homeostasis and Survival During Liver Regeneration in Mice

Abstract

BaCKgRoUND aND aIMS: Liver regeneration requires the organized and sequential activation of events that lead to restoration of hepatic mass. During this process, other vital liver functions need to be preserved, such as maintenance of blood glucose homeostasis, balancing the degradation of hepatic glycogen stores, and gluconeogenesis (GNG). Under metabolic stress, alanine is the main hepatic gluconeogenic substrate, and its availability is the rate-limiting step in this pathway. Na +-coupled neutral amino acid transporters (SNATs) 2 and 4 are believed to facilitate hepatic alanine uptake. In previous studies, we demonstrated that a member of the Ca 2+-dependent phospholipid binding annexins, Annexin A6 (AnxA6), regulates membrane trafficking along endo-and exocytic pathways. Yet, although AnxA6 is abundantly expressed in the liver, its function in hepatic physiology remains unknown. In this study, we investigated the potential contribution of AnxA6 in liver regeneration. appRoaCH aND ReSUltS: Utilizing AnxA6 knockout mice (AnxA6 −/−), we challenged liver function after partial hepatectomy (PHx), inducing acute proliferative and metabolic stress. Biochemical and immunofluorescent approaches were used to dissect AnxA6 −/− mice liver proliferation and energetic metabolism. Most strikingly, AnxA6 −/− mice exhibited low survival after PHx. This was associated with an irreversible and progressive drop of blood glucose levels. Whereas exogenous glucose administration or restoration of hepatic AnxA6 expression rescued AnxA6 −/− mice survival after PHx, the sustained hypoglycemia in partially hepatectomized AnxA6 −/− mice was the consequence of an impaired alanine-dependent GNG in AnxA6 −/− hepatocytes. Mechanistically, cytoplasmic SNAT4 failed to recycle to the sinusoidal plasma membrane of AnxA6 −/− hepatocytes 48 hours after PHx, impairing alanine uptake and, consequently, glucose production.

Lack of Annexin A6 Exacerbates Liver Dysfunction and Reduces Lifespan of Niemann-Pick Type C Protein–Deficient Mice

“…Initially we analyzed the lifespan of each strain. Similar to previous studies, the lifespan of Anxa6 -/animals was not affected, 31,32 but was reduced for Npc1 -/mice to an average of 69 days 19 compared to controls (> 1 year). However, ANXA6 deficiency further compromised lifespan of Npc1 -/mice, as survival of Npc1 -/-/Anxa6 -/mice was significantly J o u r n a l P r e -p r o o f reduced to an average of 62 days (Fig.…”

“…Immediately after, the livers and brains were removed and processed for histology, and protein and RNA extraction as previously described. 31,33 Briefly, liver and brain tissues were fixed in 4% paraformaldehyde…”

“…[28][29][30] Interestingly, multiple ANXA6 interactions likely relevant for proper hepatic functioning are often linked to NPC1, such as autophagocytosis, cholesterol homeostasis, lysosomal function or gluconeogenesis. 30,31 Indeed, upregulated ANXA6 levels contributed to the compromised cholesterol transport in NPC1-deficient cells 21 and cholesterol-sensitive lysosomal degradation, 18 while hepatic ANXA6 deficiency hindered glucose homeostasis and survival during liver regeneration. 31 In this study, analysis of double-ko mice lacking NPC1 and ANXA6 (Npc1 -/-/Anxa6 -/-) revealed a significant reduction of lifespan compared to Npc1 -/mice, which correlated with a slight amelioration of some neurological functions, but overall worsening in motor coordination abilities.…”

“…30,31 Indeed, upregulated ANXA6 levels contributed to the compromised cholesterol transport in NPC1-deficient cells 21 and cholesterol-sensitive lysosomal degradation, 18 while hepatic ANXA6 deficiency hindered glucose homeostasis and survival during liver regeneration. 31 In this study, analysis of double-ko mice lacking NPC1 and ANXA6 (Npc1 -/-/Anxa6 -/-) revealed a significant reduction of lifespan compared to Npc1 -/mice, which correlated with a slight amelioration of some neurological functions, but overall worsening in motor coordination abilities. In addition, loss of ANXA6 in NPC1-deficient animals decreased hepatic cholesterol esters (CE) without modifying unesterified cholesterol (UC) levels, deteriorated hepatic function and dramatically increased the number of foam cells in the liver, indicating increased liver inflammation.…”

Diverse Roles of Annexin A6 in Triple-Negative Breast Cancer Diagnosis, Prognosis and EGFR-Targeted Therapies

“…Accumulating evidence now suggests that AnxA6 may also affect the growth of tumor cells by modulating glucose and lipid metabolism, with consequences in cellular energy status and consumption. In support of this notion, AnxA6 deficiency compromised alanine-dependent gluconeogenesis during liver regeneration [ 82 ]. AnxA6 expression is also associated with fatty-acid-induced lipid droplet formation, with increased lipid droplet numbers and size in a cytoplasmic phospholipase A2α-dependent manner [ 83 ].…”