A membrane-associated MHC-I inhibitory axis for cancer immune evasion.

Immune-checkpoint blockade has revolutionized cancer treatment, but some cancers, such as acute myeloid leukemia (AML), do not respond or develop resistance. A potential mode of resistance is immune evasion of T cell immunity involving aberrant major histocompatibility complex class I (MHC-I) antigen presentation (AP). To map such mechanisms of resistance, we identified key MHC-I regulators using specific peptide-MHC-I-guided CRISPR-Cas9 screens in AML. The top-ranked negative regulators were surface protein sushi domain containing 6 (SUSD6), transmembrane protein 127 (TMEM127), and the E3 ubiquitin ligase WWP2. SUSD6 is abundantly expressed in AML and multiple solid cancers, and its ablation enhanced MHC-I AP and reduced tumor growth in a CD8+ T cell-dependent manner. Mechanistically, SUSD6 forms a trimolecular complex with TMEM127 and MHC-I, which recruits WWP2 for MHC-I ubiquitination and lysosomal degradation. Together with the SUSD6/TMEM127/WWP2 gene signature, which negatively correlates with cancer survival, our findings define a membrane-associated MHC-I inhibitory axis as a potential therapeutic target for both leukemia and solid cancers.

Clear optically matched panoramic access channel technique (COMPACT) for large-volume deep brain imaging.

To understand neural circuit mechanisms underlying behavior, it is crucial to observe the dynamics of neuronal structure and function in different regions of the brain. Since current noninvasive imaging technologies allow cellular-resolution imaging of neurons only within ~1 mm below the cortical surface, the majority of mouse brain tissue remains inaccessible. While miniature optical imaging probes allow access to deep brain regions, cellular-resolution imaging is typically restricted to a small tissue volume. To increase the tissue access volume, we developed a clear optically matched panoramic access channel technique (COMPACT). With probe dimensions comparable to those of common gradient-index lenses, COMPACT enables a two to three orders of magnitude greater tissue access volume. We demonstrated the capabilities of COMPACT by multiregional calcium imaging in mice during sleep. We believe that large-volume in vivo imaging with COMPACT will be valuable to a variety of deep tissue imaging applications.

Fear conditioning and extinction induce opposing changes in dendritic spine remodeling and somatic activity of layer 5 pyramidal neurons in the mouse motor cortex.

Multiple brain regions including the amygdala and prefrontal cortex are crucial for modulating fear conditioning and extinction. The primary motor cortex is known to participate in the planning, control, and execution of voluntary movements. Whether and how the primary motor cortex is involved in modulating freezing responses related to fear conditioning and extinction remains unclear. Here we show that inactivation of the mouse primary motor cortex impairs both the acquisition and extinction of freezing responses induced by auditory-cued fear conditioning. Fear conditioning significantly increases the elimination of dendritic spines on apical dendrites of layer 5 pyramidal neurons in the motor cortex. These eliminated spines are further apart from each other than expected from random distribution along dendrites. On the other hand, fear extinction causes the formation of new spines that are located near the site of spines eliminated previously after fear conditioning. We further show that fear conditioning decreases and fear extinction increases somatic activities of layer 5 pyramidal neurons in the motor cortex respectively. Taken together, these findings indicate fear conditioning and extinction induce opposing changes in synaptic connections and somatic activities of layer 5 pyramidal neurons in the primary motor cortex, a cortical region important for the acquisition and extinction of auditory-cued conditioned freezing responses.

The Phosphodiesterase 9 Inhibitor PF-04449613 Promotes Dendritic Spine Formation and Performance Improvement after Motor Learning.

The cyclic nucleotide cGMP is an intracellular second messenger with important roles in neuronal functions and animals' behaviors. The phosphodiesterases (PDEs) are a family of enzymes that hydrolyze the second messengers cGMP and cAMP. Inhibition of phosphodiesterase 9 (PDE9), a main isoform of PDEs hydrolyzing cGMP, has been shown to improve learning and memory as well as cognitive function in rodents. However, the role of PDE9 in regulating neuronal structure and function in vivo remains unclear. Here we used in vivo two-photon microscopy to investigate the effect of a selective PDE9 inhibitor PF-04449613 on the activity and plasticity of dendritic spines of layer V pyramidal neurons in the mouse primary motor cortex. We found that administration of PF-04449613 increased calcium activity of dendrites and dendritic spines of layer V pyramidal neurons in mice under resting and running conditions. Chronic treatment of PF-04449613 over weeks increased dendritic spine formation and elimination under basal conditions. Furthermore, PF-04449613 treatment over 1-7 days increased the formation and survival of new spines as well as performance improvement after rotarod motor training. Taken together, our studies suggest that elevating the level of cGMP with the PDE9 inhibitor PF-04449613 increases synaptic calcium activity and learning-dependent synaptic plasticity, thereby contributing to performance improvement after learning. © 2018 Wiley Periodicals, Inc. Develop Neurobiol 00: 000-000, 2018.

Monocular deprivation induces dendritic spine elimination in the developing mouse visual cortex.

It is well established that visual deprivation has a profound impact on the responsiveness of neurons in the developing visual cortex. The effect of visual deprivation on synaptic connectivity remains unclear. Using transcranial two-photon microscopy, we examined the effect of visual deprivation and subsequent recovery on dendritic spine remodeling of layer 5 pyramidal neurons in the mouse primary visual cortex. We found that monocular deprivation (MD), but not binocular deprivation (BD), increased dendritic spine elimination over 3 days in the binocular region of 4-week-old adolescent mice. This MD-induced dendritic spine elimination persisted during subsequent 2-4 days of binocular recovery. Furthermore, we found that average dendritic spine sizes were decreased and increased following 3-day MD and BD, respectively. These spine size changes induced by MD or BD tended to be reversed during subsequent binocular recovery. Taken together, these findings reveal differential effects of MD and BD on synaptic connectivity of layer 5 pyramidal neurons and underscore the persistent impact of MD on synapse loss in the developing visual cortex.