Heterotrimeric G Stimulatory Protein α Subunit Is Required for Intestinal Smooth Muscle Contraction in Mice

Characterization of Digestive Manifestations in Patients with Impaired PTH/PTHrP Signaling Disorder/Pseudohypoparathyroidism

INTRODUCTION

Pseudohypoparathyroidism, newly classified as inactivating PTH/PTHrP signaling disorder (iPPSD) type 2 or type 3, is a rare disease caused by defects in the GNAS imprinted gene that encodes Gsα. The most common phenotype comprises resistance to hormones binding to G protein-coupled receptors such as PTH, PTHrP, or TSH, subcutaneous ossifications, short stature, brachydactyly, and early onset obesity. Uncommon features have been described including sleep apnea, asthma, and resistance to calcitonin. At the national French reference center for rare calcium and phosphate metabolism diseases, a large cohort of patients with iPPSD type 2 and type 3 is followed. Interestingly, digestive manifestations and in particular intractable constipation were regularly reported by families of children with iPPSD type 2 or type 3.

OBJECTIVE

The aim of our study was therefore to specify the frequency and characteristics of digestive manifestations in children followed up for iPPSD2 or iPPSD3 in our reference center.

MATERIAL AND METHODS

Thirty-six patients aged between 2 and 18 years (32 followed up for iPPSD2 and 4 for iPPSD3) were included. Parents completed a specific questionnaire to assess any digestive disorders in their child. The diagnosis of constipation was established using the Bristol visual scale in the event of a score of less than 2 according to stool appearance.

RESULTS

Parents reported constipation through the questionnaires in 22/36 (over 60%) of the children. It was the most frequently reported digestive disorder. Among these 22 children, 19 (87%) had a Bristol score for stool shape and texture between 1 and 2 on a scale of 7, confirming constipation. Dedicated treatment had been initiated for 10 (55%) of them, yet only 3 families (16%) considered this treatment effective. Neonatal vomiting and eating disorders, such as lack of satiety or food selectivity, were also noted in 18 (50%) of patients, as was gastroesophageal reflux present in the neonatal period in 14 (40%) of children. There were no significant differences according to the type of iPPSD or patient age.

CONCLUSION

Our work shows for the first time that digestive manifestations, including constipation, occur frequently in children followed for iPPSD, suggesting a potential role of Gsα and G protein receptors in the digestive tract. It is well known that constipation and digestive symptoms alter quality of life. Early management is therefore essential to improve the quality of life of children followed for iPPSD. Our data need to be confirmed on a larger cohort.

Gsα Regulates Macrophage Foam Cell Formation During Atherosclerosis

BACKGROUND

Many cardiovascular pathologies are induced by signaling through G-protein-coupled receptors via Gsα (G protein stimulatory α subunit) proteins. However, the specific cellular mechanisms that are driven by Gsα and contribute to the development of atherosclerosis remain unclear.

METHODS

High-throughput screening involving data from single-cell and bulk sequencing were used to explore the expression of Gsα in atherosclerosis. The differentially expression and activity of Gsα were analyzed by immunofluorescence and cAMP measurements. Macrophage-specific Gsα knockout (Mac-GsαKO) mice were generated to study the effect on atherosclerosis. The role of Gsα was determined by transplanting bone marrow and performing assays for foam cell formation, Dil-ox-LDL (oxidized low-density lipoprotein) uptake, chromatin immunoprecipitation, and luciferase reporter assays.

RESULTS

ScRNA-seq showed elevated Gnas in atherosclerotic mouse aorta's cholesterol metabolism macrophage cluster, while bulk sequencing confirmed increased GNAS expression in human plaque macrophage content. A significant upregulation of Gsα and active Gsα occurred in macrophages from human and mouse plaques. Ox-LDL could translocate Gsα from macrophage lipid rafts in short-term and promote Gnas transcription through ERK1/2 activation and C/EBPβ phosphorylation via oxidative stress in long-term. Atherosclerotic lesions from Mac-GsαKO mice displayed decreased lipid deposition compared with those from control mice. Additionally, Gsα deficiency alleviated lipid uptake and foam cell formation. Mechanistically, Gsα increased the levels of cAMP and transcriptional activity of the cAMP response element binding protein, which resulted in increased expression of CD36 and SR-A1. In the translational experiments, inhibiting Gsα activation with suramin or cpGN13 reduced lipid uptake, foam cell formation, and the progression of atherosclerotic plaques in mice in vivo.

CONCLUSIONS

Gsα activation is enhanced during atherosclerotic progression and increases lipid uptake and foam cell formation. The genetic or chemical inactivation of Gsα inhibit the development of atherosclerosis in mice, suggesting that drugs targeting Gsα may be useful in the treatment of atherosclerosis.

Endothelial G protein stimulatory α-subunit is a critical regulator of post-ischemic angiogenesis

Post-ischemic angiogenesis is a vital pathophysiological process in diseases such as peripheral arterial disease (PAD), heart ischemia, and diabetic retinopathy. The molecular mechanisms of post-ischemic angiogenesis are complicated and not fully elucidated. The G protein stimulatory alpha subunit (Gsα) is essential for hormone-stimulated cyclic adenosine monophosphate (cAMP) production and is an important regulator for many physiological processes. In the present study, we investigated the role of endothelial Gsα in post-ischemic angiogenesis by generating adult mice with endothelial-specific Gsα deficiency (Gsα^ECKO). Gsα^ECKO mice had impaired blood flow recovery after hind limb ischemic injury, and reduced neovascularization in allograft transplanted tumors. Mechanically, Gsα could regulate the expression of angiogenic factor with G patch and FHA domains 1 (AGGF1) through cAMP/CREB pathway. AGGF1 plays a key role in angiogenesis and regulates endothelial cell proliferation as well as migration. Knockdown of CREB or mutation of the CRE site on the AGGF1 promoter led to reduced AGGF1 promoter activity. In addition, knockdown of AGGF1 reduced the proangiogenic effect of Gsα in endothelial cells, and overexpression of AGGF1 reversed the impaired angiogenesis in Gsα^ECKO mice in vivo. The finding may prove useful in designing new therapeutic targets for treatments of post-ischemic angiogenesis-related diseases.

Stimulatory G-Protein α Subunit Modulates Endothelial Cell Permeability Through Regulation of Plasmalemma Vesicle-Associated Protein

Endothelial cell leakage occurs in several diseases. Intracellular junctions and transcellular fashion are involved. The definite regulatory mechanism is complicated and not fully elucidated. The alpha subunit of the heterotrimeric G-stimulatory protein (Gsα) mediates receptor-stimulated production of cyclic adenosine monophosphate (cAMP). However, the role of Gsα in the endothelial barrier remains unclear. In this study, mice with knockout of endothelial-specific Gsα (GsαECKO) were generated by crossbreeding Gsαflox/flox mice with Cdh5-CreERT2 transgenic mice, induced in adult mice by tamoxifen treatment. GsαECKO mice displayed phenotypes of edema, anemia, hypoproteinemia and hyperlipoproteinemia, which indicates impaired microvascular permeability. Mechanistically, Gsα deficiency reduces the level of endothelial plasmalemma vesicle-associated protein (PLVAP). In addition, overexpression of Gsα increased phosphorylation of cAMP response element-binding protein (CREB) as well as the mRNA and protein levels of PLVAP. CREB could bind to the CRE site of PLVAP promoter and regulate its expression. Thus, Gsα might regulate endothelial permeability via cAMP/CREB-mediated PLVAP expression.

Upregulation of Endothelial DKK1 (Dickkopf 1) Promotes the Development of Pulmonary Hypertension Through the Sp1 (Specificity Protein 1)/SHMT2 (Serine Hydroxymethyltransferase 2) Pathway

BACKGROUND

Pulmonary hypertension (PH) is a cancer-like proliferative disease, which has no curative treatment options. The dysfunction of pulmonary artery endothelial cells plays a key role in PH. DKK1 (Dickkopf 1) is a secretory glycoprotein that exerts proproliferative effects on tumor cells. In the present study, we aimed to identify the role and underlying mechanism of DKK1 in the development of PH, which still remain unclear.

METHODS AND RESULTS

We found endothelial DKK1 expression was upregulated in serum and lung tissues obtained from patients with PH, mice with hypoxia-induced PH, and human pulmonary artery endothelial cells cultured under hypoxic conditions. Endothelium-specific DKK1-knockout (DKK1ECKO) mice significantly ameliorated hypoxia+Sugen5416 and hypoxia-induced PH. More importantly, neutralizing anti-DKK1 antibody treatment significantly attenuated established hypoxia+Sugen5416 PH. Results of proteome analysis of control and DKK1-knockdown human pulmonary artery endothelial cells identified a significantly differentially expressed protein, SHMT2 (serine hydroxymethyltransferase 2), a key metabolic enzyme in one-carbon metabolism, as a novel DKK1 target. DKK1 knockdown in human pulmonary artery endothelial cells cultured under hypoxic conditions decreased the cellular NADPH/NADP+ ratio, increased reactive oxygen species levels and the extent of mitochondrial DNA damage, and inhibited mitochondrial membrane hyperpolarization. In the context of this altered redox defense and mitochondrial disorder, DKK1 induced a proproliferative and antiapoptotic phenotype in endothelial cells. Furthermore, we confirmed that DKK1 regulated SHMT2 transcription through the AKT-Sp1 (specificity protein 1) signaling axis.

CONCLUSIONS

Our data provide robust evidence and molecular explanations for the associations between DKK1, redox defense, mitochondrial disorders, and PH and reveal a novel target for PH treatment.

Tamoxifen administration alters gastrointestinal motility in mice

BACKGROUND

Tamoxifen is widely used for Cre-estrogen receptor-mediated genomic recombination in transgenic mouse models to mark cells for lineage tracing and to study gene function. However, recent studies have highlighted off-target effects of tamoxifen in various tissues and cell types when used for induction of Cre recombination. Despite the widespread use of these transgenic Cre models to assess gastrointestinal (GI) function, the effect of tamoxifen exposure on GI motility has not been described.

METHODS

We examined the effects of tamoxifen on GI motility by measuring total GI transit, gastric emptying, small intestinal transit, and colonic contractility in wild-type adult mice.

KEY RESULTS

We observed a significant delay in total GI transit in tamoxifen-treated mice, with unaltered gastric emptying, accelerated small intestinal transit, and abnormal colonic motility.

CONCLUSION

Our findings highlight the importance of considering GI motility alterations induced by tamoxifen when designing protocols that utilize tamoxifen as a Cre-driver for studying GI function.

Gsα deficiency facilitates cardiac remodeling via CREB/ Bmp10-mediated signaling

The stimulatory G-protein alpha subunit (Gsα), a ubiquitously expressed protein, mediates G-protein receptor-stimulated signal transduction. To investigate the functions of Gsα in cardiomyocytes. We developed transverse aortic constriction (TAC)-induced heart failure mouse models and tamoxifen-inducible transgenic mice with cardiac-specific Gsα disruption. We detected alterations in Gsα expression in TAC-induced heart failure mice. Moreover, we examined cardiac function and structure in mice with genetic Gsα deletion and investigated the underlying molecular mechanisms of Gsα function. We found that Gsα expression increased during the compensated cardiac hypertrophy period and decreased during the heart failure period. Moreover, cardiac-specific Gsα disruption deteriorated cardiac function and induced severe cardiac remodeling. Mechanistically, Gsα disruption decreased CREB1 expression and inhibited the Bmp10-mediated signaling pathway. In addition, we found that Gsα regulates Bmp10 expression through the binding of CREB1 to the Bmp10 promoter. Our results suggest that fluctuations in Gsα levels may play a vital role in the development of heart failure and that loss of Gsα function facilitates cardiac remodeling.

The Anti-apoptotic Role of 3'-Untranslational Region in Response to Angiotensin II via Mcl1 Expression

Myeloid cell leukemia 1 (Mcl1), an abundant protein in the myocardium, plays an essential role in fibrosis and anti-inflammation in cardiomyocytes to prevent heart failure. However, whether Mcl1 3′-untranslated regions (3′-UTR) has the cardio-protecting function remains unclear. Down-regulation of Mcl1 was observed in adult mice heart tissues after Angiotensin II (Ang II) treatment. Consistent with in vivo results, the reduction of Mcl1 expression was identified in Ang II-treated neonatal cardiomyocytes. Mechanistically, Mcl1 3′-UTR prevented Ang II-induced cardiac apoptosis via up-regulation of Mcl1 and an angiogenic factor with a G-patch domain and a forkhead-associated domain 1 (Aggf1), which plays cardiac-protective role. Our work broadens the scope of gene therapy targets and provides a new insight into gene therapy strategies involving mRNAs’ 3′-UTRs application.

Network Pharmacology and Bioactive Equivalence Assessment Integrated Strategy Driven Q-markers Discovery for Da-Cheng-Qi Decoction to Attenuate Intestinal Obstruction

BACKGROUND

Intestinal obstruction (IO) is a kind of acute abdomen with high morbidity and mortality. Patients suffer from poor quality of life and tremendous financial pressure. Da-Cheng-Qi decoction (DCQD), a classical purgation prescription, has clinically been proven to be an effective treatment for IO.

PURPOSE

Network pharmacology integrated with bioactive equivalence assessment was used to discover the quality marker (Q-marker) of DCQD against IO.

METHODS

As there is hardly any targets recorded in database, thus the collection of IO targets was conducted by searching those of alternative diseases which have similar pathological symptoms with IO. In order to improve the reliability of the obtained targets, IO metabolomics data was introduced. Active compounds combination (ACC) was focused as potential Q-markers via component-target network analysis and function query from the identified components corresponding to the common targets. Bioequivalence between ACC and DCQD was assessed from the aspects of intestine motility (somatostatin secretion), inflammation (IL-6 secretion) and injury (wound healing assay) in vitro and was further validated in ileus rat model. PPI network analysis of core targets followed by gene pedigree classification and experimental validation confirmed the potential intervention pathway.

RESULTS

A combination of 11 ingredients, including emodin, physcion, aloe-emodin, rhein, chrysophanol, gallic acid, magnolol, honokiol, naringenin, tangeretin, and nobiletin was finally confirmed bioequivalence with DQCD to some extent and could serve as Q-markers for DCQD to attenuate IO. PI3K/AKT was verified as a possible affected pathway that DCQD exerted the effectiveness against IO.

CONCLUSION

For the disease with few recorded targets, searching those of alternative diseases which have similar pathological symptoms could be a feasible and effective approach. The proposed network pharmacology integrated bioactive equivalence evaluation paradigm is efficient to discover Q-marker of herbal formulae.

Kindlin-2 deficiency induces fatal intestinal obstruction in mice

Rationale: Smooth muscle-motility disorders are mainly characterized by impaired contractility and functional intestinal obstruction. Some of these cases are caused by genetic mutations of smooth muscle genes ACTA2, ACTG2, MYH11, MYLK and LMOD1. Still the etiology is complex and multifactorial and the underlying pathology is poorly understood. Integrin interaction protein Kindlin-2 is widely expressed in striated and smooth muscle cells (SMC). However, the function of Kindlin-2 in the smooth muscle remains elusive.

Methods: We generated two mouse models using different cre promoter transgenic mice, Kindlin-2^fl/fl SM22α-cre+ (cKO mice) and Kindlin-2^fl/fl; MYH-cre+ (iKO mice). Embryos and adult tissues were prepared for hematoxylin and eosin (H&E) staining, immunohistochemistry (IHC) and terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) apoptosis assay. We investigated ultrastructure changes of mouse smooth muscle using transmission electron microscopy (TEM) and measured smooth muscle contractile force in mounting aortic and intestinal rings using the multiwire myograph system (DMT 620M). In addition, cell traction force microscopy (CTFM) was applied to observe the functional change of primary SMC after Kindlin-2 depletion by RNAi.

Results: Depletion of Kindlin-2 encoding gene Fermt2 in embryonic smooth muscles leads to apoptosis, downregulates the key components of SMC, impairs smooth muscle development, and finally causes embryonic death at E14.5. Tamoxifen-induced Kindlin-2-specific knockout in adult mouse smooth muscle showed decreased blood pressure, intestinal hypoperistalsis, and eventually died of intestinal obstruction. Kindlin-2 depletion also leads to downregulated Myh11, α-SMA, and CNN, shortened myofilament, broken myofibrils, and impaired contractility of the smooth muscles in iKO mice. Mechanistically, loss of Kindlin-2 decreases Ca2⁺ influx in primary vascular smooth muscle cells (PVSMC) by downregulating the expression of calcium-binding protein S100A14 and STIM1.

Conclusion: We demonstrated that Kindlin-2 is essential for maintaining the normal structure and function of smooth muscles. Loss of Kindlin-2 impairs smooth muscle formation during embryonic development by inducing apoptosis and jeopardizes the contraction of adult smooth muscle by blocking Ca²⁺ influx that leads to intestinal obstruction. Mice with Kindlin-2 depletion in adult smooth muscle could be a potent animal model of intestinal obstruction for disease research, drug treatment and prognosis.

Ablation of Gsa impairs renal tubule proliferation after injury via CDK2/cyclin E

Acute kidney injury has a high global morbidity associated with an increased risk of death and chronic kidney disease. Renal tubular epithelial cell regeneration following injury may be a decisive factor in renal repair or the progression of acute kidney injury to chronic kidney disease, but the underlying mechanism of abnormal renal tubular repair remains unclear. In the present study, we investigated the role of heterotrimeric G stimulatory protein α-subunit (Gsa) in renal tubular epithelial cell regeneration. We generated renal tubule epithelium-specific Gsa knockout (Gsa^KspKO) mice to show the essential role of Gsa in renal tubular epithelial cell regeneration in two AKI models: acute aristolochic acid nephropathy (AAN) and unilateral ischemia-reperfusion injury (UIRI). Gsa^KspKO mice developed more severe renal impairment after AAN and UIRI, higher serum creatinine levels, and more substantial tubular necrosis than wild-type mice. More importantly, Gsa inactivation impaired renal tubular epithelial cell proliferation by reducing bromodeoxyuridine⁺ cell numbers in the AAN model and inhibiting cyclin-dependent kinase 2/cyclin E1 expression in the UIRI model. This reduced proliferation was further supported in vitro with Gsa-targeting siRNA. Downregulation of Gsa inhibited tubular epithelial cell proliferation in HK-2 and mIMCD-3 cells. Furthermore, Gsa downregulation inhibited cyclin-dependent kinase 2/cyclin E1 expression, which was dependent on the Raf-MEK-ERK signaling pathway. In conclusion, Gsa is required for tubular epithelial cell regeneration during kidney repair after AKI. Loss of Gsa impairs renal tubular epithelial cell regeneration by blocking the Raf-MEK-ERK pathway.

Smooth muscle-specific Gsα deletion exaggerates angiotensin II-induced abdominal aortic aneurysm formation in mice in vivo

Objective:

Abdominal aortic aneurysm (AAA) is a life-threatening vascular disease without an effective pharmaceutical treatment. Genetic studies have proved the involvement of smooth muscle phenotype switch in the development of AAA. The alpha subunit of the heterotrimeric G stimulatory protein (Gsα) mediates receptor-stimulated production of cyclic adenosine monophosphate (cAMP). However, the role of smooth muscle Gsα in AAA formation remains unknown.

Approach and results:

In this study, mice with knockout of smooth muscle-specific Gsα (Gsα^SMKO) were generated by cross-breeding Gsα^flox/flox mice with SM22-CreER^T2 transgenic mice, induced in adult mice by tamoxifen treatment. Gsα deficiency induced a smooth muscle phenotype switch from a contractile to a synthetic state. Mechanically, Gsα deletion reduced cAMP level and increased the level of human antigen R (HuR), which binds with the adenylate uridylate–rich elements of the 3′ untranslated region of Krüppel-like factor 4 (KLF4) mRNA, thereby increasing the stability of KLF4. Moreover, genetic knockdown of HuR or KLF4 rescued the phenotype switch in Gsα-deficient smooth muscle cells. Furthermore, with acute infusion of angiotensin II, the incidence of AAA was markedly higher in ApoE^−/−/Gsα^SMKO than ApoE^−/−/Gsα^flox/flox mice and induced increased elastic lamina degradation and aortic expansion. Finally, the levels of Gsα and SM α-actin were significantly lower while those of HuR and KLF4 were higher in human AAA samples than adjacent nonaneurysmal aortic sections.

Conclusions:

Gsα may play a protective role in AAA formation by regulating the smooth muscle phenotype switch and could be a potential therapeutic target for AAA disease.

Deletion of IP3R1 by Pdgfrb-Cre in mice results in intestinal pseudo-obstruction and lethality

BACKGROUND

Inositol 1,4,5-trisphosphate receptors (IP₃Rs) are a family of intracellular Ca²⁺ release channels located on the membrane of endoplasmic reticulum, which have been shown to play critical roles in various cellular and physiological functions. However, their function in regulating gastrointestinal (GI) tract motility in vivo remains unknown. Here, we investigated the physiological function of IP₃R1 in the GI tract using genetically engineered mouse models.

METHODS

Pdgfrb-Cre mice were bred with homozygous Itpr1 floxed (Itpr1^f/f) mice to generate conditional IP₃R1 knockout (pcR1KO) mice. Cell lineage tracing was used to determine where Pdgfrb-Cre-mediated gene deletion occurred in the GI tract. Isometric tension recording was used to measure the effects of IP₃R1 deletion on muscle contraction.

RESULTS

In the mouse GI tract, Itpr1 gene deletion by Pdgfrb-Cre occurred in smooth muscle cells, enteric neurons, and interstitial cells of Cajal. pcR1KO mice developed impaired GI motility, with prolonged whole-gut transit time and abdominal distention. pcR1KO mice also exhibited lethality as early as 8 weeks of age and 50% of pcR1KO mice were dead by 40 weeks after birth. The frequency of spontaneous contractions in colonic circular muscles was dramatically decreased and the amplitude of spontaneous contractions was increased in pcR1KO mice. Deletion of IP₃R1 in the GI tract also reduced the contractile response to the muscarinic agonist, carbachol, as well as to electrical field stimulation. However, KCl-induced contraction and expression of smooth muscle-specific contractile genes were not significantly altered in pcR1KO mice.

CONCLUSIONS

Here, we provided a novel mouse model for impaired GI motility and demonstrated that IP₃R1 plays a critical role in regulating physiological function of GI tract in vivo.

The ecto-enzymes CD73 and adenosine deaminase modulate 5'-AMP-derived adenosine in myofibroblasts of the rat small intestine

Adenosine is a versatile signaling molecule recognized to physiologically influence gut motor functions. Both the duration and magnitude of adenosine signaling in enteric neuromuscular function depend on its availability, which is regulated by the ecto-enzymes ecto-5'-nucleotidase (CD73), alkaline phosphatase (AP), and ecto-adenosine deaminase (ADA) and by dipyridamole-sensitive equilibrative transporters (ENTs). Our purpose was to assess the involvement of CD73, APs, ecto-ADA in the formation of AMP-derived adenosine in primary cultures of ileal myofibroblasts (IMFs). IMFs were isolated from rat ileum longitudinal muscle segments by means of primary explant technique and identified by immunofluorescence staining for vimentin and α-smooth muscle actin. IMFs confluent monolayers were exposed to exogenous 5'-AMP in the presence or absence of CD73, APs, ecto-ADA, or ENTs inhibitors. The formation of adenosine and its metabolites in the IMFs medium was monitored by high-performance liquid chromatography. The distribution of CD73 and ADA in IMFs was detected by confocal immunocytochemistry and qRT-PCR. Exogenous 5'-AMP was rapidly cleared being almost undetectable after 60-min incubation, while adenosine levels significantly increased. Treatment of IMFs with CD73 inhibitors markedly reduced 5'-AMP clearance whereas ADA blockade or inhibition of both ADA and ENTs prevented adenosine catabolism. By contrast, inhibition of APs did not affect 5'-AMP metabolism. Immunofluorescence staining and qRT-PCR analysis confirmed the expression of CD73 and ADA in IMFs. Overall, our data show that in IMFs an extracellular AMP-adenosine pathway is functionally active and among the different enzymatic pathways regulating extracellular adenosine levels, CD73 and ecto-ADA represent the critical catabolic pathway.