Renal oncometabolite L-2-hydroxyglutarate imposes a block in kidney tubulogenesis: Evidence for an epigenetic basis for the L-2HG-induced impairment of differentiation.

2-Hydroxyglutarate (2HG) overproducing tumors arise in a number of tissues, including the kidney. The tumorigenesis resulting from overproduced 2HG has been attributed to the ability of 2HG alter gene expression by inhibiting α-ketoglutarate (αKG)-dependent dioxygenases, including Ten-eleven-Translocation (TET) enzymes. Genes that regulate cellular differentiation are reportedly repressed, blocking differentiation of mesenchymal cells into myocytes, and adipocytes. In this report, the expression of the enzyme responsible for L2HG degradation, L-2HG dehydrogenase (L2HGDH), is knocked down, using lentiviral shRNA, as well as siRNA, in primary cultures of normal Renal Proximal Tubule (RPT) cells. The knockdown (KD) results in increased L-2HG levels, decreased demethylation of 5mC in genomic DNA, and increased methylation of H3 Histones. Consequences include reduced tubulogenesis by RPT cells in matrigel, and reduced expression of molecular markers of differentiation, including membrane transporters as well as HNF1α and HNF1ß, which regulate their transcription. These results are consistent with the hypothesis that oncometabolite 2HG blocks RPT differentiation by altering the methylation status of chromatin in a manner that impedes the transcriptional events required for normal differentiation. Presumably, similar alterations are responsible for promoting the expansion of renal cancer stem-cells, increasing their propensity for malignant transformation.

Differentiated tonsil-derived mesenchymal stem cells embedded in Matrigel restore parathyroid cell functions in rats with parathyroidectomy.

Parathyroid cells release parathyroid hormone (PTH), which controls calcium homeostasis. Loss of parathyroid cells results in hypoparathyroidism and consequent low-turnover bone disease. Here, we investigated whether our recently-established human tonsil-derived mesenchymal stem cells (TMSC) restore in vivo parathyroid cell function in rats with parathyroidectomy (PTX). Compared with undifferentiated control TMSC, TMSC differentiated with activin A and soluble sonic hedgehog induced a significant release of PTH as early as day 7, with increased PTH release occurring in response to lower calcium levels and vice versa. Released PTH increased osteocalcin expression and alizarin red S staining in preosteoblastic cells, indicating its functional activity. PTX rats fed calcium-free diet only survived for ∼10 days. Subcutaneous injection with TMSC alone did not increase their survival rates, regardless of differentiation. However, survival rates increased for up to 28 days in response to TMSC embedded in Matrigel (TMSC-MA), showing 40% and 80% in control and differentiated TMSC-MA, respectively. When compared with continuous increases by control TMSC-MA, stable levels of secreted PTH and serum ionized calcium were found in PTX rats with differentiated TMSC-MA. This is the first report that differentiated TMSC resemble parathyroid cells and, if embedded in Matrigel, restore in vivo parathyroid function.