Pyruvate Kinase Deficiency Causing Priapism.

Pyruvate kinase deficiency (PKD) is an autosomal recessive defect of the enzyme pyruvate kinase (PK) which is involved in catalyzing a reaction that produces ATP in the glycolytic pathway. It is the most common defect of the glycolytic pathway associated with congenital anemia. Patients usually present with signs of chronic hemolytic anemia such as hyperbilirubinemia, splenomegaly, reticulocytosis, and gallstones; the presentation can vary by age. Diagnosis is usually made by demonstration of decreased PK enzymatic activity in a spectrophotometric assay and on the detection of mutations in the PK-LR gene. Management strategies vary from full splenectomies to hematopoietic stem cell transplants with gene therapies with transfusions and administration of PK-activators coming in between. Thromboembolic complications do occur in patients with splenectomy, but there are not much data regarding this for patients with PKD. We present a case of a patient with PKD who demonstrated priapism to be a thromboembolic complication. This differs greatly as priapism has been frequently reported in patients with other chronic hemoglobinopathies such as sickle cell disease, thalassemia, and G6PD with and without splenectomy. While it is still unclear how splenectomies can result in thrombotic events in PKD, there does appear to be a correlation between splenectomies with resultant thrombocytosis with increased platelet adhesion.

Peroxisome proliferator-activated receptor γ coactivator 1α and FoxO3A mediate chondroprotection by AMP-activated protein kinase.

OBJECTIVE: AMP-activated protein kinase (AMPK) inhibits chondrocyte procatabolic responses to inflammation and biomechanical injury. This study was undertaken to test the hypothesis that peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) and FoxO3A, 2 major AMPK downstream targets, mediate the chondroprotective effect of AMPK activation. METHODS: We assessed the activity of AMPKα (threonine 172 phosphorylation) and the expression of PGC-1α and FoxO3A in human chondrocytes and AMPKα1- or AMPKα2-knockout mouse chondrocytes by Western blotting, and in mouse knee cartilage by immunohistochemistry. We also knocked down or overexpressed PGC-1α and FoxO3A by small interfering RNA or plasmid DNA transfection, respectively. We assessed mitochondrial superoxide generation using MitoSOX Red. RESULTS: Expression of PGC-1α and FoxO3A was enhanced by pharmacologic AMPK activator A-769662 but impaired in AMPKα1(-/-) or AMPKα2(-/-) mouse chondrocytes. Reduced expression of PGC-1α and FoxO3A was observed in mouse knee instability-induced osteoarthritis (OA) cartilage and in aged C57BL/6 mouse knee cartilage. Knockdown of PGC-1α and FoxO3A enhanced, but limited the ability of A-769662 to inhibit, phosphorylation of p65 NF-κB (Ser(536) ) and procatabolic responses induced by inflammatory cytokines. Forced expression of PGC-1α and FoxO3A induced increased expression of superoxide dismutase 2 (SOD2) and catalase, but A-769662 failed to increase the expression of SOD2 and catalase in either PGC-1α- or FoxO3A-knockdown chondrocytes. Last, menadione-induced superoxide generation was inhibited by AMPK pharmacologic activators and by overexpression of PGC-1α or FoxO3A. CONCLUSION: PGC-1α and FoxO3A limit oxidative stress and at least partially mediate the capacity of AMPK activity to block procatabolic responses in chondrocytes, and therefore have the potential to inhibit the progression of cartilage damage in OA.

Linked decreases in liver kinase B1 and AMP-activated protein kinase activity modulate matrix catabolic responses to biomechanical injury in chondrocytes.

INTRODUCTION: AMP-activated protein kinase (AMPK) maintains cultured chondrocyte matrix homeostasis in response to inflammatory cytokines. AMPK activity is decreased in human knee osteoarthritis (OA) chondrocytes. Liver kinase B1 (LKB1) is one of the upstream activators of AMPK. Hence, we examined the relationship between LKB1 and AMPK activity in OA and aging cartilages, and in chondrocytes subjected to inflammatory cytokine treatment and biomechanical compression injury, and performed translational studies of AMPK pharmacologic activation. METHODS: We assessed activity (phosphorylation) of LKB1 and AMPKα in mouse knee OA cartilage, in aging mouse cartilage (6 to 24 months), and in chondrocytes after mechanical injury by dynamic compression, via immunohistochemistry or western blot. We knocked down LKB1 by siRNA transfection. Nitric oxide, matrix metalloproteinase (MMP)-3, and MMP-13 release were measured by Griess reaction and ELISA, respectively. RESULTS: Knockdown of LKB1 attenuated chondrocyte AMPK activity, and increased nitric oxide, MMP-3 and MMP-13 release (P <0.05) in response to IL-1ß and TNFα. Both LKB1 and AMPK activity were decreased in mouse knee OA and aged knee cartilage, and in bovine chondrocytes after biomechanical injury. Pretreatment of bovine chondrocytes with AMPK activators AICAR and A-769662 inhibited both AMPKα dephosphorylation and catabolic responses after biomechanical injury. CONCLUSION: LKB1 is required for chondrocyte AMPK activity, thereby inhibiting matrix catabolic responses to inflammatory cytokines. Concurrent loss of LKB1 and AMPK activity in articular chondrocytes is associated with OA, aging and biomechanical injury. Conversely, pharmacologic AMPK activation attenuates catabolic responses to biomechanical injury, suggesting a potentially novel approach to inhibit OA development and progression.

C/EBP homologous protein drives pro-catabolic responses in chondrocytes.

INTRODUCTION: Excess C/EBP homologous protein (CHOP) expression is one feature of the unfolded protein response (UPR) to endoplasmic reticulum (ER) stress. Here, we focused on CHOP expression and function in chondrocytes. METHODS: We studied human knee osteoarthritis (OA) cartilage, bovine chondrocytes cultured in alginate and subjected to sub-lethal biomechanical injury, and knee chondrocytes of human autopsy donors. We performed siRNA knockdown and transfection. RESULTS: UPR activation was increased in human knee OA cartilage in situ, and in biomechanically injured cultured chondrocytes in vitro. In normal human chondrocytes, CHOP "gain of function" sensitized chondrocytes to IL-1ß induced nitric oxide (NO) and matrix metalloproteinase (MMP)-3 release without inducing these responses by itself. Excess CHOP expression, by itself, induced superoxide production and apoptosis. Conversely, siRNA knockdown of CHOP and the UPR-specific mediator X-box binding protein (XBP1) inhibited NO release by >80% (P <0.0005) in response to IL-1ß, and blunted MMP-3 release, whereas there were only minimal effects of the UPR mediator GRP78 on these responses. The anti-inflammatory metabolic "super-regulator" AMP kinase (AMPK) is known to limit UPR activation in vascular muscle cells. Here, CHOP supported the capacity of IL-1ß to suppress AMPK activity in chondrocytes. We also observed that inhibition of AMPK activity promoted an increase in chondrocyte CHOP expression. Conversely, pharmacologic activation of AMPK by 5-Aminoimidazole-4-carboxamide ribonucleotide (AICAR) blunted chondrocyte CHOP expression in response to biomechanical injury. CONCLUSIONS: Biomechanical injury and IL-1 signaling stimulate UPR activation in chondrocytes. CHOP mediates chondrocyte catabolic and apoptotic responses to IL-1ß, and does so partly by inhibiting AMPK activity. Conversely, development of excess CHOP activity is limited by AMPK activity in chondrocytes. Our findings suggest a mechanism for potential chondroprotection by AICAR and other AMPK activators. The work is of translational relevance for OA, since several drugs that activate AMPK are already in the clinic for arthritis (for example, allosteric AMPK activators sodium salicylate and high dose aspirin, and methotrexate, which activates AMPK by generating AICAR).