Neurofilament light chain (NfL) is an intermediate filament protein that constitutes intermediate filaments, a part of the cytoskeleton, of neurons (intermediate filaments are sometimes referred to as nanofilaments). Together with the other four neuronal intermediate filament proteins, namely neurofilament heavy chain, neurofilament medium chain, alpha-internexin and peripherin, NfL assembles into neurofilaments, which are important for dendritic branching and growth and stability of axons in both central and peripheral nerves and for post-traumatic axonal regeneration. Axonal damage leads to NfL release into the extracellular space.

The nucleosomal subunit organization of chromatin provides a multitude of functions. They provide a critical mechanism for stable repression of genes and other DNA-dependent activities by restricting binding of trans-acting factors to cognate DNA sequences. Nucleosomes protect the genome from DNA damaging agents and provide a lattice onto which a myriad of epigenetic signals are deposited.

Estradiol and progesterone belong to a family of steroid hormones with complex actions. Estradiol-17β (E2), the predominant and most biologically active estrogen, is an 18 carbon (C-18) steroid with an aromatic A-ring. It is synthesized mainly by the ovary; however, other organs and tissues, including adipose tissue, the brain (neurons, astrocytes, and microglia), cells of the immune system, and bone, are thought to produce it as well. Progesterone is a C-21 steroid hormone, which is not only an active hormone in and of itself, but is also a precursor to estrogens.

Estrogens (estradiol, estriol, and estrone) are important hormones that directly and indirectly regulate the metabolism and function of bone and skeletal muscle via estrogen receptors.

Osteocalcin, which is a major γ-carboxyglutamic acid (Gla) protein, is the most abundant non-collagenous protein in bone. Pre-pro-osteocalcin is initially synthesized. Carboxylated osteocalcin (Gla osteocalcin) exhibits high affinity to Ca²⁺ and adopts an α-helical conformation by binding to Ca²⁺, whereas uncarboxylated osteocalcin (Glu osteocalcin) has no affinity to Ca²⁺. Based on the relationship between the appearance of osteocalcin and mineralization, in addition to its unique hydroxyapatite-binding properties, Gla osteocalcin has also been implicated in mineralization. Gla osteocalcin was reported to inhibit hydroxyapatite growth in mineralization. Previous studies also demonstrated that it functions as a chemoattractant of osteoclast precursors.

Osteonectin was so named owing to its ability to bind to Ca²⁺, hydroxyapatite, and collagen and to nucleate hydroxyapatite deposition. Although osteonectin is highly enriched in bone, it is also expressed in a variety of other connective tissues at specific points during development, maturation, or repair processes in vivo. SPARC (secreted protein, acidic, rich in cysteine) was identified after induction by cAMP in teratocarcinoma cells and was found to be produced at very early stages of embryogenesis.

Osteopontin is the most abundant of the SIBLING proteins and is normally found in bone. Osteopontin made by stromal or inflammatory cells at sites of ectopic mineralization binds to mineral and physically inhibits crystal growth, leading to dissolution of the bioapatite. Osteopontin promotes regression of ectopic calcification and its expression is increased under conditions of injury and disease, including calcified deposits related to atherosclerotic lesions, aortic stenosis, kidney stones, and tumors.

Osteoprotegerin (OPG), a member of the TNF receptor family and expressed by osteoblasts, is now recognized for its action on the regulation of bone metabolism. It inhibits bone resorption by attaching with high affinity to its ligand RANKL, thus blocking the binding of RANKL with its receptor: RANK. This system is regulated by calciotropic hormones.

Oxytocin is a nonapeptide consisting of a cyclic six amino-acid structure and a tail of three amino acids. It was originally known for its ability to induce milk ejection and to stimulate uterine contractions. More recently, oxytocin has been shown to stimulate social behaviors, and exert pain-relieving, anti-stress/anti-inflammatory and restorative effects