FGFR1c / beta-Klotho (KLB) co-receptor complex

Class

Glycopegylated FGF21 analog

Pathway

Agonizes FGFR1c only in the presence of the co-receptor beta-Klotho, mimicking endogenous FGF21 signaling to lower triglycerides and improve lipid/metabolic parameters

FGF21 is an endocrine hormone-like fibroblast growth factor produced mainly by the liver in response to metabolic stress. It signals through a receptor complex that requires two components: fibroblast growth factor receptor 1c (FGFR1c), a tyrosine kinase receptor, and beta-Klotho (KLB), a co-receptor that confers high-affinity binding of FGF21 and restricts activity to specific tissues, chiefly liver, adipose tissue, and regions of the brain. Engaging this complex lowers circulating triglycerides, improves insulin sensitivity, increases energy expenditure, and favorably remodels lipid metabolism. Because natural FGF21 has a short half-life and modest potency, engineered analogs are used to sustain receptor engagement. Disease contexts where this mechanism is broadly relevant include severe hypertriglyceridemia, metabolic dysfunction-associated fatty liver disease and its more severe form steatohepatitis, and related metabolic disorders where excess fat accumulation in liver and blood drives organ damage. The rationale for pairing an FGFR1c-selective agonist with dependence on beta-Klotho is that this pairing narrows activity to metabolically relevant tissues rather than triggering fibroblast growth factor receptor pathways broadly, which are involved in tissue growth and repair elsewhere in the body. This selectivity is central to the therapeutic strategy of mimicking FGF21 pharmacologically.