Underexpression of messenger RNA for peripheral myelin protein 22 in hereditary neuropathy with liability to pressure palsies.

Hereditary neuropathy with liability to pressure palsies (HNPP) is associated with a deletion in chromosome 17p11.2, including the gene for the peripheral myelin protein 22 (PMP-22). Because of the proposal that a decreased dosage of the PMP-22 gene was the cause of HNPP, we evaluated sural nerves from eight patients with the 17p11.2 deletion and from five normal controls. The relative amount of PMP-22 mRNA was significantly lower in HNPP patients compared with normal controls (p < 0.02) using a semiquantitative reverse transcriptase-polymerase chain reaction. There was no significant decrease of Pzero mRNA. Sural nerves from HNPP patients showed normal immunostaining with monoclonal antibodies against PMP-22, Pzero, and myelin basic protein, and only rare myelinated fibers, classified as "tomacula," showed a patchy staining of the compact myelin with monoclonal antibody against PMP-22. The significant underexpression of PMP-22 mRNA in HNPP patients compared with normal controls demonstrates that a decreased dosage of the PMP-22 gene is the most likely pathogenetic mechanism in HNPP.

Tyrosine kinase A-nerve growth factor receptor is antigenically present in dystrophic neurites from a variety of conditions but not in Alzheimer's disease.

Tyrosine kinase A (TrkA), a high affinity receptor for nerve growth factor (NGF), is activated during differentiation and regeneration of selective neuronal population. We investigated presence, distribution and expression of TrkA in frontal cortex from cases with Alzheimer's disease (AD), normal aging and a variety of conditions (AIDS, cystic fibrosis, cerebral infarcts) in which neuroaxonal dystrophy occurs. TrkA was immunocytochemically detected in 90% of dystrophic neurites surrounding amyloid deposits in normal aging, as well as in all not amyloid-related dystrophic neurites identified by ubiquitin immunoreactivity. Conversely, the amyloid associated dystrophic neurites were not TrkA reactive in AD tissue. The levels of TrkA protein and mRNA in AD frontal cortex did not significantly differ from those of non-demented aged controls. The absence of TrkA activation in amyloid associated neurites in AD, but not in normal aging, indicates a different reaction of neuronal tissue to amyloid (protein (Abeta) deposition, and suggests that other factors, besides Abeta, mediate neuronal degeneration in AD.

Mifepristone (RU 38486) influences expression of glycoprotein Po and morphological parameters at the level of rat sciatic nerve: in vivo observations.

The observations here reported indicate that, in vivo, the expression of an important protein of peripheral myelin, the glycoprotein Po, is influenced by mifespristone (RU 38486), that is, an antagonist of progesterone (PR) and glucocorticoid (GR) receptor. In our experimental model, male rats have been treated at the first day of life with this antagonist and after repeated treatments, we have analyzed in the sciatic nerve of 20- (20d) and 30-day-old rats (30d) the mRNA and protein levels of Po. Moreover, expression of Po has also been analyzed in the sciatic nerve of animals treated during the first 30 days of postnatal life and then sacrificed at 90th day of life (90d). The results obtained have indicated that both mRNA and protein levels of Po decrease at 20d. Apparently, these effects seem to be transient because no changes are evident at the other two times of analysis. As shown by morphometric analysis, the treatment with RU 38486 is also able to induce morphological changes at the level of sciatic nerve. However, at variance to what is expected by an alteration of an important component of the myelin membranes like Po, no changes are evident at the level of the myelin compartment. On the contrary, a significant reduction of axon diameter in parallel to an increase in neurofilament (NF) density occurs since 30d. In conclusion, the present data seem to suggest that progestin and/or glucocorticoid signals are not only involved in the control of myelin compartment but also on the axon maintenance.

Effect of recombinant human nerve growth factor on cisplatin neurotoxicity in rats.

In this study we evaluated the effect of recombinant human nerve growth factor (rhNGF) on cisplatin (CDDP)-induced sensory neuronopathy in an experimental paradigm in the rat. Young adult female Wistar rats were treated with CDDP (2 mg/kg ip twice weekly for nine times) alone or in combination with rhNGF (1 mg/kg sc on alternate days). The effect of CDDP +/- NGF treatment was evaluated with behavioral (tail-flick test) and neurophysiological (nerve conduction velocity in the tail) methods immediately after treatment and after a follow-up period of 6 weeks. Pathological and morphometrical examinations of the dorsal root ganglia (DRG) and sciatic and saphenous nerves were also performed. rhNGF treatment induced a significant reduction in the CDDP-induced decrease in nerve conduction velocity (P < 0.05), and this was associated with a significant protection against the decrease in somatic (P < 0.05), nuclear (P < 0.05), and nucleolar size (P < 0.01) caused by CDDP treatment. However, for each of the parameters examined the neuroprotection obtained with rhNGF treatment was not complete. At the follow-up examination no differences between the three groups were observed in tail-flick test and nerve conduction velocity. We conclude that rhNGF, administered according to the schedule used in this experiment, exerts a biologically significant neuroprotective effect against CDDP peripheral neurotoxicity.

Correlation between PMP-22 messenger RNA expression and phenotype in hereditary neuropathy with liability to pressure palsies.

Hereditary neuropathy with liability to pressure palsies (HNPP) is associated with a deletion in chromosome 17p11.2, which includes the gene for the peripheral myelin protein 22 (PMP-22). A "gene dosage" effect is probably the mechanism underlying HNPP, but the amount of PMP-22 mRNA in sural nerves of HNPP patients is highly variable and the role of PMP-22 underexpression in impairing myelination has yet to be clarified. We have studied 6 genetically proven HNPP patients, to evaluate the relationship between PMP-22 mRNA levels, and clinical, neurophysiological, and neuropathological findings. Underexpression of PMP-22 mRNA correlates with disease severity and with mean axon diameter and g ratio, but not with myelin thickness, number of "tomacula," or nerve conduction parameters. Our findings further confirm that underexpression of PMP-22 is the main pathogenetic mechanism underlying the severity of clinical symptoms and signs in HNPP. Smaller axons in sural nerves of HNPP patients with lower PMP-22 levels suggests that underexpression of PMP-22 may also affect axon development.

Insulin treatment enhances expression of IGF-I in sural nerves of diabetic patients.

We studied the expression of insulin-like growth factor I (IGF-I) and its receptor in sural nerves from 8 diabetic patients divided into insulin-treated (IT) and non-insulin-treated (NIT) groups, compared with 5 patients with axonal neuropathies and 4 control patients (undergoing biopsies for diagnostic purposes). Insulin-like growth factor I mRNA levels did not differ in diabetic cases compared with control subjects. In sural nerves from IT patients and axonal neuropathies, IGF-I expression was higher than in NIT subjects and diagnostic controls. Changes in IGF-I receptor mRNA levels paralleled those of the ligand. Insulin-like growth factor I immunoreactivity was higher in nerves undergoing axonal degeneration and higher in IT than NIT diabetic patients and diagnostic controls. These findings suggest that insulin treatment increases IGF-I expression in diabetic nerves. Our data do not support the hypothesis of an absolute IGF-I deficiency in human diabetic neuropathy. A Schwann cell's incapacity to increase IGF-I expression after severe nerve damage, as happens in axonal neuropathies, may be a cofactor in the pathogenesis of diabetic neuropathy.

PMP22 transgenic dorsal root ganglia cultures show myelin abnormalities similar to those of human CMT1A.

Charcot-Marie-Tooth 1A (CMT1A) neuropathy is caused by duplication of the peripheral myelin protein 22 (PMP22) gene, leading to protein overexpression. Although this protein has a role in regulating Schwann cell growth and peripheral myelin compaction, how altered concentrations of PMP22 impair myelination is unknown. We established dorsal root ganglia (DRG) cultures from a transgenic rat overexpressing PMP22 (PMP22tg) to study the behavior of PMP22tg Schwann cells in early stages of development and myelination. We used reverse transcriptase-polymerase chain reaction and light and electron microscopy to study PMP22 expression and myelin formation. Myelin ultrastructure was evaluated in sural nerves from CMT1A patients to compare experimental and human findings. PMP22tg DRG cultures contained a greater number of internodes devoid of myelin, in the absence of remyelination, and increased periodicity of myelin lamellae compared with normal cultures. Widening of myelin lamellae was also observed in CMT1A biopsy specimens. Our results suggest that both functions of PMP22, in regulating Schwann cell differentiation and contributing to peripheral myelin compaction, are affected by its overexpression. The presence of similar myelin abnormalities in PMP22tg cultures and human nerves emphasizes the importance of developing in vitro models of hereditary neuropathies to study their underlying pathomechanisms.