Tissue Nonspecific Alkaline Phosphatase: More Than a Mineralizing Hormone

Author

Victoria DeMambro, MaineHealthFollow

Date of Award

Summer 8-22-2025

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Doctor of Philosophy (Biomedical Science)

Department

Biomedical Sciences

First Committee Advisor

Anyonya Guntur

Second Committee Member

Clifford Rosen

Third Committee Member

Mary Bouxsein

Additional Committee Members

Jose Luis Millan

Gregory Cox

Abstract

Hypophosphatasia (HPP) is caused by deactivating mutations in the tissue nonspecific alkaline phosphatase (TNSALP) gene (ALPL). HPP is a rare inherited disorder characterized by defective bone and teeth mineralization with a deficiency of TNSALP activity. Previous studies in vitro have suggested decreases in osteoblast and adipocyte maturation with TNSALP deficiency. Furthermore, muscle weakness and chronic fatigue symptoms in some HPP patients suggest decreased metabolism and possible mitochondrial dysfunction. Thus, it was hypothesized that defects in osteoblast and adipocyte progenitor cell metabolism could be driving the lack of mature osteoblasts and adipocytes observed with tissue nonspecific alkaline phosphatase deficiency. Utilizing AlplKO mice, as well as a late onset model of HPP Prrx1^Cre-Alpl^fl/fl and a newly created Prrx1^Cre-Alpl^fl/- (PAKO) mouse strain, bone defects, adipocyte mass, muscle strength and endurance as well as activity and energy expenditure were analyzed in vivo. In vitro, osteoblast/adipocyte progenitors were characterized in terms of differentiation, mitochondrial function, ATP levels and AMPKa signaling pathways.

In adult Prrx1^Cre-Alpl^fl/flmice significant defects in bone architecture, strength and formation with decreased osteoblast maturation and number, in addition to known mineralizing deficiencies were noted. Additional analysis of PAKO femurs revealed disorganized collagen structure, with decreased maturity and stability. In vivo PAKO mice presented with decreased muscle endurance and strength recapitulating adult HPP symptoms. Furthermore, decreased energy expenditure was noted for the first time with in vivo suggesting mitochondrial dysfunction with TNSALP deficiency¹. In vitro PAKO BMSCs treated with osteogenic media for 7 days exhibited decreases in mitochondrial function resulting in reduced ATP levels. AMPKa activity was found to be upregulated as were the expression of proteins involved in osteoblast maturation, cellular stress and mitochondrial fission. AlplKO mice exhibited significant reductions in fat mass and adipocyte size combined with decreased lipid accumulation, mitochondrial function and evidence of increased mitochondrial fission. Taken together these results suggest that TNSALP deficiency results in decreased osteoblast and adipocyte maturation coinciding with decreased mitochondrial function due to increased mitochondrial fission.

Recommended Citation

DeMambro, Victoria, "Tissue Nonspecific Alkaline Phosphatase: More Than a Mineralizing Hormone" (2025). Electronic Theses and Dissertations. 4275.
https://digitalcommons.library.umaine.edu/etd/4275