Transforming growth factor-beta (TGFβ) is a secreted cytokine, which intricately controls a plethora of physiological and pathological processes during development and carcinogenesis. TGFβ exerts antiproliferative effects and functions as a tumor suppressor during early stages of tumorigenesis, whereas at later stages it functions as a tumor promoter aiding in metastatic progression through an autocrine TGFβ loop. 

Tumor necrosis factor alpha (TNF-α) has been identified to have additional important functions as a pathological component of autoimmune diseases. TNF-α binds to two different receptors, which initiate signal transduction pathways. These pathways lead to various cellular responses, including cell survival, differentiation, and proliferation. However, the inappropriate or excessive activation of TNF-α signaling is associated with chronic inflammation and can eventually lead to the development of pathological complications. 

Expression of TNFR2 is restricted to particular cell types, including, endothelial cells, fibroblasts and subsets of neurons and immune cells (myeloid cells, T- and B-cell subsets). Activation of signaling by TNFα through TNFR1 and TNFR2 initiates a variety of potential outcomes, including cell proliferation, gene activation or cell death. Mediating this variety of cellular responses from just two receptors requires complex control of signal transduction within the cell.

PIINP is a trimeric peptide consisting of two type 2 procollagen-α1 chains and a procollagen-α2 chain which are bonded non-covalently.

PIINP exists in two main splice variants termed as type IIA and type IIB collagen NH2-propeptide (PIIANP, PIIBNP). It is the major matrix protein in articular cartilage.

Ubiquitin C-terminal hydrolase L1 (UCH-L1) is an extremely abundant protein in the brain where, remarkably, it is estimated to make up 1–5% of total neuronal protein. Beyond its expression in neurons UCH-L1 has only very limited expression in other healthy tissues but it is highly expressed in several forms of cancer. UCH-L1 is not essential for neuronal development but it is absolutely required for the maintenance of axonal integrity.

Vascular endothelial growth factor (VEGF), also known as vascular permeability factor (VPF), was originally described as an endothelial cell-specific mitogen. The activities of VEGF are not limited to the vascular system; VEGF plays a role in normal physiological functions such as bone formation, hematopoiesis, wound healing, and development.