Transferrin Promotes Oligodendroglial Differentiation Independently of Iron Binding and Release.

Abstract

Transferrin (Tf), classically known as the major iron-transport protein in mammals, also engages in potent promyelinating activity within the central nervous system by accelerating oligodendrocyte maturation. Since 1994, our group has shown that intrathecal or intranasal administration of apoTransferrin (aTf) promotes oligodendroglial differentiation and myelin protein expression in vivo and in vitro. A long-standing question, however, has been whether these effects depend on iron delivery or instead reflect an intrinsic trophic property of the protein. To directly address this point, we used the oligodendroglial precursor cell line Oli-Neu and two previously characterized non-glycosylated human Tf mutants with selective defects in iron handling: TfY (Y95F/Y188F/Y426F/Y517F), an iron-binding-deficient mutant unable to bind iron, in either lobe, and TfK (K206E/E534A), an iron-release-deficient mutant that binds iron but cannot release it. We first confirmed that Oli-Neu cells express endogenous Tf and Tf receptor 1 (TfR1), internalize exogenous human Tf, and display low, non-colocalizing TfR2 expression. Transient expression of wild-type Tf, TfY, or TfK increased myelin basic protein (MBP) immunoreactivity and induced complex oligodendrocyte-like morphologies compared with non-transfected cells. Both mutants promoted maturation despite their opposite iron-binding defects, with TfK generating highly branched arbors and TfY inducing a more compact process architecture. AlphaFold-based structural modelling demonstrated the preservation of the canonical bilobalTf scaffold in both mutants. These findings provide direct evidence that the promyelinating and promaturational actions of Tf do not require iron binding or release, but rather reside in the protein itself. By decoupling Tf's biological activity from iron metabolism, this work expands the current understanding of Tf biology and identifies Tf as an iron-independent signaling cue for oligodendrocyte differentiation.This insight opens new avenues for developing Tf-based or Tf-mimetic therapeutic strategies to enhance remyelination in demyelinating disorders such as multiple sclerosis.