Age-dependent alterations in osteoblast and osteoclast activity in human cancellous bone.

It is assumed that the activity of osteoblasts and osteoclasts is decreased in bone tissue of aged individuals. However, detailed investigation of the molecular signature of human bone from young compared to aged individuals confirming this assumption is lacking. In this study, quantitative expression analysis of genes related to osteogenesis and osteoclastogenesis of human cancellous bone derived from the distal radius of young and aged individuals was performed. Furthermore, we additionally performed immunohistochemical stainings. The young group included 24 individuals with an average age of 23.2 years, which was compared to cancellous bone derived from 11 body donators with an average age of 81.0 years. In cancellous bone of young individuals, the osteogenesis-related genes RUNX-2, OSTERIX, OSTEOPONTIN and OSTEOCALCIN were significantly up-regulated compared to aged individuals. In addition, RANKL and NFATc1, both markers for osteoclastogenesis, were significantly induced in cancellous bone of young individuals, as well as the WNT gene family member WNT5a and the matrix metalloproteinases MMP-9. However, quantitative RT-PCR analysis of BMP-2, ALP, FGF-2, CYCLIN-D1, MMP-13, RANK, OSTEOPROTEGERIN and TGFb1 revealed no significant difference. Furthermore, Tartrate-resistant acid phosphatase (TRAP) staining was performed which indicated an increased osteoclast activity in cancellous bone of young individuals. In addition, pentachrome stainings revealed significantly less mineralized bone matrix, more osteoid and an increased bone density in young individuals. In summary, markers related to osteogenesis as well as osteoclastogenesis were significantly decreased in the aged individuals. Thus, the present data extends the knowledge about reduced bone regeneration and healing capacity observed in aged individuals.

Human scaphoid non-unions exhibit increased osteoclast activity compared to adjacent cancellous bone.

Scaphoid bones have a high prevalence for non-union. Even with adequate treatment, bone regeneration may not occur in certain instances. Although this condition is well described, the molecular pathology of scaphoid non-unions is still poorly defined. In this study, gene expression of osteogenic and angiogenic growth and transcription factors as well as inflammatory mediators were analysed in human scaphoid non-unions and intraindividually compared to adjacent autologous cancellous bone from the distal radius. In addition, histology and immunohistochemical stainings were performed to verify qRT-PCR data. Gene expression analysis revealed a significant up-regulation of RANKL, ALP, CYCLIN D1, MMP-13, OPG, NFATc1, TGF-ß and WNT5A in scaphoid non-unions. Interestingly, RANKL and NFATc1, both markers for osteoclastogenesis, were significantly induced in non-unions. Moreover, WNT5A was highly up-regulated in all non-union samples. TRAP staining confirmed the observation of induced osteoclastogenesis in non-unions. With respect to genes related to osteogenesis, alkaline phosphatase was significantly up-regulated in scaphoid non-unions. No differences were detectable for other osteogenic genes such as RUNX-2 or BMP-2. Importantly, we did not detect differences in angiogenesis between scaphoid non-unions and controls in both gene expression and immunohistochemistry. Summarized, our data indicate increased osteoclast activity in scaphoid non-unions possibly as a result of the alterations in RANKL, TGF-ß and WNT5A expression levels. These data increase our understanding for the reduced bone regeneration capacity present in scaphoid non-unions and may translate into the identification of new therapeutic targets to avoid secondary damages and prevent occurrence of non-unions to scaphoid bones.

FLT3-ITD and TLR9 use Bruton tyrosine kinase to activate distinct transcriptional programs mediating AML cell survival and proliferation.

Acute myeloid leukemia (AML) is driven by niche-derived and cell-autonomous stimuli. Although many cell-autonomous disease drivers are known, niche-dependent signaling in the context of the genetic disease heterogeneity has been difficult to investigate. Here, we analyzed the role of Bruton tyrosine kinase (BTK) in AML. BTK was frequently expressed, and its inhibition strongly impaired the proliferation and survival of AML cells also in the presence of bone marrow stroma. By interactome analysis, (phospho)proteomics, and transcriptome sequencing, we characterized BTK signaling networks. We show that BTK-dependent signaling is highly context dependent. In Fms-like tyrosine kinase 3 internal tandem duplication (FLT3-ITD)-positive AML, BTK mediates FLT3-ITD-dependent Myc and STAT5 activation, and combined targeting of FLT3-ITD and BTK showed additive effects. In Fms-like tyrosine kinase 3 internal tandem duplication (FLT3-ITD)-negative AML, BTK couples Toll-like receptor 9 (TLR9) activation to nuclear factor κΒ and STAT5. Both BTK-dependent transcriptional programs were relevant for cell cycle progression and apoptosis regulation. Thus, we identify context-dependent oncogenic driver events that may guide subtype-specific treatment strategies and, for the first time, point to a role of TLR9 in AML. Clinical evaluation of BTK inhibitors in AML seems warranted.