Smooth muscle α actin is specifically required for the maintenance of lactation

The mammary hair of Monodelphis domestica and homology of the mammary pilosebacous unit

The unitary mammary gland is a synapomorphy of therian mammals and is thought to have evolved from the pilosebaceous organ in the mammalian stem lineage from which the lactogenic patch of monotremes is also derived. One of the key lines of evidence for the homology of the nipple and the lactogenic patch is that marsupials have retained a transient hair associated with developing mammary glands. However, these structures have not been documented since the early 20th-century drawings of Ernst Bresslau. In this study, we examine the developing mammary organs of Monodelphis domestica and document the presence of mammary hairs in 12-week-old females, as well as their absence after 18 weeks of age. Histochemical staining for cystine confirms the structures as keratinized hairs. Milk ducts of both juvenile and adult nipples show a division between KRT18+ luminal epithelium and KRT14+ ACTA2+ myoepithelium. These patterns match those in eutherians and suggest a conserved ductal morphology and mechanism of milk expulsion. Finally, PTHLH, a peptide hormone which promotes homeotic transformation of hairy skin into hairless nipples in the mouse, was detected in the Monodelphis milk duct during the mammary hair stage, suggesting that the mutual exclusivity of "hairless nipple" and "hair" organ identity is derived in eutherian mammals. These results reveal shared characteristics of the M. domestica nipple with both the eutherian nipple and the pilosebaceous organ, consistent with the evolutionary derivation of the mammary gland from an ancestral hair organ via developmental individualization of pilosebaceous and mammary identities.

HEARTSVG: a fast and accurate method for identifying spatially variable genes in large-scale spatial transcriptomics

Identifying spatially variable genes (SVGs) is crucial for understanding the spatiotemporal characteristics of diseases and tissue structures, posing a distinctive challenge in spatial transcriptomics research. We propose HEARTSVG, a distribution-free, test-based method for fast and accurately identifying spatially variable genes in large-scale spatial transcriptomic data. Extensive simulations demonstrate that HEARTSVG outperforms state-of-the-art methods with higherF 1 scores (averageF 1 Score=0.948), improved computational efficiency, scalability, and reduced false positives (FPs). Through analysis of twelve real datasets from various spatial transcriptomic technologies, HEARTSVG identifies a greater number of biologically significant SVGs (average AUC = 0.792) than other comparative methods without prespecifying spatial patterns. Furthermore, by clustering SVGs, we uncover two distinct tumor spatial domains characterized by unique spatial expression patterns, spatial-temporal locations, and biological functions in human colorectal cancer data, unraveling the complexity of tumors.

The molecular consequences of androgen activity in the human breast

Estrogen and progesterone have been extensively studied in the mammary gland, but the molecular effects of androgen remain largely unexplored. Transgender men are recorded as female at birth but identify as male and may undergo gender-affirming androgen therapy to align their physical characteristics and gender identity. Here we perform single-cell-resolution transcriptome, chromatin, and spatial profiling of breast tissues from transgender men following androgen therapy. We find canonical androgen receptor gene targets are upregulated in cells expressing the androgen receptor and that paracrine signaling likely drives sex-relevant androgenic effects in other cell types. We also observe involution of the epithelium and a spatial reconfiguration of immune, fibroblast, and vascular cells, and identify a gene regulatory network associated with androgen-induced fat loss. This work elucidates the molecular consequences of androgen activity in the human breast at single-cell resolution.

ΔNp63 maintains the fidelity of the myoepithelial cell lineage and directs cell differentiation programs in the murine salivary gland

Salivary glands consist of several epithelial cell types of distinct lineages and functional characteristics that are established by directed differentiation programs of resident stem and progenitor cells. We have shown that ΔNp63, a crucial transcriptional regulator of stem/progenitor cells, is enriched in both the basal and myoepithelial cell (MEC) populations and that ΔNp63 positive cells maintain all the descendent epithelial cell lineages of the adult mouse salivary glands (mSGs). Although this pivotal role of ΔNp63 in driving the broader epithelial cell fate and identity in the mSG has been demonstrated, how ΔNp63 functions specifically in the commitment and differentiation of the MEC population is less understood. Using multiple genetic mouse models that allow for cell tracing, we show that ΔNp63 is critical in maintaining and renewing MECs, in part through the transcriptional regulation of Acta2 gene expression, a defining marker of this cell population. We demonstrate that during adult mSG homeostasis, ΔNp63 enriched MECs function as bipotent progenitor cells that maintain not only the MEC population, but also the distinctly different ductal cell lineages. The fidelity of this process is dependent on ΔNp63 expression, since MEC-specific ablation of ΔNp63 results in altered MEC differentiation and affects cellular plasticity resulting in aberrant differentiation of the intercalated ducts and acinar cells. In contrast, we find that the contribution of MECs to ductal and acinar cell regeneration following severe injury is independent of ΔNp63. Our observations offer new insights into cellular mechanisms driving MEC fate choices and differentiation programs in the context of salivary gland homeostasis and in response to injury and regeneration. Long term, these findings have implications for better treatment of salivary gland dysfunction through stem cell-based approaches.

Ribosome Proteins Represented by RPL27A Mark the Development and Metastasis of Triple-Negative Breast Cancer in Mouse and Human

Triple-negative breast cancer (TNBC) is known to have a poor prognosis and limited treatment options. The lack of targeted therapies and poor prognosis of patients with TNBC have made it urgent to discover novel critical diagnosis and therapeutic targets in the TNBC field. Here, in the current study, we integrated the single-cell RNA-sequencing (scRNA-seq) data from four normal mouse mammary tissues and four mouse breast tumors. Comparative analysis was conducted to identify the gene profiles of normal epithelial cells and cancer cells at different models. Surprisingly, two ribosomal protein genes, Rpl27a and Rpl15, were significantly upregulated in the cancer cells in all the TNBC models. Next, we accessed the scRNA-seq data from human primary and metastatic TNBC tissues, and comparative analysis revealed gene profiles of human primary and metastatic TNBC cancer cells. Ribosomal protein genes, represented by RPL27A and RPL15, showed significantly upregulated expression in metastatic TNBC cancer cells. Pathway analysis on the upregulated genes of the metastatic TNBC cancer cells identified the key regulators and signaling pathways that were driving the metastasis of the TNBC cancer cells. Specifically, EIF2 signaling was significantly activated, and major member genes of this signaling pathway were upregulated. In vitro study revealed that targeting RPL27A or EIF2 signaling in a TNBC cell line, MDA-MB-231, significantly reduced cell migration and invasion. Altogether, these data suggested that the RPL27A gene is conducting critical functions in TNBC cancer development and metastasis and is a potential therapeutic target for TNBC.

An Integrative Single-cell Transcriptomic Atlas of the Post-natal Mouse Mammary Gland Allows Discovery of New Developmental Trajectories in the Luminal Compartment

The mammary gland is a highly dynamic organ which undergoes periods of expansion, differentiation and cell death in each reproductive cycle. Partly because of the dynamic nature of the gland, mammary epithelial cells (MECs) are extraordinarily heterogeneous. Single cell RNA-seq (scRNA-seq) analyses have contributed to understand the cellular and transcriptional heterogeneity of this complex tissue. Here, we integrate scRNA-seq data from three foundational reports that have explored the mammary gland cell populations throughout development at single-cell level using 10× Chromium Drop-Seq. We center our analysis on post-natal development of the mammary gland, from puberty to post-involution. The new integrated study corresponds to RNA sequences from 53,686 individual cells, which greatly outnumbers the three initial data sets. The large volume of information provides new insights, as a better resolution of the previously detected Procr⁺ stem-like cell subpopulation or the identification of a novel group of MECs expressing immune-like markers. Moreover, here we present new pseudo-temporal trajectories of MEC populations at two resolution levels, that is either considering all mammary cell subtypes or focusing specifically on the luminal lineages. Interestingly, the luminal-restricted analysis reveals distinct expression patterns of various genes that encode milk proteins, suggesting specific and non-redundant roles for each of them. In summary, our data show that the application of bioinformatic tools to integrate multiple scRNA-seq data-sets helps to describe and interpret the high level of plasticity involved in gene expression regulation throughout mammary gland post-natal development.

Lacrimal Gland Myoepithelial Cells Are Altered in a Mouse Model of Dry Eye Disease

The purpose of this study was to determine the pathogenic changes that occur in myoepithelial cells (MECs) from lacrimal glands of a mouse model of Sjögren syndrome. MECs were cultured from lacrimal glands of C57BL/6J [wild type (WT)] and thrombospondin 1 null (TSP1^-/-, alias Thbs1^-/-) mice and from mice expressing α-smooth muscle actin-green fluorescent protein that labels MECs. MECs were stimulated with cholinergic and α₁-adrenergic agonists, vasoactive intestinal peptide (VIP), and the purinergic agonists ATP and UTP. Then intracellular [Ca²⁺] was measured using fura-2, and contraction was observed using live cell imaging. Expression of purinergic receptors was determined by Western blot analysis, and mRNA expression was analyzed by microarray. The increase in intracellular [Ca²⁺]_I with VIP and UTP was significantly smaller in MECs from TSP1^-/- compared with WT mice. Cholinergic agonists, ATP, and UTP stimulated contraction in MECs, although contraction of MECs from TSP1^-/- mice was reduced compared with WT mice. The amount of purinergic receptors P2Y1, P2Y11, and P2Y13 was significantly decreased in MECs from TSP1^-/- compared with WT mice, whereas several extracellular matrix and inflammation genes were up-regulated in MECs from TSP1^-/- mice. We conclude that lacrimal gland MEC function is altered by inflammation because the functions regulated by cholinergic agonists, VIP, and purinergic receptors are decreased in TSP1^-/- compared with WT mice.

The Role of Stroma in Ovarian Cancer

Background: Ovarian cancer is one of the gynecological malignancies responsible for thousands of deaths in women worldwide. Malignant solid tumors are formed by malignant cells and stroma that influence each other, where different types of cells in the stromal environment can be recruited by malignant cells to promote tumor growth and facilitate metastasis. The chronic inflammatory response is increasingly accepted in its relation to the pathophysiology of the onset and development of tumors, sustained cell proliferation in an environment rich in inflammatory cells, growth factors, activated stroma and DNA damage agents may increase the risk to develop a neoplasm.Methods: A search for the following keywords was performed in the PubMed database; "Ovarian cancer", "stroma", "tumor-associated macrophages", "cancer-associated fibroblasts", "cytokines", "angiogenesis", "epithelial-mesenchymal transition", and "extracellular matrix".Results: The articles identified were published in English between 1971 and 2018. A total of 154 articles were selected for further analysis. Conclusion: We consider ovarian cancer as a heterogeneous disease, not only in the sense that different histological or molecular subtypes may be behind the same clinical result, but also that multiple cell types besides cancer cells, like other non-cellular components, need to be mobilized and coordinated to support tumor survival, growth, invasion and progression.

Smooth Muscle α-Actin Deficiency Leads to Decreased Liver Fibrosis via Impaired Cytoskeletal Signaling in Hepatic Stellate Cells

In the liver, smooth muscle α-actin (SM α-actin) is up-regulated in hepatic stellate cells (HSCs) as they transition to myofibroblasts during liver injury and the wound healing response. Whether SM α-actin has specific functional effects on cellular effectors of fibrosis such as HSC is controversial. Here, the relationship between SM α-actin and type 1 collagen expression (COL1A1), a major extracellular matrix protein important in liver fibrosis, is investigated with the results demonstrating that knockout of SM α-actin leads to reduced liver fibrosis and COL1 expression. The mechanism for the reduction in fibrogenesis in vivo is multifactorial, including not only a reduction in the number of HSCs, but also an HSC-specific reduction in COL1 expression in Acta2-deficient HSCs. Despite a compensatory increase in expression of cytoplasmic β-actin and γ-actin isoforms in Acta2^-/- HSCs, defects were identified in each transforming growth factor beta/Smad2/3 and ET-1/Erk1/2 signaling in Acta2^-/- HSCs. These data not only suggest a molecular link between the SM α-actin cytoskeleton and classic fibrogenic signaling cascades, but also emphasize the relationship between SM α-actin and fibrogenesis in hepatic myofibroblasts in vivo.

A Potential Role for the Existence of Pericytes in the Neurovascular Unit of the Sexually Dimorphic Nucleus of the Rat Preoptic Area to Control Blood-Brain Barrier Function

BACKGROUND

The present study aimed at determining pericytes, a missing component in the previously proposed living neurovascular unit (NVU) of the sexually dimorphic nucleus of the preoptic area (SDN-POA) in rats.

MATERIALS AND METHODS

Calbindin D28K-immunoreactivities (CB28-irs) were used to delineate the SDN-POA in which CD13-immunoreactivities (CD13-irs) or alpha-smooth muscle actinimmunoreactivities (αSMA-irs), two pericyte biomarkers serving the indexes of pericytes, were tagged using two adjacent brain sections (90-micron intervals). In addition, the nestinimmunoreactive (nestin-ir) cells in the SDN-POA were counted as pericytes referring to additional standards: location and nucleic and cellular morphology. Male SDN-POA volume (5.0±0.3x10-3 mm3) was significantly larger than the female (1.7±0.3x10-3 mm3). Within the SDN-POA, the CD13-irs were characterized as dots, densely packed and net-like in distribution, while the αSMAirs, excluding pipe-like or circular structures, appeared as short rod-like structures that were sparsely distributed.

RESULTS

The immunoreactive counts of alpha-smooth muscle actin were 353±57/mm2 in males and 124±46/mm2 in females (p<0.05). On the other hand, densities of the dot-like CD13-irs were similar between males (4009±301/mm2) and females (4018±414/ mm2). There was no difference between the male and the female in the nestin-ir pericyte count in the SDN-POA.

CONCLUSION

In conclusion, the present study adds new information concerning pericytes to the living NVU of the SDN-POA. There is a difference of sex in the count of the αSMA-irs in the living NVU of the SDN-POA. However, why such a difference exists warrants further investigations.

Effect of high-fat diet feeding and associated transcriptome changes in the peak lactation mammary gland in C57BL/6 dams

Maternal consumption of a high-fat diet (HFD) during pregnancy has established adverse effects on the developing neonate. In this study, we aimed to investigate the effect of an HFD on the murine mammary gland during midlactation. Female C57BL/6J mice were placed on either a low-fat diet (LFD/10% fat) or HFD (60% fat) from 3 wk of age through peak lactation (lactation day 11/L11). After 4 wk of consuming either the LFD or HFD, female mice were bred. There were no significant differences in milk yield between treatment groups, which was measured from L1 to L9. On L10, mice were subjected to an overnight fast and then euthanized on the morning of L11. Total RNA was isolated from inguinal mammary glands for whole transcriptome sequencing. We found 628 genes that were differentially expressed between the treatment groups. Notably, HFD feeding resulted in expression alterations of genes involved in collagen and cytoplasmic components. Additionally, genes related to inflammatory and immune responses were also impacted. Differential expression in gene transcript isoforms between the treatment groups was detected in three genes related to mammary duct development. This study sheds light as to how an HFD may affect the mammary gland transcriptome during midlactation.

PAI-1 is a novel component of the miR-17~92 signaling that regulates pulmonary artery smooth muscle cell phenotypes

We have previously reported that miR-17~92 is critically involved in the pathogenesis of pulmonary hypertension (PH). We also identified two novel mR-17/20a direct targets, PDZ and LIM domain protein 5 (PDLIM5) and prolyl hydroxylase 2 (PHD2), and elucidated the signaling pathways by which PDLIM5 and PHD2 regulate functions of pulmonary artery smooth muscle cells (PASMCs). In addition, we have shown that plasminogen activator inhibitor-1 (PAI-1) is also downregulated in PASMCs that overexpress miR-17~92. However, it is unclear whether PAI-1 is a direct target of miR-17~92 and whether it plays a role in regulating the PASMC phenotype. In this study, we have identified PAI-1 as a novel target of miR-19a/b, two members of the miR-17~92 cluster. We found that the 3'-untranslated region (UTR) of PAI-1 contains a miR-19a/b binding site and that miR-19a/b can target this site to suppress PAI-1 protein expression. MiR-17/20a, two other members of miR-17~92, may also indirectly suppress PAI-1 expression through PDLIM5. PAI-1 is a negative regulator of miR-17~92-mediated PASMC proliferation. Silencing of PAI-1 induces Smad2/calponin signaling in PASMCs, suggesting that PAI-1 is a negative regulator of the PASMC contractile phenotype. We also found that PAI-1 is essential for the metabolic gene expression in PASMCs. Furthermore, although there is no significant change in PAI-1 levels in PASMCs isolated from idiopathic pulmonary arterial hypertension and associated pulmonary arterial hypertension patients, PAI-1 is downregulated in hypoxia/Sugen-induced hypertensive rat lungs. These results suggest that miR-17~92 regulates the PASMC contractile phenotype and proliferation coordinately and synergistically by direct and indirect targeting of PAI-1.

Myoepithelial cells are a dynamic barrier to epithelial dissemination

Myoepithelial cells function collectively as a dynamic barrier to the invasion and dissemination of Twist1⁺ luminal epithelial cells and both luminal and basal phenotype breast cancer cells. Barrier function depends on myoepithelial abundance and both smooth muscle contractility and intercellular adhesion within the myoepithelium.

The mammary epithelium is composed of an inner luminal and surrounding myoepithelial cell layer. The presence of cancer cells beyond the myoepithelium defines invasive breast cancer, yet the role of the myoepithelium during invasion remains unclear. We developed a 3D organotypic culture assay to model this process through lineage-specific expression of the prometastatic transcription factor Twist1. We sought to distinguish the functional role of the myoepithelium in regulating invasion and local dissemination. Myoepithelial-specific Twist1 expression induced cell-autonomous myoepithelial cell escape. Remarkably, luminal-specific Twist1 expression was rarely sufficient for escape. Time-lapse microscopy revealed that myoepithelial cells collectively restrain and reinternalize invading Twist1⁺ luminal cells. Barrier function correlated with myoepithelial abundance and required the expression of α-smooth muscle actin and P-cadherin. We next demonstrated that myoepithelial cells can restrain and recapture invasive cancer cells. Our data establish the concept of the myoepithelium as a dynamic barrier to luminal dissemination and implicate both smooth muscle contractility and intercellular adhesion in barrier function.

Upregulation of the actin cytoskeleton via myocardin leads to increased expression of type 1 collagen

Liver fibrosis, a model wound healing system, is characterized by excessive deposition of extracellular matrix (ECM) in the liver. Although many fibrogenic cell types may express ECM, the hepatic stellate cell (HSC) is currently considered to be the major effector. HSCs transform into myofibroblast-like cells, also known as hepatic myofibroblasts in a process known as activation; this process is characterized in particular by de novo expression of smooth muscle alpha actin (SM α-actin) and type 1 collagen. The family of actins, which form the cell's cytoskeleton, are essential in many cellular processes. β-actin and cytoplasmic γ-actin (γ-actin) are ubiquitously expressed, whereas SM α-actin defines smooth muscle cell and myofibroblast phenotypes. Thus, SM α-actin is tightly associated with multiple functional properties. However, the regulatory mechanisms by which actin isoforms might regulate type 1 collagen remain unclear. In primary HSCs from normal and fibrotic rat liver, we demonstrate that myocardin, a canonical SRF cofactor, is upregulated in hepatic myofibroblasts and differentially regulates SM α-actin, γ-actin, and β-actins through activation of an ATTA box in the SM α-actin and a CCAAT box in γ-actin and β-actin promoters, respectively; moreover, myocardin differentially activated serum response factor (SRF) in CArG boxes of actin promoters. In addition, myocardin-stimulated Smad2 phosphorylation and RhoA expression, leading to increased expression of type 1 collagen in an actin cytoskeleton-dependent manner. Myocardin also directly enhanced SRF expression and stimulated collagen 1α1 and 1α2 promoter activities. In addition, overexpression of myocardin in vivo during carbon tetrachloride-induced liver injury led to increased HSC activation and fibrogenesis. In summary, our data suggest that myocardin plays a critical role in actin cytoskeletal dynamics during HSC activation, in turn, specifically regulating type I collagen expression in hepatic myofibroblasts.

Megakaryoblastic leukemia-1 is required for the development of bleomycin-induced pulmonary fibrosis

BACKGROUND

Fibrosing disorders of the lung, such as idiopathic pulmonary fibrosis, are characterized by progressive extracellular matrix accumulation that is driven by myofibroblasts. The transcription factor megakaryoblastic leukemia-1 (MKL1) mediates myofibroblast differentiation in response to several profibrotic stimuli, but the role it plays in mediating pulmonary fibrosis has not been fully elucidated. In this study, we utilized mice that had a germline deletion of MKL1 (MKL1 (-,-)) to determine the role that MKL1 plays in the development of bleomycin-induced pulmonary fibrosis.

METHODS

Bleomycin or normal saline were intratracheally delivered to 9 to 12 week old female MKL1 (+,+) and MKL1 (-,-) mice. Mice were assessed for weight loss and survival to 28 days. Inflammatory responses were assessed through bronchoalveolar lavage at days 3 and 7 post-treatment. The development of pulmonary fibrosis was characterized using hydroxyproline assay and histological staining. MKL1 (+,+) and MKL1 (-,-) mouse lung fibroblasts were isolated to compare morphologic, gene expression and functional differences.

RESULTS

MKL1 (-,-) mice demonstrated increased survival, attenuated weight loss, and decreased collagen accumulation compared to wild-type animals 28-days after intratracheal instillation of bleomycin. Histological analysis demonstrated decreased trichrome, smooth muscle α-actin, and fibronectin staining in MKL1(-,-) mice compared to MKL1 (+,+) controls. Differential cell counts from bronchoalveolar lavage demonstrated that there was attenuated neutrophilia 3 days after bleomycin administration, but no difference at day 7. Isolated mouse lung fibroblasts from MKL1 (-,-) mice had decreased contractility and deposited less fibronectin matrix compared to wild-type controls, suggesting a defect in key remodeling functions.

CONCLUSIONS

Altogether, these data demonstrate that MKL1 plays a significant role in mediating the fibrotic response to bleomycin injury. Loss of MKL1 attenuated early neutrophil influx, as well as myofibroblast-mediated remodeling. Targeting MKL1 activity may therefore be a useful strategy in treating pulmonary fibrosis.

RUNX1, a transcription factor mutated in breast cancer, controls the fate of ER-positive mammary luminal cells

RUNX1 encodes a RUNX family transcription factor (TF) and was recently identified as a novel mutated gene in human luminal breast cancers. We found that Runx1 is expressed in all subpopulations of murine mammary epithelial cells (MECs) except the secretory alveolar luminal cells. Conditional knockout of Runx1 in MECs by MMTV-Cre led to a decrease in luminal MECs, largely due to a profound reduction in the estrogen receptor (ER)-positive mature luminal subpopulation, a phenotype that could be rescued by the loss of either Trp53 or Rb1. Mechanistically RUNX1 represses Elf5, a master regulatory TF gene for alveolar cells, and regulates mature luminal TF/co-factor genes (e.g., Foxa1 and Cited1) involved in the ER program. Collectively, our data identified a key regulator of the ER⁺ luminal lineage whose disruption may contribute to the development of ER⁺ luminal breast cancer when under the background of either TP53 or RB1 loss.

DOI:http://dx.doi.org/10.7554/eLife.03881.001

Stem cells can develop into the many types of specialized cell found in the body. Several proteins regulate these transformations by switching on and off the expression of genes that are specific to different cell types. Disrupting these proteins can cause the development of cells to go awry and can lead to cancer.

A protein called RUNX1 controls gene expression to direct the development of blood cells. Mutations in the gene encoding this protein have been linked to blood cancers and a particular type of breast cancer, which begins in the cells that line the ducts that carry milk towards the nipple.

Mammary duct-lining cells develop from a pool of stem cells that produces breast tissue cells. Now van Bragt et al. have found that RUNX1 is expressed in the cells lining the ducts of the mammary glands, except those that produce milk. Deleting the gene for RUNX1 in mice reduced the number of duct-lining cells, especially a subgroup of cells that are the sensors for the hormone estrogen. Through experiments on breast cancer cells, van Bragt et al. found that RUNX1 is able to dictate the fate of duct-lining breast cells by controlling other protein regulators. RUNX1 boosts the activity of at least one regulator that encourages the cells to become duct-lining cells and represses another regulatory protein that turns cells into milk-producing cells.

Next, van Bragt et al. found that, in mice lacking the gene for RUNX1, reducing the amounts of certain proteins that normally suppress the formation of tumors restored the populations of estrogen-sensing duct-lining cells. This suggests that mutations in the gene encoding RUNX1, coupled with the loss of a tumor-suppressing protein, may contribute to the development of cancer in the cells that line the breast ducts.

The next challenge is to determine exactly how RUNX1 mutations work together with the loss of the tumor-suppressing protein to drive breast cancer development. This knowledge may translate into new approaches to prevent or treat this type of breast cancer.

DOI:http://dx.doi.org/10.7554/eLife.03881.002

Underlying mechanisms involved in the decrease of milk secretion during Escherichia coli endotoxin induced mastitis in lactating mice

Mastitis, the inflammation of mammary glands resulting from bacterial infection, disrupts milk production in lactating mammary glands. In this study, we injected lipopolysaccharide (LPS), one of the endotoxins from Escherichia coli into mouse mammary glands to disrupt milk production, and we investigated the influence of LPS on nutrient uptake, synthesis, and secretion processes for milk component production in alveolar epithelial cells (AEC). The expression of genes relevant to the three-staged milk component production process (nutrient uptake, synthesis, and secretion of milk components) were down-regulated within 12 h after LPS injection in AEC. The internalization of glucose transporter 1 (GLUT-1) from the basolateral membrane to the cytoplasm occurred in accordance with the down-regulation of gene expression 3 h after LPS injection. The abnormal localization of adipophilin and beta-casein was also observed in the LPS-injected mammary glands. SLC7A1, an amino acid transporter, was up-regulated 3 and 6 h after LPS injection. Furthermore, the inactivation of signal transducer and activator of transcription 5 (STAT5) and the activation of STAT3 and nuclear factor-kappa B (NFkappaB) occurred 3 h after LPS injection. These results indicate that the nutrient uptake, synthesis, and secretion of milk components in AEC are rapidly shut down in the lactating mammary glands after LPS injection.

Smooth muscle α actin (Acta2) and myofibroblast function during hepatic wound healing

Smooth muscle α actin (Acta2) expression is largely restricted to smooth muscle cells, pericytes and specialized fibroblasts, known as myofibroblasts. Liver injury, associated with cirrhosis, induces transformation of resident hepatic stellate cells into liver specific myofibroblasts, also known as activated cells. Here, we have used in vitro and in vivo wound healing models to explore the functional role of Acta2 in this transformation. Acta2 was abundant in activated cells isolated from injured livers but was undetectable in quiescent cells isolated from normal livers. Both cellular motility and contraction were dramatically increased in injured liver cells, paralleled by an increase in Acta2 expression, when compared with quiescent cells. Inhibition of Acta2 using several different techniques had no effect on cytoplasmic actin isoform expression, but led to reduced cellular motility and contraction. Additionally, Acta2 knockdown was associated with a significant reduction in Erk1/2 phosphorylation compared to control cells. The data indicate that Acta2 is important specifically in myofibroblast cell motility and contraction and raise the possibility that the Acta2 cytoskeleton, beyond its structural importance in the cell, could be important in regulating signaling processes during wound healing in vivo.

Whole animal knockout of smooth muscle alpha-actin does not alter excisional wound healing or the fibroblast-to-myofibroblast transition

The contractile phenotype and function of myofibroblasts have been proposed to play a critical role in wound closure. It has been hypothesized that smooth muscle α-actin expressed in myofibroblasts is critical for its formation and function. We have used smooth muscle α-actin-null mice to test this hypothesis. Full-thickness excisional wounds closed at a similar rate in smooth muscle α-actin-null and wild-type mice. In addition, fibroblasts in smooth muscle α-actin-null granulation tissue when immunostained with a monoclonal antibody that recognizes all muscle actin isoforms exhibited a myofibroblast-like distribution and a stress fiber-like pattern, showing that these cells acquired the myofibroblast phenotype. Dermal fibroblasts from smooth muscle α-actin-null and wild-type mice formed stress fibers and supermature focal adhesions, and generated similar amounts of contractile force in response to transforming growth factor-β1. Smooth muscle γ-actin and skeletal muscle α-actin were expressed in smooth muscle α-actin-null myofibroblasts, as shown by immunostaining, real-time polymerase chain reaction, and mass spectrometry. These results show that smooth muscle α-actin is not necessary for myofibroblast formation and function and for wound closure, and that smooth muscle γ-actin and skeletal muscle α-actin may be able to functionally compensate for the lack of smooth muscle α-actin in myofibroblasts.