An Entosis-Like Process Induces Mitotic Disruption in Pals1 Microcephaly Pathogenesis

Entosis is cell cannibalism utilized by tumor cells to engulf live neighboring cells for pro- or anti-tumorigenic purposes. It is unknown whether this extraordinary cellular event can be pathogenic in other diseases such as microcephaly, a condition characterized by a smaller than normal brain at birth. We find that mice mutant for the human microcephaly-causing gene Pals1, which exhibit diminished cortices due to massive cell death, also exhibit nuclei enveloped by plasma membranes inside of dividing cells. These cell-in-cell (CIC) structures represent a dynamic process accompanied by lengthened mitosis and cytokinesis abnormalities. As shown in tumor cells, ROCK inhibition completely abrogates CIC structures and restores the normal length of mitosis. Moreover, genetic elimination of Trp53 produces a remarkable rescue of cortical size along with substantial reductions of CIC structures and cell death. These results provide a novel pathogenic mechanism by which microcephaly is produced through entotic cell cannibalism

Sex and Race Disparities in Mortality and Years of Potential Life Lost Among People With HIV: A 21-Year Observational Cohort Study

BACKGROUND: Since the availability of antiretroviral therapy, mortality rates among people with HIV (PWH) have decreased; however, this does not quantify premature deaths among PWH, and disparities persist. METHODS: We examined all-cause and premature mortality among PWH receiving care at the Vanderbilt Comprehensive Care Clinic from January 1998 to December 2018. Mortality rates were compared by demographic and clinical factors, and adjusted incidence rate ratios (aIRRs) were calculated using multivariable Poisson regression. For individuals who died, age-adjusted years of potential life lost (aYPLL) per total person-years living with HIV were calculated from US sex-specific life tables, and sex and race differences were examined using multivariable linear regression. RESULTS: Among 6531 individuals (51% non-Hispanic [NH] White race, 40% NH Black race, 21% cis-gender women, 78% cis-gender men) included, 956 (14.6%) died. In adjusted analysis, PWH alive in the most recent calendar era (2014-2018) had decreased risk of mortality compared with those in the earliest calendar era (1998-2003; aIRR, 0.22; 95% CI, 0.17-0.29), and women had increased risk of death compared with men (aIRR, 1.31; 95% CI, 1.12-1.54). Of those who died, Black women had the highest aYPLL (aIRR, 592.5; 95% CI, 588.4-596.6), followed by Black men (aIRR, 470.7; 95% CI, 468.4-472.9), White women (aIRR, 411.5; 95% CI, 405.6-417.4), then White men (aIRR, 308.6; 95% CI, 308.0-309.2). In adjusted models, higher YPLL remained associated with NH Black race and cis-gender women, regardless of HIV risk factor. CONCLUSIONS: Despite marked improvement over time, sex disparities in mortality as well as sex and race disparities in YPLL remained among PWH in this cohort

Retrogradely Transportable Lentivirus Tracers for Mapping Spinal Cord Locomotor Circuits

Retrograde tracing is a key facet of neuroanatomical studies involving long distance projection neurons. Previous groups have utilized a variety of tools ranging from classical chemical tracers to newer methods employing viruses for gene delivery. Here, we highlight the usage of a lentivirus that permits highly efficient retrograde transport (HiRet) from synaptic terminals within the cervical and lumbar enlargements of the spinal cord. By injecting HiRet, we can clearly identify supraspinal and propriospinal circuits innervating motor neuron pools relating to forelimb and hindlimb function. We observed robust labeling of propriospinal neurons, including high fidelity details of dendritic arbors and axon terminals seldom seen with chemical tracers. In addition, we examine changes in interneuronal circuits occurring after a thoracic contusion, highlighting populations that potentially contribute to spontaneous behavioral recovery in this lesion model. Our study demonstrates that the HiRet lentivirus is a unique tool for examining neuronal circuitry within the brain and spinal cord

Effects of αTAT1 and HDAC5 on axonal regeneration in adult neurons

<div><p>The role of posttranslational modifications in axonal injury and regeneration has been widely studied but there has been little consensus over the mechanism by which each modification affects adult axonal growth. Acetylation is known to play an important role in a variety of neuronal functions and its homeostasis is controlled by two enzyme families: the Histone Deacetylases (HDACs) and Histone Acetyl Transferases (HATs). Recent studies show that HDAC5 deacetylates microtubules in the axonal cytoplasm as part of an injury-induced regeneration response, but little is known about how acetylation of microtubules plays a role. Alpha-tubulin acetyl transferase (αTAT1) is a microtubule specific acetyl transferase that binds to microtubules and directly affects microtubule stability in cells. We hypothesize that increasing tubulin acetylation may play an important role in increasing the rate of axonal growth. In this study, we infected cultured adult DRG neurons with αTAT1 and αTAT1-D157N, a catalytically inactive mutant, and HDAC5, using lentiviruses. We found that αTAT1 significantly increases tubulin acetylation in 293T cells and DRG neurons but αTAT1-D157N does not. Furthermore, in neurons infected with αTAT1, a significant increase in acetylated tubulin was detected towards the distal portion of the axon but this increase was not detected in neurons infected with αTAT1-D157N. However, we found a significant increase in axon lengths of DRG neurons after αTAT1 and αTAT1-D157N infection, but no effect on axon lengths after infection with HDAC5. Our results suggest that while αTAT1 may play a role in axon growth <i>in vitro</i>, the increase is not directly due to acetylation of axonal microtubules. Our results also show that HDAC5 overexpression in the axonal cytoplasm does not play a crucial role in axonal regeneration of cultured DRG neurons. We expressed these genes in DRG neurons in adult rats and performed a sciatic nerve crush. We found that axons did not regenerate any better when infected with any of the constructs compared with control animals. Thus, while αTAT1 may be important for axonal growth <i>in vitro</i>, neither αTAT1 nor HDAC5 had an effect <i>in vivo</i> on the regeneration of sciatic nerves.</p></div

De novo variants in MPP5 cause global developmental delay and behavioral changes

Membrane Protein Palmitoylated 5 (MPP5) is a highly conserved apical complex protein essential for cell polarity, fate and survival. Defects in cell polarity are associated with neurologic disorders including autism and microcephaly. MPP5 is essential for neurogenesis in animal models, but human variants leading to neurologic impairment have not been described. We identified three patients with heterozygous MPP5 de novo variants (DNV) and global developmental delay (GDD) and compared their phenotypes and magnetic resonance imaging (MRI) to ascertain how MPP5 DNV leads to GDD. All three patients with MPP5 DNV experienced GDD with language delay/regression and behavioral changes. MRI ranged from normal to decreased gyral folding and microcephaly. The effects of MPP5 depletion on the developing brain were assessed by creating a heterozygous conditional knock out (het CKO) murine model with central nervous system (CNS)-specific Nestin-Cre drivers. In the het CKO model, Mpp5 depletion led to microcephaly, decreased cerebellar volume and cortical thickness. Het CKO mice had decreased ependymal cells and Mpp5 at the apical surface of cortical ventricular zone compared with wild type. Het CKO mice also failed to maintain progenitor pools essential for neurogenesis. The proportion of cortical cells undergoing apoptotic cell death increased, suggesting that cell death reduces progenitor population and neuron number. Het CKO mice also showed behavioral changes, similar to our patients. To our knowledge, this is the first report to show that variants in MPP5 are associated with GDD, behavioral abnormalities and language regression/delay. Murine modeling shows that neurogenesis is likely altered in these individuals, with cell death and skewed cellular composition playing significant roles