Reshaping of the tumor microenvironment by cellular senescence: An opportunity for senotherapies

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Heparan Sulfate Regulates Hair Follicle and Sebaceous Gland Morphogenesis and Homeostasis

Hair follicle (HF) morphogenesis and cycling are a result of intricate autonomous epithelial-mesenchymal interactions. Once the first HF cycle is complete it repeatedly undergoes cyclic transformations. Heparan sulfate (HS) proteoglycans are found on the cell surface and in the extracellular matrix where they influence a variety of biological processes by interacting with physiologically important proteins, such as growth factors. Inhibition of heparanase (an HS endoglycosidase) in in vitro cultured HFs has been shown to induce a catagen-like process. Therefore, this study aimed to elucidate the precise role of HS in HF morphogenesis and cycling. An inducible tetratransgenic mouse model was generated to excise exostosin glycosyltransferase 1 (Ext1) in keratin 14-positive cells from P21. Interestingly, EXT1^{StEpiΔ/StEpiΔ} mice presented solely anagen HFs. Moreover, waxing the fur to synchronize the HFs revealed accelerated hair regrowth in the EXT1^{StEpiΔ/StEpiΔ} mice and hindered cycling into catagen. The ablation of HS in the interfollicular epidermal cells of mature skin led to the spontaneous formation of new HFs and an increase in Sonic Hedgehog expression resembling wild-type mice at P0, thereby indicating that the HS/Sonic Hedgehog signaling pathway regulates HF formation during embryogenesis and prevents HF formation in mature skin. Finally, the knock-out of HS also led to the morphogenesis and hyperplasia of sebaceous glands and sweat glands in mature mice, leading to exacerbated sebum production and accumulation on the skin surface. Therefore, our findings clearly show that an intricate control of HS levels is required for HF, sebaceous gland, and sweat gland morphogenesis and HF cycling.     

BMP signaling in vascular biology and dysfunction

The vascular system is critical for developmental growth, tissue homeostasis and repair but also for tumor development. Bone morphogenetic protein (BMP) signaling has recently emerged as a fundamental pathway of the endothelium by regulating cardiovascular and lymphatic development and by being causative for several vascular dysfunctions. Two vascular disorders have been directly linked to impaired BMP signaling: pulmonary arterial hypertension and hereditary hemorrhagic telangiectasia. Endothelial BMP signaling critically depends on the cellular context, which includes among others vascular heterogeneity, exposure to flow, and the intertwining with other signaling cascades (Notch, WNT, Hippo and hypoxia). The purpose of this review is to highlight the most recent findings illustrating the clear need for reconsidering the role of BMPs in vascular biology.     

Mutant PCNA alleles are associated with cdc phenotypes and sensitivity to DNA damage in fission yeast

Twenty-eight site-directed mutations were introduced into the fission yeast gene (pcn1 ⁺) that encodes proliferating cell nuclear antigen (PCNA) and their in vivo effects analyzed in a strain with a null pcn1 background. Mutants defective in enhancing processivity of DNA polymerase δ have previously been identified. In this study, we assessed all of the mutants for their sensitivities to temperature, hydroxyurea, UV irradiation and methyl methanesulfonate (MMS), and specific mutants were also tested for sensitivity to γ irradiation. One cold-sensitive allele, pcn1-3, was characterized in detail. This mutant had a recessive cold-sensitive cdc phenotype and showed sensitivity to hydroxyurea, UV, and γ irradiation. At the non-permissive temperature pcn1-3 protein was able to form homotrimers in solution and showed increased stimulation of both synthetic activity and processivity of DNA polymerase δ relative to the wild-type Pcn1⁺ protein. Epistasis analyses indicated that pcn1-3 is defective in the repair pathway involving rad2 ⁺ but not defective in the classical nucleotide excision repair pathway involving rad13 ⁺ . Furthermore, pcn1-3 is either synthetically or conditionally lethal in null checkpoint rad backgrounds and displays a mitotic catastrophe phenotype in these backgrounds. A model for how pcn1-3 defects may affect DNA repair and replication is presented. Received: 5 July 1997 / Accepted: 10 October 1997     

Virulence factors (aerobactin and mucoid phenotype) in Klebsiella pneumoniae and Escherichia coli blood culture isolates

Abstract We examined the presence of two virulence factors in 241 blood isolates of Klebsiella pneumoniae from patients hospitalized during 1989 and 1990 in 7 French hospitals, and 125 blood isolates of Escherichia coli from one hospital. Aerobactin was scored phenotypically and genotypically with an intragenic DNA probe of 2 kb. The mucoid phenotype was assessed by culture on trypticase soy agar and by genotypic analysis (intragenic DNA probe of 235 bp). Only 6% K. pneumoniae isolates were aerobactin-positive with no significant variation according to geographical location while 20% of K. pneumoniae isolates displayed the mucoid phenotype, with a significant variation according to hospital. Aerobactin was always associated with the mucoid phenotype. The frequency of aerobactin production but not mucoid phenotype (14%) was higher among E. coli isolates (48%). They harbored two types of large plasmids. Intraperitoneal injection into mice of 10³ cfu of K. pneumoniae producing both virulence factors demonstrated that capsular serotype K2 was the more virulent K23 and K28.     

Timing of Expression of r and Its Encoding mRNAs in the Developing Cerebral Neocortex and Cerebellum of the Mouse

The expression of tau mRNA and of the corresponding encoded protein variants was studied during postnatal development in two brain regions differing in their timing of differentiation: the cerebral neocortex and the cerebellum. (a) The expression of tau mRNA was different in the two regions. Maximal contents were found at early stages in the cerebral neocortex, with a 10-fold decrease at later stages. In the cerebellum, two peaks of tau mRNA were observed soon after birth and in adulthood, with minimal values at postnatal day 6. (b) The expression of total tau proteins was similar to that of their encoding mRNAs in the cerebral neocortex, i.e., high concentrations after birth and low contents at later stages. In contrast, two peaks of tau proteins were observed in the cerebellum: the first perinatally and the second with a maximum at postnatal day 15. (c) Both in the cerebral neocortex and especially in the cerebellum, increasing concentrations of mature tau variants were expressed at late developmental stages, i.e., when total tau protein contents were decreased. In conclusion, the fluctuations in expression of tau and of its encoding mRNA seen in the cerebellum seem to reflect differences in the timing of differentiation of the various cell types, i.e., the macroneurons and the interneurons, present in this brain region. The adult tau variants appear in both the neocortex and the cerebellum only at late developmental stages, i.e., when most of the circuitry has been established, although these two regions markedly differ in their timing of differentiation.     

Dynamical Systems Approach to Higher-level Heritability

To explain higher-level heritability, we propose a dynamical systems approach, based on simulations of the high-dimensional replicator equation with mutation dynamics. We assume that all variants are generated from within the groups of variants through mutations. Simulating the equation with a random interaction matrix and possible variants, we report that this system tends to have many attractors, of fixed point, chaotic and quasiperiodic type. In a chaotic attractor, special gene-like variants appear to control the heritability ofthe system, in the sense that removal of the variants would easily enable the system to depart from the attractor. Those variants do not predominate in thepopulation size, but have the lowest net reproduction and mutation rates on average. Because their rate of growth is small, they are named neutral phenotypes. Additionally, combinatorial effects of these neutral variants to the entire system are reported.     

Simple But Efficacious Enrichment of Integral Membrane Proteins and Their Interactions for In-Depth Membrane Proteomics

Membrane proteins play essential roles in various cellular processes, such as nutrient transport, bioenergetic processes, cell adhesion, and signal transduction. Proteomics is one of the key approaches to exploring membrane proteins comprehensively. Bottom–up proteomics using LC–MS/MS has been widely used in membrane proteomics. However, the low abundance and hydrophobic features of membrane proteins, especially integral membrane proteins, make it difficult to handle the proteins and are the bottleneck for identification by LC–MS/MS. Herein, to improve the identification and quantification of membrane proteins, we have stepwisely evaluated methods of membrane enrichment for the sample preparation. The enrichment methods of membranes consisted of precipitation by ultracentrifugation and treatment by urea or alkaline solutions. The best enrichment method in the study, washing with urea after isolation of the membranes, resulted in the identification of almost twice as many membrane proteins compared with samples without the enrichment. Notably, the method significantly enhances the identified numbers of multispanning transmembrane proteins, such as solute carrier transporters, ABC transporters, and G-protein–coupled receptors, by almost sixfold. Using this method, we revealed the profiles of amino acid transport systems with the validation by functional assays and found more protein–protein interactions, including membrane protein complexes and clusters. Our protocol uses standard procedures in biochemistry, but the method was efficient for the in-depth analysis of membrane proteome in a wide range of samples.