CD80 on skin stem cells promotes local expansion of regulatory T cells upon injury to orchestrate repair within an inflammatory environment

Following tissue damage, epithelial stem cells (SCs) are mobilized to enter the wound, where they confront harsh inflammatory environments that can impede their ability to repair the injury. Here, we investigated the mechanisms that protect skin SCs within this inflammatory environment. Characterization of gene expression profiles of hair follicle SCs (HFSCs) that migrated into the wound site revealed activation of an immune-modulatory program, including expression of CD80, major histocompatibility complex class II (MHCII), and CXC motif chemokine ligand 5 (CXCL5). Deletion of CD80 in HFSCs impaired re-epithelialization, reduced accumulation of peripherally generated Treg (pTreg) cells, and increased infiltration of neutrophils in wounded skin. Importantly, similar wound healing defects were also observed in mice lacking pTreg cells. Our findings suggest that upon skin injury, HFSCs establish a temporary protective network by promoting local expansion of Treg cells, thereby enabling re-epithelialization while still kindling inflammation outside this niche until the barrier is restored.

Stem cells tightly regulate dead cell clearance to maintain tissue fitness

Macrophages and dendritic cells have long been appreciated for their ability to migrate to and engulf dying cells and debris, including some of the billions of cells that are naturally eliminated from our body daily. However, a substantial number of these dying cells are cleared by 'non-professional phagocytes', local epithelial cells that are critical to organismal fitness. How non-professional phagocytes sense and digest nearby apoptotic corpses while still performing their normal tissue functions is unclear. Here, we explore the molecular mechanisms underlying their multifunctionality. Exploiting the cyclical bouts of tissue regeneration and degeneration during the hair cycle, we show that stem cells can transiently become non-professional phagocytes when confronted with dying cells. Adoption of this phagocytic state requires both local lipids produced by apoptotic corpses to activate RXRα, and tissue-specific retinoids for RARγ activation. This dual factor dependency enables tight regulation of the genes requisite to activate phagocytic apoptotic clearance. The tunable phagocytic program we describe here offers an effective mechanism to offset phagocytic duties against the primary stem cell function of replenishing differentiated cells to preserve tissue integrity during homeostasis. Our findings have broad implications for other non-motile stem or progenitor cells which experience cell death in an immune-privileged niche.

A tissue injury sensing and repair pathway distinct from host pathogen defense

Pathogen infection and tissue injury are universal insults that disrupt homeostasis. Innate immunity senses microbial infections and induces cytokines/chemokines to activate resistance mechanisms. Here, we show that, in contrast to most pathogen-induced cytokines, interleukin-24 (IL-24) is predominately induced by barrier epithelial progenitors after tissue injury and is independent of microbiome or adaptive immunity. Moreover, Il24 ablation in mice impedes not only epidermal proliferation and re-epithelialization but also capillary and fibroblast regeneration within the dermal wound bed. Conversely, ectopic IL-24 induction in the homeostatic epidermis triggers global epithelial-mesenchymal tissue repair responses. Mechanistically, Il24 expression depends upon both epithelial IL24-receptor/STAT3 signaling and hypoxia-stabilized HIF1α, which converge following injury to trigger autocrine and paracrine signaling involving IL-24-mediated receptor signaling and metabolic regulation. Thus, parallel to innate immune sensing of pathogens to resolve infections, epithelial stem cells sense injury signals to orchestrate IL-24-mediated tissue repair.

Stem cells expand potency and alter tissue fitness by accumulating diverse epigenetic memories

[Figure: see text].

Scanning electron microscopy of murine skin ultrathin sections and cultured keratinocytes

Generating high-quality electron microscopy images of the skin and keratinocytes can be challenging. Here we describe a simple protocol for scanning electron microscopy (SEM) of murine skin. The protocol enables characterization of the ultrastructure of the epidermis, dermis, hair follicles, basement membrane, and cell-cell junctions. We detail the specific steps for sample preparation and highlight the critical need for proper orientation of the sample for ultrathin sectioning. We also describe the isolation and preparation of primary keratinocyte monolayers for SEM.

For complete details on the use and execution of this protocol, please refer to Biswas et al. (2021).

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Visualizing adherens junctions in ultrathin sections of murine skin using SEM

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Generating nanometer scale sections of murine skin using an ultramicrotome

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Protocol adaptable for cultured keratinocytes

Uncovering potential interspecies signaling factors in plant-derived mixed microbial culture

Microbes use signaling factors for intraspecies and interspecies communications. While many intraspecies signaling factors have been found and characterized, discovery of factors for interspecies communication is lagging behind. To facilitate the discovery of such factors, we explored the potential of a mixed microbial culture (MMC) derived from wheatgrass, in which heterogeneity of this microbial community might elicit signaling factors for interspecies communication. The stability of Wheatgrass MMC in terms of community structure and metabolic output was first characterized by 16S ribosomal RNA amplicon sequencing and liquid chromatography/mass spectrometry (LC/MS), respectively. In addition, detailed MS analyses led to the identification of 12-hydroxystearic acid (12-HSA) as one of the major metabolites produced by Wheatgrass MMC. Stereochemical analysis revealed that Wheatgrass MMC produces mostly the (R)-isomer, although a small amount of the (S)-isomer was also observed. Furthermore, 12-HSA was found to modulate planktonic growth and biofilm formation of various marine bacterial strains. The current study suggests that naturally derived MMCs could serve as a simple and reproducible platform to discover potential signaling factors for interspecies communication. In addition, the study indicates that hydroxylated long-chain fatty acids, such as 12-HSA, may constitute a new class of interspecies signaling factors.

Impaired Epidermal to Dendritic T Cell Signaling Slows Wound Repair in Aged Skin

Aged skin heals wounds poorly, increasing susceptibility to infections. Restoring homeostasis after wounding requires the coordinated actions of epidermal and immune cells. Here we find that both intrinsic defects and communication with immune cells are impaired in aged keratinocytes, diminishing their efficiency in restoring the skin barrier after wounding. At the wound-edge, aged keratinocytes display reduced proliferation and migration. They also exhibit a dampened ability to transcriptionally activate epithelial-immune crosstalk regulators, including a failure to properly activate/maintain dendritic epithelial T cells (DETCs), which promote re-epithelialization following injury. Probing mechanism, we find that aged keratinocytes near the wound edge don't efficiently upregulate Skints or activate STAT3. Notably, when epidermal Stat3, Skints, or DETCs are silenced in young skin, re-epithelialization following wounding is perturbed. These findings underscore epithelial-immune crosstalk perturbations in general, and Skints in particular, as critical mediators in the age-related decline in wound-repair.

The hair follicle bulge: a niche for adult stem cells

Adult stem cells (SCs) are essential for tissue homeostasis and wound repair. They have the ability to both self-renew and differentiate into multiple cell types. They often reside in specialized microenvironments or niches that preserve their proliferative and tissue regenerative capacity. The murine hair follicle (HF) has a specialized and permanent compartment--the bulge, which safely lodges SCs and provides the necessary molecular cues to regulate their function. The HF undergoes cyclic periods of destruction, regeneration, and rest, making it an excellent system to study SC biology.

Disposal of cell debris from surplus lactotrophs of pituitary gland

In rats submitted to physiological and experimental stimulation of lactotrophic secretion, as in pregnancy and lactation as well as after estrogen treatment, there is a remarkable proliferation of lactotrophs in the pituitary gland. After interruption of the stimuli, this situation is reversed to basal conditions via a massive programmed cell death of the surplus lactotrophs. The regressive changes occurring in lactotrophs are autolytic in nature, until the advanced stages of degeneration when the cell debris generated by this process are engulfed by phagocytes exhibiting the morphological characteristics of stellate cells. These cells can be seen within the anterior pituitary parenchyma adherent to the wall of capillaries and in the lumen of blood vessels. The number of stellate cells with engulfed lactotroph cell remnants is relatively small in comparison to the massive cell death, an observation that suggests a rapid clearance of cell debris and phagocytic cells from the pituitary parenchyma into the blood stream. The migration of stellate cells from the adenohypophysis involves the degradation of the basement membrane and rearrangement of the capillary wall components. The final disposal of cell debris of regressing lactotrophs within the anterior pituitary therefore appears to be effected by coordination of a pituitary and systemic mononuclear phagocytic system.

Sgk3 links growth factor signaling to maintenance of progenitor cells in the hair follicle

Tyrosine kinase growth factor receptor signaling influences proliferation, survival, and apoptosis. Hair follicles undergo cycles of proliferation and apoptotic regression, offering an excellent paradigm to study how this transition is governed. Several factors are known to affect the hair cycle, but it remains a mystery whether Akt kinases that are downstream of growth factor signaling impact this equilibrium. We now show that an Akt relative, Sgk (serum and glucocorticoid responsive kinase) 3, plays a critical role in this process. Hair follicles of mice lacking Sgk3 fail to mature normally. Proliferation is reduced, apoptosis is increased, and follicles prematurely regress. Maintenance of the pool of transiently amplifying matrix cells is impaired. Intriguingly, loss of Sgk3 resembles the gain of function of epidermal growth factor signaling. Using cultured primary keratinocytes, we find that Sgk3 functions by negatively regulating phosphatidylinositol 3 kinase signaling. Our results reveal a novel and important function for Sgk3 in controlling life and death in the hair follicle.

Differential regulation of midbrain dopaminergic neuron development by Wnt-1, Wnt-3a, and Wnt-5a

The Wnts are a family of glycoproteins that regulate cell proliferation, fate decisions, and differentiation. In our study, we examined the contribution of Wnts to the development of ventral midbrain (VM) dopaminergic (DA) neurons. Our results show that beta-catenin is expressed in DA precursor cells and that beta-catenin signaling takes place in these cells, as assessed in TOPGAL [Tcf optimal-promoter beta-galactosidase] reporter mice. We also found that Wnt-1, -3a, and -5a expression is differentially regulated during development and that partially purified Wnts distinctively regulate VM development. Wnt-3a promoted the proliferation of precursor cells expressing the orphan nuclear receptor-related factor 1 (Nurr1) but did not increase the number of tyrosine hydroxylase-positive neurons. Instead, Wnt-1 and -5a increased the number of rat midbrain DA neurons in rat embryonic day 14.5 precursor cultures by two distinct mechanisms. Wnt-1 predominantly increased the proliferation of Nurr1+ precursors, up-regulated cyclins D1 and D3, and down-regulated p27 and p57 mRNAs. In contrast, Wnt-5a primarily increased the proportion of Nurr1+ precursors that acquired a neuronal DA phenotype and up-regulated the expression of Ptx3 and c-ret mRNA. Moreover, the soluble cysteine-rich domain of Frizzled-8 (a Wnt inhibitor) blocked endogenous Wnts and the effects of Wnt-1 and -5a on proliferation and the acquisition of a DA phenotype in precursor cultures. These findings indicate that Wnts are key regulators of proliferation and differentiation of DA precursors during VM neurogenesis and that different Wnts have specific and unique activity profiles.

Expression of the extra-large G protein alpha-subunit XLalphas in neuroepithelial cells and young neurons during development of the rat nervous system

XLalphas ('extra large' alpha) is a 78 kDa splice variant of the alpha-subunit of the heterotrimeric G protein, Gs (Nature 372 (1994) 804). Prompted by its neuroendocrine-specific tissue distribution in the adult (J. Biol. Chem. 275 (2000) 33622) and its ability to activate adenylyl cyclase (J. Biol. Chem. 275 (2000) 33633), we investigated the expression of XLalphas in the developing rat nervous system using immunofluorescence. Remarkably, XLalphas expression in the neural tube was found to begin at the onset of neurogenesis, being observed in a subset of mitotic neuroepithelial cells as well as in young neurons. At later developmental stages, XLalphas was associated with a subset of neurons in certain regions of the nervous system such as diencephalon, midbrain, hindbrain, spinal cord and sympathetic trunk. These results suggest a role of XLalphas in neuronal differentiation.

Characterization of the extra-large G protein alpha-subunit XLalphas. II. Signal transduction properties

In the preceding paper (Pasolli, H. A., Klemke, M., Kehlenbach, R. H. , Wang, Y., and Huttner, W. B. (2000) J. Biol. Chem. 275, 33622-33632), we report on the tissue distribution and subcellular localization of XLalphas (extra large alphas), a neuroendocrine-specific, plasma membrane-associated protein consisting of a novel 37-kDa XL domain followed by a 41-kDa alphas domain encoded by exons 2-13 of the Galphas gene. Here, we have studied the signal transduction properties of XLalphas. Like Galphas, XLalphas undergoes a conformational change upon binding of GTPgammaS (guanosine 5'-O-(thio)triphosphate), as revealed by its partial resistance to tryptic digestion, which generated the same fragments as in the case of Galphas. Two approaches were used to analyze XLalphas-betagamma interactions: (i) ADP-ribosylation by cholera toxin to detect even weak or transient XLalphas-betagamma interactions and (ii) sucrose density gradient centrifugation to reveal stable heterotrimer formation. The addition of betagamma subunits resulted in an increased ADP-ribosylation of XLalphas as well as an increased sedimentation rate of XLalphas in sucrose density gradients, indicating that XLalphas interacts with the betagamma dimer. Surprisingly, however, XLalphas, in contrast to Galphas, was not activated by the beta2-adrenergic receptor upon reconstitution of S49cyc(-) membranes. Similarly, using photoaffinity labeling of pituitary membranes with azidoanilide-GTP, XLalphas was not activated upon stimulation of pituitary adenylyl cyclase-activating polypeptide (PACAP) receptors or other Galphas-coupled receptors known to be present in these membranes, whereas Galphas was. Despite the apparent inability of XLalphas to undergo receptor-mediated activation, XLalphas-GTPgammaS markedly stimulated adenylyl cyclase in S49cyc(-) membranes. Moreover, transfection of PC12 cells with a GTPase-deficient mutant of XLalphas, XLalphas-Q548L, resulted in a massive increase in adenylyl cyclase activity. Our results suggest that in neuroendocrine cells, the two related G proteins, Galphas and XLalphas, exhibit distinct properties with regard to receptor-mediated activation but converge onto the same effector system, adenylyl cyclase.

Characterization of the extra-large G protein alpha-subunit XLalphas. I. Tissue distribution and subcellular localization

Our group previously described a new type of G protein, the 78-kDa XLalphas (extra large alphas) (Kehlenbach, R. H., Matthey, J., and Huttner, W. B. (1994) Nature 372, 804-809 and (1995) Nature 375, 253). Upon subcellular fractionation, XLalphas labeled by ADP-ribosylation with cholera toxin was previously mainly detected in the bottom fractions of a velocity sucrose gradient that contained trans-Golgi network and was differentially distributed to Galphas, which also peaked in the top fractions containing plasma membrane. Here, we investigate, using a new antibody specific for the XL domain, the tissue distribution and subcellular localization of XLalphas and novel splice variants referred to as XLN1. Upon immunoblotting and immunofluorescence analysis of various adult rat tissues, XLalphas and XLN1 were found to be enriched in neuroendocrine tissues, with a particularly high level of expression in the pituitary. By both immunofluorescence and immunogold electron microscopy, endogenous as well as transfected XLalphas and XLN1 were found to be predominantly associated with the plasma membrane, with only little immunoreactivity on internal, perinuclear membranes. Upon subcellular fractionation, immunoreactive XLalphas behaved similarly to Galphas but was differentially distributed to ADP-ribosylated XLalphas. Moreover, the bottom fractions of the velocity sucrose gradient were found to contain not only trans-Golgi network membranes but also certain subdomains of the plasma membrane, which reconciles the present with the previous observations. To further investigate the molecular basis of the association of XLalphas with the plasma membrane, chimeric proteins consisting of the XL domain or portions thereof fused to green fluorescent protein were analyzed by fluorescence and subcellular fractionation. In both neuroendocrine and non-neuroendocrine cells, a fusion protein containing the entire XL domain, in contrast to one containing only the proline-rich and cysteine-rich regions, was exclusively localized at the plasma membrane. We conclude that the physiological role of XLalphas is at the plasma membrane, where it presumably is involved in signal transduction processes characteristic of neuroendocrine cells.

Isolation of human uteroglobin from blood filtrate

The purpose of this study was to assess the possibility of isolating biologically active peptides from human blood using large volumes of blood filtrate, which are available from patients undergoing extracorporeal ultrafiltration because of renal insufficiency. This filtrate was submitted to six chromatographic separation steps, yielding one purified peptide which was completely analysed in its primary structure. It was found to be strikingly similar to proteins, described initially as rabbit uteroglobin (or blastokinin) and, more recently, from human bronchial lavage as the '10 kDa Clare cell protein', as well as from human urine as 'protein-1'. The natural molecule contains two chains of identical amino acid sequences of 70 residues which are arranged as an antiparallel dimer due to the disulphide bonds between two cysteines at positions 3 and 69. Mass analysis of the molecular forms yielded molecular weights from 15827 Da (non-oxidized form) to 15859 Da (bi-oxidized form). We conclude that this peptide isolated from the filtrate represents the human uteroglobin, and we demonstrate for the first time that this peptide may be involved as a humoral factor in reproductive or other physiological functions.

Changes in thyrotroph and somatotroph cell populations induced by stimulation and inhibition of their secretory activity

The populations of cells which produce immunoreactive growth hormone (GH) and thyroid stimulating hormone (TSH) in the rat pituitary gland do not occur in fixed percentages but vary greatly under different physiological and experimental conditions. These variations can be directly correlated to the levels of stimulation and/or inhibition of the specific secretory activity. In both types of cell, sustained stimulation with trophic hormones or blockage of the feedback mechanisms induces remarkable growth in the specific cell population. Conversely, the interruption or inhibition of the stimulus thwarted the hormonal secretion and caused a massive degeneration of redundant cells. The stimulation of both GH and TSH cells is accompanied by an enhanced secretory activity as judged by their higher concentrations in serum and hypertrophy of the cytoplasmic organelles involved in synthesis and intracellular processing of the hormones. By contrast, interruption of the stimulus is followed by a variable degree of disruption of the cytoplasmic organization, including a sizable degeneration of cells. In stimulated rats, the concentrations of both GH and TSH decreased significantly in pituitary tissue due to mobilization of the hormonal stores contained in secretory granules. On the other hand, the withdrawal of stimuli blocked the hormonal release; this is reflected by the accumulation of both hormones and secretory granules in pituitary tissue. The strict correlation between the size of the GH and TSH populations with stimulation and inhibition of hormonal secretory activity reported in this investigation further supports the critical role played by the cell renewal process in endocrine secretion.

Bioactivity and immunoreactivity of rat pituitary prolactin submitted to various extraction procedures

Pituitary glands of rats, injected with estrogen to increase the prolactin (PRL) storage in secretory granules, were submitted to various extraction procedures for prolactin. Homogenization and centrifugation of pituitary tissue, in Tris-HCl buffer, pH 7.3, yielded a small amount of radioimmunoassayable prolactin, which increased remarkably after extraction in alkaline pH, disruption of granular membranes with Lubrol and specially after treatment with 2.5 mol/l urea. Nb2 lymphoma cell and pigeon crop sac bioassay (BA) revealed higher levels of bioactivity after extraction in Tris buffer, pH 7.3, in comparison to RIA, with BA/RIA ratios of 1.4 and 2.3, respectively. Bioassays of pituitary PRL extracted with Lubrol and alkaline medium, were less effective in quantifying PRL than RIA. Treatment of pituitary homogenates with urea produced the highest levels of PRL by both BA and RIA, with BA/RIA ratios close to 1. The thorough depolymerization of big PRL effected by urea produced the release of monomeric subunits which allows a complete quantification of the total content in the pituitary gland.

The mammosomatotroph: a transitional cell between growth hormone and prolactin producing cells? An immunocytochemical study

In this report the occurrence of mammosomatotroph (MS) cells was correlated with changes in the somatotroph population of adult rat pituitary gland submitted to various experimental conditions (ovariectomized, orchidectomized and intact males, and after treatment with oestradiol benzoate). Cell and volume density of somatotrophs were assessed in sections stained with the immunogold-silver enhancement technique. Mammosomatotrophs were identified by double immunogold labelling at the electron microscopic level. Colocalization of prolactin (PRL) and growth hormone (GH) in the same cell was rarely observed. Only a few MS cells (0.1-0.2% of all parenchymal cells) were found in some experimental models. Oestrogen treatment decreased both cell and volume density of somatotrophs in ovariectomized rats. In this model, serum GH increased significantly but no changes in the pituitary content of the hormone were observed. Our results demonstrate that MS cells are an uncommon cell type in the pituitary of adult ovariectomized, orchidectomized and intact male rats. The oestrogen treatment, which is well known to induce proliferation of lactotrophs, has no effects on the MS population. Data presented in this report do not support the suggested role for mammosomatotrophs as transitional cells in the presumptive interconversion of PRL and GH producing cells.

Influence of lactotroph cell density on prolactin secretion in rats

The relationships between the stimulation of prolactin secretion and proliferation of lactotrophs was studied from a multidisciplinary standpoint in three experimental models. Administration of both oestrogen and sulpiride resulted in a significant increase in prolactin secretion and in the lactotroph population. A single injection of 10 micrograms oestradiol benzoate (OB) induced a twofold increase in the proliferation of lactotrophs (morphometrically as volume density), which increased further (2.5-fold) after three OB injections. Parallel changes were observed in the net counts made on lactotrophs sectioned through the nucleus to avoid possible distortions in volume density caused by hypertrophic cytoplasms. Comparable results were obtained with the mitotic index in the same groups of rats exposed to treatment with colchicine. The effect of sulpiride on proliferation of lactotrophs was also significant (1.7-fold) but less pronounced than in rats treated with oestrogens. The treatments with oestrogen and sulpiride did not stimulate lactotrophic activity in a similar way, as judged by the levels of serum prolactin and the storage patterns of small and big prolactin in pituitary glands. Serum prolactin (mean +/- S.E.M.) in control ovariectomized rats was 4.0 +/- 0.9 micrograms/l and one and three injections of OB raised these levels to 14.4 +/- 5.0 and 28.8 +/- 4.6 micrograms/l respectively. The highest levels of serum prolactin were seen in sulpiride-treated rats (467.2 +/- 28.7 micrograms/l). Striking differences occurred in the pituitary contents of big prolactin, the control values increasing from 5.3 +/- 0.5 to 10.2 +/- 1.3 micrograms/mg after one OB injection and to 14.7 +/- 0.7 micrograms/mg after three OB injections.(ABSTRACT TRUNCATED AT 250 WORDS)