Ectopic expression of the striatal-enriched GTPase Rhes elicits cerebellar degeneration and an ataxia phenotype in Huntington's disease.

Huntington's disease (HD) is caused by an expansion of glutamine repeats in the huntingtin protein (mHtt) that invokes early and prominent damage of the striatum, a region that controls motor behaviors. Despite its ubiquitous expression, why certain brain regions, such as the cerebellum, are relatively spared from neuronal loss by mHtt remains unclear. Previously, we implicated the striatal-enriched GTPase, Rhes (Ras homolog enriched in the striatum), which binds and SUMOylates mHtt and increases its solubility and cellular cytotoxicity, as the cause for striatal toxicity in HD. Here, we report that Rhes deletion in HD mice (N171-82Q), which express the N-terminal fragment of human Htt with 82 glutamines (Rhes(-/-)/N171-82Q), display markedly reduced HD-related behavioral deficits, and absence of lateral ventricle dilatation (secondary to striatal atrophy), compared to control HD mice (N171-82Q). To further validate the role of GTPase Rhes in HD, we tested whether ectopic Rhes expression would elicit a pathology in a brain region normally less affected in HD. Remarkably, ectopic expression of Rhes in the cerebellum of N171-82Q mice, during the asymptomatic period led to an exacerbation of motor deficits, including loss of balance and motor incoordination with ataxia-like features, not apparent in control-injected N171-82Q mice or Rhes injected wild-type mice. Pathological and biochemical analysis of Rhes-injected N171-82Q mice revealed a cerebellar lesion with marked loss of Purkinje neuron layer parvalbumin-immunoreactivity, induction of caspase 3 activation, and enhanced soluble forms of mHtt. Similarly reintroducing Rhes into the striatum of Rhes deleted Rhes(-/-)Hdh(150Q/150Q) knock-in mice, elicited a progressive HD-associated rotarod deficit. Overall, these studies establish that Rhes plays a pivotal role in vivo for the selective toxicity of mHtt in HD.

Chronic exercise confers neuroprotection in experimental autoimmune encephalomyelitis.

Multiple sclerosis (MS) is an autoimmune disease that affects the CNS, resulting in accumulated loss of cognitive, sensory, and motor function. This study evaluates the neuropathological effects of voluntary exercise in mice with experimental autoimmune encephalomyelitis (EAE), an animal model of MS. Two groups of C57BL/6J mice were injected with an emulsion containing myelin oligodendrocyte glycoprotein and then randomized to housing with a running wheel or a locked wheel. Exercising EAE mice exhibited a less severe neurological disease score and later onset of disease compared with sedentary EAE animals. Immune cell infiltration and demyelination in the ventral white matter tracts of the lumbar spinal cord were significantly reduced in the EAE exercise group compared with sedentary EAE animals. Neurofilament immunolabeling in the ventral pyramidal and extrapyramidal motor tracts displayed a more random distribution of axons and an apparent loss of smaller diameter axons, with a greater loss of fluorescence immunolabeling in the sedentary EAE animals. In lamina IX gray matter regions of the lumbar spinal cord, sedentary animals with EAE displayed a greater loss of α-motor neurons compared with EAE animals exposed to exercise. These findings provide evidence that voluntary exercise results in reduced and attenuated disability, reductions in autoimmune cell infiltration, and preservation of axons and motor neurons in the lumbar spinal cord of mice with EAE.

Tapinarof Is a Natural AhR Agonist that Resolves Skin Inflammation in Mice and Humans.

Tapinarof (GSK2894512) is a naturally derived topical treatment with demonstrated efficacy for patients with psoriasis and atopic dermatitis, although the biologic target and mechanism of action had been unknown. We demonstrate that the anti-inflammatory properties of tapinarof are mediated through activation of the aryl hydrocarbon receptor (AhR). We show that tapinarof binds and activates AhR in multiple cell types, including cells of the target tissue-human skin. In addition, tapinarof moderates proinflammatory cytokine expression in stimulated peripheral blood CD4+ T cells and ex vivo human skin, and impacts barrier gene expression in primary human keratinocytes; both of these processes are likely to be downstream of AhR activation based on current evidence. That the anti-inflammatory properties of tapinarof derive from AhR agonism is conclusively demonstrated using the mouse model of imiquimod-induced psoriasiform skin lesions. Topical treatment of AhR-sufficient mice with tapinarof leads to compound-driven reductions in erythema, epidermal thickening, and tissue cytokine levels. In contrast, tapinarof has no impact on imiquimod-induced skin inflammation in AhR-deficient mice. In summary, these studies identify tapinarof as an AhR agonist and confirm that its efficacy is dependent on AhR.

Lower-limb performance disparities: implications for exercise prescription in multiple sclerosis.

The purpose of this study was to examine unilateral lower-limb exercise tolerance during fixed-load cycling to quantify performance disparities of the legs. Eight individuals with relapsing-remitting multiple sclerosis (MS) and seven controls performed submaximal single-leg cycling. Individuals with MS performed significantly more work with the stronger leg than the weaker leg (stronger leg: 6.4 +/- 1.7 kJ, weaker leg: 4.7 +/- 2.5 kJ, p = 0.02). The control group displayed no statistical differences between limbs (p = 0.36). These results highlight a need for individualized exercise testing when prescribing training programs for those with MS.

Huntingtin promotes mTORC1 signaling in the pathogenesis of Huntington's disease.

In patients with Huntington's disease (HD), the protein huntingtin (Htt) has an expanded polyglutamine (poly-Q) tract. HD results in early loss of medium spiny neurons in the striatum, which impairs motor and cognitive functions. Identifying the physiological role and molecular functions of Htt may yield insight into HD pathogenesis. We found that Htt promotes signaling by mTORC1 [mechanistic target of rapamycin (mTOR) complex 1] and that this signaling is potentiated by poly-Q-expanded Htt. Knocking out Htt in mouse embryonic stem cells or human embryonic kidney cells attenuated amino acid-induced mTORC1 activity, whereas overexpressing wild-type or poly-Q-expanded Htt in striatal neuronal cells increased basal mTOR activity. Striatal cells expressing endogenous poly-Q-expanded Htt showed an increase in the number and size of mTOR puncta on the perinuclear regions compared to cells expressing wild-type Htt. Pull-down experiments indicated that amino acids stimulated the interaction of Htt and the guanosine triphosphatase (GTPase) Rheb (a protein that stimulates mTOR activity), and that Htt forms a ternary complex with Rheb and mTOR. Pharmacologically inhibiting PI3K (phosphatidylinositol 3-kinase) or knocking down Rheb abrogated mTORC1 activity induced by expression of a poly-Q-expanded amino-terminal Htt fragment. Moreover, striatum-specific deletion of TSC1, encoding tuberous sclerosis 1, a negative regulator of mTORC1, accelerated the onset of motor coordination abnormalities and caused premature death in an HD mouse model. Together, our findings demonstrate that mutant Htt contributes to the pathogenesis of HD by enhancing mTORC1 activity.

Bilateral differences in lower-limb performance in individuals with multiple sclerosis.

Bilateral differences in lower-limb strength in people with multiple sclerosis (MS) have been clinically observed. The objectives of this study were to quantify bilateral differences in lower-limb performance and metabolism during exercise. Eight ambulatory individuals with mild MS with an Expanded Disability Status Scale score of 2.6 +/- 1.6 and seven non-MS controls completed bilateral assessments of muscle strength and incremental cycling. Individuals with MS had significant (p < 0.05) between-leg differences in leg strength (strong leg: 43.3 +/- 12.7 kg vs weak leg: 37.7 +/- 15.2 kg), peak oxygen uptake (strong leg: 13.7 +/- 3.2 mL/kg/min vs weak leg: 10.6 +/- 3.0 mL/kg/min), and peak workload (strong leg: 73.4 +/- 22.3 W vs weak leg: 56.3 +/- 26.2 W). No between-leg differences were found in controls (p > 0.05). As anticipated, individuals with MS exhibited significantly greater asymmetry for strength, oxygen uptake, and workload than controls (p < 0.05). The differences between legs varied from 2% to 30% for maximal strength and 4% to 66% for cycling workload in the MS group and 4% to 24% and 0% to 8% for the control group, respectively. Preliminary evidence suggests that the magnitude of differences may be related to limitations in aerobic function.