Fgf7, also known as keratinocyte growth factor (KGF), is a member of the fibroblast growth factor family. It plays crucial roles in various biological processes. Specifically, it is involved in unidirectional mesenchyme-to-epithelium signaling, which is essential for the development of most organs, glands, and limbs. Fgf7 specifically activates the "b" isoforms of FGFR1 (FGFR1b) and FGFR2 (FGFR2b) by engaging in specific contacts with two alternatively spliced loop regions in the immunoglobulin-like domain 3 (D3) of these receptors [2].

Single-cell RNA-seq analysis revealed that Fgf7 mediates a novel interaction between muscle fibro-adipogenic progenitors (FAPs) and satellite cells. Exogenous Fgf7 can augment the proliferation of satellite cells, which benefits muscle regeneration and counteracts age-related myopathy [1]. In the context of COVID-19, Fgf7 enhances the expression of ACE2 in human islet organoids, facilitating SARS-CoV-2 infection and resulting in impaired insulin secretion [3]. In rhabdomyosarcomas, Fgf7-FGFR2 autocrine signaling increases growth and chemoresistance of fusion-positive cases [4]. In ovarian cancer, cancer-associated fibroblast-secreted Fgf7 promotes cancer progression by inhibiting the ubiquitination and degradation of HIF-1α via FGFR2 interaction [5].

In conclusion, Fgf7 is involved in multiple biological processes, including organ development, muscle regeneration, and cell-cell communication. Its role in diseases such as age-related myopathy, COVID-19-associated diabetes, rhabdomyosarcomas, and ovarian cancer has been revealed through various studies. Understanding the function of Fgf7 provides potential therapeutic targets for these diseases.