The HIF-1α/PLOD2 axis integrates extracellular matrix organization and cell metabolism leading to aberrant musculoskeletal repair

While hypoxic signaling has been shown to play a role in many cellular processes,its role in metabolism-linked extracellular matrix(ECM)organization and downstream processes of cell fate after musculoskeletal injury remains to be determined.Heterotopicossification(HO)is a debilitating condition where abnormal bone formation occurs within extra-skeletal tissues.Hypoxia andhypoxia-inducible factor 1α(HIF-1α)activation have been shown to promote HO.However,the underlying molecular mechanisms bywhich the HIF-1αpathway in mesenchymal progenitor cells(MPCs)contributes to pathologic bone formation remain to beelucidated.Here,we used a proven mouse injury-induced HO model to investigate the role of HIF-1αon aberrant cell fate.Usingsingle-cell RNA sequencing(scRNA-seq)and spatial transcriptomics analyses of the HO site,we found that collagen ECM organizationis the most highly up-regulated biological process in MPCs.Zeugopod mesenchymal cell-specific deletion of Hif1α(Hoxa11-CreER^(T2);Hif1a^(fl/fl))significantly mitigated HO in vivo.ScRNA-seq analysis of these Hoxa11-CreER^(T2);Hif1a^(fl/fl)mice identified the PLOD2/LOXpathway for collagen cross-linking as downstream of the HIF-1αregulation of HO.Importantly,our scRNA-seq data and mechanisticstudies further uncovered that glucose metabolism in MPCs is most highly impacted by HIF-1αdeletion.From a translational aspect,a pan-LOX inhibitor significantly decreased HO.A newly screened compound revealed that the inhibition of PLOD2 activity in MPCssignificantly decreased osteogenic differentiation and glycolytic metabolism.This suggests that the HIF-1α/PLOD2/LOX axis linked tometabolism regulates HO-forming MPC fate.These results suggest that the HIF-1α/PLOD2/LOX pathway represents a promisingstrategy to mitigate HO formation.

Clinical,pathological,and adjuvant chemotherapy use differences among microsatellite unstable and microsatellite stable colon cancers

Background:Colon cancers are categorized into mismatch repair deficient/microsatellite unstable(MSI-H)and mismatch repair proficient/microsatellite stable(MSS)cancers.This study aims to compare the disease char-acteristics and trends in the utilization of cancer therapies across different age groups and stages in these two groups.Methods:MSI-H and MSS colon adenocarcinomas from 2010 to 2016 were identified using the National Can-cer Database.We compared patient and disease characteristics between the two groups and evaluated the use of adjuvant chemotherapy across age groups and cancer stages.Within MSI-H and MSS groups,we conducted a land-mark analysis after propensity score matching for adjuvant chemotherapy versus no chemotherapy to determine its effect on survival.Results:Of the 542,368 patients that met inclusion criteria,120,751(22%)had mismatch repair results avail-able-out of these 96,928(80%)had MSS colon cancers while 23,823(19.7%)had MSI-H cancers.MSI-H disease had a bimodal age distribution(<40 years=22%;≥75 years=26%)and was frequent among females(22%)and non-Hispanic Whites(20%).Among those<65 years,15%of low-risk stage 2 MSI-H patients and 40%of high-risk stage 2 MSI-H patients received adjuvant chemotherapy.More than two-thirds of stage 3 patients<65 years received adjuvant chemotherapy in both groups.After conducting propensity-score matching for age,gender,and co-morbidities,we found that adjuvant chemotherapy use had a trend towards lower overall survival(OS)in low-risk stage 2 MSI-H(HR=1.8[95%CI,0.8-4.02])and high-risk stage 2 MSI-H(HR=1.42[95%CI,0.96-2.12])groups.Adjuvant chemotherapy significantly improved OS in stage 3 colon cancer patients irrespective of microsatellite status or risk category of disease.Conclusions:MSI-H colon cancer had bimodal age distribution.Among stage 2 MSI-H patients<65 years,a notable proportion received adjuvant chemotherapy.Among MSI-H stage 2 patients,adjuvant chemotherapy use was associated with lower survival while it significantly improved survival for stage 3 patients,irrespective of MSI status.

Spatial transcriptomic interrogation of the murine bone marrow signaling landscape

Self-renewal and differentiation of skeletal stem and progenitor cells(SSPCs)are tightly regulated processes,with SSPC dysregulation leading to progressive bone disease.While the application of single-cell RNA sequencing(scRNAseq)to the bone field has led to major advancements in our understanding of SSPC heterogeneity,stem cells are tightly regulated by their neighboring cells which comprise the bone marrow niche.However,unbiased interrogation of these cells at the transcriptional level within their native niche environment has been challenging.Here,we combined spatial transcriptomics and scRNAseq using a predictive modeling pipeline derived from multiple deconvolution packages in adult mouse femurs to provide an endogenous,in vivo context of SSPCs within the niche.This combined approach localized SSPC subtypes to specific regions of the bone and identified cellular components and signaling networks utilized within the niche.Furthermore,the use of spatial transcriptomics allowed us to identify spatially restricted activation of metabolic and major morphogenetic signaling gradients derived from the vasculature and bone surfaces that establish microdomains within the marrow cavity.Overall,we demonstrate,for the first time,the feasibility of applying spatial transcriptomics to fully mineralized tissue and present a combined spatial and single-cell transcriptomic approach to define the cellular components of the stem cell niche,identify cell-cell communication,and ultimately gain a comprehensive understanding of local and global SSPC regulatory networks within calcified tissue.