Arginase activity is associated with fibrosis in experimental infection with Taenia crassiceps, but does not play a major role in resistance to infection

MLKL is involved in the regulation of skin wound healing and interplay between macrophages and myofibroblasts in mice

Mixed lineage kinase domain-like protein (MLKL), a critical necroptosis effector, is strongly linked to inflammation, a key component of skin wound healing. However, its precise role in the wound healing process remains inadequately characterized. This study revealed sustained MLKL overexpression throughout the wound healing process, not limited to the early inflammation phase. Wound healing was delayed in MLKL-deficient (MLKL-/-) mice compared to wild type C57BL/6J (MLKL+/+) mice, with impaired morphological and pathological recovery. MLKL deficiency reduced the synthesis of inflammatory factors (IL-6, TNF-α, PGE2), tissue repair molecules (EGF, VEGF, ERα, MMP-9), and apoptosis markers (Caspase-3, p53, Bcl-2) at wound site. Subsequently, a co-culture system was established to explore the roles of MLKL in macrophage-fibroblast interactions. M1 or M2 macrophages (M1ø or M2ø) were co-cultured with fibroblast-conditioned medium (MFbCM), and fibroblasts were co-cultured with macrophage-conditioned medium (M1ø CM or M2ø CM). The results indicated that MLKL+/+ M1ø CM and M2ø CM significantly increased ERα, VEGF and MMP-9 protein expression levels in fibroblasts, whereas this effect was impaired when MLKL-/- M1ø CM or M2ø CM were used. Similarly, MLKL+/+ MFbCM upregulated IL-6, NO, and TNF-α in M1ø and IL-10, arginase, and Ym-1 in M2ø, but these effects were diminished with MLKL-/- MFbCM treatment. These results indicate bidirectional crosstalk between macrophages and fibroblasts, in which MLKL plays a role. Additionally, PGE2 was identified as a downstream mediator of MLKL-mediated interactions between macrophages and fibroblasts. In conclusion, these findings identify MLKL as a multifunctional regulator in skin wound healing in mice.

Impact of a previous infection with Taenia crassiceps cysticerci on the susceptibility to Leishmania (L.) major or L. (V.) braziliensis

The development of leishmaniasis depends on the ability of Leishmania to invade and survive within macrophages. Macrophages can either promote parasite elimination or support its survival, depending on whether they are classically (M1) or alternatively (M2) activated. Mice chronically infected with Taenia crassiceps cysticerci (TC) develop a predominantly Th2 immune response, which leads to an increased number of M2 macrophages. In this study, we assessed the susceptibility of BALB/c mice previously infected with TC to Leishmania (V.) braziliensis or Leishmania (L.) major. Mice were first inoculated intraperitoneally with TC and after eight weeks infected either L. (V.) braziliensis or L. (L.) major in the paw. We evaluated footpad swelling and parasite load in different organs. We also assessed parasite load in vitro at 3 h, 3, 6, and 9 days; nitric oxide (NO) production, and arginase activity. Macrophages obtained from TC-infected mice (TcMΦ) were more susceptible to L. (V.) braziliensis infection, maintaining a stable parasite load without significant proliferation, while the parasite was killed in thioglycolate-elicited macrophages (TgMΦ). In contrast, L. (L.) major proliferated intensely in TcMΦ, leading to a higher parasite load compared to TgMΦ. In vivo, infection with L. (V.) braziliensis in TC-coinfected mice did not alter the parasite load compared to the group without cysticerci. However, mice infected with L. (L.) major exhibited greater swelling and higher parasite burdens. These findings suggest that infection with TC modulates the immune response of mice but is unable to render resistant mice susceptible to L. (V.) braziliensis.

NLRP3: a key regulator of skin wound healing and macrophage-fibroblast interactions in mice

Wound healing is a highly coordinated process driven by intricate molecular signaling and dynamic interactions between diverse cell types. Nod-like receptor pyrin domain-containing protein 3 (NLRP3) has been implicated in the regulation of inflammation and tissue repair; however, its specific role in skin wound healing remains unclear. This study highlights the pivotal role of NLRP3 in effective skin wound healing, as demonstrated by delayed wound closure and altered cellular and molecular responses in NLRP3-deficient (NLRP3-/-) mice. Histological analysis revealed impaired healing processes, accompanied by reduced expression of key inflammatory mediators, including interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and prostaglandin E2 (PGE2). Deficiencies in apoptosis were evident through altered expression of cysteine-aspartic acid protease 3 (Caspase-3), P53, and B-cell lymphoma-2 (Bcl-2). Furthermore, critical growth factors such as vascular endothelial growth factor (VEGF), epidermal growth factor (EGF), and matrix metalloproteinase-9 (MMP-9) were significantly decreased at the excisional skin wound sites. Furthermore, using co-culture systems, we found that NLRP3 mediated the interaction between macrophages and myofibroblasts. Wild-type fibroblast-conditioned media (MFbCM) enhanced nitric oxide (NO), IL-6, and tumor necrosis factor-α (TNF-α) production in M1 macrophages and arginase activity, chitinase 3-like protein 1 (Ym1), and IL-10 expression in M2 macrophages, effects significantly diminished with NLRP3-/- MFbCM. Similarly, conditioned media from wild-type M1 or M2 macrophages promoted the expression of FGF-2, VEGF, and MMP-2 expression in myofibroblasts, which was attenuated when using NLRP3-/- macrophage-conditioned media. PGE2 levels were reduced in both NLRP3-/- macrophages and myofibroblasts. Supplementing NLRP3-/- conditioned media with PGE2 partially restored the impaired functions, suggesting that PGE2 acts as a downstream mediator of NLRP3-regulated macrophage-myofibroblast interactions. These findings indicate that NLRP3 is a key regulator of skin wound healing, facilitating macrophage-myofibroblast communication.

Selective inhibition of arginase-2 in endothelial cells but not proximal tubules reduces renal fibrosis

Fibrosis is the final common pathway in the pathophysiology of most forms of chronic kidney disease (CKD). As treatment of renal fibrosis still remains largely supportive, a refined understanding of the cellular and molecular mechanisms of kidney fibrosis and the development of novel compounds are urgently needed. Whether arginases play a role in the development of fibrosis in CKD is unclear. We hypothesized that endothelial arginase-2 (Arg2) promotes the development of kidney fibrosis induced by unilateral ureteral obstruction (UUO). Arg2 expression and arginase activity significantly increased following renal fibrosis. Pharmacologic blockade or genetic deficiency of Arg2 conferred kidney protection following renal fibrosis, as reflected by a reduction in kidney interstitial fibrosis and fibrotic markers. Selective deletion of Arg2 in endothelial cells (Tie2Cre/Arg2fl/fl) reduced the level of fibrosis after UUO. In contrast, selective deletion of Arg2 specifically in proximal tubular cells (Ggt1Cre/Arg2fl/fl) failed to reduce renal fibrosis after UUO. Furthermore, arginase inhibition restored kidney nitric oxide (NO) levels, oxidative stress, and mitochondrial function following UUO. These findings indicate that endothelial Arg2 plays a major role in renal fibrosis via its action on NO and mitochondrial function. Blocking Arg2 activity or expression could be a novel therapeutic approach for prevention of CKD.

Effect of dexamethasone on albendazole cysticidal activity in experimental cysticercosis by Taenia crassiceps in BALB/c mice: In vitro and in vivo evaluation

Taenia solium is a parasite whose larvae (cysticerci) can locate in the central nervous system of humans and cause neurocysticercosis (NC). The introduction of cysticidal drugs such as albendazole (ABZ) for the treatment of NC has significantly improved its prognosis. However, treatment is not always effective, and the high levels of corticosteroids used to prevent inflammatory complications in this disease could be, partly, the cause of this observation. In this context, this study investigated, using the experimental mouse model of intraperitoneal infection with Taenia crassiceps, the influence of corticosteroid administration on the therapeutic efficacy of ABZ. We evaluated and compared the effects of ABZ, dexamethasone (DXM) and their combination (ABZ + DXM) on cyst viability, both in vitro and in vivo. Serum levels of IL-4, IFN-gamma, IL-6 and IL-10 were evaluated in the in vivo study. Results showed that the treatment with ABZ, in vitro and in vivo, was associated with a high number of parasites deaths. Concomitant treatment with DXM did not alter ABZ in vitro cysticidal activity but reduced its effectiveness significantly in the in vivo experimental model. Cytokine serum levels did not change significantly in treated mice compared to the controls. The results of this study are relevant as they indicate a negative effect of corticosteroids on the efficacy of cysticidal therapy. In human neurocysticercosis, control of inflammation is of great importance to most patients in order to avoid complications. Corticosteroids are generally used for this purpose and the results of this study demonstrate the need to find other therapeutic strategies. Further studies are needed to better understand the mechanisms involved.

Interactions between Macrophages and Cyst-Lining Epithelial Cells Promote Kidney Cyst Growth in Pkd1-Deficient Mice

BACKGROUND

Autosomal-dominant polycystic kidney disease (ADPKD) is the leading inherited renal disease worldwide. The proproliferative function of macrophages is associated with late-stage cyst enlargement in mice with PKD; however, the way in which macrophages act on cyst-lining epithelial cells (CLECs) has not been well elucidated.

METHODS

We generated a rapid-onset PKD mouse model by inactivating Pkd1 on postnatal day 10 (P10) and compared cell proliferation and differential gene expression in kidney tissues of the PKD mice and wild-type (WT) littermates.

RESULTS

The cystic phenotype was dominant from P18. A distinct peak in cell proliferation in polycystic kidneys during P22-P30 was closely related to late-stage cyst growth. Comparisons of gene expression profiles in kidney tissues at P22 and P30 in PKD and WT mice revealed that arginine metabolism was significantly activated; 204 differentially expressed genes (DEGs), including Arg1, an arginine metabolism-associated gene, were identified in late-stage polycystic kidneys. The Arg1-encoded protein, arginase-1 (ARG1), was predominantly expressed in macrophages in a time-dependent manner. Multiple-stage macrophage depletion verified that macrophages expressing high ARG1 levels accounted for late-stage cyst enlargement, and inhibiting ARG1 activity significantly retarded cyst growth and effectively lowered the proliferative indices in polycystic kidneys. In vitro experiments revealed that macrophages stimulated CLEC proliferation, and that L-lactic acid, primarily generated by CLECs, significantly upregulated ARG1 expression and increased polyamine synthesis in macrophages.

CONCLUSIONS

Interactions between macrophages and CLECs promote cyst growth. ARG1 is a key molecule involved in this process and is a potential therapeutic target to help delay ADPKD progression.

EXPERIMENTAL SUBCUTANEOUS CYSTICERCOSIS BY Taenia crassiceps IN BALB/c AND C57BL/6 MICE

Human cysticercosis is one of the most severe parasitic infections affecting tissues. Experimental models are needed to understand the host-parasite dynamics involved throughout the course of the infection. The subcutaneous experimental model is the closest to what is observed in human cysticercosis that does not affect the central nervous system. The aim of this study was to evaluate macroscopically and microscopically the experimental subcutaneous cysticercosis caused by Taenia crassiceps cysticerci in BALB/c and C57BL/6 mice. Animals were inoculated in the dorsal subcutaneous region and macroscopic and microscopic aspects of the inflammatory process in the host-parasite interface were evaluated until 90 days after the inoculation (DAI). All the infected animals presented vesicles containing cysticerci in the inoculation site, which was translucent at 7 DAI and then remained opaque throughout the experimental days. The microscopic analysis showed granulation tissue in BALB/c mice since the acute phase of infection evolving to chronicity without cure, presenting 80% of larval stage cysticerci at 90 DAI. While C57BL/6 mice presented 67% of final stage cysticerci at 90 DAI, the parasites were surrounded by neutrophils evolving to the infection control. It is possible to conclude that the genetic features of susceptibility (BALB/c) or resistance (C57BL/6) were confirmed in an experimental subcutaneous model of cysticercosis.

Bidirectional crosstalk via IL-6, PGE2 and PGD2 between murine myofibroblasts and alternatively activated macrophages enhances anti-inflammatory phenotype in both cells

BACKGROUND AND PURPOSE

Alternatively activated macrophages (AAMs) are important cells in the resolution of inflammation and tissue repair. We examined the impact of myofibroblasts, a vital cell in wound healing and tissue repair, on the development and function of AAMs.

EXPERIMENTAL APPROACH

The interaction between AAMs and myofibroblasts was tested using conditioned medium from murine dermal myofibroblasts and bone marrow-derived macrophages. AAMs were differentiated with IL-4 and IL-13.

KEY RESULTS

Conditioned medium from myofibroblasts enhanced the expression of AAM markers, arginase 1 and Ym1 (chitinase-3-like 3) and the spontaneous production of IL-10, while suppressing LPS-induced nitric oxide production. IL-6 from the myofibroblasts contributed to the amplification of the AAM phenotype; the selective COX-2 inhibitor, NS-398, significantly reduced the ability of myofibroblasts to promote an AAM phenotype. Pharmacological analyses indicated that myofibroblast-derived IL-6 enhanced arginase activity and spontaneous IL-10 output, while PGE2 , via the EP4 receptor, enhanced arginase expression and LPS-evoked IL-10 production. PGD2 suppressed LPS-evoked nitric oxide via the DP1 receptor. Reciprocally, conditioned medium from macrophages treated with IL-4 + IL-13 and myofibroblast conditioned medium components, but not macrophages given IL-4 + IL-13 only, reduced myofibroblast migration, the expression of COX-2, and the production of PGE2 and PGD2 .

CONCLUSIONS AND IMPLICATIONS

These findings define mechanisms by which myofibroblasts enhance an AAM phenotype, which can promote wound healing directly, and/or via feedback communication to the myofibroblast, subsequently down-regulating its capacity to promote AAM function. This is an important homeostatic regulatory pathway in wound healing that can also limit unwanted fibrosis.

Cellular immune response in intraventricular experimental neurocysticercosis

Neurocysticercosis (NCC) is considered a neglected parasitic infection of the human central nervous system. Its pathogenesis is due to the host immune response, stage of evolution and location of the parasite. The aim of this study was to evaluate thein situand systemic immune response through cytokines dosage (IL-4, IL-10, IL-17 and IFN-γ) as well as the local inflammatory response of the experimental NCC withTaenia crassiceps. Thein situand systemic cellular and inflammatory immune response were evaluated through the cytokines quantification at 7, 30, 60 and 90 days after inoculation and histopathological analysis. All cysticerci were found within the cerebral ventricles. There was a discrete intensity of inflammatory cells of mixed immune profile, polymorphonuclear and mononuclear cells, at the beginning of the infection and predominance of mononuclear cells at the end. The systemic immune response showed a significant increase in all the analysed cytokines and predominance of the Th2 immune profile cytokines at the end of the infection. These results indicate that the location of the cysticerci may lead to ventriculomegaly. The acute phase of the infection showed a mixed Th1/Th17 profile accompanied by high levels of IL-10 while the late phase showed a Th2 immune profile.

Extraintestinal Helminth Infection Limits Pathology and Proinflammatory Cytokine Expression during DSS-Induced Ulcerative Colitis: A Role for Alternatively Activated Macrophages and Prostaglandins

Chronic inflammation of the intestinal mucosa is characteristic of inflammatory bowel diseases such as ulcerative colitis and Crohn's disease. Helminth parasites have developed immunomodulatory strategies that may impact the outcome of several inflammatory diseases. Therefore, we investigated whether Taenia crassiceps infection is able to decrease the inflammatory effects of dextran sulfate sodium- (DSS-) induced ulcerative colitis in BALB/c and C57BL/6 mice. Preinfection significantly reduced the manifestations of DSS-induced colitis, as weight loss and shortened colon length, and decreased the disease activity index independently of the genetic background of the mice. Taenia infection decreased systemic levels of proinflammatory cytokines while increasing levels of IL-4 and IL-10, and the inflammatory infiltrate into the colon was also markedly reduced. RT-PCR assays from colon showed that T. crassiceps-infected mice displayed increased expression of Arginase-1 but decreased expression of iNOS compared to DSS-treated uninfected mice. The percentages of T regulatory cells were not increased. The adoptive transfer of alternatively activated macrophages (AAMФs) from infected mice into mice with DSS-induced colitis reduced the severity of colon inflammation. Administration of indomethacin abrogated the anticolitic effect of Taenia. Thus, T. crassiceps infection limits the pathology of ulcerative colitis by suppressing inflammatory responses mechanistically associated with AAMФs and prostaglandins.