Neuronal activity and axonal sprouting differentially regulate CNTF and CNTF receptor complex in the rat supraoptic nucleus

Abstract

We demonstrated previously that the hypothalamic supraoptic nucleus (SON) undergoes a robust axonal sprouting response following unilateral transection of the hypothalamo-neurohypophysial tract. Concomitant with this response is an increase in ciliary neurotrophic factor (CNTF) and CNTF receptor alpha (CNTFRα) expression in the contralateral non-uninjured SON from which the axonal outgrowth occurs. While these findings suggest that CNTF may act as a growth factor in support of neuronal plasticity in the SON, it remained to be determined if the observed increase in neurotrophin expression was related to the sprouting response per se or more generally to the increased neurosecretory activity associated with the post-lesion response. Therefore we used immunocytochemistry and Western blot analysis to examine the expression of CNTF and the components of the CNTF receptor complex in sprouting versus osmotically-stimulated SON. Western blot analysis revealed a significant increase in CNTF, CNTFRα, and gp130, but not LIFRβ, protein levels in the sprouting SON at 10 days post lesion in the absence of neuronal loss. In contrast, osmotic stimulation of neurosecretory activity in the absence of injury resulted in a significant decrease in CNTF protein levels with no change in CNTFRα, gp130, or LIFRβ protein levels. Immunocytochemical analysis further demonstrated gp130 localization on magnocellular neurons and astrocytes while the LIFRβ receptor was found only on astrocytes in the SON. These results are consistent with the hypothesis that increased CNTF and CNTFR complex in the sprouting, metabolically active SON are related directly to the sprouting response and not the increase in neurosecretory activity.

Inhibition of the Jak-STAT pathway prevents CNTF-mediated survival of axotomized oxytocinergic magnocellular neurons in organotypic cultures of the rat supraoptic nucleus

“…We did not observe pSTAT3-immunoreactivity in magnocellular neurons following rrCNTF injection. This is in accordance with our previous observation that magnocellular neurons in the SON are not immunoreactive for LIFRß (Askvig, et al, 2012), which CNTF requires to mediate an intracellular signaling cascade (Davis, et al, 1993). Consistent with our results, neurons of the hippocampus, neocortex, cerebellar cortex, and olfactory bulb express CNTFRα and tSTAT3, yet CNTF administration does not lead to STAT3 activation within these neurons (MacLennan, et al, 2000).…”

“…In support of this hypothesis we demonstrated that following axotomy CNTF and the CNTF receptor components are increased in the SON both during the period of axonal sprouting and neuronal injury (Askvig, et al, 2012). Others have shown that injury to the lens of the eye resulted in STAT3 activation in retinal ganglion cells along with elevated levels of endogenous CNTF in retinal astrocytes during the period of axonal regeneration in the rat retina (Muller, et al, 2007).…”

“…We previously hypothesized that CNTF plays a role in the axonal reorganization of magnocellular neurons in the SON following injury (Askvig, et al, 2012, Lo, et al, 2008, Watt, et al, 2006, Watt, et al, 2009). In support of this hypothesis we demonstrated that following axotomy CNTF and the CNTF receptor components are increased in the SON both during the period of axonal sprouting and neuronal injury (Askvig, et al, 2012).…”

“…The mouse anti-GFAP, guinea pig anti-OT, and guinea pig anti-VP antibodies specifically label astrocytes and magnocellular neurons within the SON, respectively (Askvig, et al, 2012). The anti-pSTAT3 antibody does not cross react with other STAT molecules when phosphorylated on the corresponding residue (manufacturer's technical information).…”

“…The axonal recovery results from a collateral sprouting response arising from the non-injured, contralateral magnocellular neurons in the absence of a functional deficit (Watt and Paden, 1991). Coincident with the sprouting response, ciliary neurotrophic factor (CNTF) and the CNTF specific receptor, CNTF receptor alpha (CNTFRα), levels increase in the intact contralateral SON from which the sprouting response originates (Askvig, et al, 2012, Watt, et al, 2006, Watt, et al, 2009). CNTF has been previously implicated in hypothalamic magnocellular neuron sprouting in vitro (Vutskits, et al, 1998) and has been demonstrated to promote motor neuron sprouting in vivo (Gurney, et al, 1992, Guthrie, et al, 1997, Kwon and Gurney, 1994, Oyesiku and Wigston, 1996, Siegel, et al, 2000, Simon, et al, 2010, Ulenkate, et al, 1994, Wright, et al, 2007, Xu, et al, 2009).…”