Senescent Cells Inhibit Muscle Differentiation by Releasing the Lipid 15d-PGJ2 that Modifies and Activates HRas

Core Concepts

Senescent cells release the lipid 15d-PGJ2 as part of their SASP, which covalently modifies and activates HRas, leading to inhibition of muscle cell differentiation.

Abstract

The study investigates how senescent cells, characterized by increased senescence markers and SASP factors, negatively impact muscle differentiation. Key findings: Doxorubicin treatment induces senescence in mouse skeletal muscles and C2C12 mouse myoblasts, as evidenced by increased senescence markers and SASP factors. Senescent C2C12 cells show elevated synthesis and release of the lipid 15d-PGJ2, a non-enzymatic dehydration product of prostaglandin PGD2. The conditioned medium from senescent C2C12 cells inhibits myoblast differentiation, and this inhibition is rescued by blocking the synthesis of PGD2/15d-PGJ2. 15d-PGJ2 directly inhibits the proliferation and differentiation of mouse and human myoblasts in a dose-dependent manner. 15d-PGJ2 covalently modifies the small GTPase HRas at cysteine 184, leading to its activation and increased localization at the plasma membrane. The inhibitory effect of 15d-PGJ2 on myoblast differentiation is dependent on the modification of HRas at cysteine 184, as the C184S mutant is resistant to this effect. The study provides a mechanism by which senescent cells, through the release of the lipid 15d-PGJ2, can negatively impact muscle homeostasis and regeneration, particularly in the context of chemotherapy-induced senescence.

Stats

Doxorubicin treatment increases the mRNA levels of senescence markers p16 and p21, and SASP factors CXCL1, CXCL2, TNFα1, IL6, and TGFβ1 in mouse skeletal muscles. Doxorubicin treatment increases the mRNA levels of cell cycle inhibitor p21 and SASP factors IL6 and TGFβ in C2C12 myoblasts. The concentration of 15d-PGJ2 released by senescent C2C12 cells is approximately 100-fold higher than that released by quiescent C2C12 cells. Treatment with 15d-PGJ2 decreases the proliferation and fusion of C2C12 myoblasts in a dose-dependent manner. Covalent modification of HRas by 15d-PGJ2 occurs at cysteine 184, but not cysteine 181.

Quotes

"15d-PGJ2 contains an electrophilic cyclopentenone ring in its structure, allowing 15d-PGJ2 to covalently modify and form Michael adducts with cysteine residues of proteins." "Preferential activation of the HRas-MAPK pathway over the HRas-PI3K pathway after treatment with 15d-PGJ2 can be a possible mechanism by which 15d-PGJ2 can inhibit the differentiation of myoblasts." "Alteration of intracellular distribution of HRas affects the HRas-mediated inhibition of the differentiation of myoblasts."

Key Insights Distilled From

Senescent cells inhibit muscle differentiation via the SASP-lipid 15d-PGJ2 mediated modification and control of HRas

by Pundlik,S. S... at www.biorxiv.org 12-24-2023

https://www.biorxiv.org/content/10.1101/2023.12.23.573200v2

Deeper Inquiries

How might the inhibitory effects of 15d-PGJ2 on muscle differentiation be leveraged for therapeutic applications, such as in the context of muscle wasting diseases?

The inhibitory effects of 15d-PGJ2 on muscle differentiation could be leveraged for therapeutic applications in muscle wasting diseases by targeting the synthesis and release of this lipid from senescent cells. By understanding the mechanisms by which 15d-PGJ2 inhibits muscle differentiation, potential therapeutic strategies could be developed to modulate its levels in the microenvironment. For example, targeting the enzymes involved in the synthesis of PGD2/15d-PGJ2, such as PTGS1, PTGS2, and PTGDS, could be a potential approach to reduce the levels of 15d-PGJ2 in the context of muscle wasting diseases. Additionally, inhibiting the covalent modification of HRas by 15d-PGJ2 at cysteine 184 could be another strategy to prevent the inhibitory effects of 15d-PGJ2 on muscle differentiation. By targeting these specific pathways, it may be possible to restore muscle homeostasis and promote muscle regeneration in individuals with muscle wasting diseases.

What other cellular pathways or transcriptional regulators might be affected by the covalent modification of HRas by 15d-PGJ2, and how could this impact muscle homeostasis?

The covalent modification of HRas by 15d-PGJ2 could potentially impact other cellular pathways and transcriptional regulators beyond the HRas-MAPK pathway. One possible impact could be on the PI3K-Akt pathway, as HRas is known to regulate both the MAPK and PI3K pathways. The activation of HRas by 15d-PGJ2 may lead to downstream effects on the PI3K-Akt pathway, which is also crucial for muscle homeostasis and regeneration. Additionally, the covalent modification of HRas by 15d-PGJ2 could affect other signaling pathways involved in muscle differentiation, such as the Wnt signaling pathway or the Notch signaling pathway. These pathways play important roles in regulating myogenesis and muscle regeneration, and alterations in their activity due to HRas modification by 15d-PGJ2 could impact muscle homeostasis.

Given the diverse effects of 15d-PGJ2 on different cell types, what are the broader implications of this lipid-mediated signaling in the context of aging and tissue regeneration beyond the skeletal muscle system?

The diverse effects of 15d-PGJ2 on different cell types have broader implications in the context of aging and tissue regeneration beyond the skeletal muscle system. 15d-PGJ2 is known to be a key component of the SASP, which is associated with aging and age-related pathologies. In various tissues, the accumulation of senescent cells and the release of SASP factors contribute to tissue dysfunction and impaired regeneration. By targeting 15d-PGJ2 and its effects on cellular pathways, it may be possible to modulate the aging process and promote tissue regeneration in different organ systems. Additionally, the covalent modification of proteins by 15d-PGJ2, such as HRas, could have implications for cellular senescence, inflammation, and tissue homeostasis in a broader context. Understanding the role of 15d-PGJ2 in aging and tissue regeneration could lead to the development of novel therapeutic strategies for age-related diseases and tissue repair beyond skeletal muscle.