Wnt Signaling is Altered by Spinal Cord Neuronal Dysfunction in Amyotrophic Lateral Sclerosis Transgenic Mice

Abstract

Amyotrophic lateral sclerosis (ALS) is a chronic neurodegenerative disease characterized by progressive degeneration of the motor neurons in the cortex, brainstem, and spinal cord. The etiology and mechanisms of selective motor neuron loss in ALS remain unknown. Wnt signaling is involved in neurodegenerative processes but little is known about the kinetic changes in Wnt signaling during ALS progression. In this study we used transcriptional microarray analysis to examine the expression of Wnt signaling components in the spinal cords of ALS transgenic SOD1G93A mice at different stages. We found that ALS onset led to the upregulation of Wnt signaling components and target genes involved in growth regulation and proliferation. We also determined the expression of Wnt inhibitory factor-1 (Wif1) and Wnt4 in the spinal cord of ALS transgenic mice at different stages by Western blot and immunofluorescence analysis. The protein levels of Wif1 and Wnt4 in the spinal cords of ALS transgenic mice were upregulated compared to those in wild-type mice. Moreover, the expression of Wif1 and Wnt4 in mature GFAP+ astrocytes was increased at the end stage of ALS. Our findings demonstrate that Wnt signaling is altered by spinal cord neuronal dysfunction in adult ALS transgenic mice, which provides new insight into ALS pathogenesis.

Wnts Are Expressed in the Spinal Cord of Adult Mice and Are Differentially Induced after Injury

“…[46][47][48] Our results are in accord with the increasingly accepted role for Wnts in the modulation of fundamental aspects of the homeostasis and neuronal function of the adult CNS. 14,17,18,[49][50][51][52][53] In this line of thought, we provide supporting evidences of previous reports describing the expression of most Wnt ligands and receptors by PCR 39 and in situ hybridization analysis, 35 as well as a constitutive active b-catenin-mediated transcription in the dorsal horns and the central canal of the adult spinal cord of mice. 22,32 Interestingly, Wnt3a and Wnt5a have been recently described to be expressed by neurons of the ventral and dorsal horn of adult mice, and that the latter received Wnt3a and Wnt5a synapsis from dorsal root ganglia sensory neurons, with at least involvement of the b-catenin pathway, as evidenced by its enrichment in the pre-and postsynaptic contacts.…”

“…In this sense, the studies describing a physiological expression of the Wnt family of proteins in the adult spinal cord of mice and their involvement in amyotrophic lateral sclerosis (ALS) neurodegeneration or the development of neuropathic pain also used an inbred C57BL/6 or BS6JL, instead of an outbred CD1, mouse strain. [28][29][30]39 In agreement, another interesting point arises from our observation that, after hemisection SCI, the expression of Wnt3a and Wnt5a is down-regulated and b-catenin signaling is not up-regulated in either sensory neurons or proliferating reactive astrocytes, in contraposition to the response described for neurodegeneration or peripheral nerve damage. 29,30,33 This could be a result of a different pathophysiological response preceding trauma or specific cell damage, such as the massive death of neurons and oligodendrocytes induced by trauma, and have been claimed to express both ligands.…”

“…79 Strikingly, Yu and colleagues have recently shown a strong up-regulation of Wif1 by, predominantly, neurons in the locus of neurodegeneration at the middle stages of ALS progression, which has been claimed as a putative mechanism of motor neuron death and neurogenesis inhibition. 39 After SCI, our results demonstrate an early induction of both Wnt1 and its inhibitor, Dkk1, as well as a persistent down-regulation of Wnt3a, followed by prominent up-regulation of Wif1, which coincides with the highest period of neuronal death. Moreover, our results show that Fz1 was expressed in neurons and oligodendroglial cells not only in the uninjured spinal cord, but also after injury in the preserved spinal cord parenchyma that surrounded the injured tissue, which are thought to be affected by the secondary cell death processes associated with the progression of SCI.…”

“…24,25,[28][29][30][33][34][35]39 Therefore, by using a similar experimental design to our previous study in rats, but with spinal cord dorsal hemisection as an injury paradigm to reproduce the only report describing a role for Wnts in traumatic SCI, 28 we decided to assess, by qPCR, the temporal pattern of mRNA expression for all Wnt ligands in both uninjured and injured mice up to 14 days after spinal cord hemisection lesion. Consistent with our previous results in rats, most Wnt ligands were found to be expressed in the uninjured adult spinal cord.…”

The role of the Wnt canonical signaling in neurodegenerative diseases

“…Specifically, Yu et al [152] have observed an upregulation of Wnt3a, Lrp5, and Fzd receptors, as well as increased levels of the Wnt target genes Cyclin D1,c-myc, Fosl1 and Pitx2 in SOD1 G93A mice at the end stage of ALS. Likewise, Wang et al [153] reported an upregulation of the Wnt1 ligand in primary cultured astrocytes isolated from SOD1 G93A mice.…”