A small-molecule Nrf1 and Nrf2 activator mitigates polyglutamine toxicity in spinal and bulbar muscular atrophy.

Spinal and bulbar muscular atrophy (SBMA, also known as Kennedy's disease) is one of nine neurodegenerative disorders that are caused by expansion of polyglutamine-encoding CAG repeats. Intracellular accumulation of abnormal proteins in these diseases, a pathological hallmark, is associated with defects in protein homeostasis. Enhancement of the cellular proteostasis capacity with small molecules has therefore emerged as a promising approach to treatment. Here, we characterize a novel curcumin analog, ASC-JM17, as an activator of central pathways controlling protein folding, degradation and oxidative stress resistance. ASC-JM17 acts on Nrf1, Nrf2 and Hsf1 to increase the expression of proteasome subunits, antioxidant enzymes and molecular chaperones. We show that ASC-JM17 ameliorates toxicity of the mutant androgen receptor (AR) responsible for SBMA in cell, fly and mouse models. Knockdown of the Drosophila Nrf1 and Nrf2 ortholog cap 'n' collar isoform-C, but not Hsf1, blocks the protective effect of ASC-JM17 on mutant AR-induced eye degeneration in flies. Our observations indicate that activation of the Nrf1/Nrf2 pathway is a viable option for pharmacological intervention in SBMA and potentially other polyglutamine diseases.

Selective modulation of the androgen receptor AF2 domain rescues degeneration in spinal bulbar muscular atrophy.

Spinal bulbar muscular atrophy (SBMA) is a motor neuron disease caused by toxic gain of function of the androgen receptor (AR). Previously, we found that co-regulator binding through the activation function-2 (AF2) domain of AR is essential for pathogenesis, suggesting that AF2 may be a potential drug target for selective modulation of toxic AR activity. We screened previously identified AF2 modulators for their ability to rescue toxicity in a Drosophila model of SBMA. We identified two compounds, tolfenamic acid (TA) and 1-[2-(4-methylphenoxy)ethyl]-2-[(2-phenoxyethyl)sulfanyl]-1H-benzimidazole (MEPB), as top candidates for rescuing lethality, locomotor function and neuromuscular junction defects in SBMA flies. Pharmacokinetic analyses in mice revealed a more favorable bioavailability and tissue retention of MEPB compared with TA in muscle, brain and spinal cord. In a preclinical trial in a new mouse model of SBMA, MEPB treatment yielded a dose-dependent rescue from loss of body weight, rotarod activity and grip strength. In addition, MEPB ameliorated neuronal loss, neurogenic atrophy and testicular atrophy, validating AF2 modulation as a potent androgen-sparing strategy for SBMA therapy.

Sexual Reassignment Fails to Prevent Kennedy's Disease.

Spinal and bulbar muscular atrophy is caused by polyglutamine expansion in the androgen receptor. As an X-linked disease dependent on androgens, symptoms and findings are only fully manifest in males. Here we describe a 40-year-old male-to-female transgender SBMA patient who developed full disease manifestations despite undetectable levels of androgens. We used cell culture and animal models to show that spironolactone, the anti-androgen she had taken for 15 years, promotes nuclear localization and toxicity of the mutant protein, which may explain the disease manifestations in this patient.

Axonal transport of TDP-43 mRNA granules is impaired by ALS-causing mutations.

The RNA-binding protein TDP-43 regulates RNA metabolism at multiple levels, including transcription, RNA splicing, and mRNA stability. TDP-43 is a major component of the cytoplasmic inclusions characteristic of amyotrophic lateral sclerosis and some types of frontotemporal lobar degeneration. The importance of TDP-43 in disease is underscored by the fact that dominant missense mutations are sufficient to cause disease, although the role of TDP-43 in pathogenesis is unknown. Here we show that TDP-43 forms cytoplasmic mRNP granules that undergo bidirectional, microtubule-dependent transport in neurons in vitro and in vivo and facilitate delivery of target mRNA to distal neuronal compartments. TDP-43 mutations impair this mRNA transport function in vivo and in vitro, including in stem cell-derived motor neurons from ALS patients bearing any one of three different TDP-43 ALS-causing mutations. Thus, TDP-43 mutations that cause ALS lead to partial loss of a novel cytoplasmic function of TDP-43.

Cellular observations enabled by microculture: paracrine signaling and population demographics.

The cellular microenvironment plays a critical role in shaping and directing the process of communication between the cells. Soluble signals are responsible for many cellular behaviors such as cell survival, proliferation and differentiation. Despite the importance of soluble signals, canonical methods are not well suited to the study of soluble factor interactions between multiple cell types. Macro-scale technology often puts cells into a convective environment that can wash away and dilute soluble signals from their targets, minimizing local concentrations of important factors. In addition, current methods such as transwells, require large numbers of cells and are limited to studying just two cell types. Here, we present data supporting the use of microchannels to study soluble factor signaling providing improved sensitivity as well as the ability to move beyond existing co-culture and conditioned medium paradigms. In addition, we present data suggesting that microculture can be used to unmask effects of population demographics. In this example the data support the hypothesis that a growth promoting subpopulation of cells exists in the mouse mammary gland.

The Wnt receptor, Lrp5, is expressed by mouse mammary stem cells and is required to maintain the basal lineage.

BACKGROUND: Ectopic Wnt signaling induces increased stem/progenitor cell activity in the mouse mammary gland, followed by tumor development. The Wnt signaling receptors, Lrp5/6, are uniquely required for canonical Wnt activity. Previous data has shown that the absence of Lrp5 confers resistance to Wnt1-induced tumor development. METHODOLOGY/PRINCIPAL FINDINGS: Here, we show that all basal mammary cells express Lrp5, and co-express Lrp6 in a similar fashion. Though Wnt dependent transcription of key target genes is relatively unchanged in mammary epithelial cell cultures, the absence of Lrp5 specifically depletes adult regenerative stem cell activity (to less than 1%). Stem cell activity can be enriched by >200 fold (over 80% of activity), based on high Lrp5 expression alone. Though Lrp5 null glands have apparent normal function, the basal lineage is relatively reduced (from 42% basal/total epithelial cells to 22%) and Lrp5-/- mammary epithelial cells show enhanced expression of senescence-associated markers in vitro, as measured by expression of p16(Ink4a) and TA-p63. CONCLUSIONS/SIGNIFICANCE: This is the first single biomarker that has been demonstrated to be functionally involved in stem cell maintenance. Together, these results demonstrate that Wnt signaling through Lrp5 is an important component of normal mammary stem cell function.