Focal sclerosis permeability factor (FSPF) (FSPF)

Focal sclerosis permeability factor (FSPF) is a circulating factor identified in the plasma of patients with Focal Segmental Glomerulosclerosis (FSGS), particularly those experiencing disease recurrence after kidney transplantation [1, 2, 7]. It is characterized as a low-molecular-weight, anionic protein (approximately 30-50 kDa) that increases the permeability of the glomerular capillary wall to albumin, leading to massive proteinuria and podocyte injury [4, 9]. While its exact molecular identity remains a subject of ongoing research, it has been closely linked to Cardiotrophin-like cytokine factor 1 (CLCF1) and Soluble urokinase-type plasminogen activator receptor (suPAR) [1, 3, 12]. FSPF is thought to disrupt the glomerular filtration barrier by interacting with podocyte receptors or the glycocalyx [2, 7]. Therapeutic strategies include physical removal via plasmapheresis or immunoadsorption, and pharmacological inactivation using oral galactose, which binds to the factor's galactose-binding sites [4, 6, 8]. Despite its pathogenic role, clinical trials have shown that reducing FSPF activity does not always result in clinical remission, suggesting a complex multifactorial disease process [6, 10].

Other names

FSGS permeability factorCirculating permeability factorFSPFCardiotrophin-like cytokine factor 1CLCF1Soluble urokinase-type plasminogen activator receptorsuPAR

Galactose binds to and inactivates the factor, preventing its interaction with the glomerular filtration barrier [2, 4, 6]. Plasmapheresis and immunoadsorption physically remove the factor from the patient's circulation [1, 8]. JAK2 inhibitors may block downstream signaling pathways activated by the factor, such as the STAT3 pathway [12].