Summary Renal ciliopathies are a leading cause of kidney failure, but their exact etiology is poorly understood. NEK8/NPHP9 is a ciliary kinase associated with two renal ciliopathies in humans and mice, nephronophthisis (NPHP) and polycystic kidney disease. Here, we identify NEK8 as a key effector of the ATR-mediated replication stress response. Cells lacking NEK8 form spontaneous DNA double-strand breaks (DSBs) which further accumulate when replication forks stall, and they exhibit reduced fork rates, unscheduled origin firing, and increased replication fork collapse. NEK8 suppresses DSB formation by limiting cyclin A-associated CDK activity. Strikingly, a mutation in NEK8 that is associated with renal ciliopathies affects its genome maintenance functions. Moreover, kidneys of NEK8 mutant mice accumulate DNA damage, and loss of NEK8 or replication stress similarly disrupts renal cell architecture in a 3D-culture system. Thus, NEK8 is a critical component of the DNA damage response that links replication stress with cystic kidney disorders.

An investigation consisting of both analysis and experiments was performed to study impact damage mechanisms and mechanics of laminated composites subjected to low-velocity impact. In order to fundamentally understand the impact damage of laminated composites, a unique test program was developed and performed by using a specially designed line-loading impactor. Experimental findings from the tests were obtained and presented in the first part of this series on the impact study. In this paper, an analysis will be presented for predicting the impact damage resulting from the line-loading impact and for determining essential parameters governing the impact damage. The model consists of a transient dynamic finite element analysis for calculating stresses, strains and deformations of composite plates during impact, and a failure analysis for predicting the threshold of impact damage and initiation of delaminations and micro-cracks. The predictions based on the analysis agreed with the test results reasonably well. Based on the unique approach, the proposed analysis, coupled with the experiment, was able to provide comprehensive information for fundamentally understanding the impact damage mechanisms and mechanics of laminated composites.

Senescence, defined as irreversible cell-cycle arrest, is the main driving force of aging and age-related diseases. Here, we performed high-throughput screening to identify compounds that alleviate senescence and identified the ataxia telangiectasia mutated (ATM) inhibitor KU-60019 as an effective agent. To elucidate the mechanism underlying ATM's role in senescence, we performed a yeast two-hybrid screen and found that ATM interacted with the vacuolar ATPase V subunits ATP6V1E1 and ATP6V1G1. Specifically, ATM decreased E-G dimerization through direct phosphorylation of ATP6V1G1. Attenuation of ATM activity restored the dimerization, thus consequently facilitating assembly of the V and V domains with concomitant reacidification of the lysosome. In turn, this reacidification induced the functional recovery of the lysosome/autophagy system and was coupled with mitochondrial functional recovery and metabolic reprogramming. Together, our data reveal a new mechanism through which senescence is controlled by the lysosomal-mitochondrial axis, whose function is modulated by the fine-tuning of ATM activity.

SummaryHutchinson‐Gilford progeria syndrome (HGPS) constitutes a genetic disease wherein an aging phenotype manifests in childhood. Recent studies indicate that reactive oxygen species (ROS) play important roles in HGPS phenotype progression. Thus, pharmacological reduction in ROS levels has been proposed as a potentially effective treatment for patient with this disorder. In this study, we performed high‐throughput screening to find compounds that could reduce ROS levels in HGPS fibroblasts and identified rho‐associated protein kinase (ROCK) inhibitor (Y‐27632) as an effective agent. To elucidate the underlying mechanism of ROCK in regulating ROS levels, we performed a yeast two‐hybrid screen and discovered that ROCK1 interacts with Rac1b. ROCK activation phosphorylated Rac1b at Ser71 and increased ROS levels by facilitating the interaction between Rac1b and cytochrome c. Conversely, ROCK inactivation with Y‐27632 abolished their interaction, concomitant with ROS reduction. Additionally, ROCK activation resulted in mitochondrial dysfunction, whereas ROCK inactivation with Y‐27632 induced the recovery of mitochondrial function. Furthermore, a reduction in the frequency of abnormal nuclear morphology and DNA double‐strand breaks was observed along with decreased ROS levels. Thus, our study reveals a novel mechanism through which alleviation of the HGPS phenotype is mediated by the recovery of mitochondrial function upon ROCK inactivation.