TGF‐β1 enhances Kv2.1 potassium channel protein expression and promotes maturation of cerebellar granule neurons

Abstract

Members of the transforming growth factor-β (TGF-β) family of cytokines are involved in diverse physiological processes. Although TGF-β is known to play multiple roles in the mammalian central nervous system (CNS), its role in neuronal development has not been explored. We have studied the effects of TGF-β1 on the electrophysiological properties and maturation of rat primary cerebellar granule neurons (CGNs). We report that incubation with TGF-β1 increased delayed rectifier potassium current (I(K) ) amplitudes in a dose- and time-dependent manner, but did not affect the kinetic properties of the channel. Exposure to TGF-β1 (20 ng/ml) for 36 h led to a 37.2% increase in I(K) amplitudes. There was no significant change in mRNA levels for the key Kv2.1 channel protein, but translation blockade abolished the increase in protein levels and channel activity, arguing that TGF-β1 increases I(K) amplitudes by upregulating translation of the Kv2.1 channel protein. Although TGF-β1 treatment did not affect the activity of protein kinase A (PKA), and constitutive activation of PKA with forskolin failed to increase I(K) amplitudes, inhibition of PKA prevented channel upregulation, demonstrating that basal PKA activity is required for TGF-β1 stimulation of I(K) channel activity. TGF-β1 also promoted the expression of the γ-aminobutyric acid (GABA(A) ) receptor α6 subunit, a marker of mature CGNs, and calcium influx during depolarizing stimuli was reduced by TGF-β1. The effects of TGF-β1 were only observed during a narrow developmental time-window, and were lost as CGNs matured. These findings suggest that TGF-β1 upregulates K(+) channel expression and I(K) currents and thereby promotes CGN maturation.

GDF15 regulates Kv2.1-mediated outward K+ current through the Akt/mTOR signalling pathway in rat cerebellar granule cells

“…Our previous study reported that TGFβ1 increases the I K amplitudes by up-regulating Kv2.1 expression, which requires PKA (protein kinase A) activity [12]. However, although the GDF15-induced increase in the I K densities and Kv2.1 expression was similar to that caused by TGFβ1, the mechanism and biological significance seem quite different.…”

“…Owing to their postnatal generation and the well-defined developmental pathway in vitro , primary cultures of rat CGNs have been established as a model for studying neuronal maturation, apoptosis, differentiation and synaptic plasticity [10]. Previous studies have indicated that growth and differentiation factors can either stimulate or inhibit CGN development and maturation by regulating multiple signalling pathways [11,12]. Moreover, GDF15 can induce neuroprotective effects that prevent the death of K + -deprived CGNs by activating Akt and inhibiting constitutively active ERK (extracellular signal-regulated kinase) [13].…”

“…One of the key activities during CGN development and maturation is the regulation of the expression of the K + channels [11,12]. CGNs grown in primary culture display several voltage-activated outward K + currents, including the I A (fast-transient outward K + current), I K (delayed-rectifier outward K + current), I K(so) (non-inactivating K + current) and B K(Ca) (calcium-activated K + current).…”

“…In the normal development state, however, increases in I K and I A improved the migration and maturation of CGNs [16,17]. Furthermore, TGFβ1, a member of the TGFβ family, promoted CGN maturation by increasing the expression of Kv2.1, the main α-subunit of the I K channel, via a non-Smad pathway [12]. …”

Neuritin Activates Insulin Receptor Pathway to Up-regulate Kv4.2-mediated Transient Outward K+ Current in Rat Cerebellar Granule Neurons

“…In view of their well defined developmental pathway, CGNs are invaluable models for studying neuronal maturation differentiation and synaptic plasticity (9). Previous studies indicated that growth and differentiation factors can either stimulate or inhibit CGN development and maturation by regulating multiple signaling pathways (10, 11). …”