Evidence for an Additive Neurorestorative Effect of Simultaneously Administered CDNF and GDNF in Hemiparkinsonian Rats: implications for Different Mechanism of Action

Abstract

Parkinson’s disease (PD) is a neurodegenerative disorder associated with a progressive loss of dopaminergic (DAergic) neurons of the substantia nigra (SN) and the accumulation of intracellular inclusions containing α-synuclein. Current therapies do not stop the progression of the disease and the efficacy of these treatments wanes over time. Neurotrophic factors (NTF) are naturally occurring proteins promoting the survival and differentiation of neurons and the maintenance of neuronal contacts. CDNF (cerebral dopamine neurotrophic factor) and GDNF (glial cell line-derived neurotrophic factor) are able to protect DAergic neurons against toxin-induced degeneration in experimental models of PD. Here we report an additive neurorestorative effect of co-administration of CDNF and GDNF in the unilateral 6-hydroxydopamine (6-OHDA) lesion model of PD in rats. The NTFs were given into the striatum four weeks after unilateral intrastriatal injection of 6-OHDA (20 µg). Amphetamine-induced (2.5 mg/kg, i.p.) rotational behavior was measured every two weeks. Number of tyrosine hydroxylase (TH)-positive cells from SN pars compacta and density of TH-positive fibers in the striatum were analyzed at 12 weeks post lesion. CDNF and GDNF alone restored the DAergic function and one specific dose combination had an additive effect: CDNF (2.5µg) and GDNF (1µg) co-administration led to a stronger trophic effect relative to either of the single treatments alone. The additive effect may indicate different mechanism of action for the NTFs. Indeed, both NTFs activated the survival promoting PI3 kinase-Akt signaling pathway, but only CDNF decreased the expression level of tested endoplasmatic reticulum (ER) stress markers ATF6, GRP78 and phosphorylation of eIF2α.

Significance Statement CDNF (cerebral dopamine neurotrophic factor) and GDNF (glial cell line-derived neurotrophic factor) have shown neuroprotective and neurorestorative effects in rodent and non-human primate models of Parkinson’s disease (PD). Here we show for the first time that defined doses of CDNF and GDNF have an additive effect in restoring DAergic function and number of TH-positive neurons in substantia nigra of 6-OHDA lesioned rats. The additive effect suggested different mechanisms of action for the NTFs. Our results indicate that CDNF has a dual action via activation of survival promoting PI3K/Akt and inhibition of ER stress pathways. CDNF decreased the expression level and activity of ER stress markers in vitro and in vivo whereas GDNF had no effect.