Plasma cell-derived mtDAMPs activate the macrophage STING pathway, promoting myeloma progression.

Mitochondrial damage-associated molecular patterns (mtDAMPs) include proteins, lipids, metabolites, and DNA and have various context-specific immunoregulatory functions. Cell-free mitochondrial DNA (mtDNA) is recognized via pattern recognition receptors and is a potent activator of the innate immune system. Cell-free mtDNA is elevated in the circulation of trauma patients and patients with cancer; however, the functional consequences of elevated mtDNA are largely undefined. Multiple myeloma (MM) relies upon cellular interactions within the bone marrow (BM) microenvironment for survival and progression. Here, using in vivo models, we describe the role of MM cell-derived mtDAMPs in the protumoral BM microenvironment and the mechanism and functional consequence of mtDAMPs in myeloma disease progression. Initially, we identified elevated levels of mtDNA in the peripheral blood serum of patients with MM compared with those of healthy controls. Using the MM1S cells engrafted into nonobese diabetic severe combined immunodeficient gamma mice, we established that elevated mtDNA was derived from MM cells. We further show that BM macrophages sense and respond to mtDAMPs through the stimulator of interferon genes (STING) pathway, and inhibition of this pathway reduces MM tumor burden in the KaLwRij-5TGM1 mouse model. Moreover, we found that MM-derived mtDAMPs induced upregulation of chemokine signatures in BM macrophages, and inhibition of this signature resulted in egress of MM cells from the BM. Here, we demonstrate that malignant plasma cells release mtDNA, a form of mtDAMPs, into the myeloma BM microenvironment, which in turn activates macrophages via STING signaling. We establish the functional role of these mtDAMP-activated macrophages in promoting disease progression and retaining MM cells in the protumoral BM microenvironment.

Perlecan (HSPG2) promotes structural, contractile, and metabolic development of human cardiomyocytes.

Perlecan (HSPG2), a heparan sulfate proteoglycan similar to agrin, is key for extracellular matrix (ECM) maturation and stabilization. Although crucial for cardiac development, its role remains elusive. We show that perlecan expression increases as cardiomyocytes mature in vivo and during human pluripotent stem cell differentiation to cardiomyocytes (hPSC-CMs). Perlecan-haploinsuffient hPSCs (HSPG2+/-) differentiate efficiently, but late-stage CMs have structural, contractile, metabolic, and ECM gene dysregulation. In keeping with this, late-stage HSPG2+/- hPSC-CMs have immature features, including reduced ⍺-actinin expression and increased glycolytic metabolism and proliferation. Moreover, perlecan-haploinsuffient engineered heart tissues have reduced tissue thickness and force generation. Conversely, hPSC-CMs grown on a perlecan-peptide substrate are enlarged and display increased nucleation, typical of hypertrophic growth. Together, perlecan appears to play the opposite role of agrin, promoting cellular maturation rather than hyperplasia and proliferation. Perlecan signaling is likely mediated via its binding to the dystroglycan complex. Targeting perlecan-dependent signaling may help reverse the phenotypic switch common to heart failure.

Regulation of intestinal senescence during cholestatic liver disease modulates barrier function and liver disease progression.

Background & Aims: Senescence has been reported to have differential functions in cholangiocytes and hepatic stellate cells (HSCs) during human and murine cholestatic disease, being detrimental in biliary cells and anti-fibrotic in HSCs. Cholestatic liver disease is associated with loss of intestinal barrier function and changes in the microbiome, the mechanistic cause of which is undetermined. Methods: Intestinal samples were analysed from controls and patients with primary sclerosing cholangitis, as well as wild-type (WT) and p16-3MR transgenic mice. Cholestatic liver disease was induced by bile duct ligation (BDL) and DDC diet feeding. Fexaramine was used as an intestinal-restricted FXR agonist and antibiotics were given to eliminate the intestinal microbiome. Senescent cells were eliminated in p16-3MR mice with ganciclovir and in WT mice with the senolytic drug ABT-263. In vitro studies were done in intestinal CaCo-2 cells and organoids were generated from intestinal crypts isolated from mice. Results: Herein, we show increased senescence in intestinal epithelial cells (IECs) in patients with primary sclerosing cholangitis and in mice after BDL and DDC diet feeding. Intestinal senescence was increased in response to reduced exposure to bile acids and increased presence of lipopolysaccharide in vitro and in vivo during cholestatic liver disease. Senescence of IECs was associated with lower proliferation but increased intestinal stem cell activation, as supported by increased organoid growth from intestinal stem cells. Elimination of senescent cells with genetic and pharmacological approaches exacerbated liver injury and fibrosis during cholestatic liver disease, which was associated with increased IEC apoptosis and permeability. Conclusions: Senescence occurs in IECs during cholestatic disease and the elimination of senescent cells has a detrimental impact on the gut-liver axis. Our results point to cell-specific rather than systemic targeting of senescence as a therapeutic approach to treat cholestatic liver disease. Impact and implications: Cholestatic liver disease associates with the dysregulation of intestinal barrier function, while the mechanisms mediating the disruption of the gut-liver axis remain largely undefined. Here, we demonstrate that senescence, a cellular response to stress, is activated in intestinal cells during cholestatic liver disease in humans and mice. Mechanistically, we demonstrate that the reduction of bile acids and the increased presence of bacterial products mediate the activation of intestinal senescence during cholestatic liver disease. Importantly, the elimination of these senescent cells promotes further damage to the intestine that aggravates liver disease, with increased tissue damage and fibrosis. Our results provide evidence that therapeutic strategies to treat cholestatic liver disease by eliminating senescent cells may have unwanted effects in the intestine and support the need to develop cell/organ-specific approaches.

Low protein diet protects the liver from Salmonella Typhimurium-mediated injury by modulating the mTOR/autophagy axis in macrophages.

Western diets are the underlying cause of metabolic and liver diseases. Recent trend to limit the consumption of protein-rich animal products has become more prominent. This dietary change entails decreased protein consumption; however, it is still unknown how this affects innate immunity. Here, we studied the influence of a low protein diet (LPD) on the liver response to bacterial infection in mice. We found that LPD protects from Salmonella enterica serovar Typhimurium (S. Typhimurium)-induced liver damage. Bulk and single-cell RNA sequencing of murine liver cells showed reduced inflammation and upregulation of autophagy-related genes in myeloid cells in mice fed with LPD after S. Typhimurium infection. Mechanistically, we found reduced activation of the mammalian target of rapamycin (mTOR) pathway, whilst increased phagocytosis and activation of autophagy in LPD-programmed macrophages. We confirmed these observations in phagocytosis and mTOR activation in metabolically programmed human peripheral blood monocyte-derived macrophages. Together, our results support the causal role of dietary components on the fitness of the immune system.