Progeterone treatment of spinal cord injury: effects on progesterone receptors, neurotrophisn and myelination

DE NICOLA, A; GONZALEZ, S; LABOMBARDA, F; GONZALEZ DENISELLE, C; GARAY, L; GUENNOUN, R; SCHUMACHER M

Italia

Simposio; International Meeting on Steroids and Nervous System; 2005

International Group on Steroids

It is now widely accepted that progesterone (PROG) brings neuroprotection in lesions of the peripheral and central nervous system [ 1 ]. In the spinal cord, trauma leads to neuronal degeneration, astrogliosis, demyelination and proliferation of oligodendrocyte-precursor cells (OPC) [ 2 ]. Here, we provide evidences that PROG treatment of spinal cord-injured rats restored to normal abnormalities of motoneurons and myelin synthesis arising as a consequence of the imposed trauma. Since motoneurons and myelin-forming cells express classical intracellular PROG receptors (PR), it is likely that both cell types are steroid targets [ 3 ]. In rats with spinal cord injury at T10 level, PROG treatment (4 mg/kg/day during 3 days) restored to normal the deficient levels of choline acetyl-transferase (ChAT) and of the a3 and b1 subunits Na,K-ATPase mRNA, while levels of the growth associated protein GAP-43 mRNA were further stimulated in motoneurons located below the lesion site [ 4 ]. Recent studies suggest that neurotrophins are possible mediators of hormone action, and in agreement with this assumption, PROG treatment of rats with spinal cord injury increased the expression of brain-derived neurotrophic factor (BDNF) at both the mRNA and protein levels in ventral horn motoneurons [ 5 ]. Thus, in situ hybridization (ISH) data showed that injury reduced BDNF mRNA levels by 50% in spinal motoneurons, while PROG administration elicited a 3-fold increase in grain density. In addition to enhancement of mRNA levels, PROG increased BDNF immunoreactivity in perikaryon and cell processes of motoneurons of the lesioned spinal cord, and also prevented the lesion-induced chromatolytic degeneration as determined by Nissl staining. The increased expression of BDNF correlated with increased nuclear immunoreactivity for the BDNF receptor TrkB and with increased imunoreactivity for pCREB in motoneurons from rats with spinal cord injury receiving PROG therapy. In subsequent work employing the same model of total spinal cord transection, we studied if PROG increased myelination, by measuring three variable in the lumbar L4 region below the lesion site: (a) expression of myelin basic protein (MBP) at the protein and mRNA levels; (b) density of NG2-immunopositive cells as markers for OPC and (c) number of RIP immunopositive cells, considered mature oligodendrocytes. In spinal cord lesioned rats, we found decreased MBP immunostaining in the corticospinal tract (CST) and dorsal ascending tract (DAT) but not the ventral funiculus (VF). NG2+ cells, albeit absent in controls, appeared moderately in the gray and white matter after lesion. RIP-positive cell number, however, remained unchanged. PROG treatment of lesioned rats enhanced the expression of MBP protein and mRNA in CST and DAT, but not VF and highly stimulated NG2+ cell density over untreated lesioned rats. Instead, density of RIP positive cells was similar in the PROG-treated and untreated lesioned groups. Thus, a positive effect of PROG on myelination and NG2 cells was observed following spinal cord injury, at the same time that the hormone regulated motoneuron parameters [ 6 ]. Thus, our work demonstrated that in motoneurons from injured rats PROG modulated neurotrophin and receptor expression, whereas myelinogenesis was also positively modulated at the level of glial cells. PROG enhancement of endogenous neuronal BDNF could provide a trophic environment within the lesioned spinal cord and might be part of the PROG activated-pathways to provide neuroprotection. Interestingly, there are similarities in the regulation of molecular parameters and some cellular events attributed to PROG and those shown for BDNF (i.e., ChAT, Na,K-ATPase, MBP, chromatolysis), suggesting that BDNF and PROG actions may share common intracellular pathways in prevention of neuronal damage. Furthermore, it also suggest that BDNF may be an intermediate in PROG action. In this view, PROG-induced BDNF may act in a paracrine or autocrine fashion to positively regulate the function of neurons and perhaps other cell types, such as oligodendrocytes. Autocrine effects may take place after binding to TrkB in BDNF-producing motoneurons, increasing cellular responses associated with neuroprotection. With regards to PROG effects on myelin, we would like to postulate that remyelination may be due in part to increased proliferation and differentiation of OPC. Further work will indicate the role of the BDNF and pCREB in this pathway . Thus, PROG beneficial effects in spinal cord injury may involve combined mechanisms exerted upon motoneurons and glial cells.