Activins

About Activins

Activins are a group of cytokines belonging to the transforming growth factor-beta (TGF-β) superfamily and are disulfide-linked dimeric proteins. They were originally purified from gonadal fluid and primarily stimulate pituitary follicle-stimulating hormone (FSH) release. Activin proteins have a wide range of biological activities, including roles in mesoderm induction, neural cell differentiation, bone remodeling, hematopoiesis, and reproductive physiology. Activin isoforms and other members of the TGF-β superfamily exert their biological roles by binding to heterodimeric complexes of type I and type II serine-threonine kinase receptors, both of which are required for signal transduction. Activins are homodimers or heterodimers of various β-subunit isoforms, whereas inhibins are heterodimers of the unique α-subunit and one of the various β-subunits. To date, five β subunits have been cloned (mammalian β A, β B, β C, β E, and African clawed toad β D). The activin/inhibitor nomenclature reflects the subunit composition of the proteins: activin A (beta A - beta A), activin B (beta B - beta B), activin AB (beta A - beta B), inhibin A (alpha - beta A) and inhibin B (alpha - beta B). Initial studies of activins surfaced in their ability to promote the differentiation of pluripotent embryonal carcinoma cells into endodermal and mesodermal lineages. Subsequent studies revealed their involvement in various aspects of hematopoiesis, such as the proliferation and differentiation of hematopoietic stem cells (HSCs) and the maintenance of hematopoietic homeostasis.

Functions of Activins

Activins are a class of proteins that belong to the transforming growth factor beta (TGF-β) superfamily. They play important roles in various biological processes and have diverse functions in different tissues and organs. Here are some key functions of activins:

• Regulation of Growth and Development

Activins are involved in the regulation of cell growth, proliferation, and differentiation during embryonic development and tissue formation. They influence the development of various organs, including the nervous system, skeletal system, and reproductive system.

• Reproductive Functions

Activins play a crucial role in reproductive physiology and function. In females, activins are involved in the maturation and release of eggs from the ovaries (ovulation), follicular development, and regulation of the menstrual cycle. In males, they contribute to spermatogenesis and testicular function.

• Endocrine Regulation

Activins act as hormones and participate in the regulation of the endocrine system. They influence the secretion of hormones from various glands, including the pituitary gland, adrenal gland, and gonads. Activins can stimulate or inhibit hormone synthesis and release, depending on the specific context.

• Immune Modulation

Activins have immunomodulatory properties and can regulate immune responses. They influence the development and function of immune cells, such as lymphocytes and macrophages. Activins can promote or inhibit immune cell activation, cytokine production, and inflammatory processes.

• Tissue Repair and Regeneration

Activins are involved in tissue repair and regeneration processes. They contribute to wound healing, tissue remodeling, and regeneration by regulating cell proliferation, migration, and differentiation. Activins can stimulate the production of extracellular matrix components and promote tissue remodeling after injury.

• Neural Functions

Activins play a role in the development and function of the nervous system. They influence neuronal differentiation, axon guidance, and synaptic plasticity. Activins are also involved in the regulation of neurogenesis and neural stem cell maintenance in the adult brain.

• Metabolic Regulation

Activins participate in the regulation of metabolic processes, including glucose and lipid metabolism. They can influence insulin secretion, adipocyte differentiation, and energy balance. Activins play a role in the regulation of body weight and metabolism-related disorders, such as obesity and diabetes.

• Cancer Development and Progression

Dysregulation of activin signaling has been implicated in cancer development and progression. Activins can have both tumor-suppressive and tumor-promoting effects, depending on the specific context and cellular environment. They influence cell proliferation, apoptosis, angiogenesis, and metastasis in different types of cancer.

Overall, activins are versatile proteins that play diverse roles in various physiological and pathological processes. Their functions extend to multiple organ systems and contribute to fundamental biological processes, making them important targets for research and potential therapeutic interventions.

Reference:

1. Vaidya A, Kale VP. TGF-β signaling and its role in the regulation of hematopoietic stem cells [J]. Syst Synth Biol. 2015;9(1-2):1-10.
2. Activin A promotes hematopoietic fated mesoderm development through the upregulation of brachyury in human embryonic stem cells. [J]. Stem Cells and Development, 2012.DOI:10.1089/scd.2012.0053.