Fibroblast growth factors (FGFs) control organ morphogenesis during development as well as tissue homeostasis and repair in the adult organism. Despite their importance, many mechanisms that regulate FGF function are still poorly understood. Interestingly, the thermodynamic stability of 22 mammalian FGFs varies widely, with some FGFs remaining stable at body temperature for more than 24 h, while others lose their activity within minutes. How thermodynamic stability contributes to the function of FGFs during development remains unknown. Here we show that FGF10, an important limb and lung morphogen, exists as an intrinsically unstable protein that is prone to unfolding and is rapidly inactivated at 37 °C. Using rationally driven directed mutagenesis, we have developed several highly stable (STAB) FGF10 variants with a melting temperature of over 19 °C more than that of wildtype FGF10. In cellular assays in vitro, the FGF10-STABs did not differ from wildtype FGF10 in terms of binding to FGF receptors, activation of downstream FGF receptor signaling in cells, and induction of gene expression. In mouse embryonal lung explants, FGF10-STABs, but not wildtype FGF10, suppressed branching, resulting in increased alveolarization and expansion of epithelial tissue. Similarly, FGF10-STAB1, but not FGF10 wildtype, inhibited the growth of mouse embryonic tibias and markedly altered limb morphogenesis when implanted into chicken limb buds, collectively demonstrating that thermal instability should be considered an important regulator of FGF function that prevents ectopic signaling. Furthermore, we show enhanced differentiation of human iPSC-derived lung organoids and improved regeneration in ex vivo lung injury models mediated by FGF10-STABs, suggesting an application in cell therapy.

• Keywords
• Development, FGF10, Fibroblast growth factor, Lung, Morphogen, Stability,
• MeSH
• Fibroblast Growth Factor 10 * metabolism   genetics   chemistry   MeSH
• Humans MeSH
• Mice MeSH
• Lung metabolism   embryology   MeSH
• Receptors, Fibroblast Growth Factor metabolism   MeSH
• Signal Transduction * MeSH
• Protein Stability MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Fgf10 protein, mouse MeSH Browser
• Fibroblast Growth Factor 10 * MeSH
• Receptors, Fibroblast Growth Factor MeSH

Achondroplasia is the most common form of human dwarfism caused by mutations in the FGFR3 receptor tyrosine kinase. Current therapy begins at 2 years of age and improves longitudinal growth but does not address the cranial malformations including midface hypoplasia and foramen magnum stenosis, which lead to significant otolaryngeal and neurologic compromise. A recent clinical trial found partial restoration of cranial defects with therapy starting at 3 months of age, but results are still inconclusive. The benefits of achondroplasia therapy are therefore controversial, increasing skepticism among the medical community and patients. We used a mouse model of achondroplasia to test treatment protocols aligned with human studies. Early postnatal treatment (from day 1) was compared with late postnatal treatment (from day 4, equivalent to ~5 months in humans). Animals were treated with the FGFR3 inhibitor infigratinib and the effect on skeleton was thoroughly examined. We show that premature fusion of the skull base synchondroses occurs immediately after birth and leads to defective cranial development and foramen magnum stenosis in the mouse model to achondroplasia. This phenotype appears significantly restored by early infigratinib administration when compared with late treatment, which provides weak to no rescue. In contrast, the long bone growth is similarly improved by both early and late protocols. We provide clear evidence that immediate postnatal therapy is critical for normalization of skeletal growth in both the cranial base and long bones and the prevention of sequelae associated with achondroplasia. We also describe the limitations of early postnatal therapy, providing a paradigm-shifting argument for the development of prenatal therapy for achondroplasia.

The article provides clear evidence that achondroplasia should be treated immediately after birth, not only to increase height (appendicular growth), but more importantly to prevent defective cranial skeletogenesis and associated severe neurological complications. Although later treatment promotes growth of the long bones (achondroplasia patients grow taller), the defective head skeleton that forms before and/or early after birth cannot be restored if therapy is not started immediately after birth. We also describe the limitations of postnatal treatment and make a strong case for the development of prenatal therapy for achondroplasia, which appears necessary for a comprehensive treatment of this condition.

• Keywords
• Fgfr3, achondroplasia, fibroblast growth factor, infigratinib, postnatal, treatment,
• MeSH
• Achondroplasia * pathology   drug therapy   MeSH
• Skull pathology   drug effects   MeSH
• Humans MeSH
• Disease Models, Animal * MeSH
• Mice MeSH
• Receptor, Fibroblast Growth Factor, Type 3 * genetics   metabolism   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Receptor, Fibroblast Growth Factor, Type 3 * MeSH

BACKGROUND: Achondroplasia (ACH) is one of the most prevalent genetic forms of short-limbed skeletal dysplasia, caused by gain-of-function mutations in the receptor tyrosine kinase FGFR3. In August 2021, the C-type natriuretic peptide (CNP) analog vosoritide was approved for the treatment of ACH. A total of six other inhibitors of FGFR3 signaling are currently undergoing clinical evaluation for ACH. This progress creates an opportunity for children with ACH, who may gain early access to the treatment by entering clinical trials before the closure of their epiphyseal growth plates and cessation of growth. Pathophysiology associated with the ACH, however, demands a long observational period before admission to the interventional trial. Public patient registries can facilitate the process by identification of patients suitable for treatment and collecting the data necessary for the trial entry. RESULTS: In 2015, we established the prospective ACH registry in the Czechia and the Slovak Republic ( http://www.achondroplasia-registry.cz ). Patient data is collected through pediatric practitioners and other relevant specialists. After informed consent is given, the data is entered to the online TrialDB system and stored in the Oracle 9i database. The initial cohort included 51 ACH children (average age 8.5 years, range 3 months to 14 years). The frequency of selected neurological, orthopedic, or ORL diagnoses is also recorded. In 2015-2021, a total of 89 measurements of heights, weights, and other parameters were collected. The individual average growth rate was calculated and showed values without exception in the lower decile for the appropriate age. Evidence of paternal age effect was found, with 58.7% of ACH fathers older than the general average paternal age and 43.5% of fathers older by two or more years. One ACH patient had orthopedic limb extension and one patient received growth hormone therapy. Low blood pressure or renal impairment were not found in any patient. CONCLUSION: The registry collected the clinical information of 51 pediatric ACH patients during its 6 years of existence, corresponding to ~ 60% of ACH patients living in the Czechia and Slovak Republic. The registry continues to collect ACH patient data with annual frequency to monitor the growth and other parameters in preparation for future therapy.

• Keywords
• Achondroplasia, FGFR3, ReACH, Registry, Skeletal dysplasia, Treatment,
• MeSH
• Achondroplasia * epidemiology   genetics   MeSH
• Child MeSH
• Infant MeSH
• Humans MeSH
• Mutation MeSH
• Child, Preschool MeSH
• Prospective Studies MeSH
• Receptor, Fibroblast Growth Factor, Type 3 genetics   MeSH
• Registries MeSH
• Check Tag
• Child MeSH
• Infant MeSH
• Humans MeSH
• Child, Preschool MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Geographicals
• Czech Republic epidemiology   MeSH
• Slovakia MeSH
• Names of Substances
• Receptor, Fibroblast Growth Factor, Type 3 MeSH

In 1994, the field of bone biology was significantly advanced by the discovery that activating mutations in the fibroblast growth factor receptor 3 (FGFR3) receptor tyrosine kinase (TK) account for the common genetic form of dwarfism in humans, achondroplasia (ACH). Other conditions soon followed, with the list of human disorders caused by FGFR3 mutations now reaching at least 10. An array of vastly different diagnoses is caused by similar mutations in FGFR3, including syndromes affecting skeletal development (hypochondroplasia [HCH], ACH, thanatophoric dysplasia [TD]), skin (epidermal nevi, seborrhaeic keratosis, acanthosis nigricans), and cancer (multiple myeloma [MM], prostate and bladder carcinoma, seminoma). Despite many years of research, several aspects of FGFR3 function in disease remain obscure or controversial. As FGFR3-related skeletal dysplasias are caused by growth attenuation of the cartilage, chondrocytes appear to be unique in their response to FGFR3 activation. However, the reasons why FGFR3 inhibits chondrocyte growth while causing excessive cellular proliferation in cancer are not clear. Likewise, the full spectrum of molecular events by which FGFR3 mediates its signaling is just beginning to emerge. This article describes the challenging journey to unravel the mechanisms of FGFR3 function in skeletal dysplasias, the extraordinary cellular manifestations of FGFR3 signaling in chondrocytes, and finally, the progress toward therapy for ACH and cancer.

• MeSH
• Chondrocytes metabolism   pathology   MeSH
• Cartilage abnormalities   metabolism   MeSH
• Fibroblast Growth Factors genetics   metabolism   MeSH
• Phosphatidylinositol 3-Kinases genetics   metabolism   MeSH
• Bone and Bones abnormalities   metabolism   MeSH
• Skin metabolism   pathology   MeSH
• Genes, Lethal MeSH
• Humans MeSH
• MAP Kinase Signaling System genetics   MeSH
• Cell Communication MeSH
• Mutation MeSH
• Skin Neoplasms genetics   metabolism   pathology   MeSH
• Natriuretic Peptide, C-Type genetics   metabolism   MeSH
• Osteochondrodysplasias genetics   metabolism   pathology   MeSH
• Cell Proliferation MeSH
• Receptor, Fibroblast Growth Factor, Type 3 * genetics   metabolism   MeSH
• Gene Expression Regulation MeSH
• Signal Transduction MeSH
• STAT1 Transcription Factor genetics   metabolism   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Research Support, N.I.H., Extramural MeSH
• Names of Substances
• FGFR3 protein, human MeSH Browser
• Fibroblast Growth Factors MeSH
• Phosphatidylinositol 3-Kinases MeSH
• Natriuretic Peptide, C-Type MeSH
• Receptor, Fibroblast Growth Factor, Type 3 * MeSH
• STAT1 protein, human MeSH Browser
• STAT1 Transcription Factor MeSH