Lnk Deficiency Leads to TPO-Mediated Osteoclastogenesis and Increased Bone Mass Phenotype.

The Lnk adapter protein negatively regulates the signaling of thrombopoietin (TPO), the main megakaryocyte (MK) growth factor. Lnk-deficient (-/-) mice have increased TPO signaling and increased MK number. Interestingly, several mouse models exist in which increased MK number leads to a high bone mass phenotype. Here we report the bone phenotype of these mice. MicroCT and static histomorphometric analyses at 20 weeks showed the distal femur of Lnk-/- mice to have significantly higher bone volume fraction and trabecular number compared to wild-type (WT) mice. Notably, despite a significant increase in the number of osteoclasts (OC), and decreased bone formation rate in Lnk-/- mice compared to WT mice, Lnk-/- mice demonstrated a 2.5-fold greater BV/TV suggesting impaired OC function in vivo. Additionally, Lnk-/- mouse femurs exhibited non-significant increases in mid-shaft cross-sectional area, yet increased periosteal BFR compared to WT femurs was observed. Lnk-/- femurs also had non-significant increases in polar moment of inertia and decreased cortical bone area and thickness, resulting in reduced bone stiffness, modulus, and strength compared to WT femurs. Of note, Lnk is expressed by OC lineage cells and when Lnk-/- OC progenitors are cultured in the presence of TPO, significantly more OC are observed than in WT cultures. Lnk is also expressed in osteoblast (OB) cells and in vitro reduced alkaline phosphatase activity was observed in Lnk-/- cultures. These data suggest that both direct effects on OB and OC as well as indirect effects of MK in regulating OB contributes to the observed high bone mass. J. Cell. Biochem. 118: 2231-2240, 2017. © 2017 Wiley Periodicals, Inc.

Association of Plasma SDF-1 with Bone Mineral Density, Body Composition, and Hip Fractures in Older Adults: The Cardiovascular Health Study.

Aging is associated with an increase in circulating inflammatory factors. One, the cytokine stromal cell-derived factor 1 (SDF-1 or CXCL12), is critical to stem cell mobilization, migration, and homing as well as to bone marrow stem cell (BMSC), osteoblast, and osteoclast function. SDF-1 has pleiotropic roles in bone formation and BMSC differentiation into osteoblasts/osteocytes, and in osteoprogenitor cell survival. The objective of this study was to examine the association of plasma SDF-1 in participants in the cardiovascular health study (CHS) with bone mineral density (BMD), body composition, and incident hip fractures. In 1536 CHS participants, SDF-1 plasma levels were significantly associated with increasing age (p < 0.01) and male gender (p = 0.04), but not with race (p = 0.63). In multivariable-adjusted models, higher SDF-1 levels were associated with lower total hip BMD (p = 0.02). However, there was no significant association of SDF-1 with hip fractures (p = 0.53). In summary, circulating plasma levels of SDF-1 are associated with increasing age and independently associated with lower total hip BMD in both men and women. These findings suggest that SDF-1 levels are linked to bone homeostasis.

A novel role for thrombopoietin in regulating osteoclast development in humans and mice.

Emerging data suggest that megakaryocytes (MKs) play a significant role in skeletal homeostasis. Indeed, osteosclerosis observed in several MK-related disorders may be a result of increased numbers of MKs. In support of this idea, we have previously demonstrated that MKs increase osteoblast (OB) proliferation by a direct cell-cell contact mechanism and that MKs also inhibit osteoclast (OC) formation. As MKs and OCs are derived from the same hematopoietic precursor, in these osteoclastogenesis studies we examined the role of the main MK growth factor, thrombopoietin (TPO) on OC formation and bone resorption. Here we show that TPO directly increases OC formation and differentiation in vitro. Specifically, we demonstrate the TPO receptor (c-mpl or CD110) is expressed on cells of the OC lineage, c-mpl is required for TPO to enhance OC formation in vitro, and TPO activates the mitogen-activated protein kinases, Janus kinase/signal transducer and activator of transcription, and nuclear factor-kappaB signaling pathways, but does not activate the PI3K/AKT pathway. Further, we found TPO enhances OC resorption in CD14+CD110+ human OC progenitors derived from peripheral blood mononuclear cells, and further separating OC progenitors based on CD110 expression enriches for mature OC development. The regulation of OCs by TPO highlights a novel therapeutic target for bone loss diseases and may be important to consider in the numerous hematologic disorders associated with alterations in TPO/c-mpl signaling as well as in patients suffering from bone disorders.

CD166 and regulation of hematopoiesis.

PURPOSE OF REVIEW: Many surface antigens have been previously used to identify hematopoietic stem cells or cellular elements of the hematopoietic niche. However, to date, not a single surface marker has been identified as a common marker expressed on murine and human hematopoietic stem cells and on cells of the hematopoietic niche. Recently, a few laboratories, including ours, recognized the importance of CD166 as a functional marker on both stem cells and osteoblasts and have begun to characterize the role of CD166 in hematopoiesis. RECENT FINDINGS: Expression of CD166 on hematopoietic cells and cells in the marrow microenvironment was first reported more than a decade ago. Lately, however, a more prominent role for CD166 in normal hematopoiesis and in cancer biology including metastasis began to emerge. This review will cover the significance of CD166 in identifying normal hematopoietic stem cells and cells of the hematopoietic niche and highlight how CD166-mediated homophilic interactions between both cell types may be critical for stem cell function. SUMMARY: The conserved homology between murine and human CD166 and its involvement in metastasis provides an excellent bridge for translational investigations aimed at enhancing stem cell engraftment and clinical utility of stem cells and at using CD166 as a therapeutic target in cancer.

The changing balance between osteoblastogenesis and adipogenesis in aging and its impact on hematopoiesis.

Osteoblasts (OBs) and adipocytes (APs) share a common mesenchymal ancestor. It is now clear that mesenchymal stem cell (MSC) maturation along the OB lineage comes at the expense of adipogenesis and vice versa. During aging, this balance increasingly favors the formation of APs. Hematopoiesis also slowly declines during the aging process. The role of OB lineage cells in hematopoiesis has been studied, but less is known about how APs regulate hematopoiesis. A few studies have demonstrated a negative relationship between APs and hematopoiesis; however, there is also evidence that brown adipose tissue (BAT) may promote hematopoiesis. This review will examine the current knowledge of how adipogenesis and osteogenesis change with aging and the implications of this changing environment on hematopoeisis.

Peripheral arterial disease: A small and large vessel problem.

Peripheral arterial disease (PAD) is one clinical manifestation of systemic atherosclerosis and is very common. Despite its prevalence, PAD remains underdiagnosed, undertreated, and understudied. The most common symptom in patients with PAD is intermittent claudication (IC), or pain in the lower extremities with walking or exertion, which is relieved after a short period of rest. Many patients with confirmed PAD are asymptomatic or have symptoms other than IC. Regardless of symptoms, patients with PAD have poor cardiovascular outcomes. PAD has largely been viewed a disease of large vessel atherosclerosis but what is becoming clear is that arterial plaques and occlusions are only one piece of the puzzle. Recent work has shown that abnormalities in the microvasculature contribute to the outcome of patients with PAD. From the perspective of the leg, limitation in blood flow is not the only problem as patients have a myriad of other problems, including muscle fibrosis, neuropathic changes, changes in the cellular respiration machinery and dysfunction of the small vessels that perfuse skeletal muscle and the supporting structures. Supervised exercise training remains one of the most effective tool to treat patients with PAD, however, the mechanisms behind its effectiveness are still being elucidated and use of structured exercise programs is not widespread. Medical therapy to treat systemic atherosclerosis is underutilized in patients with PAD. Invasive therapies are used only when patients with PAD have reached an advanced stage. While invasive strategies are effective in some patients with PAD, these strategies are costly, carry risk, and many patients are not amenable to invasive therapy. Appreciating the complex pathophysiology of PAD will hopefully spur new research and development of effective therapies for PAD.

Chemotherapy in Pregnancy: Assessing the Safety of Adriamycin Administration in Pregnancy Complicated by Breast Cancer.

Pregnancy-associated breast cancer is challenging to treat. Treatment with chemotherapeutic agents such as anthracyclines poses a risk of cardiotoxicity, despite being considered safe after the second trimester of pregnancy. Management requires multidisciplinary comanagement with cardio-obstetrics, cardiology-oncology, maternal-fetal medicine, and oncology.

Hematopoietic cell regulation of osteoblast proliferation and differentiation.

The last several decades have revealed numerous interactions between cells of the hematopoietic lineage and osteoblasts (OBs) of the mesenchymal lineage. For example, OBs are important players in the hematopoietic stem cell (HSC) niche and OBs are known to impact osteoclast (OC) development. Thus, although much is known regarding the impact OBs have on hematopoietic cells, less is known about the impact of hematopoietic cells on OBs. Here we will review this reciprocal relationship: the effects of hematopoietic cells on OBs. Specifically, we will examine the impact of hematopoietic cells such as HSCs, lymphocytes, and megakaryocytes, as well as the hematopoietic cell-derived OCs on OB proliferation, differentiation, and function.

End-stage renal disease in patients with rheumatoid arthritis.

OBJECTIVES: To determine the frequency of end-stage renal disease (ESRD) in patients with rheumatoid arthritis (RA), the causes of ESRD, and the treatment of RA in the setting of ESRD. METHODS: Cross-sectional study of RA (N = 3754) and non-RA (N = 326,776) patients in the United States Renal Data System (USRDS) during 2011 (N = 330,530). The epidemiology of ESRD in RA was determined and the etiology of ESRD in patients with and without RA was compared. The frequency of patients with RA with at least one filled prescription for prednisone/prednisolone, a DMARD, and/or a biologic in 2011 was determined. RESULTS: The prevalence of RA with ESRD in the USRDS in 2011 was 1.1%. There were significant differences in age, race, sex, and BMI category between the groups (p < 0.01). Diabetes (33.5%) and hypertension (30.6%) were the most common primary causes of ESRD in patients with RA. Amyloidosis, vasculitis, and analgesic nephropathy combined accounted for less than 10% of cases of ESRD. Prednisone was the most commonly filled medication that could be used to treat RA (45.9% of RA patients). Hydroxychloroquine was the most frequently filled DMARD (13.5%); biologics were uncommon (etanercept 2.5%, adalimumab 1.5%; golimumab, infliximab, anakinra, and abatacept <1%). CONCLUSIONS: The co-occurrence of RA with ESRD was 1.1% in the USRDS by 2011. Physicians should be aware of the critical impact of the comorbidities of diabetes and hypertension in causing ESRD in RA patients. Use of DMARDS other than hydroxychloroquine and biologics to treat RA in the setting of ESRD appears to be infrequent. Further prospective studies of treatment strategies for RA in ESRD are needed.

Hydroxychloroquine in patients with systemic lupus erythematosus with end-stage renal disease.

OBJECTIVES: To determine dosing patterns and examine predictors of filled hydroxychloroquine (HCQ) prescriptions in patients with systemic lupus erythematosus (SLE) with end-stage renal disease (ESRD). METHODS: This was a retrospective cohort study of patients with SLE in the US Renal Data System (USRDS) database in fiscal year 2011. All patients were Medicare Part D beneficiaries. Patients with a diagnosis of SLE were identified by the International Classification of Diseases, 9th revision code 710. The prevalence, dosing, and predictors of filled HCQ prescriptions (demographic factors, dialysis type, and provider subspecialty) were determined. RESULTS: There were 10,276 patients with SLE identified; 2048 (19.9%) had a prescription for HCQ filled. The mean daily dose of HCQ was 321 mg (range 58-2000 mg). The most common daily doses were 200 (n=768, 37.5%) and 400 mg (n=1161, 56.7%). In multivariable logistic regression analysis, significant predictors of filled HCQ prescriptions included black/African-American race (OR 1.34, 95% CI (1.17 to 1.46)), hemodialysis (1.50, 95% CI (1.29 to 1.74)), and care from a rheumatologist (5.06, 95% CI (4.56 to 5.62)). Negative predictors of filled HCQ prescriptions included male gender (OR 0.72, 95% CI (0.63 to 0.83)) and those aged 45 years or older (compared to 20 years old and younger, aged 45-64 years, OR 0.66, 95% CI (0.54 to 0.79); aged 65-74 years, OR 0.58, 95% CI (0.44 to 0.76); aged 75 years and older, OR 0.56, 95% CI (0.39 to 0.82)). CONCLUSIONS: In patients with SLE with ESRD, the dosing strategies for HCQ with regard to potential toxicity and disparities in prescribing patterns need further study.

A historical study of appendicular fractures in veterans with traumatic chronic spinal cord injury: 2002-2007.

OBJECTIVE: Describe the incidence and distribution of appendicular fractures in a cohort of veterans with spinal cord injury (SCI). DESIGN: Retrospective, observational study of fractures in veterans with a chronic traumatic SCI. SETTING: The Veterans Health Administration (VA) healthcare system. PARTICIPANTS: Veterans included in the VA Spinal Cord Dysfunction Registry from Fiscal Years (FY) FY2002-FY2007. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Description of fractures by site and number. Mortality at one year following incident fracture among men with single vs. multiple fractures. RESULTS: Male and female veterans sustained incident fractures with similar observed frequency (10.5% vs 11.5%). The majority of fractures occurred in the lower extremities for both men and women. In men, a complete extent of injury (compared to incomplete) was associated with 41% greater relative risk (RR) of incident fracture (RR 1.41, 95% confidence interval [1.17, 1.70]) among those with tetraplegia, but not paraplegia. Furthermore, many men (33.9%, n = 434) sustained multiple fractures over the course of the study. There were no differences in mortality between men who sustained a single fracture and those who had multiple fractures. CONCLUSIONS: The extent of injury may be an important predictor of fracture risk for male veterans with tetraplegia. Once a fracture occurs, male veterans with SCI appear to be at high risk for additional fractures.

Sodium Intake and Osteoporosis. Findings From the Women's Health Initiative.

In this large, prospective, observational cohort study of postmenopausal women in the WHI, Cox proportional hazard regression models showed that sodium intake at or near recommended levels is not likely to impact bone metabolism.

Urinary Tract Stones and Osteoporosis: Findings From the Women's Health Initiative.

Kidney and bladder stones (urinary tract stones) and osteoporosis are prevalent, serious conditions for postmenopausal women. Men with kidney stones are at increased risk of osteoporosis; however, the relationship of urinary tract stones to osteoporosis in postmenopausal women has not been established. The purpose of this study was to determine whether urinary tract stones are an independent risk factor for changes in bone mineral density (BMD) and incident fractures in women in the Women's Health Initiative (WHI). Data were obtained from 150,689 women in the Observational Study and Clinical Trials of the WHI with information on urinary tract stones status: 9856 of these women reported urinary tract stones at baseline and/or incident urinary tract stones during follow-up. Cox regression models were used to determine the association of urinary tract stones with incident fractures and linear mixed models were used to investigate the relationship of urinary tract stones with changes in BMD that occurred during WHI. Follow-up was over an average of 8 years. Models were adjusted for demographic and clinical factors, medication use, and dietary histories. In unadjusted models there was a significant association of urinary tract stones with incident total fractures (HR 1.10; 95% CI, 1.04 to 1.17). However, in covariate adjusted analyses, urinary tract stones were not significantly related to changes in BMD at any skeletal site or to incident fractures. In conclusion, urinary tract stones in postmenopausal women are not an independent risk factor for osteoporosis.

In vitro construction of 2D and 3D simulations of the murine hematopoietic niche.

Hematopoietic stem cells (HSC) undergo multilineage differentiation or self-renewal to maintain normal hematopoiesis and to sustain the size of the HSC pool throughout life. These processes are determined by a complex interplay of molecular signals between HSC and other cellular components such as osteoblasts (OB), stromal cells, endothelial cells, and a number of extracellular matrix (ECM) proteins. Through changes in its physical properties within the bone marrow (BM) microenvironment, collagen, which is one of the most critical ECM proteins, can modulate HSC function and maintenance of the competence of the hematopoietic niche (HN). At present, there is no consensus as to how different cellular elements of the niche collaborate and interact to promote HSC self-renewal or differentiation to maintain hematopoiesis. Deciphering these interactions and the impact of mechanical properties of the collagen microstructures within the HN has critical clinical implications in the areas of stem cell homing, engraftment, and maintenance of HSC function. In this chapter, we describe several of the in vitro methodologies for establishing and maintaining HSC in vitro including the isolation of OB, stromal cells, and hematopoietic progenitor cells, as well as the establishment of both two-dimensional (2D) and three-dimensional (3D) coculture systems.