Exogenous delivery of heat shock protein 70 increases lifespan in a mouse model of amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) is a debilitating neurodegenerative disorder that results in the progressive loss of motoneurons (MNs) in the CNS. Several survival and death mechanisms of MNs have been characterized and it has been determined that MNs do not appear to mount a complete stress response, as determined by the lack of heat shock protein 70 (Hsp70) upregulation after several stress paradigms. Hsp70 has been shown to confer neuroprotection and the insufficient availability of Hsp70 may contribute to MNs' susceptibility to death in ALS mice. In this study, recombinant human Hsp70 (rhHsp70) was intraperitoneally injected three times weekly, beginning at postnatal day 50 until endstage, to G93A mutant SOD1 (G93A SOD1) mice. The administration of rhHsp70 was effective at increasing lifespan, delaying symptom onset, preserving motor function and prolonging MN survival. Interestingly, injected rhHsp70 localized to skeletal muscle and was not readily detected in the CNS. Treatment with rhHsp70 also resulted in an increased number of innervated neuromuscular junctions compared with control tissue. Together these results suggest rhHsp70 may delay disease progression in the G93A SOD1 mouse via a yet to be identified peripheral mechanism.

The lack of effect of specific overexpression of IGF-1 in the central nervous system or skeletal muscle on pathophysiology in the G93A SOD-1 mouse model of ALS.

The ability of insulin like growth factor 1 (IGF-1) to prevent the pathophysiology associated with amyotrophic lateral sclerosis (ALS) is currently being explored with animal models and in clinical trials with patients. Several studies have reported positive effects of IGF-1 in reducing motor neuron death, delaying the onset of motor performance decline, and increasing life span, in SOD-1 mouse models of ALS and in one clinical trial. However, a second clinical trial produced no positive results raising questions about the therapeutic efficacy of IGF-1. To investigate the effect of specific and sustained IGF-1 expression in skeletal muscle or central nervous system on motor performance, life span, and motor neuron survival, human-IGF-1 transgenic mice were crossed with the G93A SOD-1 mutant model of ALS. No significant differences were found in onset of motor performance decline, life span, or motor neuron survival in the spinal cord, between SOD+/IGF-1+ and SOD+/IGF-1- hybrid mice. IGF-1 concentration levels, measured by radioimmunoassay, were found to be highly increased throughout life in the central nervous system (CNS) and skeletal muscle of IGF-1 transgenic hybrid mice. Additionally, increased CNS weight in SOD+ mice crossbred with CNS IGF-1 transgenic mice demonstrates that IGF-1 overexpression is biologically active even after the disease is fully developed. Taken together, these results raise questions concerning the therapeutic value of IGF-1 and indicate that further studies are needed to examine the relationship between methods of IGF-1 administration and its potential therapeutic value.

Overexpression of glial cell line-derived neurotrophic factor in the CNS rescues motoneurons from programmed cell death and promotes their long-term survival following axotomy.

To study the role of one of the most potent motoneuron (MN) survival factors, glial cell line-derived neurotrophic factor (GDNF) derived from the CNS, we generated transgenic animals overexpressing GDNF under the control of an astrocyte-specific GFAP promoter. In situ hybridization revealed that GDNF was expressed at high levels in astrocytes throughout the brain and spinal cord. We analyzed the effects of CNS-derived GDNF on MN survival during the period of programmed cell death (PCD) and after nerve axotomy. In GFAP-GDNF mice at E15, E18, and P1, the survival of brachial MNs was increased on average by 30%, lumbar MNs by 20%, and thoracic MNs at P1 by 33%. GDNF also prevented MN PCD in several cranial motor nuclei. We demonstrated for the first time that the number of MNs in the mouse abducens nucleus was also increased by 40%, thus extending known MN populations that are responsive to GDNF. Next, we tested if GDNF could support complete and relatively long-term survival of MNs following neonatal facial nerve axotomy. We found that virtually all MNs (91%) in GFAP-GDNF mice survived for up to 18 weeks post-axotomy. This is the longest GDNF-mediated survival of neonatal MNs reported following axotomy. Most of surviving MNs were not atrophic, and MN-specific ChAT and neurofilament immunoreactivity (IR) were preserved. Furthermore, GDNF attenuated axotomy-induced astroglial activation. These data demonstrate that overexpression of GDNF in the CNS has very profound effects on MN survival both during the PCD period and after neuronal injury. GFAP-GDNF mice will be valuable to study the effects of CNS-derived GDNF in mouse models of MN degenerative diseases and axonal regeneration in vivo.

GDNF and BDNF alter the expression of neuronal NOS, c-Jun, and p75 and prevent motoneuron death following spinal root avulsion in adult rats.

In the present study, we examined the effects of glial cell line-derived neurotrophic factor (GDNF), brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF), and insulin growth factor (IGF-1) on adult motoneuron survival following spinal root avulsion. The expression of neuronal nitric oxide synthase (nNOS), c-Jun, and the low-affinity neurotrophin receptor (P75) following treatment with these neurotrophic factors was also examined. In control animals, approximately 80% of spinal motoneurons were nNOS positive at 3 weeks following the lesion, whereas in GDNF or BDNF treated animals no nNOS positive motoneurons were found at the same time point. Following injury and treatment with GDNF and BDNF increased numbers of motoneurons were c-Jun and P75 positive. By 6 weeks following the lesion, only approximately 28% of motoneurons persisted in control animals whereas about 90% of motoneurons survived injury following treatment with either GDNF or BDNF. In contrast, CNTF and IGF-1 were ineffective in either inhibiting nNOS expression or preventing motoneuron death. Our results provide in vivo evidence that the survival of injured adult mammalian motoneurons can be promoted by specific neurotrophic factors, and that this effect is associated with inhibition of nNOS expression and up-regulation of c-Jun and P75 expression.