Temperature-dependent autoactivation associated with clinical variability of PDGFRB Asn666 substitutions

Ocular pterygium-digital keloid dysplasia (OPDKD) presents in childhood with ingrowth of vascularized connective tissue on the cornea leading to severely reduced vision. Later the patients develop keloids on digits but are otherwise healthy. The overgrowth in OPDKD affects body parts that typically have lower temperature than 37°C. We present evidence that OPDKD is associated with a temperature sensitive, activating substitution, p.(Asn666Tyr), in PDGFRB. Phosphorylation levels of PDGFRB and downstream targets were higher in OPDKD fibroblasts at 37°C but were further greatly increased at the average corneal temperature of 32°C. This suggests that the substitution cause significant constitutive autoactivation mainly at lower temperature. In contrast, a different substitution in the same codon, p.(Asn666Ser), is associated with Penttinen type of premature aging syndrome. This devastating condition is characterized by widespread tissue degeneration, including pronounced chronic ulcers and osteolytic resorption in distal limbs. In Penttinen syndrome fibroblasts, equal and high levels of phosphorylated PDGFRB was present at both 32°C and 37°C. This indicates that this substitution causes severe constitutive autoactivation of PDGFRB regardless of temperature. In line with this, most downstream targets were not affected by lower temperature. However, STAT1, important for tissue wasting, did show further increased phosphorylation at 32°C. Temperature-dependent autoactivation offers an explanation to the strikingly different clinical outcomes of substitutions in the Asn666 codon of PDGFRB.

The Role of The ?klotho Gene, Fgf21 and Fgfr1 in Cancerogenesis

Klotho was discovered in 1997 as an anti-aging gene that, when overexpressed, may extend the life span, but when it is disrupted, it may be a factor responsible for premature aging syndrome. The structure and the role of αKlotho and βKlotho genes from Klotho family in malignant tumors is described. The expression profile of the βKlotho gene is significantly different from the expression of the αKlotho gene. Analysis of Klotho expression in breast cancer, cervical cancer as well as endometrial cancer are discussed. The available data indicate the involvement of βKlotho in the neoplastic transformation of the endometrium. More advanced disease is related to negative expression of βKlotho gene. Fibroblast growth factors (FGFs) are a large family of proteins characterized by different functions in the cell development and metabolism. The FGF signaling is also associated with cancerogenesis. The relation between some FGF subfamilies and endometrial cancer clinical data is reported. The interaction between FGF subfamilies and the Klotho subfamily proteins acting as a co-receptor is stressed. Disorders in signaling of the FGF / FGFR pathway have been confirmed in gynecology. It can be assumed that increased expression of FGF21 might be a suppressor factor in endometrial cancer. The FGF21 factor, like the βKlotho protein, achieves its biological effect via the FGFR1 receptor. High expression of the FGFR1 gene inhibits further tumor growth. FGFR1 has the potential to perform both a suppressor and promoter role in the oncogenesis process.

Molecular Mechanisms Underlying Accelerated Aging by Defects in the FGF23-Klotho System

The basic research of aging has been primarily focused on elucidating mechanisms of aging and longevity that are evolutionarily conserved from yeasts to primates. Such efforts have culminated in the notion that (1) senescence at the cellular level is associated with aging at the organismal level and that (2) calorie restriction and growth suppression decelerate aging. However, these important findings in the basic research have not necessarily been linked to improvement of daily medical practice in the aging society. It has become increasingly important to investigate mechanisms of aging unique to mammals or humans and apply the research fruits for the treatment of major age-related disorders to extend the health span. Seminal studies on the klotho mouse, a mutant exhibiting a premature aging syndrome, have identified phosphate as a proaging factor in mammals. In this review, mechanisms of phosphate-induced premature aging and potential therapeutic targets will be discussed, which may be directly applicable for developing novel strategies for the treatment of chronic kidney disease and its complications.