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Multicellular organisms contain a variety of structurally and functionally distinct cell types, but the DNA in all the cells originated from the same parent cells. The differences in the cells can be attributed to the differential gene expression. Liver cells, whose functions include detoxification of blood, production of bile to metabolize fats, and synthesis of proteins essential for metabolism, must express a specific set of genes to perform their functions. Gene expression also varies with...
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Membrane lipids such as phosphatidylinositol (PI) are precursors for several membrane-bound and soluble second messengers. Specific kinases phosphorylate PI and produce phosphorylated inositol phospholipids. One such inositol phospholipids are the  phosphatidylinositol-4,5 bisphosphate [PI(4,5)P2], present in the inner half of the lipid bilayer. Upon ligand binding, GPCR stimulates Gq proteins to turn on phospholipase Cꞵ. Activated phospholipase Cꞵ cleaves PI(4,5)P2 and...
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Cyclic Adenosine Monophosphate (cAMP) is an essential second messenger that activates protein kinase A (PKA) and regulates various biological processes. A single epinephrine molecule binds to GPCR and activates several heterotrimeric G proteins, each stimulating multiple adenylyl cyclase, amplifying the signal, and synthesizing large numbers of cAMP molecules. Small changes in cAMP concentration affect PKA activity. The binding of four cAMP molecules induces a conformational change in PKA,...
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Insulin action is mediated through a receptor tyrosine kinase, akin to the IGF-1 receptor. The number of receptors per cell varies significantly, from 40 on erythrocytes to 300,000 on adipocytes and hepatocytes. The insulin receptor consists of linked α/β subunit dimers, forming a heterotetramer glycoprotein with two extracellular α subunits and two β subunits spanning the membrane. The α subunits inhibit the inherent tyrosine kinase activity of the β subunits, but...
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The mammalian target of rapamycin  (mTOR) is a serine/threonine kinase that regulates growth, proliferation, and cell survival in response to hormones, growth factors, or nutrient availability. This kinase exists in two structurally and functionally distinct forms: mTOR complex 1  (mTORC1) and mTOR complex 2  (mTORC2). The first form (mTORC1) is composed of a rapamycin-sensitive Raptor and proline-rich Akt substrate, PRAS40. In contrast,  mTORC2 consists of a...
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Related Experiment Video

Updated: May 20, 2025

Confocal Laser Scanning Microscopy of Calcium Dynamics in Acute Mouse Pancreatic Tissue Slices
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Confocal Laser Scanning Microscopy of Calcium Dynamics in Acute Mouse Pancreatic Tissue Slices

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TMEM55A-mediated PI5P signalling regulates alpha cell actin depolymerisation and glucagon secretion.

Xiong Liu1,2, Theodore Dos Santos1,2, Aliya F Spigelman1,2

  • 1Department of Pharmacology, University of Alberta, Edmonton, AB, Canada.

Diabetologia
|March 27, 2025
PubMed
Summary
This summary is machine-generated.

The lipid phosphatase TMEM55A regulates glucagon secretion by controlling phosphatidylinositol-5-phosphate (PI5P) levels and F-actin remodeling in pancreatic alpha cells, offering new insights into diabetes mechanisms.

Keywords:
Alpha cellsExocytosisF-actinGlucagonIsletsPI5PPIP2RhoATMEM55A

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Area of Science:

  • Endocrinology
  • Cell Biology
  • Molecular Biology

Background:

  • Diabetes is linked to pancreatic alpha cell dysfunction, impacting glucagon secretion.
  • The role of phospholipids in regulating glucagon secretion is poorly understood.
  • Phosphatidylinositol-4,5-bisphosphate (PIP2) metabolism by TMEM55A correlates with alpha cell function.

Purpose of the Study:

  • To investigate the role of TMEM55A in alpha cell function and glucagon secretion.
  • To identify potential signaling molecules involved in TMEM55A-mediated regulation.
  • To elucidate the mechanisms by which TMEM55A influences glucagon release.

Main Methods:

  • Patch-clamp electrophysiology and single-cell RNA sequencing were used.
  • Human and mouse islets were studied using siRNA knockdown and electrophysiology.
  • Glucagon secretion was measured via islet perfusion, and TMEM55A activity was assessed.
  • F-actin remodeling was quantified using confocal microscopy.

Main Results:

  • TMEM55A knockdown impaired alpha cell exocytosis and glucagon secretion.
  • Reintroduction of phosphatidylinositol-5-phosphate (PI5P) rescued exocytosis.
  • PI5P, not PIP2, increased glucagon secretion by remodeling F-actin via RhoA inactivation.
  • This remodeling was independent of Ca2+ channel activity and linked to oxidative stress.

Conclusions:

  • TMEM55A regulates alpha cell exocytosis through PI5P production.
  • A novel pathway involving TMEM55A, PI5P, and F-actin remodeling controls glucagon secretion.
  • This finding provides new insights into alpha cell function and diabetes.