Progesterone and Allopregnanolone Neuroprotective Effects in the Wobbler Mouse Model of Amyotrophic Lateral Sclerosis

Abstract

Progesterone regulates a number of processes in neurons and glial cells not directly involved in reproduction or sex behavior. Several neuroprotective effects are better observed under pathological conditions, as shown in the Wobbler mouse model of amyotrophic laterals sclerosis (ALS). Wobbler mice are characterized by forelimb atrophy due to motoneuron degeneration in the spinal cord, and include microgliosis and astrogliosis. Here we summarized current evidence on progesterone reversal of Wobbler neuropathology. We demonstrated that progesterone decreased motoneuron vacuolization with preservation of mitochondrial respiratory complex I activity, decreased mitochondrial expression and activity of nitric oxide synthase, increased Mn-dependent superoxide dismutase, stimulated brain-derived neurotrophic factor, increased the cholinergic phenotype of motoneurons, and enhanced survival with a concomitant decrease of death-related pathways. Progesterone also showed differential effects on glial cells, including increased oligodendrocyte density and downregulation of astrogliosis and microgliosis. These changes associate with reduced anti-inflammatory markers. The enhanced neurochemical parameters were accompanied by longer survival and increased muscle strength in tests of motor behavior. Because progesterone is locally metabolized to allopregnanolone (ALLO) in nervous tissues, we also studied neuroprotection by this derivative. Treatment of Wobbler mice with ALLO decreased oxidative stress and glial pathology, increased motoneuron viability and clinical outcome in a progesterone-like manner, suggesting that ALLO could mediate some progesterone effects in the spinal cord. In conclusion, the beneficial effects observed in different parameters support the versatile properties of progesterone and ALLO in a mouse model of motoneuron degeneration. The studies foresee future therapeutic opportunities with neuroactive steroids for deadly diseases like ALS.

Keywords: Allopregnanolone; Amyotrophic lateral sclerosis; Neurodegeneration; Neuroprotection; Progesterone; Wobbler mouse.

Fig. 1

Progesterone receptors and binding molecules in the nervous system. Progesterone is a ligand for the classical nuclear receptor (PR) that binds as homodimers to sequences on the DNA and regulates transcription of target genes. PR can also activate extranuclear signaling pathways after protein–protein interaction with the Src family of proteins. Additionally, progesterone binds to membrane receptors (mPR) associated with G proteins, or the progesterone receptor membrane component 1 (PGRMC1) associated to osmoregulatory functions. The progesterone reduced metabolite allopregnanolone (ALLO) binds to GABAa receptors, Sigma-1 receptor and pregnane X receptor (PXR), influencing different signaling mechanisms. ( Modified from Schumacher et al. 2008)

Fig. 2

Effects of progesterone on oxidative stress and mitochondrial morphology and function of Wobbler mice. Electron microscopy of motoneurons (left-hand images) shows normal morphology of soma and mitochondria from a control mouse (top), vacuolated soma and mitochondria from a Wobbler mouse (middle) and restored soma and mitochondrial structure in Wobbler mouse receiving progesterone (bottom). The inserts show high power photographs of mitochondria pointed with arrows in main images. The right-hand top cartoon depicts mitochondria in motoneurons from Wobbler mice with increased nNOS, low MnSOD, high levels of nitric oxide (NO^·), superoxide anion (O₂^·) and peroxynitrite (ONOO⁻) and low activity of mitochondrial complexes I, II and III. The lower cartoon depicts mitochondria in motoneurons from progesterone-treated Wobbler mice with decreased nNOS, increased MnSOD, decreased NO^·, O₂^·− and ONOO⁻ and increased activity of complex I with slight, non-significant higher activity of complexes II and III

Fig. 3

Effects of steroid treatment of Wobbler mice on growth factors, choline acetyltransferase (ChAT) and cell signaling molecules. Wobbler mice show low expression of BDNF and its cognate receptor TrkB in motoneurons, whereas treatment with progesterone increases BDNF and TrkB vs. untreated Wobbler mice (*p < 0.05 and **p < 0.01, respectively). Similar results were obtained for BDNF and TrkB with ALLO treatment. The intracellular domain of the death receptor p75^NTR expressed in ventral horn neurons was increased in untreated Wobblers and decreased by progesterone and ALLO treatment (*p < 0.05 for both vs untreated Wobbler group). ChAT immunostaining of motoneurons was increased following prolonged treatment with progesterone (***p < 0.001) or ALLO (**p < 0.01) compared to the untreated Wobbler group. The two bottom graphs show opposite changes of cell signaling molecules: pJNK protein expression was decreased by progesterone (*p < 0.05) and ALLO (**p < 0.01) treatment, whereas pAKT was increased by progesterone (**p < 0.01) and ALLO (*p < 0.05) treatment of Wobbler mice. (Data modified from Meyer et al 2017). Results shown as % of control. ALLO allopregnanolone