Parathyroid hormone-related protein is a mitogenic and a survival factor of mesangial cells from male mice: role of intracrine and paracrine pathways

Oral bacteria induce IgA autoantibodies against a mesangial protein in IgA nephropathy model mice

IgA nephropathy (IgAN) is caused by deposition of IgA in the glomerular mesangium. The mechanism of selective deposition and production of IgA is unclear; however, we recently identified the involvement of IgA autoantibodies. Here, we show that CBX3 is another self-antigen for IgA in gddY mice, a spontaneous IgAN model, and in IgAN patients. A recombinant antibody derived from gddY mice bound to CBX3 expressed on the mesangial cell surface in vitro and to glomeruli in vivo. An elemental diet and antibiotic treatment decreased the levels of autoantibodies and IgAN symptoms in gddY mice. Serum IgA and the recombinant antibody from gddY mice also bound to oral bacteria of the mice and binding was competed with CBX3. One species of oral bacteria was markedly decreased in elemental diet-fed gddY mice and induced anti-CBX3 antibody in normal mice upon immunization. These data suggest that particular oral bacteria generate immune responses to produce IgA that cross-reacts with mesangial cells to initiate IgAN.

Identification of IgA autoantibodies targeting mesangial cells redefines the pathogenesis of IgA nephropathy

Immunoglobulin A (IgA) nephropathy (IgAN) is the most common type of primary glomerulonephritis, often progressing to renal failure. IgAN is triggered by IgA deposition in the glomerular mesangium by an undefined mechanism. Here, we show that grouped ddY (gddY) mice, a spontaneous IgAN model, produce serum IgA against mesangial antigens, including βII-spectrin. Most patients with IgAN also have serum anti-βII-spectrin IgA. As in patients with IgAN, IgA⁺ plasmablasts accumulate in the kidneys of gddY mice. IgA antibodies cloned from the plasmablasts carry substantial V-region mutations and bind to βII-spectrin and the surface of mesangial cells. These IgAs recognize transfected and endogenous βII-spectrin exposed on the surface of embryonic kidney-derived cells. Last, we demonstrate that the cloned IgA can bind selectively to glomerular mesangial regions in situ. The identification of IgA autoantibody and its antigen in IgAN provides key insights into disease onset and redefines IgAN as a tissue-specific autoimmune disease.

Parathyroid hormone-like hormone plays a dual role in neuroblastoma depending on PTH1R expression

We have previously reported the expression of parathyroid hormone‐like hormone (PTHLH) in well‐differentiated, Schwannian stroma‐rich neuroblastic tumors. The aim of this study was to functionally assess the role of PTHLH and its receptor, PTH1R, in neuroblastoma. Stable knockdown of PTHLH and PTH1R was conducted in neuroblastoma cell lines to investigate the succeeding phenotype induced both in vitro and in vivo. Downregulation of PTHLH reduced MYCN expression and subsequently induced cell cycle arrest, senescence, and migration and invasion impairment in a MYCN‐amplified, TP53‐mutated neuroblastoma cell line. These phenotypes were associated with reduced tumorigenicity in a murine model. We also show that PTHLH expression is not under the control of the calcium‐sensing receptor in neuroblastoma. Conversely, its production is stimulated by epidermal growth factor receptor (EGFR). Accordingly, irreversible EGFR inhibition with canertinib abolished PTHLH expression. The oncogenic role of PTHLH appeared to be a consequence of its intracrine function, as downregulation of its receptor, PTH1R, increased anchorage‐independent growth and induced a more undifferentiated, invasive phenotype. Respectively, high PTH1R mRNA expression was found in MYCN nonamplified primary tumors and also significantly associated with other prognostic factors of good outcome. This study provides the first evidence of the dual role of PTHLH in the behavior of neuroblastomas. Moreover, the identification of EGFR as a transcriptional regulator of PTHLH in neuroblastoma provides a novel therapeutic opportunity to promote a less aggressive tumor phenotype through irreversible inhibition of EGFR tyrosine kinase activity.

Parathyroid hormone-related protein induces fibronectin up-regulation in rat mesangial cells through reactive oxygen species/Src/EGFR signaling

Parathyroid hormone-related protein (PTHrP) is known to be up-regulated in both glomeruli and tubules in patients with diabetic kidney disease (DKD), but its role remains unclear. Previous studies show that PTHrP-induced hypertrophic response in mesangial cells (MCs) and epithelial-mesenchymal transition (EMT) in tubuloepithelial cells can be mediated by TGF-β1. In the present study, although long-term PHTrP (1-34) treatment increased the mRNA and protein level of TGF-β1 in primary rat MCs, fibronectin up-regulation occurred earlier, suggesting that fibronectin induction is independent of TGF-β1/Smad signaling. We thus evaluated the involvement of epidermal growth factor receptor (EGFR) signaling and found that nicotinamide adenine dinucleotide phosphate oxidase-derived reactive oxygen species mediates PTHrP (1-34)-induced Src kinase activation. Src phosphorylates EGFR at tyrosine 845 and then transactive EGFR. Subsequent PI3K activation mediates Akt and ERK1/2 activation. Akt and ERK1/2 discretely lead to excessive protein synthesis of fibronectin. Our study thus demonstrates the new role of PTHrP in fibronectin up-regulation for the first time in glomerular MCs. These data also provided new insights to guide development of therapy for glomerular sclerosis.

Reappraising the exteriorization of the mammalian testes through evolutionary physiology

A number of theories have been proposed to explain the exteriorization of the testicles in most mammalian species. None of these provide a consistent account for the wide variety of testicular locations found across the animal kingdom. It is proposed that testicular location is the result of coordinate action of testicular tissue ecologies to sustain preferential states of homeostatic equipoise throughout evolutionary development in response to the advent of endothermy.

Suppressor of Cytokine Signaling-1/STAT1 Regulates Renal Inflammation in Mesangial Proliferative Glomerulonephritis Models

Mesangial proliferative glomerulonephritis (MsGN) is a significant global threat to public health. Inflammation plays a crucial role in MsGN; however, the underlying mechanism remains unknown. Herein, we demonstrate that suppression of the cytokine signaling-1 (SOCS1)/signal transducer and activator of transcription 1 (STAT1) signaling pathway is associated with renal inflammation and renal injury in MsGN. Using MsGN rat (Thy1.1 GN) and mouse (Habu GN) models, renal SOCS1/STAT1 was determined to be associated with CD4+ T cell infiltration and related cytokines. In vitro, SOCS1 overexpression repressed IFN-γ-induced MHC class II and cytokine levels and STAT1 phosphorylation in mesangial cells. SOCS1 and STAT1 inhibitors significantly inhibited IFN-γ-induced CIITA promoter activity and MHC class II expression. In conclusion, our study emphasizes the pivotal role of the SOCS1/STAT1 axis in the regulation of inflammation in MsGN.

Unitary Physiology

The common relationships among a great variety of biological phenomena seem enigmatic when considered solely at the level of the phenotype. The deep connections in physiology, for example, between the effects of maternal food restriction in utero and the subsequent incidence of metabolic syndrome in offspring, the effects of microgravity on cell polarity and reproduction in yeast, stress effects on jellyfish, and their endless longevity, or the relationship between nutrient abundance and the colonial form in slime molds, are not apparent by phenotypic observation. Yet all of these phenomena are ultimately determined by the Target of Rapamycin (TOR) gene and its associated signaling complexes. In the same manner, the unfolding of evolutionary physiology can be explained by a comparable application of the common principle of cell-cell signaling extending across complex developmental and phylogenetic traits. It is asserted that a critical set of physiologic and phenotypic adaptations emanated from a few crucial, ancestral receptor gene duplications that enabled the successful terrestrial transition of vertebrates from water to land. In combination, mTor and its cognate receptors and a few crucial genetic duplications provide a mechanistic common denominator across a diverse spectrum of biological responses. The proper understanding of their purpose yields a unified concept of physiology and its evolutionary development. © 2018 American Physiological Society. Compr Physiol 8:761-771, 2018.

Autocrine and Paracrine Regulation of the Murine Skeleton by Osteocyte-Derived Parathyroid Hormone-Related Protein

Parathyroid hormone-related protein (PTHrP) and parathyroid hormone (PTH) have N-terminal domains that bind a common receptor, PTHR1. N-terminal PTH (teriparatide) and now a modified N-terminal PTHrP (abaloparatide) are US Food and Drug Administration (FDA)-approved therapies for osteoporosis. In physiology, PTHrP does not normally circulate at significant levels, but acts locally, and osteocytes, cells residing within the bone matrix, express both PTHrP and the PTHR1. Because PTHR1 in osteocytes is required for normal bone resorption, we determined how osteocyte-derived PTHrP influences the skeleton. We observed that adult mice with low PTHrP in osteocytes (targeted with the Dmp1(10kb)-Cre) have low trabecular bone volume and osteoblast numbers, but osteoclast numbers were unaffected. In addition, bone size was normal, but cortical bone strength was impaired. Osteocyte-derived PTHrP therefore stimulates bone formation and bone matrix strength, but is not required for normal osteoclastogenesis. PTHrP knockdown and overexpression studies in cultured osteocytes indicate that osteocyte-secreted PTHrP regulates their expression of genes involved in matrix mineralization. We determined that osteocytes secrete full-length PTHrP with no evidence for secretion of lower molecular weight forms containing the N-terminus. We conclude that osteocyte-derived full-length PTHrP acts through both PTHR1 receptor-mediated and receptor-independent actions in a paracrine/autocrine manner to stimulate bone formation and to modify adult cortical bone strength. © 2017 American Society for Bone and Mineral Research.

Parathyroid hormone-related protein modulates inflammation in mouse mesangial cells and blunts apoptosis by enhancing COX-2 expression

Injury of mesangial cells (MC) is a prominent feature of glomerulonephritis. Activated MC secrete inflammatory mediators that induce cell apoptosis. Parathyroid hormone-related peptide (PTHrP) is a locally active cytokine that enhances cell survival and is upregulated by proinflammatory factors in many cell types. The aim of this study was to analyze the regulation of PTHrP expression by inflammatory cytokines and to evaluate whether PTHrP itself acts as a proinflammatory and/or survival factor on male murine MC in primary culture. Our results showed that IL-1β (10 ng/ml) and TNF-α (10 ng/ml) rapidly and transiently upregulated PTHrP expression in MC. The effects of IL-1β were both transcriptional and posttranscriptional, with stabilization of the PTHrP mRNA by human antigen R (HuR). Proteome profiler arrays showed that PTHrP itself enhanced cytokines within 2 h in cell lysates, mainly IL-17, IL-16, IL-1α, and IL-6. PTHrP also stimulated sustained expression (2-4 h) of chemokines, mainly regulated upon activation normal T cell expressed and secreted (RANTES)/C-C motif chemokine 5 (CCL5) and macrophage inflammatory protein-2 (MIP-2)/C-X-C motif chemokine 2 (CXCL2), thymus and activation-regulated chemokine (TARC)/CCL17, and interferon-inducible T cell α-chemoattractant (I-TAC)/CXCL11. Moreover, PTHrP markedly enhanced cyclooxygenase-2 (COX-2) expression and elicited its autoinduction through the activation of the NF-κB pathway. PTHrP induced MC survival via the COX-2 products, and PTHrP overexpression in MC blunted the apoptotic effects of IL-1β and TNF-α. Altogether, these findings suggest that PTHrP functions as a booster of glomerular inflammatory processes and may be a negative feedback loop preserving MC survival.

Dual roles of parathyroid hormone related protein in TGF-β1 signaling and fibronectin up-regulation in mesangial cells

Little is known about the cross-talk between parathyroid hormone (PTH) related protein (PTHrP) and TGF-β1 in mesangial cells (MCs). Our results showed that PTHrP treatment (≤3 h) induced internalization of PTH1R (PTH/PTHrP receptor)–TβRII (TGF-β type 2 receptor) complex and suppressed TGF-β1-mediated Smad2/3 activation and fibronectin (FN) up-regulation. However, prolonged PTHrP treatment (12–48 h) failed to induce PTH1R–TβRII association and internalization. Total protein levels of PTH1R and TβRII were unaffected by PTHrP treatment. These results suggest that internalization of PTH1R and TβRII after short PTHrP treatment might not lead to their proteolytic destruction, allowing the receptors to be recycled back to the plasma membrane during prolonged PTHrP exposure. Receptor re-expression at the cell surface allows PTHrP to switch from its initial inhibitory effect to promote induction of FN. Our study thus demonstrates the dual roles of PTHrP on TGF-β1 signaling and FN up-regulation for the first time in glomerular MCs. These data also provided new insights to guide development of therapy for diabetic kidney disease (DKD).

The Molecular Apgar Score: A Key to Unlocking Evolutionary Principles

One of the first "tools" used for systematically evaluating successful newborn transitional physiology at birth was the Apgar Score, devised by Virginia Apgar in 1953. This objective assessment tool allowed clinicians to immediately gauge the relative success of a newborn infant making the transition from the in utero liquid immersive environment to the ex utero gas environment in the delivery room during the first minutes after birth. The scoring system, although eponymous, is generally summarized as an acronym based on Appearance, Pulse, Grimace, Activity, and Respiration, criteria evaluated and scored at 1 and 5 min after birth. This common clinical appraisal is a guide for determining the elements of integrated physiology involved as the infant makes the transition from a "sea water" environment of 3% oxygen to a "land" environment in 21% oxygen. Appearance determines the perfusion of the skin with oxygenated blood-turning it pink; Pulse is the rate of heart beat, reflecting successful oxygen delivery to organs; Grimace, or irritability, is a functional marker for nervous system integration; Activity represents locomotor capacity; and, of course, Respiration represents pulmonary function as well as the successful neuro-feedback-mediated drive to breathe, supplying oxygen by inspiring atmospheric gas. Respiration, locomotion, and metabolism are fundamental processes adapted for vertebrate evolution from a water-based to an atmosphere-based life and are reflected by the Apgar Score. These physiologic processes last underwent major phylogenetic changes during the water-land transition some 300-400 million years ago, during which specific gene duplications occurred that facilitated terrestrial adaptation, in particular the parathyroid hormone-related protein receptor, the β-adrenergic receptor, and the glucocorticoid receptor. All these genetic traits and the gene regulatory networks they comprise represent the foundational substructure of the Apgar Score. As such, these molecular elements can be examined using a Molecular Apgar evaluation of keystone evolutionary events that predict successful evolutionary adaptation of physiologic functions necessary for neonatal transition and survival.

The Unicellular State as a Point Source in a Quantum Biological System

A point source is the central and most important point or place for any group of cohering phenomena. Evolutionary development presumes that biological processes are sequentially linked, but neither directed from, nor centralized within, any specific biologic structure or stage. However, such an epigenomic entity exists and its transforming effects can be understood through the obligatory recapitulation of all eukaryotic lifeforms through a zygotic unicellular phase. This requisite biological conjunction can now be properly assessed as the focal point of reconciliation between biology and quantum phenomena, illustrated by deconvoluting complex physiologic traits back to their unicellular origins.

On the Evolution of the Mammalian Brain

Hobson and Friston have hypothesized that the brain must actively dissipate heat in order to process information (Hobson et al., 2014). This physiologic trait is functionally homologous with the first instantation of life formed by lipids suspended in water forming micelles- allowing the reduction in entropy (heat dissipation). This circumvents the Second Law of Thermodynamics permitting the transfer of information between living entities, enabling them to perpetually glean information from the environment, that is felt by many to correspond to evolution per se. The next evolutionary milestone was the advent of cholesterol, embedded in the cell membranes of primordial eukaryotes, facilitating metabolism, oxygenation and locomotion, the triadic basis for vertebrate evolution. Lipids were key to homeostatic regulation of calcium, forming calcium channels. Cell membrane cholesterol also fostered metazoan evolution by forming lipid rafts for receptor-mediated cell-cell signaling, the origin of the endocrine system. The eukaryotic cell membrane exapted to all complex physiologic traits, including the lung and brain, which are molecularly homologous through the function of neuregulin, mediating both lung development and myelinization of neurons. That cooption later exapted as endothermy during the water-land transition (Torday, 2015a), perhaps being the functional homolog for brain heat dissipation and conscious/mindful information processing. The skin and brain similarly share molecular homologies through the “skin-brain” hypothesis, giving insight to the cellular-molecular “arc” of consciousness from its unicellular origins to integrated physiology. This perspective on the evolution of the central nervous system clarifies self-organization, reconciling thermodynamic and informational definitions of the underlying biophysical mechanisms, thereby elucidating relations between the predictive capabilities of the brain and self-organizational processes.

PTHrP Nuclear Localization and Carboxyl Terminus Sequences Modulate Dental and Mandibular Development in Part via the Action of p27

To determine whether the action of the PTHrP nuclear localization sequence and C terminus is mediated through p27 in modulating dental and mandibular development, compound mutant mice, which are homozygous for both p27 deletion and the PTHrP1-84 knock-in mutation (p27(-/-)Pthrp(KI/KI)), were generated. Their teeth and mandibular phenotypes were compared with those of p27(-/-), Pthrp(KI/KI), and wild-type mice. At 2 weeks of age, the mandibular mineral density, alveolar bone volume, osteoblast numbers, and dental volume, dentin sialoprotein-immunopositive areas in the first molar were increased significantly in p27(-/-) mice and decreased dramatically in both Pthrp(KI/KI) and p27(-/-) Pthrp(KI/KI) mice compared with wild-type mice; however, these parameters were partly rescued in p27(-/-) Pthrp(KI/KI) mice compared with Pthrp(KI/KI) mice. These data demonstrate that the deletion of p27 in Pthrp(KI/KI) mice can partially rescue defects in dental and mandibular development. Furthermore, we found that deletion of p27 in Pthrp(KI/KI) mice partially corrected the dental and mandibular phenotype by modulating cell cyclin-regulating molecules and antioxidant enzymes. This study therefore indicates that the p27 pathway may function downstream in the action of PTHrP nuclear localization sequence to regulate dental and mandibular development.

The Emergence of Physiology and Form: Natural Selection Revisited

Natural Selection describes how species have evolved differentially, but it is descriptive, non-mechanistic. What mechanisms does Nature use to accomplish this feat? One known way in which ancient natural forces affect development, phylogeny and physiology is through gravitational effects that have evolved as mechanotransduction, seen in the lung, kidney and bone, linking as molecular homologies to skin and brain. Tracing the ontogenetic and phylogenetic changes that have facilitated mechanotransduction identifies specific homologous cell-types and functional molecular markers for lung homeostasis that reveal how and why complex physiologic traits have evolved from the unicellular to the multicellular state. Such data are reinforced by their reverse-evolutionary patterns in chronic degenerative diseases. The physiologic responses of model organisms like Dictyostelium and yeast to gravity provide deep comparative molecular phenotypic homologies, revealing mammalian Target of Rapamycin (mTOR) as the final common pathway for vertical integration of vertebrate physiologic evolution; mTOR integrates calcium/lipid epistatic balance as both the proximate and ultimate positive selection pressure for vertebrate physiologic evolution. The commonality of all vertebrate structure-function relationships can be reduced to calcium/lipid homeostatic regulation as the fractal unit of vertebrate physiology, demonstrating the primacy of the unicellular state as the fundament of physiologic evolution.

Heterochrony as Diachronically Modified Cell-Cell Interactions

Heterochrony is an enabling concept in evolution theory that metaphorically captures the mechanism of biologic change due to mechanisms of growth and development. The spatio-temporal patterns of morphogenesis are determined by cell-to-cell signaling mediated by specific soluble growth factors and their cognate receptors on nearby cells of different germline origins. Subsequently, down-stream production of second messengers generates patterns of form and function. Environmental upheavals such as Romer’s hypothesized drying up of bodies of water globally caused the vertebrate water-land transition. That transition caused physiologic stress, modifying cell-cell signaling to generate terrestrial adaptations of the skeleton, lung, skin, kidney and brain. These tissue-specific remodeling events occurred as a result of the duplication of the Parathyroid Hormone-related Protein Receptor (PTHrPR) gene, expressed in mesodermal fibroblasts in close proximity to ubiquitously expressed endodermal PTHrP, amplifying this signaling pathway. Examples of how and why PTHrPR amplification affected the ontogeny, phylogeny, physiology and pathophysiology of the lung are used to substantiate and further our understanding through insights to the heterochronic mechanisms of evolution, such as the fish swim bladder evolving into the vertebrate lung, interrelated by such functional homologies as surfactant and mechanotransduction. Instead of the conventional description of this phenomenon, lung evolution can now be understood as adaptive changes in the cellular-molecular signaling mechanisms underlying its ontogeny and phylogeny.

Molecular mechanisms associated with PTHrP-induced proliferation of colon cancer cells

Parathyroid Hormone-related Protein (PTHrP) is normally produced in many tissues and is recognized for its endocrine, paracrine, autocrine and intracrine modes of action. PTHrP is also implicated in different types of cancer and its expression correlates with the severity of colon carcinoma. Using the human colon cell line Caco-2 we recently obtained evidence that PTHrP, through a paracrine pathway, exerts a protective effect under apoptotic conditions. However, if exogenous PTHrP is able or not to induce the proliferation of these intestinal tumor cells is not known. We found that PTHrP treatment increases the number of live Caco-2 cells. The hormone induces the phosphorylation and nuclear translocation of ERK 1/2, α p38 MAPK, and Akt, without affecting JNK phosphorylation. In addition, PTHrP-dependent ERK phosphorylation is reverted when PI3K activity was inhibited. Following MAPKs nuclear translocation, the transcription factors ATF-1 and CREB were activated in a biphasic manner. In addition PTHrP induces the translocation into the nucleus of β-catenin, protein that plays key role in maintaining the growth and proliferation of colorectal cancer, and increases the amount of both positive cell cycle regulators c-Myc and Cyclin D. Studies with ERK1/2, α p38 MAPK, and PI3K specific inhibitors showed that PTHrP regulates Caco-2 cell proliferation via these signaling pathways. In conclusion, the results obtained in this work expand our knowledge on the role of exogenous PTHrP in intestinal tumor cells and identify the signaling pathways that are involved in the mitogenic effect of the hormone on Caco-2 cells.

Functional roles of the nuclear localization signal of parathyroid hormone-related protein (PTHrP) in osteoblastic cells

PTHrP is an important regulator of bone remodelling, apparently by acting through several sequence domains. We here aimed to further delineate the functional roles of the nuclear localization signal (NLS) comprising the 88-107 amino acid sequence of PTHrP in osteoblasts. PTHrP mutants from a human PTHrP (-36/+139) cDNA (wild type) cloned into pcDNA3.1 plasmid with deletion (Δ) of the signal peptide (SP), NLS, T(107), or T107A replacing T(107) by A(107) were generated and stably transfected into osteoblastic MC3T3-E1 cells. In these cells, intracellular trafficking, cell proliferation and viability, as well as cell differentiation were evaluated. In these transfected cells, PTHrP was detected in the cytoplasm and also in the nucleus, except in the NLS mutant. Meanwhile, the PTH type 1 receptor (PTH1R) accumulates in the cytoplasm except for the ΔSP mutant in which the receptor remains at the cell membrane. PTHrP-wild type cells showed enhanced growth and viability, as well as an increased matrix mineralization, alkaline phosphatase activity, and osteocalcin gene expression; and these features were inhibited or abolished in ΔNLS or ΔT(107) mutants. Of note, these effects of PTHrP overexpression on cell growth and function were similarly decreased in the ΔSP mutant after PTH1R small interfering RNA transfection or by a PTH1R antagonist. The present in vitro findings suggest a mixed model for PTHrP actions on osteoblastic growth and function whereby this protein needs to be secreted and internalized via the PTH1R (autocrine/paracrine pathway) before NLS-dependent shuttling to the nucleus (intracrine pathway).