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Department of Animal Sciences
The Robert H. Smith Faculty
of Agricultural, Food & Environment

The Hebrew University of Jerusalem.

P.O. Box 12, Rehovot 76100, Israel
Phone: +972-(0)8-9489119;
Fax: +972-(0)8-9465763;
Yael Lewitus, Department's Secretary
e-mail: yaellew@savion.huji.ac.il

Publications

2019
Basavaraja, R. ; Madusanka, S. T. ; Drum, J. N. ; Shrestha, K. ; Farberov, S. ; Wiltbank, M. C. ; Sartori, R. ; Meidan, R. Interferon-Tau Exerts Direct Prosurvival and Antiapoptotic Actions in Luteinized Bovine Granulosa Cells. Scientific Reports 2019, 9. Publisher's VersionAbstract
Interferon-tau (IFNT), serves as a signal to maintain the corpus luteum (CL) during early pregnancy in domestic ruminants. We investigated here whether IFNT directly affects the function of luteinized bovine granulosa cells (LGCs), a model for large-luteal cells. Recombinant ovine IFNT (roIFNT) induced the IFN-stimulated genes (ISGs; MX2, ISG15, and OAS1Y). IFNT induced a rapid and transient (15–45 min) phosphorylation of STAT1, while total STAT1 protein was higher only after 24 h. IFNT treatment elevated viable LGCs numbers and decreased dead/apoptotic cell counts. Consistent with these effects on cell viability, IFNT upregulated cell survival proteins (MCL1, BCL-xL, and XIAP) and reduced the levels of gamma-H2AX, cleaved caspase-3, and thrombospondin-2 (THBS2) implicated in apoptosis. Notably, IFNT reversed the actions of THBS1 on cell viability, XIAP, and cleaved caspase-3. Furthermore, roIFNT stimulated proangiogenic genes, including FGF2, PDGFB, and PDGFAR. Corroborating the in vitro observations, CL collected from day 18 pregnant cows comprised higher ISGs together with elevated FGF2, PDGFB, and XIAP, compared with CL derived from day 18 cyclic cows. This study reveals that IFNT activates diverse pathways in LGCs, promoting survival and blood vessel stabilization while suppressing cell death signals. These mechanisms might contribute to CL maintenance during early pregnancy. © 2019, The Author(s).
Shrestha, K. ; Rodler, D. ; Sinowatz, F. ; Meidan, R. Chapter 16 - Corpus Luteum Formation. In The Ovary (Third Edition); Leung, P. C. K. ; Adashi, E. Y., Ed. The Ovary (Third Edition); Academic Press, 2019; pp. 255 - 267. Publisher's Version
2018
Farberov, S. ; Meidan, R. Fibroblast growth factor-2 and transforming growth factor-beta1 oppositely regulate miR-221 that targets thrombospondin-1 in bovine luteal endothelial cells. Biology of Reproduction 2018, 98, 366-375. Publisher's VersionAbstract
Thrombospondin-1 (THBS1) affects corpus luteum (CL) regression. Highly induced during luteolysis, it acts as a natural anti-angiogenic, proapoptotic compound. THBS1 expression is regulated in bovine luteal endothelial cells (LECs) by fibroblast growth factor-2 (FGF2) and transforming growth factor-beta1 (TGFB1) acting in an opposite manner. Here we sought to identify specific microRNAs (miRNAs) targeting THBS1 and investigate their possible involvement in FGF2 and TGFB1-mediated THBS1 expression. Several miRNAs predicted to target THBS1 mRNA (miR-1, miR-18a, miR-144, miR-194, and miR-221) were experimentally tested. Of these, miR-221 was shown to efficiently target THBS1 expression and function in LECs. We found that this miRNA is highly expressed in luteal cells and in mid-cycle CL. Consistent with the inhibition of THBS1 function, miR-221 also reduced Serpin Family E Member 1 [SERPINE1] in LECs and promoted angiogenic characteristics of LECs. Plasminogen activator inhibitor-1 (PAI-1), the gene product of SERPINE1, inhibited cell adhesion, suggesting that PAI-1, like THBS1, has anti-angiogenic properties. Importantly, FGF2, which negatively regulates THBS1, elevates miR-221. Conversely, TGFB1 that stimulates THBS1, significantly reduces miR-221. Furthermore, FGF2 enhances the suppression of THBS1 caused by miR-221 mimic, and prevents the increase in THBS1 induced by miR-221 inhibitor. In contrast, TGFB1 reverses the inhibitory effect of miR-221 mimic on THBS1, and enhances the upregulation of THBS1 induced by miR-221 inhibitor. These data support the contention that FGF2 and TGFB1 modulate THBS1 via miR-221. These in vitro data propose that dynamic regulation of miR-221 throughout the cycle, affecting THBS1 and SERPINE1, can modulate vascular function in the CL. © The Author(s) 2017. Published by Oxford University Press on behalf of Society for the Study of Reproduction. All rights reserved.
Ochoa, J. C. ; Peñagaricano, F. ; Baez, G. M. ; Melo, L. F. ; Motta, J. C. L. ; Garcia-Guerra, A. ; Meidan, R. ; Pinheiro Ferreira, J. C. ; Sartori, R. ; Wiltbank, M. C. Mechanisms for rescue of corpus luteum during pregnancy: Gene expression in bovine corpus luteum following intrauterine pulses of prostaglandins e 1 and F 2α. Biology of Reproduction 2018, 98, 465-479. Publisher's VersionAbstract
In ruminants, uterine pulses of prostaglandin (PG) F 2α characterize luteolysis, while increased PGE 2 /PGE 1 distinguish early pregnancy. This study evaluated intrauterine (IU) infusions of PGF 2α and PGE 1 pulses on corpus luteum (CL) function and gene expression. Cows on day 10 of estrous cycle received 4 IU infusions (every 6 h; n = 5/treatment) of saline, PGE 1 (2 mg PGE 1), PGF 2α (0.25 mg PGF 2α), or PGE 1 + PGF 2α. A luteal biopsy was collected at 30 min after third infusion for determination of gene expression by RNA-Seq. As expected, IU pulses of PGF 2α decreased (P < 0.01) P4 luteal volume. However, there were no differences in circulating P4 or luteal volume between saline, PGE 1, and PGE 1 + PGF 2α, indicating inhibition of PGF 2α -induced luteolysis by IU pulses of PGE 1. After third pulse of PGF 2α, luteal expression of 955 genes were altered (false discovery rate [FDR] < 0.01), representing both typical and novel luteolytic transcriptomic changes. Surprisingly, after third pulse of PGE 1 or PGE 1 + PGF 2α, there were no significant changes in luteal gene expression (FDR > 0.10) compared to saline cows. Increased circulating concentrations of the metabolite of PGF 2α (PGFM; after PGF 2α and PGE 1 + PGF 2α) and the metabolite PGE (PGEM; after PGE 1 and PGE 1 + PGF 2α) demonstrated that PGF 2α and PGE 1 are entering bloodstream after IU infusions. Thus, IU pulses of PGF 2α and PGE 1 allow determination of changes in luteal gene expression that could be relevant to understanding luteolysis and pregnancy. Unexpectedly, by third pulse of PGE 1, there is complete blockade of either PGF 2α transport to the CL or PGF 2α action by PGE 1 resulting in complete inhibition of transcriptomic changes following IU PGF 2α pulses. © The Author(s) 2017. Published by Oxford University Press on behalf of Society for the Study of Reproduction. All rights reserved. For permissions, please e-mail:.
Farberov, S. ; Basavaraja, R. ; Meidan, R. Thrombospondin-1 at the crossroads of corpus luteum fate decisions. Reproduction 2018.Abstract
The multimodular matricellular protein thrombospondin-1 (THBS1) was among the first identified endogenous antiangiogenic molecules. Recent studies have shown THBS1-mediated suppression of angiogenesis and other critical activities for corpus luteum (CL) regression. THBS1 is specifically induced by prostaglandin F2alpha in mature CL undergoing regression, whereas luteinizing signals such as luteinizing hormone and insulin reduced its expression. THBS1 interacts both synergistically and antagonistically with other essential luteal factors, such as fibroblast growth factor 2, transforming growth factor beta1, and serpin family E member 1, to promote vascular instability, apoptosis, and matrix remodeling during luteal regression. Expression of THBS1 is also downregulated by pregnancy recognition signals to maintain the CL during early pregnancy. This dynamic pattern of luteal expression, the extensive interactivity with other luteal factors, and strong antiangiogenic and proapoptotic activities indicate that THBS1 is a major determinant of CL fate.
Shrestha, K. ; Meidan, R. The cAMP-EPAC Pathway Mediates PGE2-Induced FGF2 in Bovine Granulosa Cells. Endocrinologyendo 2018, 159, 3482 - 3491. Publisher's VersionAbstract
During the periovulatory period, the profile of fibroblast growth factor 2 (FGF2) coincides with elevated prostaglandin E2 (PGE2) levels. We investigated whether PGE2 can directly stimulate FGF2 production in bovine granulosa cells and, if so, which prostaglandin E2 receptor (PTGER) type and signaling cascades are involved. PGE2 temporally stimulated FGF2. Accordingly, endoperoxide-synthase2–silenced cells, exhibiting low endogenous PGE2 levels, had reduced FGF2. Furthermore, elevation of viable granulosa cell numbers by PGE2 was abolished with FGF2 receptor 1 inhibitor, suggesting that FGF2 mediates this action of PGE2. Epiregulin (EREG), a known PGE2-inducible gene, was studied alongside FGF2. PTGER2 agonist elevated cAMP as well as FGF2 and EREG levels. However, a marked difference between cAMP-induced downstream signaling was observed for FGF2 and EREG. Whereas FGF2 upregulated by PGE2, PTGER2 agonist, or forskolin was unaffected by the protein kinase A (PKA) inhibitor H89, EREG was significantly inhibited. FGF2 was dose-dependently stimulated by the exchange protein directly activated by cAMP (EPAC) activator; a similar induction was observed for EREG. However, forskolin-stimulated FGF2, but not EREG, was inhibited in EPAC1-silenced cells. These findings ascribe a novel autocrine role for PGE2, namely, elevating FGF2 production in granulosa cells. This study also reveals that cAMP-activated EPAC1, rather than PKA, mediates the effect of PGE2/PTGER2 on the expression of FGF2. Stimulation of EREG by PGE2 is also mediated by PTGER2 but, in contrast to FGF2, EREG was found to be PKA sensitive. PGE2-stimulated FGF2 can act to maintain granulosa cell survival; it can also act on ovarian endothelial cells to promote angiogenesis.
Kfir, S. ; Basavaraja, R. ; Wigoda, N. ; Ben-Dor, S. ; Orr, I. ; Meidan, R. Genomic profiling of bovine corpus luteum maturation. PLOS ONE 2018, 13, e0194456 -. Publisher's VersionAbstract
To unveil novel global changes associated with corpus luteum (CL) maturation, we analyzed transcriptome data for the bovine CL on days 4 and 11, representing the developing vs. mature gland. Our analyses revealed 681 differentially expressed genes (363 and 318 on day 4 and 11, respectively), with ≥2 fold change and FDR of <5%. Different gene ontology (GO) categories were represented prominently in transcriptome data at these stages (e.g. days 4: cell cycle, chromosome, DNA metabolic process and replication and on day 11: immune response; lipid metabolic process and complement activation). Based on bioinformatic analyses, select genes expression in day 4 and 11 CL was validated with quantitative real-time PCR. Cell specific expression was also determined in enriched luteal endothelial and steroidogenic cells. Genes related to the angiogenic process such as NOS3, which maintains dilated vessels and MMP9, matrix degrading enzyme, were higher on day 4. Importantly, our data suggests day 11 CL acquire mechanisms to prevent blood vessel sprouting and promote their maturation by expressing NOTCH4 and JAG1, greatly enriched in luteal endothelial cells. Another endothelial specific gene, CD300LG, was identified here in the CL for the first time. CD300LG is an adhesion molecule enabling lymphocyte migration, its higher levels at mid cycle are expected to support the transmigration of immune cells into the CL at this stage. Together with steroidogenic genes, most of the genes regulating de-novo cholesterol biosynthetic pathway (e.g HMGCS, HMGCR) and cholesterol uptake from plasma (LDLR, APOD and APOE) were upregulated in the mature CL. These findings provide new insight of the processes involved in CL maturation including blood vessel growth and stabilization, leucocyte transmigration as well as progesterone synthesis as the CL matures.
Shrestha, K. ; Onasanya, A. E. ; Eisenberg, I. ; Wigoda, N. ; Yagel, S. ; Yalu, R. ; Meidan, R. ; Imbar, T. miR-210 and GPD1L regulate EDN2 in primary and immortalized human granulosa-lutein cells. Reproduction 2018, 155, 197-205.Abstract
Endothelin-2 (EDN2), expressed at a narrow window during the periovulatory period, critically affects ovulation and corpus luteum (CL) formation. LH (acting mainly via cAMP) and hypoxia are implicated in CL formation; therefore, we aimed to elucidate how these signals regulate using human primary (hGLCs) and immortalized (SVOG) granulosa-lutein cells. The hypoxiamiR, microRNA-210 (miR-210) was identified as a new essential player in expression. Hypoxia (either mimetic compound-CoCl, or low O) elevated hypoxia-inducible factor 1A (HIF1A), miR-210 and Hypoxia-induced miR-210 was suppressed in HIF1A-silenced SVOG cells, suggesting that miR-210 is HIF1A dependent. Elevated miR-210 levels in hypoxia or by miR-210 overexpression, increased Conversely, miR-210 inhibition reduced levels, even in the presence of CoCl, indicating the importance of miR-210 in the hypoxic induction of A molecule that destabilizes HIF1A protein, glycerol-3-phosphate dehydrogenase 1-like gene-, was established as a miR-210 target in both cell types. It was decreased by miR-210-mimic and was increased by miR-inhibitor. Furthermore, reducing by endogenously elevated miR-210 (in hypoxia), miR-210-mimic or by siRNA resulted in elevated HIF1A protein and levels, implying a vital role for in the hypoxic induction of Under normoxic conditions, forskolin (adenylyl cyclase activator) triggered changes typical of hypoxia. It elevated , and miR-210 while inhibiting Furthermore, HIF1A silencing greatly reduced forskolin's ability to elevate and miR-210. This study highlights the novel regulatory roles of miR-210 and its gene target, GPD1L, in hypoxia and cAMP-induced by human granulosa-lutein cells.
2017
Basavaraja, R. ; Przygrodzka, E. ; Pawlinski, B. ; Gajewski, Z. ; Kaczmarek, M. M. ; Meidan, R. Interferon-tau promotes luteal endothelial cell survival and inhibits specific luteolytic genes in bovine corpus luteum. Reproduction 2017, 154. Publisher's Version
Farberov, S. ; Meidan, R. Fibroblast growth factor-2 and transforming growth factor-beta1 oppositely regulate miR-221 that targets thrombospondin-1 in bovine luteal endothelial cells. Biology of Reproduction 2017, 98, 366 - 375. Publisher's VersionAbstract
Thrombospondin-1 (THBS1) affects corpus luteum (CL) regression. Highly induced during luteolysis, it acts as a natural anti-angiogenic, proapoptotic compound. THBS1 expression is regulated in bovine luteal endothelial cells (LECs) by fibroblast growth factor-2 (FGF2) and transforming growth factor-beta1 (TGFB1) acting in an opposite manner. Here we sought to identify specific microRNAs (miRNAs) targeting THBS1 and investigate their possible involvement in FGF2 and TGFB1-mediated THBS1 expression. Several miRNAs predicted to target THBS1 mRNA (miR-1, miR-18a, miR-144, miR-194, and miR-221) were experimentally tested. Of these, miR-221 was shown to efficiently target THBS1 expression and function in LECs. We found that this miRNA is highly expressed in luteal cells and in mid-cycle CL. Consistent with the inhibition of THBS1 function, miR-221 also reduced Serpin Family E Member 1 [SERPINE1] in LECs and promoted angiogenic characteristics of LECs. Plasminogen activator inhibitor-1 (PAI-1), the gene product of SERPINE1, inhibited cell adhesion, suggesting that PAI-1, like THBS1, has anti-angiogenic properties. Importantly, FGF2, which negatively regulates THBS1, elevates miR-221. Conversely, TGFB1 that stimulates THBS1, significantly reduces miR-221. Furthermore, FGF2 enhances the suppression of THBS1 caused by miR-221 mimic, and prevents the increase in THBS1 induced by miR-221 inhibitor. In contrast, TGFB1 reverses the inhibitory effect of miR-221 mimic on THBS1, and enhances the upregulation of THBS1 induced by miR-221 inhibitor. These data support the contention that FGF2 and TGFB1 modulate THBS1 via miR-221. These in vitro data propose that dynamic regulation of miR-221 throughout the cycle, affecting THBS1 and SERPINE1, can modulate vascular function in the CL.
Ochoa, J. C. ; Peñagaricano, F. ; Baez, G. M. ; Melo, L. F. ; Motta, J. C. L. ; Garcia-Guerra, A. ; Meidan, R. ; Pinheiro Ferreira, J. C. ; Sartori, R. ; Wiltbank, M. C. Mechanisms for rescue of corpus luteum during pregnancy: gene expression in bovine corpus luteum following intrauterine pulses of prostaglandins E1 and F2α†. Biology of Reproductionbiolreprod 2017, 98, 465 - 479. Publisher's VersionAbstract
In ruminants, uterine pulses of prostaglandin (PG) F2α characterize luteolysis, while increased PGE2/PGE1 distinguish early pregnancy. This study evaluated intrauterine (IU) infusions of PGF2α and PGE1 pulses on corpus luteum (CL) function and gene expression. Cows on day 10 of estrous cycle received 4 IU infusions (every 6 h; n = 5/treatment) of saline, PGE1 (2 mg PGE1), PGF2α (0.25 mg PGF2α), or PGE1 + PGF2α. A luteal biopsy was collected at 30 min after third infusion for determination of gene expression by RNA-Seq. As expected, IU pulses of PGF2α decreased (P < 0.01) P4 luteal volume. However, there were no differences in circulating P4 or luteal volume between saline, PGE1, and PGE1 + PGF2α, indicating inhibition of PGF2α-induced luteolysis by IU pulses of PGE1. After third pulse of PGF2α, luteal expression of 955 genes were altered (false discovery rate [FDR] < 0.01), representing both typical and novel luteolytic transcriptomic changes. Surprisingly, after third pulse of PGE1 or PGE1 + PGF2α, there were no significant changes in luteal gene expression (FDR > 0.10) compared to saline cows. Increased circulating concentrations of the metabolite of PGF2α (PGFM; after PGF2α and PGE1 + PGF2α) and the metabolite PGE (PGEM; after PGE1 and PGE1 + PGF2α) demonstrated that PGF2α and PGE1 are entering bloodstream after IU infusions. Thus, IU pulses of PGF2α and PGE1 allow determination of changes in luteal gene expression that could be relevant to understanding luteolysis and pregnancy. Unexpectedly, by third pulse of PGE1, there is complete blockade of either PGF2α transport to the CL or PGF2α action by PGE1 resulting in complete inhibition of transcriptomic changes following IU PGF2α pulses.
Meidan, R. ; Girsh, E. ; Mamluk, R. ; Levy, N. ; Farberov, S. Luteolysis in Ruminants: Past Concepts, New Insights, and Persisting Challenges. In The Life Cycle of the Corpus Luteum; Meidan, R., Ed. The Life Cycle of the Corpus Luteum; Springer International Publishing: Cham, 2017; pp. 159–182. Publisher's VersionAbstract
It is well established that in ruminants, and in other species with estrous cycles, luteal regression is stimulated by the episodic release of prostaglandin F2$\alpha$ (PGF2$\alpha$) from the uterus, which reaches the corpus luteum (CL) through a countercurrent system between the uterine vein and the ovarian artery. Because of their luteolytic properties, PGF2$\alpha$ and its analogues are routinely administered to induce CL regression and synchronization of estrus, and as such, it is the basis of protocols for synchronizing ovulation. Luteal regression is defined as the loss of steroidogenic function (functional luteolysis) and the subsequent involution of the CL (structural luteolysis). During luteolysis, the CL undergoes dramatic changes in its steroidogenic capacity, vascularization, immune cell activation, ECM composition, and cell viability. Functional genomics and many other studies during the past 20 years elucidated the mechanism underlying PGF2$\alpha$ actions, substantially revising old concepts. PGF2$\alpha$ acts directly on luteal steroidogenic and endothelial cells, which express PGF2$\alpha$ receptors (PTGFR), or indirectly on immune cells lacking PTGFR, which can be activated by other cells within the CL. Accumulating evidence now indicates that the diverse processes initiated by uterine or exogenous PGF2$\alpha$, ranging from reduction of steroid production to apoptotic cell death, are mediated by locally produced factors. Data summarized here show that PGF2$\alpha$ stimulates luteal steroidogenic and endothelial cells to produce factors such as endothelin-1, angiopoietins, nitric oxide, fibroblast growth factor 2, thrombospondins, transforming growth factor-B1, and plasminogen activator inhibitor-B1, which act sequentially to inhibit progesterone production, angiogenic support, cell survival, and ECM remodeling to accomplish CL regression.
Meidan, R. ; Girsh, E. ; Mamluk, R. ; Levy, N. ; Farberov, S. Luteolysis in Ruminants: Past Concepts, New Insights, and Persisting Challenges. In The Life Cycle of the Corpus Luteum; Meidan, R., Ed. The Life Cycle of the Corpus Luteum; Springer International Publishing: Cham, 2017; pp. 159–182. Publisher's VersionAbstract
It is well established that in ruminants, and in other species with estrous cycles, luteal regression is stimulated by the episodic release of prostaglandin F2$\alpha$ (PGF2$\alpha$) from the uterus, which reaches the corpus luteum (CL) through a countercurrent system between the uterine vein and the ovarian artery. Because of their luteolytic properties, PGF2$\alpha$ and its analogues are routinely administered to induce CL regression and synchronization of estrus, and as such, it is the basis of protocols for synchronizing ovulation. Luteal regression is defined as the loss of steroidogenic function (functional luteolysis) and the subsequent involution of the CL (structural luteolysis). During luteolysis, the CL undergoes dramatic changes in its steroidogenic capacity, vascularization, immune cell activation, ECM composition, and cell viability. Functional genomics and many other studies during the past 20 years elucidated the mechanism underlying PGF2$\alpha$ actions, substantially revising old concepts. PGF2$\alpha$ acts directly on luteal steroidogenic and endothelial cells, which express PGF2$\alpha$ receptors (PTGFR), or indirectly on immune cells lacking PTGFR, which can be activated by other cells within the CL. Accumulating evidence now indicates that the diverse processes initiated by uterine or exogenous PGF2$\alpha$, ranging from reduction of steroid production to apoptotic cell death, are mediated by locally produced factors. Data summarized here show that PGF2$\alpha$ stimulates luteal steroidogenic and endothelial cells to produce factors such as endothelin-1, angiopoietins, nitric oxide, fibroblast growth factor 2, thrombospondins, transforming growth factor-B1, and plasminogen activator inhibitor-B1, which act sequentially to inhibit progesterone production, angiogenic support, cell survival, and ECM remodeling to accomplish CL regression.
2016
Meidan, R. ; Girsh, E. ; Mamluk, R. ; Levy, N. ; Farberov, S. Luteolysis in ruminants: Past concepts, new insights, and persisting challenges. In The Life Cycle of the Corpus Luteum; The Life Cycle of the Corpus Luteum; 2016; pp. 159 - 182. Publisher's Version
Meidan, R. The life cycle of the corpus luteum; The Life Cycle of the Corpus Luteum; 2016; pp. 1 - 283. Publisher's Version
Farberov, S. ; Meidan, R. Thrombospondin-1 Affects Bovine Luteal Function via Transforming Growth Factor-Beta1-Dependent and Independent Actions1. Biology of Reproductionbiolreprod 2016, 94. Publisher's VersionAbstract
Thrombospondin-1 (THBS1) and transforming growth factor-beta1 (TGFB1) are specifically up-regulated by prostaglandin F2alpha in mature corpus luteum (CL). This study examined the relationship between the expression of THBS1 and TGFB1 and the underlying mechanisms of their actions in luteal endothelial cells (ECs). TGFB1 stimulated SMAD2 phosphorylation and SERPINE1 levels in dose- and time-dependent manners in luteal EC. THBS1 also elevated SERPINE1; this effect was abolished by TGFB1 receptor-1 kinase inhibitor (SB431542). The findings here further imply that THBS1 activates TGFB1 in luteal ECs: THBS1 increased the effects of latent TGFB1 on phosphorylated SMAD (phospho-SMAD) 2 and SERPINE1. THBS1 silencing significantly decreased SERPINE1 and levels of phospho-SMAD2. Lastly, THBS1 actions on SERPINE1 were inhibited by LSKL peptide (TGFB1 activation inhibitor); LSKL also counteracted latent TGFB1-induced phospho-SMAD2. We found that TGFB1 up-regulated its own mRNA levels and those of THBS1. Both compounds generated apoptosis, but THBS1 was significantly more effective (2.5-fold). Notably, this effect of THBS1 was not mediated by TGFB1. THBS1 and TGFB1 also differed in their activation of p38 mitogen-activated protein kinase. Whereas TGFB1 rapidly induced phospho-p38, THBS1 had a delayed effect. Inhibition of p38 pathway by SB203580 did not modulate TGFB1 effect on cell viability, but it amplified THBS1 actions. THBS1-stimulated caspase-3 activation coincided with p38 phosphorylation, suggesting that caspase-induced DNA damage initiated p38 phosphorylation. The in vitro data suggest that a feed-forward loop exists between THBS1, TGFB1, and SERPINE1. Indeed all these three genes were similarly induced in the regressing CL. Their gene products can promote vascular instability, apoptosis, and matrix remodeling during luteolysis.