What Is The Function Of Phospholipids In The Body – If you were to go to the dentist to have a tooth pulled, you would not feel any pain. The dentist would inject an anesthetic into your gums and numb them. One theory of why anesthetics work involves the movement of ions across the cell membrane. The anesthetic penetrates the membrane and causes changes in the way ions cross the membrane. If the movement of ions is interrupted, nerve impulses will not be transmitted and you will not feel pain – at least not until the anesthetic wears off.

A phospholipid is a lipid that contains a phosphate group and is a major component of the cell membrane. A phospholipid consists of a hydrophilic (water-loving) head and a hydrophobic (hydrophobic) tail (see figure below). The phospholipid is actually a triglyceride where a fatty acid has been replaced by a phosphate group of some kind.

What Is The Function Of Phospholipids In The Body

Figure (PageIndex): A phospholipid consists of a head and a tail. The “head” of the molecule contains the phosphate group and is hydrophilic, meaning it dissolves in water. The “slope” of the molecule is made of two fatty acids, which are hydrophobic and do not dissolve in water.

Phosphatidylcholine: Beyond Cellular Integrity

According to the rule of “like dissolves like”, the hydrophilic head of the phospholipid molecule dissolves easily in water. The long fatty acid chains of phospholipids are nonpolar and thus avoid water due to their insolubility. In water, phospholipids spontaneously form a double layer called a lipid bilayer, where the hydrophobic tails of phospholipid molecules are sandwiched between two layers of hydrophilic heads (see figure below). Thus, only the heads of the molecules are exposed to water, while the hydrophobic tails only interact with each other.

Figure (PageIndex): In aqueous solution, phospholipids form a bilayer in which the hydrophobic tails point inwards and only the hydrophilic heads are exposed to water.

Phospholipid bilayers are important components of the cell membrane. The lipid bilayer acts as a barrier to the passage of molecules and ions into and out of the cell. However, an important function of the cell membrane is to allow the selective passage of certain substances into and out of cells. This is done by inserting various protein molecules into and through the lipid bilayer (see figure below). These proteins form channels through which certain specific ions and molecules can move. Many membrane proteins also contain attached carbohydrates on the outside of the lipid bilayer, which allows it to form hydrogen bonds with water.

Figure (PageIndex): The phospholipid bilayer of a cell membrane contains embedded protein molecules, which allow the selective passage of ions and molecules through the membrane. Phospholipids are the major membrane lipids that comprise lipid bilayers. This basic cellular structure acts as a barrier to protect the cell from various environmental insults and, more importantly, allows many cellular processes to take place in subcellular compartments. Numerous studies have linked the complexity of membrane lipids to signal transduction, organ function, as well as physiological processes and diseases in humans. Recently, the important roles of membrane lipids in the aging process have begun to emerge. In this study, we summarized the current progress in our understanding of the relationship between membrane lipids and aging with a focus on phospholipid species. We investigated how major phospholipid species change with age in different organisms and tissues, and some common patterns of membrane lipid changes during aging were proposed. Furthermore, the role of different phospholipid molecules in regulating health and lifespan, as well as their potential mechanisms of action, were also discussed.

Phospholipid Bilayer Structure, Types, Properties, Functions

The relationship between lipids and aging has been well known. Fatty acid (FA) content, composition and metabolism are altered in aged or long-lived humans and model organisms (Papsdorf and Brunet, 2019). Furthermore, studies in model organisms such as Caenorhabditis elegans have revealed that various FA species could extend lifespan when added to the diet, which include monounsaturated oleic acid, palmitoleic acid, cis-vaccenic acid, and oleoylethanolamine, as well as polyunsaturated α-linolenic acid. , arachidonic acid and dihomo-g-linolenic acid (Goudeau et al., 2011; Rourke et al., 2013; Folick et al., 2015; Han et al., 2017; Qi et al., 2017). These unsaturated FAs mainly act with classical longevity factors, such as DAF-16/FOXO3, SKN-1/Nrf2 and HSF-1/HSF1, to regulate health and lifespan (Labbadia et al., 2015; Steinbaugh et al., 2015; Papsdorf and Brunet, 2019).

Despite these advances linking FA to the regulation of longevity, little is known about their mechanisms of action. In general, FAs function through several major mechanisms, including signaling molecules, energy resources, substrates for post-translational modifications, and components of complex lipids (Van Meer et al., 2008; Shimizu, 2009; Nakamura et al., 2014; Saliba et al. ., 2015; Resh, 2016; Harayama and Riezman, 2018). Take oleoylethanolamine as an example, it acts as a signaling molecule and regulates animal lifespan through direct binding and activation of the nuclear hormone receptor NHR-80 (Folick et al., 2015). But so far, only a few FAs have been found to function directly as signaling molecules, or as substrates for post-translational modifications. The majority of FAs are incorporated into complex lipids such as membrane lipids as their acyl chains and thus affect the structure, composition and function of the membrane (Van Meer et al., 2008; Sezgin et al., 2017; Harayama and Riezman, 2018). Therefore, it is possible that FAs may regulate lifespan by acting as critical components of membrane lipids, potentially linking membrane homeostasis to lifespan regulation.

Membrane lipids, mainly phospholipids (PLs; also known as glycerophospholipids), comprise the lipid bilayer that acts as barriers between the cell and the environment, and between different cellular compartments. However, numerous studies indicate that the lipid bilayer not only acts as structural barriers but also plays an important role in the regulation of many cellular processes (Shimizu, 2009; Wu et al., 2016; Sunshine and Iruela-Arispe, 2017; Harayama and Riezman, 2018 ). This idea is also supported by the diversity of membrane lipids (different membrane lipid species and different acyl chains within certain membrane lipids) (Hishikawa et al., 2014; Antonny et al., 2015), which far exceeds the need for barrier function. Regarding the aging process, studies in several model organisms have reported the relationship of the content and composition of several membrane lipids with animal age (Papsdorf and Brunet, 2019), supporting the potential role of membrane lipids in aging modulation. In this review, we focused on PLs and summarized recent advances linking PL homeostasis to the aging process and discussed their potential mechanisms of action. Other membrane lipids such as sphingolipids were not discussed in this review.

Phospholipids are the major structural lipids of the eukaryotic membrane, including phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylinositol (PI), phosphatidic acid (PA), and cardiolipin (CL). These major PL species share similar structures that contain two FAs attached to the sn-1 and sn-2 positions and a different phosphate head group at the sn-3 position of the glycerol backbone. The different composition of these PLs can explain the membrane diversity of various subcellular compartments and thus the function of organelles. Take PCs as an example, they are the most abundant PLs representing over 50% of the total PLs in the cell. It resides mainly in the endoplasmic reticulum (ER), the site of membrane lipid synthesis, but its content is relatively less in the plasma membrane (Van Meer et al., 2008). Maintenance of PC homeostasis is important for organelle function, but reduction of PC represents cellular stress called lipid bilayer stress (Volmer et al., 2013; Halbleib et al., 2017; Shyu et al., 2019). Therefore, the cell develops an elegant adaptive mechanism to explore the contents of PC, and loss of PC has been found to affect many cellular processes through this stress-responsive pathway (Koh et al., 2018; Ho et al., 2020). Another extreme example of diversity of PL composition is organ-specific PLs. CL is a mitochondrial-specific membrane lipid, whose content has been shown to have a profound effect on mitochondrial function and is associated with various mitochondrial diseases (Chicco and Sparagna, 2007; Houtkooper and Vaz, 2008; Schlame, 2008; Pizzuto and Pelegrin, 2020).

Biological Functions Of Cardiolipin. As The Signature Phospholipid Of…

The acyl chain composition also accounts for the diversity of PLs, which vary widely in the length of the chains and the number and position of the double bonds. These chemical changes can affect membrane protein-lipid interactions and consequently the signaling properties of membrane proteins ( Antonny et al., 2015 ; Saliba et al., 2015 ; Wu et al., 2016 ; Harayama and Riezman, 2018 ). In addition, PL containing the unsaturated acyl chains are more volatile than the saturated ones, and thus the overall level of FA unsaturation in PL could affect membrane fluidity, which has been found to regulate numerous signaling pathways, cellular processes and diseases in humans (Los and Murata, 2004; D’Auria and Bongarzone , 2016; Ammendolia et al., 2021). Therefore, in terms of the aging study, it is important to understand how the content and composition of PLs interact with proteins in longevity processes and how such interactions determine health status and lifespan. In the following section, we will discuss the relationship between aging and essential PLs.

Many studies have reported

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