The therapeutic potential of blocking the activin signalling pathway

Tubule-Derived Follistatin Is Increased in the Urine of Rats with Renal Ischemia and Reflects the Severity of Acute Tubular Damage

Activin A, a member of the TGF-beta superfamily, is a negative regulator of tubular regeneration after renal ischemia. Activin action is controlled by an endogenous antagonist, follistatin. However, the role of follistatin in the kidney is not fully understood. In the present study, we examined the expression and localization of follistatin in normal and ischemic rat kidneys and measured urinary follistatin in rats with renal ischemia to assess whether urinary follistatin could serve as a biomarker for acute kidney injury. Using vascular clamps, renal ischemia was induced for 45 min in 8-week-old male Wistar rats. In normal kidneys, follistatin was localized in distal tubules of the cortex. In contrast, in ischemic kidneys, follistatin was localized in distal tubules of both the cortex and outer medulla. Follistatin mRNA was mainly present in the descending limb of Henle of the outer medulla in normal kidneys but was upregulated in the descending limb of Henle of both the outer and inner medulla after renal ischemia. Urinary follistatin, which was undetectable in normal rats, was significantly increased in ischemic rats and peaked 24 h after reperfusion. There was no correlation between urinary follistatin and serum follistatin. Urinary follistatin levels were increased according to ischemic duration and were significantly correlated with the follistatin-positive area as well as the acute tubular damage area. These results suggest that follistatin normally produced by renal tubules increases and becomes detectable in urine after renal ischemia. Urinary follistatin might be useful to assess the severity of acute tubular damage.

Effect of Hesperidin against Induced Colon Cancer in Rats: Impact of Smad4 and Activin A Signaling Pathway

SCOPE

To evaluate the chemopreventive efficacy of hesperidin (Hsd) in 1,2-dimethylhydrazine (DMH)-induced colorectal cancer (CRC) and demonstrate its role in mothers against decapentaplegic homolog 4(Smad4) and activin A signaling pathways.

METHODS AND RESULTS

A CRC rat model was established by DMH exposure, and the animals were randomly divided into five groups: Control group, Hsd, DMH, DMH + Hsd, and DMH followed by Hsd. The resected colon was subjected to macroscopic, microscopic, molecular, histopathological, and immunohistochemical examination. Activin A, Smad4, malondialdehyde (MDA), nitric oxide (NO), reduced glutathione (GSH), and superoxide dismutase (SOD) levels in tissues were also measured. The DMH group exhibited a significant increase in the gene and protein expression of activin A as well as MDA and NO levels in tissues. There was a significant reduction in the gene and protein expression of Smad4 as well as GSH and SOD levels in tissues. Administration of Hsd significantly upregulated Smad4 and activin A gene expressions in both the DMH + Hsd and DMH followed by Hsd groups. Moreover, Hsd improved the antioxidant status of the former two groups.

CONCLUSION

This study demonstrated the chemopreventive effect of Hsd against CRC by modulating Smad4 and activin A signaling in vivo. Further studies are needed to demonstrate its clinical value and explore its possible role in advanced malignancy.

The Combination of Low Skeletal Muscle Mass and High Tumor Interleukin-6 Associates with Decreased Survival in Clear Cell Renal Cell Carcinoma

Clear cell renal carcinoma (ccRCC) is frequently associated with cachexia which is itself associated with decreased survival and quality of life. We examined relationships among body phenotype, tumor gene expression, and survival. Demographic, clinical, computed tomography (CT) scans and tumor RNASeq for 217 ccRCC patients were acquired from the Cancer Imaging Archive and The Cancer Genome Atlas (TCGA). Skeletal muscle and fat masses measured from CT scans and tumor cytokine gene expression were compared with survival by univariate and multivariate analysis. Patients in the lowest skeletal muscle mass (SKM) quartile had significantly shorter overall survival versus the top three SKM quartiles. Patients who fell into the lowest quartiles for visceral adipose mass (VAT) and subcutaneous adipose mass (SCAT) also demonstrated significantly shorter overall survival. Multiple tumor cytokines correlated with mortality, most strongly interleukin-6 (IL-6); high IL-6 expression was associated with significantly decreased survival. The combination of low SKM/high IL-6 was associated with significantly lower overall survival compared to high SKM/low IL-6 expression (26.1 months vs. not reached; p < 0.001) and an increased risk of mortality (HR = 5.95; 95% CI = 2.86–12.38). In conclusion, tumor cytokine expression, body composition, and survival are closely related, with low SKM/high IL-6 expression portending worse prognosis in ccRCC.

Autocrine activin A signalling in ovarian cancer cells regulates secretion of interleukin 6, autophagy, and cachexia

BACKGROUND

The majority of patients with advanced cancer develop cachexia, a weight loss syndrome that severely reduces quality of life and limits survival. Our understanding of the underlying mechanisms that cause the condition is limited, and there are currently no treatment options that can completely reverse cachexia. Several tumour-derived factors and inflammatory mediators have been suggested to contribute to weight loss in cachectic patients. However, inconsistencies between studies are recurrent. Activin A and interleukin 6 (IL-6) are among the best studied factors that seem to be important, and several studies support their individual role in cachexia development.

METHODS

We investigated the interplay between activin A and IL-6 in the cachexia-inducing TOV21G cell line, both in culture and in tumours in mice. We previously found that the human TOV21G cells secrete IL-6 that induces autophagy in reporter cells and cachexia in mice. Using this established cachexia cell model, we targeted autocrine activin A by genetic, chemical, and biological approaches. The secretion of IL-6 from the cancer cells was determined in both culture and tumour-bearing mice by a species-specific ELISA. Autophagy reporter cells were used to monitor the culture medium for autophagy-inducing activities, and muscle mass changes were evaluated in tumour-bearing mice.

RESULTS

We show that activin A acts in an autocrine manner to promote the synthesis and secretion of IL-6 from cancer cells. By inhibiting activin A signalling, the production of IL-6 from the cancer cells is reduced by 40-50% (up to 42% reduction on protein level, P = 0.0048, and 48% reduction on mRNA level, P = 0.0308). Significantly reduced IL-6 secretion (P < 0.05) from the cancer cells is consistently observed when using biological, chemical, and genetic approaches to interfere with the autocrine activin A loop. Inhibiting activin signalling also reduces the ability of the cancer cells to accelerate autophagy in non-cancerous cells (up to 43% reduced autophagy flux, P = 0.0006). Coherent to the in vitro data, the use of an anti-activin receptor 2 antibody in cachectic tumour-bearing mice reduces serum levels of cancer cell-derived IL-6 by 62% (from 417 to 159 pg/mL, P = 0.03), and, importantly, it reverses cachexia and counteracts loss of all measured muscle groups (P < 0.0005).

CONCLUSIONS

Our data support a functional link between activin A and IL-6 signalling pathways and indicate that interference with activin A-induced IL-6 secretion from the tumour has therapeutic potential for cancer-induced cachexia.

An autocrine ActivinB mechanism drives TGFβ/Activin signaling in Group 3 medulloblastoma

Medulloblastoma (MB) is a pediatric tumor of the cerebellum divided into four groups. Group 3 is of bad prognosis and remains poorly characterized. While the current treatment involving surgery, radiotherapy, and chemotherapy often fails, no alternative therapy is yet available. Few recurrent genomic alterations that can be therapeutically targeted have been identified. Amplifications of receptors of the TGFβ/Activin pathway occur at very low frequency in Group 3 MB. However, neither their functional relevance nor activation of the downstream signaling pathway has been studied. We showed that this pathway is activated in Group 3 MB with some samples showing a very strong activation. Beside genetic alterations, we demonstrated that an ActivinB autocrine stimulation is responsible for pathway activation in a subset of Group 3 MB characterized by high PMEPA1 levels. Importantly, Galunisertib, a kinase inhibitor of the cognate receptors currently tested in clinical trials for Glioblastoma patients, showed efficacy on orthotopically grafted MB‐PDX. Our data demonstrate that the TGFβ/Activin pathway is active in a subset of Group 3 MB and can be therapeutically targeted.

Activin receptor ligand traps in chronic kidney disease

PURPOSE OF REVIEW

Sotatercept and luspatercept are recombinant soluble activin type-II receptor-IgG-Fc fusion proteins that are tested in clinical trials for the treatment of various types of anemias, including renal anemia. The mechanism of the action of the novel drugs is incompletely understood, but it seems to be based on the inactivation of soluble proteins of the transforming growth factor-ß (TGFß) family. This review considers pros and cons of the clinical use of the drugs in reference to the current therapy with recombinant erythropoiesis-stimulating agents (ESAs).

RECENT FINDINGS

One or more activin type-II receptor (ActRII) ligands appear to inhibit erythroid precursors, for example growth and differentiation factor 11. Trapping of these ligands by the recombinant ActRII fusion proteins, sotatercept and luspatercept increases red blood cell numbers and hemoglobin levels in humans. Reportedly, the novel compounds were well tolerated in trials on healthy volunteers and patients suffering from anemia due to chronic kidney disease or malignancies. On approval, the drugs may prove particularly useful in patients suffering from ineffective erythropoiesis, such as in myelodysplastic syndrome, multiple myeloma or ß-thalassemia, where ESAs are of little use. Independent of their effect on erythropoiesis, ActRII ligand traps were found to exert beneficial effects on renal tissue in experimental animals.

SUMMARY

ESAs are likely to remain standard of care in renal anemia. There is a need for a better understanding of the effects of ActRII ligand traps on TGFß-like proteins. The novel drugs have not been approved for sale as therapeutics so far. Their long-term efficacy and safety still needs to be proven, particularly with respect to immunogenicity. Antifibrotic effects may be worthy to be investigated in humans.

Targeting the vascular dysfunction: Potential treatments for preeclampsia

Preeclampsia is a pregnancy-specific disorder, primarily characterized by new-onset hypertension in combination with a variety of other maternal or fetal signs. The pathophysiological mechanisms underlying the disease are still not entirely clear. Systemic maternal vascular dysfunction underlies the clinical features of preeclampsia. It is a result of oxidative stress and the actions of excessive anti-angiogenic factors, such as soluble fms-like tyrosine kinase, soluble endoglin, and activin A, released by a dysfunctional placenta. The vascular dysfunction then leads to impaired regulation and secretion of relaxation factors and an increase in sensitivity/production of constrictors. This results in a more constricted vasculature rather than the relaxed vasodilated state associated with normal pregnancy. Currently, the only effective "treatment" for preeclampsia is delivery of the placenta and therefore the baby. Often, this means a preterm delivery to save the life of the mother, with all the attendant risks and burdens associated with fetal prematurity. To lessen this burden, there is a pressing need for more effective treatments that target the maternal vascular dysfunction that underlies the hypertension. This review details the vascular effects of key drugs undergoing clinical assessment as potential treatments for women with preeclampsia.

Activin Biology After Lung Transplantation

BACKGROUND

Activins A and B, members of the TGF-β superfamily, are produced as part of the physiological response to tissue damage and the resulting proinflammatory response. Given that lung allograft reperfusion results in an inflammatory response, it is likely that the activins and their binding protein follistatin will form part of the regulatory response. There is a need to document the response of these proteins to allograft reperfusion to determine if there is a role for the use of follistatin to control the biological actions of the activins because some of these are potentially damaging.

METHODS

Serum from 48 consecutive patients undergoing lung transplantation (LTx) was collected at 2, 6, 12, and 26 weeks post-LTx. The serum levels of activin A and B and follistatin were measured by enzyme-linked immunosorbent assay and specific radioimmunoassays and compared with clinical events.

RESULTS

Serum activin A and B levels were at the upper limit of the normal ranges at 2 weeks post-LTx decreasing thereafter to 12 weeks post-LTx (P < 0.05). In contrast, serum follistatin levels were unchanged between 2 and 12 weeks, with a late significant increase at 24 week post-LTx (P < 0.01). Patients with primary graft dysfunction had lower serum follistatin levels (7.7 vs 9.5 ng/mL; P = 0.04) and a higher activin A/follistatin ratio (13.1 vs 10.4; P = 0.02) at 2 weeks post-LTx.

CONCLUSIONS

Activin and follistatin levels vary with time form LTX and reflect a proinflammatory environment. Future studies will elucidate associations with chronic lung allograft dysfunction and the therapeutic potential of exogenous follistatin administration.

Activins and activin antagonists in the human ovary and ovarian cancer

Activins are members of the transforming growth factor β superfamily that play an important role in controlling cell proliferation and differentiation in many organs including the ovary. It is essential that activin signalling be tightly regulated as imbalances can lead to uncontrolled cell proliferation and cancer. This review describes the expression and function of the activins and their known antagonists in both normal and cancerous human ovaries.

Longitudinal analysis of maternal serum Follistatin concentration in normal pregnancy and preeclampsia

OBJECTIVE

Follistatin (FST) is a regulator of the biological activity of activin A (Act A), binding and blocking it, which could contribute to the modulation of its pro-inflammatory activity during pregnancy. We sought to investigate, in this nested case-control study, FST serum levels during normal pregnancy and correlate it with the FST profile in preeclamptic pregnant women, normal pregnant women followed 3 months postpartum and eumenorrheic nonpregnant women throughout the menstrual cycle.

SUBJECTS AND METHODS

Follistatin serum levels determined by ELISA, biochemical and anthropometric variables were measured in normal pregnant (n = 28) and preeclamptic (n = 20) women during three periods of gestation. In addition, FST serum levels were measured in a subset of normal pregnant women (n = 13) followed 3 months postpartum and in eumenorrheic nonpregnant women (n = 20) during the follicular and luteal phases of the menstrual cycle.

RESULTS

Follistatin serum levels in the eumenorrheic nonpregnant and postpartum group were significantly lower when compared to levels throughout gestation (P < 0·01). Serum FST levels increased in each period of pregnancy analysed, being significantly higher towards the end of gestation (P < 0·01). FST levels were lower in late pregnancy in preeclamptic women compared to normal pregnant women (P < 0·05). Finally, FST levels were higher in the luteal phase when compared with the follicular phase of the menstrual cycle (P < 0·05).

CONCLUSIONS

These analyses would permit the consideration that changes in FST levels during pregnancy contribute to the control of the Act A system.

Activin A regulates proliferation, invasion and migration in osteosarcoma cells

Activin A is a member of the TGF‑β superfamily. Previous studies have demonstrated that activin A exhibited pluripotent effects in several tumours. However, the roles of activin A signaling in osteosarcoma pathogenesis have not been previously investigated. Therefore, the present study aimed to investigate the effects of activin A on osteosarcoma cell proliferation, invasion and migration. Firstly, the expression of activin A in osteosarcoma cell lines (MG63, SaOS‑2 and U2OS) and a human osteoblastic cell line (hFOB1.19) was detected using reverse transcription quantitative polymerase chain reaction and western blotting. Activin A was upregulated in osteosarcoma cell lines compared with hFOB1.19 cells. To investigate the effects of activin A on osteosarcoma cell proliferation, invasion and migration, MG63 cells were generated in which activin A was either overexpressed or depleted. MTT staining, propidium iodide staining and a Transwell assay were used to analyze the cell cycle, proliferation, invasion and migration of MG63 cells, respectively. The results of the present study revealed that the abilities of proliferation, invasion and migration were suppressed in MG63 cells in which activin A was depleted, while they were enhanced in activin A-overexpressing cells. In conclusion, the results of the present study suggested that activin A may facilitate proliferation, invasion and migration of osteosarcoma cells, and it may therefore be a potential target for the treatment of osteosarcoma.

The ESA scenario gets complex: from biosimilar epoetins to activin traps

Recombinant human erythropoietin (rhEpo, epoetin) has proved beneficial in preventing transfusion-dependent anaemia in patients with chronic kidney disease. Apart from copied epoetins distributed in less regulated markets, 'biosimilar' epoetins have gained currency in many regions, where they compete with the originals and with rhEpo analogues with prolonged survival in circulation ('biobetter'). Recombinant erythropoiesis stimulating agents are potent and well tolerated. However, their production is costly, and they must be administered by the parenteral route. Hence, other anti-anaemia treatments are being evaluated. Clinical trials are being performed with stabilizers of the hypoxia-inducible transcription factors (HIFs), which increase endogenous Epo production. HIF stabilizers are chemical drugs and they are active on oral administration. However, there is fear that they may promote tumour growth. Epo mimetic peptides have also raised expectations. Yet the prototype peginesatide was recalled after just 1 year of its widespread use in the USA because of serious side-effects including cases of death. Most recently, clinical trials have been initiated with sotatercept, a recombinant soluble activin receptor type 2A IgG-Fc fusion protein. Sotatercept binds distinct members of the transforming growth factor-β family, thereby preventing the inhibitory action of these factors in erythropoiesis. Taken together, rhEpo and its long-acting recombinant analogues will likely remain mainstay of anti-anaemia therapies in the near future.